Head removal in the frame?

[rjsteiner01]

Hi All,

 

I have a 1998 RSTD and have low compression. I did the compression checks and it looks like I have burnt or high carbon loaded cylinders. I also suspect that I have a sticky valve. I will take the bike down for its winter nap soon and wanted to know if I have to remove the engine for head removal or can it be done in the frame?

I have other work I will be doing (tires, coolant & carb work). Thanks in advance for your input

[DarrinGT]

From what I have read in the past, it is Engine Removal to pull heads,...should be a lot of fun!

[Karaboo]

Did you check valve clearance? If you are too tight, you would see low compression.

[baylensman]

I pulled heads and cyclinders in frame to regasket when they blew no easy but can be done, the frame on the 96 had a section that bolted in at the top, with that removed rear head and carb could be lifted right out leaving room to remove front head and slide it back and out

[GeorgeS]

Hi All,

 

I have a 1998 RSTD and have low compression. I did the compression checks and it looks like I have burnt or high carbon loaded cylinders. I also suspect that I have a sticky valve. I will take the bike down for its winter nap soon and wanted to know if I have to remove the engine for head removal or can it be done in the frame?

I have other work I will be doing (tires, coolant & carb work). Thanks in advance for your input

 

How many miles on this engine ?? Can you list the compression numbers you found ??

Would be interesting

[rjsteiner01]

Thanks for the info on pulling the heads in the frame, nice to know it can be done. Don't want to do it if I can help it, but glad the hear I don't have to remove the engine to do so.

 

I have not checked the valve clearance. I have low compression on all four cylinders, let me ask this... if the clearance of these valves are changed with shims and the engines wears with use, would the valve clearance not increase with mileage? Thus the valves would stay closed longer? If the valves are closed they would hold compression (unless held open by carbon or burnt). If I understand the valve clearance adjustment method on these engines correctly, we would always add shims to make up for the wear?

 

I was thinking that maybe this bike was run lean (K&N filter and drilled exhaust pipes) leading to toasty valves, thus low compressions.

 

GeorgeS, the bike has 21K for miles. I will respond to your PM shortly.

 

I will point out two things I noticed as of the last few times I had it out:

 

Started it one cold morning (46-48 F) and the bike did less popping.

 

When ever I throttle up (in 4th) going down the road, the bike chatters/is not smooth, like the clutch slipping or I'm dumping fuel into a cylinder that's not burning properly.

 

I appreciate the response, this is such a good looking bike and the PO put a lot of $ into the extras. I would just like to get the MPGs back and get rid of the popping. Again, thanks for support and look forward to the response.

[KICKSHOT]

Lower compression in a cylinder can be caused by a lot of things. Fuel not being burned and washing down a cylinder can lead to lower compression readings. Did you do a wet test also (add a little oil to the cylinder and see if the reading comes up to par with the rest)? I have a 2005 RSTD and pulled the rear head because of a blown head gasket. Really not to bad. Timing was my main concern. But I got around that pretty easily also. Getting a good diagnosis is the best thing you can do so you don't do work that is not needed.

kickshot

[RSTDdog]

Valves on these motors tend to get tighter not looser. Most people report the engine sounding nosier after a valve adjustment. With 21000 miles on the clock, the first valve adjustment is not due until 26000. My friend who is a mechanic showed me burned valve out of a stock RSTD motor with 96000 miles on it. Never had valves adjusted. These bikes are set up pretty rich stock. K&N's and drilled mufflers typically won't be that lean to burn valves. If the PO let it sit and ran it with a partially plugged main jet, that's another story.

 

How low is low on compression? Are the numbers the same on all four? Holding Throttle wide open when doing test? All four plugs are out and the battery fully charged? Did you add oil to cylinder and see if compression came up? Is oil over full or does it smell like there is gas in the crankcase?

 

Did the bike sit? Are the carbs clean? Will it idle off the choke when warmed up? All four exhaust pipes are hot at idle? have you confirmed good spark on all four cylinders?

