Engine won't rev past about 4600rom

[Beau-Kat]

Hey guys.

 

First off, I have been working on engines over 45 years, but realize I can still be looking in the wrong direction for problems. So, I wanna pick your brains on this one.

 

On my '88, a couple of months back, I went through my carbs (they actually were really clean and no real gunk), drilled out the caps and adjusted my screws out to 2 1/4 turns. Also did the valve adjustment then (@ only 22,000 miles, but valve covers were leaking badly). Then I did my carb synch. Synchs ok, but still idles a little rough. I do run fuel stabilizer on my bikes. Sometimes, Sea foam. Sometimes, Techron. Sometimes, Startron. Haven't seen any real difference among them.

 

Anyway, I did not take the diaphragms out during the carb service because they seemed to be working ok (looking through the throats and watching the "bounce" when operating the throttle) before I removed the carbs. All looked to be moving well. I also didn't want to pull those old rubbers and have trouble getting them back in place. Wondering if any liquid got into the vacuum ports. But thought it would have evaporated by now.

 

I have been moving to our new home upstate and haven't had an opportunity to test it out since the service.

 

So, I took the bike on a 475 mile trip yesterday.

 

As soon as I was on the road, I discovered it wouldn't rev past about 4600 or so. After that, it just flat bogs out. Tried easing it up there. Nope. I tried holding it wot for several seconds. Nope. It just wouldn't rev. Under 4600, it runs kinda ok on the highway. Can run 80 mph, but gas mileage is falling off some.

 

Seems to be running on 3 cylinders. But I did the cool pipe test after the service. All seemed to be getting hot evenly.

 

Searched this forum and found some airbox mods or bad diaphragms could cause these issues. I had a Virago that had the problem and it was a diaphragm.

 

Also, I recently did the same service on my Millenium. It runs great.

 

Anyway, any thoughts, personal experiences like this with a first or second gen?

 

Where can we get diaphragms for the first gens?

 

I found this info on the cx500 site. Worked on one of those bikes years ago, but for different issues.

 

http://cx500forum.com/forum/technical-help-forum/13657-won-t-rev-past-4500-a.html

[flyday58]

Running on only 3 cylinders is a very real possibility and very hard to detect once the engine is thoroughly heat-soaked. You'll convince yourself all 4 are firing. If you suspect it's down to 3 cylinders do a quick cold start and check your pipes, it's how I found mine. Unless that's what you mean by 'cool pipe test'. Mileage was down and wouldn't maintain speed up a small incline on mine.

[Prairiehammer]

Anyway, I did not take the diaphragms out during the carb service because they seemed to be working ok (looking through the throats and watching the "bounce" when operating the throttle) before I removed the carbs. All looked to be moving well. I also didn't want to pull those old rubbers and have trouble getting them back in place. Wondering if any liquid got into the vacuum ports. But thought it would have evaporated by now.

 

As soon as I was on the road, I discovered it wouldn't rev past about 4600 or so. After that, it just flat bogs out. Tried easing it up there. Nope. I tried holding it wot for several seconds. Nope. It just wouldn't rev. Under 4600, it runs kinda ok on the highway. Can run 80 mph, but gas mileage is falling off some.

 

Where can we get diaphragms for the first gens?

 

 

I think you are on the right track with suspecting the diaphragms. 'Holey' diaphragms will still dance at idle, but when you want to go fast, the holes prevent sufficient vacuum to fully open up the slides and needles.

Bite the bullet and remove the diaphragms and carefully inspect them. It is an easy-peasy task.

There are two sources for new diaphragms that I am aware of.

SCI (SIRIUS CONSOLIDATED INC) is a Canadian company that sells diaphragms for the Venture.

JBM Industries is a another source. http://jbmindustries.com/

[BlueSky]

How old is the gas filter?

[Beau-Kat]

Filter is new. Air filter is new.

 

I was thinking this over this morning.

 

I finally remembered the bike stumbling and not reving BEFORE I did the carb and valve maintenance. I thought it was probably bad gas.

But then, it seemed to not do it again. Or maybe I'm old and don't remember...

 

Anyway, it's doing it again now.

 

Probably gonna replace all four diaphragms anyway as a precaution.

[Beau-Kat]

Thanks for your responses. I'm gonna go out and look the diaphragms over now.

[Beau-Kat]

Still have the problem. Haven't been able to put a lot of time into fiddling with it.

Did find this in a google search:

http://www.justanswer.com/motorcycle/75wth-yamaha-venture-royale-working-1987-yamaha-xvz1300-venture.html#

In the last statement by the mechanic, he stated the Ventures would "twist the slides".

Haven't heard of that before.

Anyone know what he is talking about?

