Carb 3 & 4 mixture screws do nothing

[infinity999]

So I rebuilt my carbs a couple of weeks ago. Tanked them, sprayed carb cleaner through everything etc. Also replaced all gaskets, o-rings, etc. I did notice that there were aftermarket needle valves in the carbs so I went ahead and put it back together, adjusted the mixture screws to 2.5 turns and tried to sync it. Exhaust had a very strong smell of raw fuel and I could not get carbs 3 & 4 to do anything with the screws turned all the way in. It seemed to me that the needle vavles were not working correctly and the carbs were being flooded..

So I ordered new Yamaha needle valves, installed them today and it's the same issue. You can turn the mixture screws all the way in on carbs 3 & 4 and the bike just keeps idling. The strong gas odor is gone though. I have not done a wet check on the floats but they were adjusted lining up the circles etc. The idle isn't too bad but it does jump around a little bit. I am beginning to wonder if carbs 3 & 4 are not idling on the idle circuit? Could it be something with the linkage between carbs 1/2 & 3/4? Turning in the mixture screws on either 1 or 2 will make the engine stumble and die.. Any ideas? Thank you.

 

[mr.maxx]

sounds like you still have some plugged passages...did you remove the jet blocks and really deep clean the carbs? what kind of carb gaskets did you use? if you used keyster there may be a plugged passage in the jetblock gaskets.

 

[infinity999]

All 4 carbs were completely disassembled. Bodies, jets, jet blocks etc. were soaked in the gallon can on Chemtool and then I blew carb cleaner through everything. Carbs were rebuilt using all Yamaha parts. The only things that were not changed were all the diaphragms which looked good. Seems odd to me both 3 & 4 are having the same issue..

 

[NHVmaxpower]

I just did mine today I used k&l kits. I won't be firing her up for a while n it's my first on a vmax I'm hoping she runs good and don't have issues. I have heard that keyster kits aren't to good but I had no choice I used what Kyle sent me. I didn't set floats w gas I was told line up casting marks n all should be fine.
Did you blow everything out super good?

 

[infinity999]

Yes, all the passages are definitely clear. Carb cleaner came through everything.

 

[mr.maxx]

could be the throttle plates arent closed far enough to get vaccum....check to see if they are the same as carbs 1$2

 

[infinity999]

Checked the butterflies, looked equal then did a sync, all seems to be ok. Mixture screws still do nothing on carbs 3 & 4.. Also, used a thermal gun to check the temps on the exhaust headers..

cyl 1: 195
cyl 2: 306
cyl 3: 120
cyl 4: 115

I would assume 3 & 4 are a bit cool, but why is #2 over 300? All mixture screws are turned out 3 turns.

 

[dannymax]

The casting marks can be way off, you need to do a wet level check to verify your float settings. Also, the needle seats may not be pressed in the carb bodies to the same depth....another reason to do a wet level check.

 

[infinity999]

Yes, I agree, the floats could still be out of adjustment. I was just looking at the butterflies and the one on carb 1 is a little wet.

I'll get some clear tubing and check the levels tomorrow.

So if they are way off, which I assume they are, how do you set the levels without the casting marks? Thought that was supposed to work 90% of the time? Guess I could be in that 10%.

 

[Rusty McNeil]

Checked the butterflies, looked equal then did a sync, all seems to be ok. Mixture screws still do nothing on carbs 3 & 4.. Also, used a thermal gun to check the temps on the exhaust headers..

cyl 1: 195
cyl 2: 306
cyl 3: 120
cyl 4: 115

I would assume 3 & 4 are a bit cool, but why is #2 over 300? All mixture screws are turned out 3 turns.

I'll skip over any left over blockages or left behinds from your rebuild. Only you can know how clean they are.
Except to mention that the pilot fuel jet in the jet block has a ridiculously tiny hole in it and clogs really easily.

What exhaust do you have? The stock is a little tuff to get temps from due to the double walls and heat shields etc. with aftermarket exhaust mine runs between 250-300 at idle with a infrared temp gun aimed about 2-3 inches from the head.

Possible it's not running on those two cylinders.

I would mechanically synch the throttle plates first, using a small gauge anything to set the throttle butterfly gaps. Use your idle set screw to set master carb to fit your "feeler gauge" and then adjust the rest of the carbs to match. I use a small piece of tie wire to do this, it's easier to do from the bottom side with the carbs off.
This procedure will usually get it close enough that it'll fire and run on all four carbs and then vacuum synching it goes much better.

While checking exhaust temp at idle slowly creep the rpm's up till the throttle synch isn't such a big issue and it may start firing on the dead cylinder if it is due to synch. You should see the temp go up when this happens.

You can also use an inductive timing light to prove the plugs are getting fire, you're not aiming it at anything or timing anything, just checking to see that the plug is getting fire.

Also, that super tiny o-ring on the needle can get out of place, crushed, turn sideways or otherwise block the hole. Sometimes the old one can get left in there too. Takes a bent pick hook, a magnifying glass and good lighting to double check this.

Is the Vboost closed? If its not then one idle screw won't really have any effect either.

It's not really that unusual to get idle screws that don't make the bike respond on every cylinder. Mines done it on cylinder 1 since day one.

In that case i would just match it to the "responding" ones and live with it.

 

[infinity999]

I have a Kerker 4 into 1.

I'll wet check the float levels and then bench synch the carbs with a feeler gauge or a wire.

I assume the o-ring you are talking about is the one at the end of the mixture screw?

Yes, the V-Boost is definitely closed, adjusted it last week..

I checked with the timing light and all four cylinders are getting spark.

Also, with the idle screw removed, should the butterfly on carb 2 be closed? Mine is slightly open.