 

If it will idle and run warmed up, Before I pulled the heads, I would drain the oil and replace if you haven't already. Use something cheap, you will be changing it again. Then get Yamaha Spray Combustion Chamber cleaner or equivalent and a bottle of Ring Free. Pull the fuel tank and run on test bottle. Mix fuel with Yamaha ring free in the test bottle and spray combustion chamber cleaner alternately into the cylinders as directed on can. let sit as directed. Reinstall fuel tank and run a tank of fuel through at the clean up dosage using Yamaha Ring free (2 oz per gallon, read bottle). Have a spare set of plugs on hand and a way to change them. If its a carbon build up or stuck ring issue, that typically should cure it. it will run like crap for while and smoke until it starts cleaning up. Depending how bad it is you may have to repeat the process. Change the oil again after doing this.

 

If you still have low compression after doing the above, everything should be relatively clean when you do pull the head.

 

If you pull the carbs, you can inspect the intake side of the head through the intake boots for carbon build up. If you pull the valve covers you can check for a stuck valve. If its an intake valve, you can probably free it up spraying cleaner through the intake side with the carbs off and working the valve. On the exhaust side you can pull the head pipe for access.

 

Anyway, Some on the bike service you can try before doing a complete disassembly.

 

RSTDdog

[rjsteiner01]

Lower compression in a cylinder can be caused by a lot of things. Fuel not being burned and washing down a cylinder can lead to lower compression readings. Did you do a wet test also (add a little oil to the cylinder and see if the reading comes up to par with the rest)? I have a 2005 RSTD and pulled the rear head because of a blown head gasket. Really not to bad. Timing was my main concern. But I got around that pretty easily also. Getting a good diagnosis is the best thing you can do so you don't do work that is not needed.

kickshot

 

Yes did a wet test with WOT, compression improved by about 5 psi (not much higher) that's what made me think about the valves. thanks.

[MiCarl]

I'd really be thinking that if they were all more or less uniformly low and not much change wet that I should rule out a lot of things before pulling heads:

 

1) Try a different compression tester.

2) Do a leak down test to see where the compression is going.

[rjsteiner01]

Valves on these motors tend to get tighter not looser. Most people report the engine sounding nosier after a valve adjustment. With 21000 miles on the clock, the first valve adjustment is not due until 26000. My friend who is a mechanic showed me burned valve out of a stock RSTD motor with 96000 miles on it. Never had valves adjusted. These bikes are set up pretty rich stock. K&N's and drilled mufflers typically won't be that lean to burn valves. If the PO let it sit and ran it with a partially plugged main jet, that's another story.

 

How low is low on compression? Are the numbers the same on all four? Holding Throttle wide open when doing test? All four plugs are out and the battery fully charged? Did you add oil to cylinder and see if compression came up? Is oil over full or does it smell like there is gas in the crankcase?

 

Did the bike sit? Are the carbs clean? Will it idle off the choke when warmed up? All four exhaust pipes are hot at idle? have you confirmed good spark on all four cylinders?

 

If it will idle and run warmed up, Before I pulled the heads, I would drain the oil and replace if you haven't already. Use something cheap, you will be changing it again. Then get Yamaha Spray Combustion Chamber cleaner or equivalent and a bottle of Ring Free. Pull the fuel tank and run on test bottle. Mix fuel with Yamaha ring free in the test bottle and spray combustion chamber cleaner alternately into the cylinders as directed on can. let sit as directed. Reinstall fuel tank and run a tank of fuel through at the clean up dosage using Yamaha Ring free (2 oz per gallon, read bottle). Have a spare set of plugs on hand and a way to change them. If its a carbon build up or stuck ring issue, that typically should cure it. it will run like crap for while and smoke until it starts cleaning up. Depending how bad it is you may have to repeat the process. Change the oil again after doing this.

 

If you still have low compression after doing the above, everything should be relatively clean when you do pull the head.

 

If you pull the carbs, you can inspect the intake side of the head through the intake boots for carbon build up. If you pull the valve covers you can check for a stuck valve. If its an intake valve, you can probably free it up spraying cleaner through the intake side with the carbs off and working the valve. On the exhaust side you can pull the head pipe for access.

 

Anyway, Some on the bike service you can try before doing a complete disassembly.

 

RSTDdog

 

Thanks for the advice, I do need to get some carbon remover to clean the combustion chambers. Compression was in the 180s ( I would have thought that would be good, Specs say it should be 240 psi I think).

 

I'm not making oil and that's a good thing (fuel dumping in cylinder). I was also thinking a stuck valve or maybe an intermittent ignition problem, maybe the plug isn't firing every time it should. Anyway, I appreciate all the good feedback.

[MiCarl]

Compression was in the 180s ( I would have thought that would be good, Specs say it should be 240 psi I think).

