need carb help

[bkuhr]

just finished clean and rebuild carbs 83 xvz12t, all new gaskets and orings, started rough but smoothed out when warm. during sync 1&2 come together good, 3&4 close but wont stabalize with each other. 3&4 much higher vacum than 1&2, and while trying to bring together, idle gets to low, and have maxed out idle adjust up to screw limit

 

also notice that vacum sliders in bores 1&2 respone well, and vibrate with idle vacum.

4 barely vibrates at idle, but starts to open with throttle, 3 doesn't even start to open until even more throttle. rubbers diaphrams had no holes during cleaning

 

any suggestions short of carb removal and teardown again

 

history, got this bike 3 months ago in very rough shape-planned winter project. all kinds electrical problems-fixed, carbs and gas tank seriously coated in rust-tank cleaned,repaired and por15'd

 

did i miss a vacum jet in carbs 3&4? which jet and can i spray carb cleaner stiil onbike?

thanks for any input

brian

Edited December 27, 2009 by bkuhr

[Yammer Dan]

Do a Sea-Foam soak and hope it will get something you missed? Run it in very strong 3/4 Sea-Foam 1/4 gas. Put it in there at fuel pump. I don't use straight sea-Foam because it is hard to start on it. Let it soak for a couple days after you make sure you have it in there good.

[fishrepair]

I agree, a Sea-Foam soak will most likely do it. It's some good stuff.

[MiCarl]

... 3&4 much higher vacum than 1&2, and while trying to bring together, idle gets to low, and have maxed out idle adjust up to screw limit

 

That sounds like a cylinder (or 2) not firing. 3&4 are holding 1&2 open, increasing the idle speed. As you start to bring them together 1&2 are closing and the idle drops because 3&4 not picking up their share of the load. Probably 3 or 4 is the culprit.

 

also notice that vacum sliders in bores 1&2 respone well, and vibrate with idle vacum.

4 barely vibrates at idle, but starts to open with throttle, 3 doesn't even start to open until even more throttle. rubbers diaphrams had no holes during cleaning

 

I wouldn't even think about this until they're synced.

 

any suggestions short of carb removal and teardown again

 

Check compression. If compression is good on all 4 then you need to check for bad plug or missing spark. If all that looks good disconnect 1 coil at a time and see which cylinder(s) can be disconnected without affecting idle. If you're going to pull plug wires to do this you should insert a spare plug in the disconnected wire and ground the body to avoid damaging coils. Once you isolate the one that's not firing replace with a known good plug to double check (engine should speed up a lot if problem is in the plug).

 

If the problem isn't resolved you have identified the carburetor which is the problem. You can try opening the mixture screw but odds are you will have to pull the carbs and re-clean this one to get what you missed first time.

 

Before pulling them off you might want to spray starting fluid or carb cleaner around the intake boot to make sure the problem isn't a vacuum leak there.

 

 

did i miss a vacum jet in carbs 3&4? which jet and can i spray carb cleaner stiil onbike?

thanks for any input

 

There aren't "vacuum" jets. You probably mean air jet. Could be but most likely you've got a problem with the fuel side of the idle circuit. A passage or jet not open, OR, massive vacuum leak.

Edited December 27, 2009 by MiCarl

[zlMark]

I would pull the idle air screw and flush with carb cleaner and compressed air before pulling the carbs again. The seafoam trick works pretty good too!

Before pulling them off you might want to spray starting fluid or carb cleaner around the intake boot to make sure the problem isn't a vacuum leak there.

Never spray flammable liquids to look for vacuum leaks, I learned this the hard way! Use WD40 or similiar!!

[GeorgeS]

And Also, check the Intake Manifolds, where they bolt to the Heads. The O-Rings there are small diameter. Even if replaced, they can still leak. Also, only 2 bolts holding them onto the heads. Some folks have reported that a Gasket Sealant in addition to the O-Rings is needed.

 

Also, double check the Clamps above and below, the Carbs for Vaccume leaks.