 

[davesax36]

could be the throttle plates arent closed far enough to get vaccum.

Explain please.... I might have unsynched mine so bad that this is the case.

 

[dannymax]

Yes, I agree, the floats could still be out of adjustment. I was just looking at the butterflies and the one on carb 1 is a little wet.

I'll get some clear tubing and check the levels tomorrow.

So if they are way off, which I assume they are, how do you set the levels without the casting marks? Thought that was supposed to work 90% of the time? Guess I could be in that 10%.

If you don't have a pre-set gauge of some sort it's a trial & error process. But, they always need to be wet checked afterwards because of the possible variables.

 

[sdt354]

could be the throttle plates arent closed far enough to get vaccum....check to see if they are the same as carbs 1$2

That problem can move to different carbs if way out of sync. I've had to use extreme measures to get circuits clean before. Guitar wire works well. The same sensitivity in all 4 mixture screws is how it should be.. Also, you could be getting fuel fed from another place other than the idle circuits.
Some issues I've had that screwed me up: The post that the float hinges ride on being bent, hanging up a float.
Throttle plates not closed properly at idle.(sync)
Hard deposits in the circuits that didn't get cleaned completely.
The o-ring on the main nozzle in the wrong place. The nozzle loose.
Steve-o

 

[sdt354]

I have a Kerker 4 into 1.

I'll wet check the float levels and then bench synch the carbs with a feeler gauge or a wire.

I assume the o-ring you are talking about is the one at the end of the mixture screw?

Yes, the V-Boost is definitely closed, adjusted it last week..

I checked with the timing light and all four cylinders are getting spark.

Also, with the idle screw removed, should the butterfly on carb 2 be closed? Mine is slightly open.

They should be checked with the stop screw installed. Bench sync can get you close, but the final check should be running.

 

[NHVmaxpower]

If the casting mark isn't always correct how do the guys that rebuild carbs set them? I'm talking if someone mailed there carbs to be rebuilt do they have a bike they mount them to adjust floats remove and mail back? There are a couple threads that say use casting mark. Hmmmm now I'm nervous about that after reading infinity thread.

 

[dannymax]

If the casting mark isn't always correct how do the guys that rebuild carbs set them? I'm talking if someone mailed there carbs to be rebuilt do they have a bike they mount them to adjust floats remove and mail back? There are a couple threads that say use casting mark. Hmmmm now I'm nervous about that after reading infinity thread.

I use a gauge and verify with a wet level check.

You can use the casting mark if you want, in most cases it's pretty close, just be sure to check your setting with wet level verification.

Edit: I do mount every rebuild on a bike before shipping them out but that is for idle speed & sync adjust....the floats are already set & verified by then.

 

[Rusty McNeil]

If the casting mark isn't always correct how do the guys that rebuild carbs set them? I'm talking if someone mailed there carbs to be rebuilt do they have a bike they mount them to adjust floats remove and mail back? There are a couple threads that say use casting mark. Hmmmm now I'm nervous about that after reading infinity thread.

I ignore the casting marks, too subjective a method due to parralax. (Viewing angle, and Mfgr'ing tolerances)

I Use a Mic and measure it like in the sticky section, setting them between 1.105" to 1.115" inches......Those numbers aren't for everybody tho', my engine is "not so stock", you can peruse that thread and come up with your own. Measured this way the smaller the number the higher the level, and the richer the carb in areas where float level has more impact.

How to set float levels on bench sticky
http://www.vmaxforum.net/showthread.php?t=1427&page=2

Here's a good read with some info on the impact of float levels, and some handy tuning methods
http://ww.factorypro.com/tech/tech_tuning_procedures/carbtun.html

Here's another link with enough info to make your eyes roll back. Its from the "How to and FAQ" section, not sure why it isn't a sticky in the carb section too?
http://www.vmaxforum.net/showthread.php?t=3809

I nailed mine spot on at 1.110", you have to hold the carb upside down and play with them to get a feel for the measurement process. Hard to distinguish between the float resting on the caliper (not good) or just barely touching, which is what you want.

Then follow with a wet check to make sure the floats aren't screwed up or the seating tension isn't different for each carb, or the needle seats different etc, there can be some variance in each carb, But All things being equal if you Mic them and set them right then the wet check oughta come out right, but not always which is why a wet check is a good thing...it's only my opinion but a real wet check needs to account for fuel pump pressure..........There are ways to do that on the bench too, I just run an extension hose from the bike to the carbs and use the pump on the bike, having the carbs close to the bike and at the same level as installed relative to the fuel pump


The pic shows the proper place to measure them, courtesy of Mike. although when I do it I get off that curve of the body and on the flat.

 

[PATMAX]

Why anyone would do a first time full tear down and rebuild without the Vmax Carb video from Damon Ferriauolo is beyond me. Unless they don't know about it but this thing answers everything and then some. It's cheap too. Cheaper than lots of the parts you buy for a rebuild. Do you guys enjoy doing it twice or more? Not trying to be discouraging, it's just that it almost makes the job foolproof.
My guess is reused jet block rubber plugs. I'm not good enough to diagnose carb issues from afar. Do let us know how this problem is resolved. Perhaps it can help the next guy with a fix!
Thanks for sharing.

 

[NHVmaxpower]

Well just finished my carbs. I did the dry float adjustment then did the wet?2 &4 were dead on 1 was rich 3was lean. I'm glad I did this off the bike cause it's a pita once there mounted. Infinity 999 if I was you most definable do the wet float adjustment it's well worth it before you reinstall the carbs.. Oh Ya I took my needles out of diaphragm to shim them n low n behold they have adjustable needles the clips are set on 3rd down from top. Does this mean I have a stage kit? Has stock air filter.