 

I think you should double check your specs. IIRC the spec for a 1st gen 1300 is 175psi. I'd expect yours to be similar.

[rjsteiner01]

I checked the manual (Yamaha manual P/N LIT-11616-10-67) and normal compression is 216 psi & minimum is 185 psi with a maximum difference of 14 PSI between high and low reading.

[V7Goose]

I am not real familiar with the pre-1999 bikes (I like to refer to those as gen 1.5, since the carbs and engines are somewhat different than the "true" 2nd gens starting with the RSV in 1999), but I'll give you some thoughts based on general mechanics and my knowledge of the RSV. I have read your thread from July about your low fuel mileage and low compression as well as this one. Many members have already given you some good points and ideas, particularly RSTDdog above, and I will be repeating a number of them.

 

First of all, your compression is not THAT low, assuming the specs on your engine are actually the same as for the 99 RSV engine. As you have noted, the std is 216, with a minimum of 185. Was your engine warm when you did the test? It does not have to be at full operating temp, but it should be at least hot to the touch - enough that you need to be careful or wear gloves when taking out the plugs.

 

Other points that are important for a good compression reading:

 

• engine warm
  
• all plugs out
  
• air filter out
  
• wide open throttle (better to remove carbs with CV type carbs)
  
• fully charged battery
  

The reason I suggest to remove the carbs is simply that the slides in a constant velocity design do not open from the throttle, but from the pressure difference on the diaphragms caused by the air flow in a running engine - the throttle just opens the butterfly plate between the carb and the engine. And if you remove the carbs, you obviously do not have to worry about the WOT or air filter.

 

 

As for the results of your compression test, if you do not get a big jump from adding the oil to the cylinder, you do NOT have a ring problem - neither worn nor stuck from carbon. Secondly, if the compression is low instead of high, you do NOT have a carbon build-up problem. Third, if all four cylinders are similar in compression, you do NOT have a valve problem.

 

 

So bottom line is that I do not think you have a compression problem at all. But I'd still do a leak-down test as a final check.

 

 

The rest of your problems clearly sound fuel or ignition related to me. Either (or both together) could cause your symptoms, but I'd strongly suspect fuel first. And "fuel" here includes the correct fuel mixture, not just fuel supply, so you need to do a thorough check for vacuum leaks as well as a complete carb inspection/cleaning.

 

 

Understand that adding any type of cleaner to the gas can ONLY help if the problem is a PARTIALLY blocked passage in the carb; the only part of a carburetor that is submerged in fuel is the float valve and the bottom of the float bowl. All of the jets and other passages in the carb only have fuel in them when a mist is being sucked out of the float bowl by the air currents caused by the engine vacuum; therefore, if any jet or passage is completely closed from deposits, it can never be cleaned by the gas/cleaner that cannot touch it.

 

 

The RSV carbs are very easy to properly clean, but I believe yours are somewhat different internally, so I cannot give you detailed advice other than you need to insure you have the right specs for them instead of the '99 and later bikes. Verify you have the correct jets in all locations (I seem to recall that they are all the same in yours instead of the three different sizes in the RSV, but I am not sure). To clean the jets, soak them in some cleaner, then use compressed air - NEVER poke ANYTHING through them. When you look through a clean jet towards a bright light, you can easily tell the difference between a perfect circle of light and a partly occluded jet that may let light through but won't look like a clean circle. Dismantle all parts of the carb that you can and inspect each gasket and o-ring. If you can find the correct parts breakdown for your carbs, this will help a lot to verify all the parts you should be finding. Clean all the air passages in the carb body by using the red nozzle on a can of spray cleaner to force the cleaner through each hole you find. If you have any doubt about how clean they are, repeat this spray cleaning about three times, letting the carb sit for about half hour in between for the cleaner to soften any deposits. Use compressed air to blow out any remaining cleaner and crud from each passage before putting it all back together. Do not forget to verify the enriching plungers ("choke") are all moving smoothly and in perfect sync with each other, and that they are completely in when the choke is off. Problems here are quite common, and your bike does sound like it is running rich as well as having problems with the pilot circuits.

 

 

When the carbs are back on the bike, make CERTAIN that any vent lines are properly attached, not kinked, and routed as they were from the factory. The vents on a CV carb are CRITICAL for proper operation, as they provide the difference in atmospheric pressure on the opposite side of the diaphragm that causes it to open in response to the engine's attempt to draw more air. If they hoses are improperly routed but not kinked, the bike may run fine at idle but have problems when riding at speed due to the air flow by the hoses.

