One cylinder running rich

[James t]

Hello everyone I've been trying to chase down a running rich problem for a while now, it is the back left carburetor which I call number two the front left being number one, it loads up at low RPM, high RPM it runs great, with the throttle barely open it feels like it needs to clear its throat, I'm getting spark on all coils, all the coils ohm out to spec, I've got the carburetors torn apart here are some photos of my plugs and the inside of that carburetor that is running rich, all AF needles are two turns out from lightly seated. I do notice that all of the diaphragms are coated with gasoline on the inside and the outside is this normal, also can somebody tell me the thickness of the washer that that's under the diaphragm needle the bike is entirely stock 5000 MI, can somebody point out to me what I should be looking for in the carburetor

 

[Radioguylogs]

Pilot air jet is clear in the troublsome carb?

 

[James t]

Yes clear, all jets are clear , it's funny this is the same carburetor that when I turn the a f mixture screw I get no response from the bike, I have the carburetors off and I'm going to be getting into them in the next couple weeks , I'm going to order a good quality rebuild kit and go from there

 

[Fire-medic]

The factory manual says LR is #1, LF is #2, RR is #3, and RF is #4. It helps us to use the proper labelling according to what the manufacturer says, to avoid any misunderstanding. Think of drawing the capital letter N and starting at the bottom left.



If the diaphragm isn't torn or it doesn't have any holes if you hold the slide/diaphragm up to the light, and it's secured well to the slide, and it wasn't folded askew instead of resting in the channel for the outside edge of the diaphragm. I suspect that somewhere in the passages of the carb body, you have an obstruction.

I think most of us who have carbs apart frequently recommend the use of an ultrasonic tank to clean carb bodies and pieces.

https://dn790009.ca.archive.org/0/i...ice-manual/yamahavmaxvmx12-service-manual.pdf

It might be time to check compression and perhaps a leak-down test to see if that one cyl gives widely-different readings from the others.

 

[James t]

My compression is good and consistent on all 4 , all 4 are around 137 psi , this is cylinder no 1 by the book

 

[Parminio]

Running that rich sounds like a high float level to the point gas is just pouring in.

 

[James t]

Possibly, I'll check float level later today, exact float level is critical on these carbs , thanks

 

[James t]

Where can I get a good quality rebuild kit for these carbs

 

[Fire-medic]

Use the search function. Use OEM brass for any jets you choose to replace. Usually, the brass only needs a good soak/cleaning, unless someone tried to 'cheap-out,' and drilled them out seeking to make more HP.

I like the K&L kits for the commonly-replaced jet block gasket, and the O-rings. It also comes with a new float needle seat and float needle, I rarely have found a need to replace the float needle valve seat. The jet block often tears-apart upon disassembly.

dannymax prefers the OEM needle valves to those in the K&L kit.



This is the K&L kit I usually use. Pieces are labelled for ease of installation.




https://www.vmaxforum.net/threads/carb-kits-questions.52635/#post-528910

Be aware there are counterfeit parts on the 'net. Read the thread, Kyle posted the address of the seller he and I have both used.

Sean Morley also stocks OEM new parts for this rebuild.

 

[James t]

Yes the last time I rebuilt these I bought a cheap set on fleabay and that's part of the problem, I need to get all OEM parts and go from there, what is the best way to get the brass seat out without damaging the carburetor I would assume it comes out in the direction underneath the brass plug

 

[Fire-medic]

Use a C-clamp and a short socket able to pass the top of the seat thru it as it's pressed-out being removed from the top-side.

My compression is good and consistent on all 4 , all 4 are around 137 psi , this is cylinder no 1 by the book

From the factory shop manual, which I used just the illustration of the cylinders; here's the entire page. It's page 89 of 405 pages, if you use the .pdf page counter. If you use the manual headings, it's 2-6 under



Below is the entire page, check in the lower-right of the page for the (first) factory shop manual section reference number, which is section 2; and (second) the consecutive page number, which is page 6, coming under that factory shop manual section reference number. In the illustration, the arrow on the left is pointing to the front of the motorcycle.


It's possible that the book you're using may use a different cylinder numbering method than the factory shop service manual.

 

[James t]

I have the same Yamaha service manual so I'm talking about the left rear cylinder which is number one I just have my own numbering system but officially it's the back left

 

[James t]

Thanks for all your help guys I'm just trying to figure out why this one is running rich. This should explain my low RPM loading up.

 

[Gbianchi]

Thanks for all your help guys I'm just trying to figure out why this one is running rich. This should explain my low RPM loading up.

Thanks for all your help guys I'm just trying to figure out why this one is running rich. This should explain my low RPM loading up.

I’m also going with a float level check?

 

[Rauno Vekkila]

Hi, you made that compression test with cold engine? I mean, if there’s any issues with valve clearances, at first it occurs when engine is hot. I had that same issue wih both of the rear cylinders (plus wrong cam timing but it’s a different story)

 

[James t]

Yes cylinders were cold and dry, okay guys here's some photos of my float level tell me what you think

 

[James t]

Well guys I found my problem I must have screwed up the last time I rebuilt them low and behold here's my main jet, I must not have had my glasses on for that one, or somebody took the carburetors apart after me and rebuilt them and put the wrong jet in,

 

[Radioguylogs]

Hmmm....main jet is not in play at low RPM where you had trouble...might be more to the picture?

 

[James t]

Okay I agree but the one cylinder that's running rich just happened to be the one that has a larger jet, I'm going to tear them all apart again and verify everything again and go from there I may even drop them down to 147.5 on the main jet. I'm still working on things and tearing things apart thanks for all your input guys, at what RPM does the main jet start to come into play

 

[dannymax]

A misplaced #170 would suggest there is a #152.5 or #150 (whatever mains you are using) misplaced also.