[Patch]

So Beau- a couple of things, as you know the slides are steadied by a bring counter force, if the boots have holes then you can do a quick check by gently siding them with a finger!

Now here is what you want to look for, SMOOTH action, slow steady as you push her in and it should run as far the the bore itself (flush to the wall, not beyond)

DO you feel any BINDING- any at all?

Next when you remove your finger from the piston, does it move completely back to the resting position, EVENLY and SLOWER than the pressure of the spring?

 

I think your link refers to the boot twisting, and usually where you'll find cracks or holes!

 

Now for myself with a high rpm rev problem, I think, "filling" or "advance" first;; so for me I would do a compression test. I prefer to do it when CV are off but it's not necessary.

 

The results and the cylinder suspected cyl & corresponding numbers would be helpful.

 

What are you using to check the pipes? How many minutes after start time, my 1st readings are done after 2 and completed within 4 minutes. Where on the pipes are you measuring?

 

Patch

[flyday58]

Beau, will it not rev past 4600 in ANY gear, or just top gear? If it revs in all but top gear, would still seem to be a 3-cylider motor instead of 4. If it's ALL gears, then hmm, do the newer year models have rev limiters?

[Flyinfool]

Rev limiters did not appear until the 2nd gen motor.

Did you pull the diaphragms and hold them up to a light to check for pin holes? There is no big deal to just pull them to check them. (except for the one security screw on each cover.)

 

While I have never heard of the slides actually twisting. there is an air hole on the slide that is supposed be be located at the bottom. I never heard of the slides actually losing that alignment but it something to pay attention to if you replace the diaphragms.

[cowpuc]

Hold on here a second guys,, if memory serves me correctly there is small alignment indentation on the outer edge of the diaphram on these first gen carbs thats seems like it would hold the entire assembly in position . If a slide were to rotate it seems like it would have to loosen itself from the sealing between itself and the diaphram - if this happened the diaphram and the slide would definitely not remain as a sealed unit (IMHO) = failed diaphram. Something just dont add up with the comment made by that motorcycle commentor guy - not that he aint wayyy smarter than yours truly (I am sure he is) but I am having a hard time seeing what he is saying as a possibilty as feasible... I am probably missing something in my logic..

[Great White]

Hold on here a second guys,, if memory serves me correctly there is small alignment indentation on the outer edge of the diaphram on these first gen carbs thats seems like it would hold the entire assembly in position . If a slide were to rotate it seems like it would have to loosen itself from the sealing between itself and the diaphram - if this happened the diaphram and the slide would definitely not remain as a sealed unit (IMHO) = failed diaphram. Something just dont add up with the comment made by that motorcycle commentor guy - not that he aint wayyy smarter than yours truly (I am sure he is) but I am having a hard time seeing what he is saying as a possibilty as feasible... I am probably missing something in my logic..

 

You are correct. Only way the slide can "rotate" in its bore is if it becomes separated from the diphram, which will present the same as a failed diaphragm.

 

There is an indentation in the diaphragm seat, but even if using an aftermarket diaphragm without the tab, it would still have to separate to rotate as the diaphragm is held captive by the cover.

 

Just went through this myself. The slide had separated from the sleeve that holds the diaphragm captive and it presented symptoms the same as a failed diaphragm.

 

I don't see how the slide rotating makes any difference (other than it has separated from the diaphragm). Outside of the mentioned holes, the slide and needle are symmetrical....

[Patch]

Hey guys.

 

Anyway, I did not take the diaphragms out during the carb service because they seemed to be working ok (looking through the throats and watching the "bounce" when operating the throttle) before I removed the carbs. All looked to be moving well. I also didn't want to pull those old rubbers and have trouble getting them back in place. Wondering if any liquid got into the vacuum ports. But thought it would have evaporated by now.

 

Seems to be running on 3 cylinders. But I did the cool pipe test after the service. All seemed to be getting hot evenly.

 

 

You may be right but does this sound like separated boots?

 

Patch

[Beau-Kat]

So Beau- a couple of things, as you know the slides are steadied by a bring counter force, if the boots have holes then you can do a quick check by gently siding them with a finger!

Now here is what you want to look for, SMOOTH action, slow steady as you push her in and it should run as far the the bore itself (flush to the wall, not beyond)

DO you feel any BINDING- any at all?

Next when you remove your finger from the piston, does it move completely back to the resting position, EVENLY and SLOWER than the pressure of the spring?

 

I think your link refers to the boot twisting, and usually where you'll find cracks or holes!

 

Now for myself with a high rpm rev problem, I think, "filling" or "advance" first;; so for me I would do a compression test. I prefer to do it when CV are off but it's not necessary.

