Carb problems still!

[MSGU1-4936]

Well I had the carbs apart again, cleaned them all out, not that they were dirty, everyting went back where it should, all screws tight etc. still cant get over 3000-4000rpm. I dont know what the freaking problem is, I got good spark on all plugs, compression is good, carbs synced, it just dosent work. Everything is stock except for the slip ons, new plugs, gaped, and I'm out at about 3 turns. Do I go farther out, I read something about shimming the needles, not sure what they mean? Everytime I turn the screw out I check my plugs, they look brand new still! All pistons are firing they all heat up. seems when there is a load applied to the engine there is no power, idle is poor until warmed up.

any suggestions at all

Ron:bang head:

 

[shawn kloker]

Sounds to me like you are sucking air in somewhere.

Airbox lid or boots,carb boots,vboost boots.

 

[MSGU1-4936]

I checked all the seals they look good, as well I just purchased new carb boots. Anything that can be applied to create a better seal?

Ron

 

[shawn kloker]

I checked all the seals they look good, as well I just purchased new carb boots. Anything that can be applied to create a better seal?

Ron

I would not apply anything to them.

What year is this bike?

Alot of the time with older bikes the airbox boots get rock hard and the airbox will just pop right off.Then suck air and run like ****.I had a cracked vboost boot that only acted up at 6k rpm.Started popping like it was leaning out.It was hard to find under the clamps.

 

[maxcruiser]

From the info you gave so far, you have a couple of possibilities causing the problem; fuel flow, intake air leak or poor/no spark advance.

Fuel flow - did you check or change your fuel filter. If not, after replacing it, cut the old one open to see what type of debris is in it - the steel tanks have a tendecy to rust if not kept full during the off season. You can also drain fuel tank from the drain plug at the bottom of tank and see if there is any debris in tank. Also check connections at fuel pump for corrosion 9can also do a voltage check on fuel pump)

Air leak - It sounds like the carbs are good and clean and probably not the problem. You say that the manifold & vboost rubber boots are good or new (only way to check is take them off bend them around to check for cracks). Did you check the rubber o'rings between the manifolds and motor? Those will age and leak air. As previously mentioned, check the rubber boots on the air box to carb connection.
Tune the carbs idle, midrange and topend - see http://vmaxoutlaw.com/main.html - go to "vmax tech & info" icon and scroll to cv carb tuning

Poor/no spark advance - there's two ignition systems used by yamaha for the vmax - from 1985 to 1990 & 1990 to 2007 - so depending what year you have will determine what to check - One simple check is the hose coming off the manifold on the front left carb - it goes to the intake pressure sensor. if cracked it will give false readings to the ECU computer

Good luck

 

[MSGU1-4936]

Airbox boots are not hard and not cracked, the bike was running pretty good actually prior to replacing the cracked manifold boots. The bike is a 1988 with 12000 miles. Fuel filter was changed less than 6 months ago.

 

[red98vmax]

Airbox boots are not hard and not cracked, the bike was running pretty good actually prior to replacing the cracked manifold boots. The bike is a 1988 with 12000 miles. Fuel filter was changed less than 6 months ago.

You can check for intake leaks by spraying a flammable substance around the rubber boots that may be compromised, do while idling the engine, of course. I use propane with a nozzle that lets you get right in to the boots. Keep a CO2 extinguisher close, although any flames would be short lived. If the idle increases, you have an input leak around that point. start at the bottom boots and work your way up because propane is heavier that air and will settle downwards. Testing for as short a time as you can and be in a fairly open area so the propane can disperse into a wide area with no ignition sources. Best of luck, lots of people have used this technique with different flammables like carb cleaners. Some use to use WD40, but I'm not sure that it is still flammable. Both of these seem like they would make a mess...

Steve

 

[MSGU1-4936]

Just tried some of suggestions everything appears to be ok, the one thing I did notice was the rear left carb is the only one that does not stumble when I screw the air / fuel mixture screw in all the way. what would that mean.

Ron

 

[Neil-3446]

Just tried some of suggestions everything appears to be ok, the one thing I did notice was the rear left carb is the only one that does not stumble when I screw the air / fuel mixture screw in all the way. what would that mean.

Ron

That would almost make me think that #1 is not in the equation at all ??? IE...the problem???

When you talk about the rpm level, what is it doing??? Is it starving for fuel, flattening out (spark)...or what???

:confused2:

Neil

 

[MSGU1-4936]

That would almost make me think that #1 is not in the equation at all ??? IE...the problem???

When you talk about the rpm level, what is it doing??? Is it starving for fuel, flattening out (spark)...or what???

:confused2:

Neil

Neil the RPM is steady at 1000rpm, once warmed up, my oil pressure gauge does flutter, I can get the bike to 5000rpm when idling, once I put myself on it and try to ride more so on an incline I cant get pass 3-4000rpm, it hesitates, once the groud levels out it seems to pick up a bit.
The rpm does not change at all when I screw the air/fuel mixture screw in or out for the rear left carb, it does on all the other 3 cylinders.

I get some backfire from the muffler.

All plugs are indicating lean, at 3 turns out.

Ron

 

[maxcruiser]

Here's a bit of a shot in the dark, have you removed any or all of the needle jets from the rubber diaphrams (you mentioned in an earlier thread that one of the white plastic screws was loose). If so, maybe one or more of the needle jets are not seated properly.

Easy enough check and you don't have to take the carb bank off.

 

[jfeagins]

Are you sure the linkages between carbs are OK? After taking carbs off, I've seen the linkages come apart and I even managed to put my Venture carbs back on one time with the linkage between two right carbs missing the spring. Bike didn't even want to start. My bad. Recheck the sync too.

Also, if you've got crap in the tank, it won't matter how new the fuel filter is. It may already be plugged up. Only way to be sure of flow is to take it off and inspect close up. Just don't light up soon after blowing through it.

 

[MSGU1-4936]

Here's a bit of a shot in the dark, have you removed any or all of the needle jets from the rubber diaphrams (you mentioned in an earlier thread that one of the white plastic screws was loose). If so, maybe one or more of the needle jets are not seated properly.

Easy enough check and you don't have to take the carb bank off.

I checked and all is good, the screw/nut that I made ref to was the brass nut that tightens the enricher, and the brass screw that holds down the part that houses the main jet in the float bowl.

Ron

 

[shawn kloker]

The needle jet(nozzle).