 

 

Now you are ready to try and properly adjust the carbs. You will need vacuum gauges and a tach to do do this. The first step is to set the mixture screws, and it makes no difference if the carbs are in sync or not. Start by setting all mixture screws about 3 1/2 turns out. With the engine fully warmed up, set the idle speed at 1,000 using the throttle stop screw. Now go to the first carb and begin by slowly turning the mixture screw IN while monitoring the RPM - you should immediately begin noticing a drop is revs - this proves both that the pilot circuit in that carb is working properly AND the cylinder is firing. If turning the mixture screw in does not cause the RPM to drop, then you can go no further until you find/fix the problem with either the carburetor or the ignition.

 

 

If turning the screw in does cause a drop in revs, simply begin slowly turning the mixture screw OUT until the engine speed quits increasing, then turn it back in about 1/2 turn. This will be a very good approximation of the correct setting if you had a CO gauge. Now repeat that whole process for the other three cylinders, resetting the idle speed to 1,000 as necessary after each carb is set.

 

 

Once the mixture screws are set on all four carbs, you want to verify they are all in proper sync, then note the vacuum reading at idle. On the RSV this should be about 10" Hg - the actual spec is 280mm or 11", but I rarely see an engine that pulls that high. But anything LESS than 10" indicates some ongoing problem with either the compression or the carburetor. The most common cause of low vacuum at idle is low fuel through the pilot circuits so that the idle screw has to be used to offset that by forcing the slides to stay open some and allow a bit of fuel to be sucked through the main jets (the more the slides are open at any specific RPM, the lower the vacuum will be due to less restriction to air flow). The same problem can be caused by one or more cylinders not firing well at idle so that the throttle stop needs to be cranked up to allow the other cylinders to pick up the load - the effect is the same - slides open more at 1,000 RPM causing lower vacuum readings.

 

 

And that is about it for setting things up at idle. If the carbs are set right and all cylinders are firing, any further problem with rough idle or popping is going to be either a problem with low back pressure in the pipes (commonly caused by anyone who decides to just start drilling holes so they can offend everybody around them with unwanted noise), and air leak in the exhaust headers or vacuum leaks in the intake. If there are no other problems at idle, but you still have complaints about rideability or fuel mileage, then that is a whole different discussion. But we won't even try to go there until this first part is good.

 

Good luck, and let me know if there is anything else you think I can help with or clarify.

Goose

Edited December 13, 2013 by V7Goose
forgot to mention choke issues

[rjsteiner01]

Goose,

 

That is the most detailed description I have read on setting the idle mixture screws, I will try it!

 

As for the rest let me try to answer:

 

The bike was hot when I did the compression test.

All plugs were removed and hot to handle! (used gloves)

The air filter WAS NOT removed.

Battery was fully charged.

 

I did have 160-165 on the right front cylinder while all other readings were 180-185 (this is the cylinder that sounds like it "sneezes" in the exhaust manifold every so often when at an easy cruising speed (3rd-30 mph) steady throttle) Sticky valve?

 

I'm with you on the fuel cleaners, they only work on a somewhat restricted passage.

I removed the carbs from the bike and went through all of the and could not any thing wrong, float were set good, jest clean ect. I did not record jet #s and wish I did just to see if they were stock or re-jetted. I did not remove the intake manifolds and check the orings.

 

When I reinstalled the carbs I did put the vent lines in the correct location (they were facing forward before).

 

What is all involved in the leak down test? Special tool?

 

I will try adjusting the idle mixture screws 3.5 turns and see if I get the effect while turning in and out this weekend and let you know how that went.

 

I also at one time plugged all holes that were drilled into the pipes (pipe plug and exhaust dope). No improvement in popping.

 

In the next week or so I will be removing the carbs and going through all wiring looking for the obvious.

 

Goose, I appreciate the in-depth response and let you know how it goes this weekend.

[V7Goose]

Based on your detailed response, I think a leakdown test is very important now. It does require a special tool, but they are not terribly expensive. You can often borrow one free at the major chain auto parts stores such as AutoZone or O'Riley. You can get a really cheap one at Harbor Freight that will technically work, but has some big problems (that means it will give you useable results if you understand what is wrong with it). I do not recommend it at all. If you want to buy one, check out Jegs.com. A proper leakdown test will both confirm the compression test results and pinpoint exactly where the compression is leaking if there is a problem - no reason to pull a head just to see if a valve might be leaking.