 

The results and the cylinder suspected cyl & corresponding numbers would be helpful.

 

What are you using to check the pipes? How many minutes after start time, my 1st readings are done after 2 and completed within 4 minutes. Where on the pipes are you measuring?

 

Patch

 

O.K. Thanks for your responses. This is what I've done so far.

First off, got the bike from Indiana in 2009 with nearly 16,000 on it. Had supposedly been properly stored inside for many years. Previous owner kept good service records. Only major thing I saw was that he had installed a new fuel tank. The Yamaha dealer where I got it had gone through it and it ran fine when I got it. The bike only has about 23,000 miles on it now.

 

So, before all this started, I installed new NGK plugs and wires with new NGK caps. Bike ran well.

 

Since I posted last, I have:

First, drained the carbs. All looked ok. Each dispensed the same amount of fuel. Operation of the fuel pump seemed fine.

Removed and checked all diaphragms. Had a slight itty bitty tear near the outside edge in one. Replaced that diaphragm with good one from a 535 Virago I had once (same part #).

Pushed the slides and got good even response from each one. All seemed normal.

Bike seemed a little better, but revved to about 4800 before loading up, dying, whatever.

Would quickly run up to that 4800 in any gear, then just quit. Back off a bit and it would pick up again, but not past about 4800.

While riding, I would pull in the clutch and rev it quickly to nearly redline. No problem.

Back to the garage. Loosened the carb rack clamps and made sure they were really seated well on the boots.

Removed the airbox and made sure everything went back snug.

Re-synched the carbs. Were already nearly perfect.

Then it got too late to test ride last night.

Today, raining here. So, I warmed it up on the center stand. Gave it the throttle. It quickly revved to nearly redline and cut the throttle. WooHoo! Returns to good idle.

Still on the center stand, leaning way forward, front brake squeezed, dropped it into first gear and revved it to nearly redline. Seemed to have perfect response to throttle.

Gonna cross my fingers and try to test it on the road tomorrow.

 

Didn't do the cool pipe test today. But when I do that, I run it for about 60 to 90 seconds, then feel the individual pipes close to the head. No cool pipes.

 

If still runs crappy, will do a compression test.

Edited May 28, 2015 by Beau-Kat

[flyday58]

I had an issue like this on a 78 DT175, wouldn't rev past 3000 in any gear. Beat my head against the wall for awhile, parked it for several years. Turned out to be a bad source coil. So maybe yours is electrical, maybe? Pickup coil, ignition coil, TCI if you have one, pickup coil connector?

[Patch]

This is an interesting problem? Things that can be confusing like full or easy rev with no load..... misleading.

So we need to rule out the simple stuff, the intake clamps are not interfering with the carb linkage? to know for certain you need to inspect the action while twisting the throttle, make certain the linkage runs full open.

Next full pump pressure, it isn't enough to say, we have fuel, we see fuel, we here the pump, that's fine when we are looking for a no run situation, but leaves doubt when figuring a high RPM problem! AS is tank venting!

 

Please allow me vent for a moment>>> I have a problem on one cyl of six cylinder on a pretty sophisticated engine! This is my daily ride, my never let me down, absolutely reliable tun the key and go car! I built the fuel system for this, I pulled plugs after 80K and found them to be in perfect condition except for #6 , these are sequential fire 2 plugs per cyl. One cylinder tells two differ stories when I read the plugs, however they are both suggesting cold combustion. So I decided to check compression, well in all my years I have never had such a confusing result. Cutting to the point the readings on the one cyl are all over the place, so my mind says mechanical, right? But then why would one cyl with 2 plugs read completely differently- that is to say two different stories on the same cylinder are told by the plugs? My compression test suggests spring failure, whether its a lifter spring or valve spring. The only thing I can rule out for certain is that it's not the compression ring; and I had already ruled out wiring based on the compression result; now I have to think I have more than one thing a miss here!?

 

This problem is relevant because it proves we need to rule possible causes off the check list, if we allow mileage high or low to rule for us then we start to chase our tails!

Fuel pressure is important, also and maybe not likely is the filter in the right way?

When you disconnect the vacuum advance and plug the port does the idle change? Could the tube be faulty?

 

Patch

[mralex714]

Have you tried to check the voltage at the fuel pump when it bogs down.

[Beau-Kat]

OK. Tested yesterday.

Bike still just stumbles, craps out, bogs, dies, whatever you wanna call it about 5 grand in gear.

Looking at the way the slide dances on #4 carb, pretty much convinced it is a problem with #4 .

Pulled all plugs. Checked spark. Good spark on all plugs.

#4 was the only one that was very sooty.

