Big plans and problems at a bad time

[likembikem]

I have about a 5 hour trip coming up for an army reunion that we haven't seen each other in 34 years! Because of the fun and gas prices I've planned on the Vmax since planning first started. It's been running great, until yesterday when I experianced back firing through the air filter.I did the shotgun carb cleaning and with it running I noticed gas bubbling out the top of the front left carb. Vacuum piston was the only one not moving. I removed the diaphragm to make sure it was seated right and the little vacuum piston was jumping around like the rest. I then did a carb sync. Gas smells strong on the left exhaust. It is about 3 weeks before my trip and I am now thinking of pulling the carbs and checking the float and jets in the front left, probably all of them. Hoping this gives me ordering time in case I break a gasket or find something needing replacing. One of the worse parts is the extreme heat making working on this very difficult. I also temp checked the exhaust pipes and all were around 260 degrees except the left front being around 165. Problem seems mostly low RPM. I getting ready to pull out the whole mess and sit it on the work bench and open the up. Any ideas or suggestions? Thanks

 

[Fire-medic]

little vacuum piston was jumping around like the rest.

Could you tell us what part # is doing that? Are you referring to #9, below? That is the CV carburetor diaphragm and slide. The conical tapered part in the diagram is the black rubber diaphragm.

I noticed gas bubbling out the top of the front left carb

Can you show us exactly where that is happening?

I suspect your pilot jet (part #42) for that carb is probably plugged. You said,
Problem seems mostly low RPM

I would be removing the carbs, splitting them into two pairs, removing the float bowls, the floats (part #27), and the jet blocks (part #32), and then the parts #42 and 44. Get four gaskets part #35 as they often tear apart trying to remove the jet block casting.

Part #36 is the float needle valve seat and needle valve, together. I usually just clean with carburetor spray and the red wand the float needle valve seat, using a Q-tip for each carb. If I open the carbs, I usually just replace the needle valve. K & L sells them individually or in a 5-pack, yes, I know "I only have four carburetors." AFAIK, Yamaha only sells the float needle valve seat and needle valve together, and four will be > $100. The four needle valves, with the viton-tipped rubber conical end, are available from K & L much cheaper.

K & L 18-2879 has the jet block gasket, the float bowl gasket, a needle valve, needle valve seat and the starter enrichment piston cover gasket (part #17). There are a few O-rings included. Buying this saves you considerably over the Yamaha prices. K & L makes parts for the Japanese motorcycle companies. Did you know Yamaha also makes bikes in Thailand?


Check online carefully, as you may not get all the parts shown here in some offerings, caveat emptor. One supplier I found:
https://www.ebay.com/itm/2027759417...t2cz63YiVGzoY-ZfLAUyFdIKGhTRFsjsaAlPwEALw_wcB
If the LF carburetor pilot jet is plugged, it won't be giving gas to the combustion chamber at idle/low RPM's. No gas in the combustion chamber, no ignition of gas. Your exhaust temperature will read low, as yours does.

 

[likembikem]

Yes the vacuum controlled piston I refered to is part #9. You know how they all move around as you blip the throttle, that one didn't until I checked the fitting of the diaphragm again then it worked as the rest. The fuel bubbling out stopped also. Just while ago I rode about 8 miles and topped off (1 and 1/2 gal.) with 100% gas. Felt like a running issue coming home (passed a cop doing 105! who never turned around). Got home added good bit of seafoam and about to take carbs off but ran idle for a while. Temps with infrared thermometer showed all cylinders about the same temp. I'm wondering if it works good enough till I can do a full carb rebuild in the winter. I blew out the fuel filter, looks ok but I'm going to replace. Hope something close can be bought at local parts store. Thanks for replying back I really appreciate it .

 

[likembikem]

I'll send a picture soon of where the gas was bubbling out from.

 

[likembikem]

Slide, of course. I knew I called it the wrong thing but hoped you would understand.

 

[Fire-medic]

Sounds like you found an issue, good. See CaptainKyle's remark in what did you do to your bike today, part 2, about his opinion of K & L parts.

Yes, you can get a replacement gas filter for < $10 at your local car parts store. You can get name brands and part numbers if you use the forum search function in the upper-right. The OEM filter is probably ~$23. Russell sells a replaceable element aluminum one, and there are knock-offs on ebay. Your local speed shop probably has something like that but the internet should be cheaper. It uses a sintered bronze replaceable filter element.

 

[likembikem]

Fire-medic, I appreciate the help (again). I will use this forum for more research before I order anything. This evening I did about a 10 mile ride and it seems to be running good, but I know if there is a carb problem it will return until it's been taken apart and repaired. Here is a picture of left front carb with screwdriver tip showing the jet that was spewing fuel. Not doing that now, but all related to plugged jets, passages and sticky float. I guess while at it I should replace fuel lines too, they are original from 2001. Thanks for the advice, I get panicky when I have plans to use it soon.

 

[likembikem]

The reunion I mentioned is just down the road from Captain Kyle!

 

[Coastal Grey]

Seafoam