 

Also, just to cover this point. You are aware that these engines " Run like Crap " if the Air Cleaner Cover is NOT INSTALLED !!!!

 

One other thing to check, is the plug wires if you have not replaced them. The wires will screw out of the Caps, And, the Coils.

Remove the wires, ( they are solid copper core wire ) and nip off about 1/4 inch of the ends, and rescrew them back into place. ( as they might

not be makeing a good electrical connection ) ( To replace the wires, just buy some bulk solid core plug wire at most any Auto Parts store. I would check at a NAPA auto parts for some of this )

 

One other point, on the " Idle Mix Adjust Screw setting " 1 1/8 to 1 1/4 turn CCW from the full closed setting is the agreed upon correct setting. This point is not covered in the Service Manual.

Also, did you Carefully inspect these jet needles to be sure they are not Damaged ??? If so, you should replace them.

 

Another Problem Point, is when Replaceing the Diaphram covers, you have the large O-Ring, and the Small one. any chance you forgot to install the small O-Ring at bottom of the diaphram Cover. ( I did that once ) Simply missed one of them.

 

Also, there have been reports of the Large O-Ring not makeing a good seal, when replaceing the Diaphram cover. Double check those.

Edited December 27, 2009 by GeorgeS

[bkuhr]

great suggestions all, just completed compression checks, 3&4=150psi

1=160psi

2=110psi-increased to 150 psi w oil in spark plug hole, worn rings one cylinder only?

only 38,000 miles on odometer

 

new question, can the forward juggs be removed on the bike, or should i just plan on pulling motor

 

having to work out of town m-f, can only work on on weekends, looks like long winter project

 

thanks for all the help

 

additional info=when i first got bike noticed only ran on 1 cyl, only 1 pipe got even warm(dont remember which)

possible cyl 2 rings carboned up and may spring back to cyl walls if cleaned? should i pour bunch of seafoan in #2 & let sit over the week?

 

drained carb bowls of fuel through drain ports, then refilled bowls with 100% seafoam through fuel pump, plan to let sit over week

 

can not find air idle mix screw advised to remove/adjust. all needles on in fuel block in fuel bowl

Edited December 27, 2009 by bkuhr
additional info

[Yammer Dan]

Valve too tight?? These motors are almost Bullit proof.

[MiCarl]

g

 

can not find air idle mix screw advised to remove/adjust. all needles on in fuel block in fuel bowl

 

It's actually a fuel mixture screw (no air screw on these). If you don't know where they are they are likely your problem. Generally get pulled for a good cleaning.

 

They face outboard on the carburetors, in a well, next to the cover over the diaphragm. I think on the bottom side of the cap. The well may have a cover on it.

[Monty]

Never spray flammable liquids to look for vacuum leaks, I learned this the hard way! Use WD40 or similiar!!

 

 

WD-40 is very flammable. You can use it as a starting fluid. I've used it all my life.

 

 

Soapy water in a spray bottle is best for finding vacuum leaks.

[skydoc_17]

Hey Brian,

Attached below is a pic of the right side of my 87'VR and the yellow arrows are pointing to the hole where the Idle Mixture Screws are located. This is going to take a pretty small screw driver, like a #1 or #2. I usually squirt WD40 in the holes to loosen up the crud BEFORE removing them. Remove, clean orifice with Carb. cleaner, a slight blast of compressed air, WD40 the screws, reinstall, LIGHTLY BOTTOM the screws! (if you crank them into the seat you will damage the Carb. body and the only fix is to replace the Carb. body!) Then turn out 2 1/4 to 2 1/2 turns. on all 4 Carbs. I use a digital Tach. to fine tune them after that but this will get you pretty close.

Earl

[warthogcrewchief]

You should never add oil into the cylinder from the spark plug while doing (or just before) a compression check. As you found out, doing so will show an erroneously high reading. This is a trick that aircraft mechanics will do to get an aircraft to pass inspection (very dangerous too!).

[rhncue]

You should never add oil into the cylinder from the spark plug while doing (or just before) a compression check. As you found out, doing so will show an erroneously high reading. This is a trick that aircraft mechanics will do to get an aircraft to pass inspection (very dangerous too!).