 

With the miles on your bike, any valve problem is very unlikely. It is possible one or more valves could be a bit tight, but highly unlikely they would be tight enough to not fully close, and even if they ARE that tight, it is extraordinarily unlikely that a valve could be burnt by now.

 

By the way, with most modern engines, the valves do get tighter with wear, not looser. This is because there is very limited wear in the OHV parts, but the valves do slowly erode into the heads.

Goose

[rjsteiner01]

OK, checked on the leak down test tools and watch some vids on how it's don. I think I can go with the Harbor Freight based on the expense and how often I will use it.

 

What is the problem with the Harbor Freight tool Goose?

 

Any how, didn't have a lot of time to mess with the bike but I was given a laser thermometer this weekend and figured I would try measuring the exhaust ports to see how it would work.

 

Cranked up the bike and it run rougher than normal (40 deg out). I also don't recall it popping the first few moments after start up. Had to use full choke for about two min. After pushing in in the choke, bike would not run without a little throttle, I up the throttle stop and it ran for a min or two between 900-1400, it was not a steady rpm. Then rpms got steady and climbed to 2k+, had to move the throttle stop back down! Thought to myself one of the cylinders was not doing it's fair share of the work! Don't know if it's fuel, spark or compression.

 

Long story short, took temps of the cylinder exhaust ports (above where the pipes flanges mate up). By now the bike was warmed up and I had that nasty occasional pop on the right bank. Readings are as follows: #1 300, #2 198, #3 254 & #4 177.

 

I will be doing a leak down test next, seems simple and I can see if I have a mechanical problem right off.

[V7Goose]

I am sorry, but I cannot remember the details about the HF leakdown tester. I bought one about three years ago and tested it before returning it. Read the user reviews on the HF site for some of the problems. I do seem to remember that the instructions were wrong and the gauge does NOT read the pressure being applied to the cylinder, but only the source pressure. Careful evaluation of general leakdown test instructions from the internet along with comparison with the HF tool and some of the user comments should help you identify the problems and what you need to do to get a useable test.

 

I do not trust using a laser temp gauge for head readings - I have tried it and find that even minute changes in the pointing spots can result in big variations of the temp reading.

 

Goose

[rjsteiner01]

Ok folks wanted to get back with some test results/findings with my bike performance problem. (popping, low compression and poor fuel mileage).

 

Purchased a Milton leak down tester and finally had some time and a nice day to perform the test, tested all four cylinders and all passed with flying colors!

 

Found # 3 exhaust manifold pipe loose ( I have checked this in the past and found them tight) This time I did have a loose bolt. I now have no popping in the right bank.

 

Found that #4 cylinder must not be getting fuel because after 15 minutes of running the exhaust pipe never got warmer than 100 degrees, all other pipes very hot. I checked the spark and have it, I let the bike run on the spark tester for about 5 minutes and found no intermittent spark...it was steady. #4 cylinder was still cool to the touch.

 

I tapped on the side of the carp thinking I could free a stuck float but no results.

 

I turned in on the idle mixture screw as Goose suggested with no results. All other carbs responded immediately.

 

Good news, no head removal. Carb removal is next, I'm only running on three cylinders. That will affect the MPGs!

[rjsteiner01]

Goose,

 

I have not removed the carbs yet on the bike but have made this observation: Along with a cold cylinder temp on the #4, I can turn the idle mixture screw and it makes no difference to rpm, I did check to see if fuel was getting to carb by opening fuel drain on the bowl, it is getting plenty of fuel. I also have spark for that cylinder.

 

I am not real familiar with the pre-1999 bikes (I like to refer to those as gen 1.5, since the carbs and engines are somewhat different than the "true" 2nd gens starting with the RSV in 1999), but I'll give you some thoughts based on general mechanics and my knowledge of the RSV. I have read your thread from July about your low fuel mileage and low compression as well as this one. Many members have already given you some good points and ideas, particularly RSTDdog above, and I will be repeating a number of them.