Changed it to new hotter (NGK DPR7EA-9) plug. Ran about 30 miles, letting it bog like it has been doing.

Pulled all plugs again. 1,2,3 look perfect. #4 sooty again.

Drained carbs and left the drains open. Received the same amount of gas from each carb.

Disconnected the fuel line from the fuel pump and blew air through it, through the carbs, and watched it spit through the drain tubes. No fuel restriction indicated.

With fuel line discharge disconnected from pump, turned on key. Pump works well. Although, I have no idea about pump pressure other than just listening to clicks after pump starts.

Blew back through the fuel filter. All clear.

Hooked up all lines, closed carb drains. Turned on key. Fuel pump clicked for several seconds as bowls filled again. Comparing to work I have done on my Vmax and Millenium carbs, clicked about the same amount after I had drained those bowls. Pretty normal to me.

Note:

I have seen no fuel come from the overflow from any of the carbs. So, that, and the fact that all drained bowls rendered the same amount of fuel, I pretty much am ruling out a stuck float.

Tried to do a compression test. I think I have a problem with my old gauge set-up. Got only 30 psi on #4 cylinder. So, I tried #3 cylinder. Same results. It's such a pain to get the adapter down into the #3 spark plug hole, I haven't tried #1 or #2 yet.

Anyway, since this in an old bike, I have ordered all 4 new carb slide diaphragms from Sirius. Should be here next week.

Whether that's the problem or not, I was gonna replace them anyway.

Probably won't fool with it until next week.

 

Really appreciate your comments.

Sooner or later, we'll get this sorted out.

Edited May 31, 2015 by Beau-Kat
correctd plug number.

[Beau-Kat]

Have you tried to check the voltage at the fuel pump when it bogs down.

Good idea.

Haven't tried that yet, since it only bogs while riding and in any gear.

Pull in the clutch and it will rev freely.

Kinda weird.

[flyday58]

You could experiment by removing the #4 plug cap and going for a ride, see if there's any change or if if runs exactly the same. We all know the X will run on 3 cylinders, and with a known sooty plug I'd be focusing on that. Don't want to open up the 'what plug do you use' discussion again, but I'd try a new plug in #4 position. Several members have reported having shorted NGKs after way too few miles.

[Beau-Kat]

You could experiment by removing the #4 plug cap and going for a ride, see if there's any change or if if runs exactly the same. We all know the X will run on 3 cylinders, and with a known sooty plug I'd be focusing on that. Don't want to open up the 'what plug do you use' discussion again, but I'd try a new plug in #4 position. Several members have reported having shorted NGKs after way too few miles.

 

I bought these plug wires with the caps already installed.

I pulled the cap while idling and it definitely dropped the cylinder. So that cylinder is definitely firing, at least at idle.

Maybe it drops out later in the revs.

[Beau-Kat]

I have also checked the operation of all cables, butterflies, and the enrichment plungers.

Open and close operation is smooth and normal.

The bike is really gassy smelling at idle. Not raw gas, but partially burnt, chokey smelling. I don't see any "well it's flooded" kinda smokey stuff coming from the exhaust. But you can really smell it.

No exhaust leaks. The exhaust system is perfect, including the collector box.

[Patmac6075]

Perhaps this is the overkill of all overkill solutions, but have you considered taking your bike to a local dyno-tuner? I know we have at least 3 motorcycle specific here in Milwaukee...At least there you can get it up to speed and check off what's not causing the issue.

I'd continue to focus on that #4 cylinder...my checklist would start with #1 . Are the valve clearances in spec? #2 . Is your compression within spec? #3 . We're pretty confident you're getting fuel (sooty plug), have any of the jets within #4 carb been disturbed? Loosend up, fallen out, cross-threaded, mixed up, clogged (I know I'm reaching here). #4 . Can you get your hands on a known good TCI? Are you sure all electrical connections are solid on both primary and secondary side of the coil all the way to the spark plug?

We've already addressed the most common cause (diaphragms), we know it getting fuel (sooty plugs leads me to believe it's not a fuel delivery issue, doesn't rule out starvation, but I'd look elsewhere for now)....I'm just typing out loud here, so bear with me...OP stated it ran better with a new clean plug, albeit for a short time...only variable needed is compression.

[mralex714]

Good idea.

Haven't tried that yet, since it only bogs while riding and in any gear.

Pull in the clutch and it will rev freely.

Kinda weird.

I guess you could connect the pump directly to the battery and see if it happens then. You also might want to test the boost sensor.

[Beau-Kat]

I guess you could connect the pump directly to the battery and see if it happens then. You also might want to test the boost sensor.

 

I'll check the boost sensor. But that should affect overall advance to all cylinders. Only getting soot on #4 plug.