 

I've done that for 50 years when the pressure is low in a cylinder. If it is a valve or out of time the oil makes no difference in readings. If the reading increases much then it is usually a bad ring. It just eliminates valves. The best test however is a leak down test. Make up an on/off valve with a male hose connector on one end and a female at the other. Then connect between your air supply and the compression tester hose with the gauge removed, put the cylinder in question at tdc and with the engine in gear so that the crank doesn't revolve open the valve and listen to where the air is escaping. If through the carb it's intake valve, through the exhaust it's exhaust valve, through the crankcase breather it's rings or piston and if in bubbles in radiator a crack in cylinder wall or blown head gasket or such.

 

Dick

[Yammer Dan]

I've done that for 50 years when the pressure is low in a cylinder. If it is a valve or out of time the oil makes no difference in readings. If the reading increases much then it is usually a bad ring. It just eliminates valves. The best test however is a leak down test. Make up an on/off valve with a male hose connector on one end and a female at the other. Then connect between your air supply and the compression tester hose with the gauge removed, put the cylinder in question at tdc and with the engine in gear so that the crank doesn't revolve open the valve and listen to where the air is escaping. If through the carb it's intake valve, through the exhaust it's exhaust valve, through the crankcase breather it's rings or piston and if in bubbles in radiator a crack in cylinder wall or blown head gasket or such.

 

Dick

 

 

Good One!! Remember all these things from school but you forget some of them. Thanks for refreshing my memory. Now who am I??

 

[Venturous Randy]

I have a suspicion it is a vacuum leak and may be related to the YICS system. Take those hoses off and plug them with a good heavyduty plug. The leak may be in the hoses or the box.

Monty, I have never used soapy water on a vacuum leak. How does it react?

RandyA

[Monty]

The solution is pulled into the opening, and seems to hang there for a second, allowing the engine to smooth out for a bit. It's a great way to find leaks.

[bkuhr]

I have a suspicion it is a vacuum leak and may be related to the YICS system. Take those hoses off and plug them with a good heavyduty plug. The leak may be in the hoses or the box.

 

i also have 750 seca with YICS. requires special tool i made to plug YICS ports for sync

dont recall reading YICS needs to be plugged off during sync on VR, but only makes sense as YICS chamber causes cylinders to share vacum/fuel mix from other chambers, therby causing error vacum reading during sync, and if bad YICSchamber or hose, low readings with vacum leak

 

talk about ringing bells, can't wait to get home this weekend and try this out

 

brian

[skydoc_17]

Hey Brian,

I am pretty sure that Randy is suggesting that you plug off the YICS System on your VR FOR GOOD! Not just to do the Carb. Sync. If I am wrong, I'm sure he will chime in! Because I don't own an MKI VR, I have never plugged off the YICS System to eliminate Vacuum leaks but I could see where all that extra tubing and the box could cause problems. I know a lot of the MKI guys do this mod but I personally have never tried it and have never measured the effects of this mod.

Just an FYI.

Earl

[Dano]

The YICS system on a MKI WILL start to leak at some point in time, just remove the whole thing and plug the ports on the intake manifold(s). Do as suggested and check for vacuum leaks all around the carbs. Keep the air filter and box cover on when running the motor, too much air getting in there with it off.

 

Good luck,

 

Dan

[Venturous Randy]

The YICS system on a MKI WILL start to leak at some point in time, just remove the whole thing and plug the ports on the intake manifold(s). Do as suggested and check for vacuum leaks all around the carbs. Keep the air filter and box cover on when running the motor, too much air getting in there with it off.

 

Good luck,

 

Dan

 

Yeah, Dan beat me to it. Take it all off and the bike runs just fine. The only suggestion is to put good clamps on the heavy duty plug caps so a minor backfire will not blow a plug cap off. And, keep an extra plug cap or two with a clamp in your tool bag. Ask me how I know to do this. (The bike runs really bad at low rpm's with the plug cap off)

RandyA