 

First of all, your compression is not THAT low, assuming the specs on your engine are actually the same as for the 99 RSV engine. As you have noted, the std is 216, with a minimum of 185. Was your engine warm when you did the test? It does not have to be at full operating temp, but it should be at least hot to the touch - enough that you need to be careful or wear gloves when taking out the plugs.

 

Other points that are important for a good compression reading:

 

 

• engine warm
  
• all plugs out
  
• air filter out
  
• wide open throttle (better to remove carbs with CV type carbs)
  
• fully charged battery
  

The reason I suggest to remove the carbs is simply that the slides in a constant velocity design do not open from the throttle, but from the pressure difference on the diaphragms caused by the air flow in a running engine - the throttle just opens the butterfly plate between the carb and the engine. And if you remove the carbs, you obviously do not have to worry about the WOT or air filter.

 

 

As for the results of your compression test, if you do not get a big jump from adding the oil to the cylinder, you do NOT have a ring problem - neither worn nor stuck from carbon. Secondly, if the compression is low instead of high, you do NOT have a carbon build-up problem. Third, if all four cylinders are similar in compression, you do NOT have a valve problem.

 

 

So bottom line is that I do not think you have a compression problem at all. But I'd still do a leak-down test as a final check.

 

 

The rest of your problems clearly sound fuel or ignition related to me. Either (or both together) could cause your symptoms, but I'd strongly suspect fuel first. And "fuel" here includes the correct fuel mixture, not just fuel supply, so you need to do a thorough check for vacuum leaks as well as a complete carb inspection/cleaning.

 

 

Understand that adding any type of cleaner to the gas can ONLY help if the problem is a PARTIALLY blocked passage in the carb; the only part of a carburetor that is submerged in fuel is the float valve and the bottom of the float bowl. All of the jets and other passages in the carb only have fuel in them when a mist is being sucked out of the float bowl by the air currents caused by the engine vacuum; therefore, if any jet or passage is completely closed from deposits, it can never be cleaned by the gas/cleaner that cannot touch it.

 

 

The RSV carbs are very easy to properly clean, but I believe yours are somewhat different internally, so I cannot give you detailed advice other than you need to insure you have the right specs for them instead of the '99 and later bikes. Verify you have the correct jets in all locations (I seem to recall that they are all the same in yours instead of the three different sizes in the RSV, but I am not sure). To clean the jets, soak them in some cleaner, then use compressed air - NEVER poke ANYTHING through them. When you look through a clean jet towards a bright light, you can easily tell the difference between a perfect circle of light and a partly occluded jet that may let light through but won't look like a clean circle. Dismantle all parts of the carb that you can and inspect each gasket and o-ring. If you can find the correct parts breakdown for your carbs, this will help a lot to verify all the parts you should be finding. Clean all the air passages in the carb body by using the red nozzle on a can of spray cleaner to force the cleaner through each hole you find. If you have any doubt about how clean they are, repeat this spray cleaning about three times, letting the carb sit for about half hour in between for the cleaner to soften any deposits. Use compressed air to blow out any remaining cleaner and crud from each passage before putting it all back together. Do not forget to verify the enriching plungers ("choke") are all moving smoothly and in perfect sync with each other, and that they are completely in when the choke is off. Problems here are quite common, and your bike does sound like it is running rich as well as having problems with the pilot circuits.

 

 

When the carbs are back on the bike, make CERTAIN that any vent lines are properly attached, not kinked, and routed as they were from the factory. The vents on a CV carb are CRITICAL for proper operation, as they provide the difference in atmospheric pressure on the opposite side of the diaphragm that causes it to open in response to the engine's attempt to draw more air. If they hoses are improperly routed but not kinked, the bike may run fine at idle but have problems when riding at speed due to the air flow by the hoses.

 

 

Now you are ready to try and properly adjust the carbs. You will need vacuum gauges and a tach to do do this. The first step is to set the mixture screws, and it makes no difference if the carbs are in sync or not. Start by setting all mixture screws about 3 1/2 turns out. With the engine fully warmed up, set the idle speed at 1,000 using the throttle stop screw. Now go to the first carb and begin by slowly turning the mixture screw IN while monitoring the RPM - you should immediately begin noticing a drop is revs - this proves both that the pilot circuit in that carb is working properly AND the cylinder is firing. If turning the mixture screw in does not cause the RPM to drop, then you can go no further until you find/fix the problem with either the carburetor or the ignition.

 

 

If turning the screw in does cause a drop in revs, simply begin slowly turning the mixture screw OUT until the engine speed quits increasing, then turn it back in about 1/2 turn. This will be a very good approximation of the correct setting if you had a CO gauge. Now repeat that whole process for the other three cylinders, resetting the idle speed to 1,000 as necessary after each carb is set.

 

 

Once the mixture screws are set on all four carbs, you want to verify they are all in proper sync, then note the vacuum reading at idle. On the RSV this should be about 10" Hg - the actual spec is 280mm or 11", but I rarely see an engine that pulls that high. But anything LESS than 10" indicates some ongoing problem with either the compression or the carburetor. The most common cause of low vacuum at idle is low fuel through the pilot circuits so that the idle screw has to be used to offset that by forcing the slides to stay open some and allow a bit of fuel to be sucked through the main jets (the more the slides are open at any specific RPM, the lower the vacuum will be due to less restriction to air flow). The same problem can be caused by one or more cylinders not firing well at idle so that the throttle stop needs to be cranked up to allow the other cylinders to pick up the load - the effect is the same - slides open more at 1,000 RPM causing lower vacuum readings.

 

 

And that is about it for setting things up at idle. If the carbs are set right and all cylinders are firing, any further problem with rough idle or popping is going to be either a problem with low back pressure in the pipes (commonly caused by anyone who decides to just start drilling holes so they can offend everybody around them with unwanted noise), and air leak in the exhaust headers or vacuum leaks in the intake. If there are no other problems at idle, but you still have complaints about rideability or fuel mileage, then that is a whole different discussion. But we won't even try to go there until this first part is good.

 

Good luck, and let me know if there is anything else you think I can help with or clarify.

Goose

[baylensman]

Most commercial spark checkers either the type that go between the plug and wire or the ones that go on the wire measure the signal being sent (i.e. voltage spike)

 

the spike can travel thru the wire into the plug and to ground with out causing a spark in the combustion chamber.

 

swap the bad cylinder plug with a known good one (switch two plugs) and try your test again.

 

As far as your carb situation do you smell any unburnt exhaust (eye watering gas smell) at back of bike? If not then fuel air mix not getting in to cylinder. Why? cloged fuel orifice in carb (all of them?) or stuck intake valve?

[Hucklecatt]

Great thread here! I would only add that our early bikes now suffer from pinholes in the rubber carb diaphragm, and the inlet boots as well. I will again be stripping the carbs to replace both (x4) items over the winter myself as a preventative task.

[V7Goose]

Goose,

 

I have not removed the carbs yet on the bike but have made this observation: Along with a cold cylinder temp on the #4, I can turn the idle mixture screw and it makes no difference to rpm, I did check to see if fuel was getting to carb by opening fuel drain on the bowl, it is getting plenty of fuel. I also have spark for that cylinder.

This is nothing more than a blocked idle jet. Assuming I am right, if you open the throttle about half way while the engine ins running, that cylinder should heat right up because it will be running on the main jet.

Goose

[baylensman]

This is nothing more than a blocked idle jet. Assuming I am right, if you open the throttle about half way while the engine ins running, that cylinder should heat right up because it will be running on the main jet.

Goose

Good call out Goose. I remember my 86 would run like a 125cc bike at idle up to about 1/3 to 1/2 throttle then "Wake up" I had dirt and corrision on the idle screws on two of four carbs.

[rjsteiner01]

Winter time in Eastern Oklahoma so I took some time to dismantle the carbs and here is what I found:

 

All jets clear on #4 cylinder, Pilot jet is a #17.5 & main jet is a #95. This looks stock to me (not jetted).

 

I blew out all ports and passages, not sure if that idle passage is clear because when I apply air to where the idle screw goes (screw is removed) and hold my finger over the small hole that enters the carb throat, I don't think air goes any where, hard to tell. Might have to put them in a pulse tank to clean them up.

 

I found the plastic stop on the jet needle to be on the last position towards the pointy end(notch #5), is this correct? Any one know what setting it is supposed to be set at on the Gen 1.5, 28mm carbs?

 

Another big find is a very loose almost noncontact connection on the white wire for the #4 coil!!! It turns out the PO wanted to hook his tachometer to the # 4 coil, he added some of those two on one spade connectors to the white and red coil wires. Can this tachometer interfere with the coil signal??

 

Is there any info on the 28mm carbs on how they work (circuitry)?

 

I think I'm getting some where on solving this long thread.