Vmax suddenly barely idles…won’t run

[blackbirdxx]

I admit that I don’t ride my max as much as I should, so now with that said, I think the bike is getting back at me. Everything had been working perfectly the last time I rode…then, I want to ride it after about a month and a half of sitting, and the bike will barely run. With the choke on, it idles but not very well, will not run at all with the choke off. When idling with the choke on, it doesn’t want to rev.

I have gone through the shotgun cleaning method and cleaned the carbs/jets the best I could. Interestingly enough, if it matters, 3 of the 4 idle mixture screws were set at 4 1/4 turns out (I left them that way when putting it back together).
No difference.
Other things I have done:
Replaced fuel tank
Replaced fuel filter

Still nothing has been able to work. I’m not sure if it is spark related but I guess I can try that next.

Anyone out there have any ideas?

I have a video of it running, but it was too big to attach. Here is a link to it on YT:

Thanks in advance for any ideas!

 

[Traumahawk]

It sounds like a definite clogged pilot jets, (because at idle and just running around town, that the circuit that the Vmax is running off of) and so taking them out, and cleaning them is needed. Ive had good luck with taking out PAJ#2, to get a full blast of air into the jets for a good shotgun cleaning.

 

[for_gdw]

i wont run right without the air box on!!

 

[MaxMidnight]

i wont run right without the air box on!!

But it will idle satisfactory when testing.

 

[Batlet]

It seems that you have problems with the pilot jets, they are probably clogged, to clean them you have to disassemble the carburettors. But to find out if that is the problem, you can operate the choke lever. If the performance improves with the lever operated, the problem is with the pilot jets, if there is no change, the problem is not the pilot jets.
(excuse my English level)

 

[jfeagins]

Did you check that the fuel pump had adequate outflow?

 

[blackbirdxx]

Thanks to all who have replied.

I have again used the "shotgun" method to blast out PAJs 1 and 2. It does idle a bit better, but only with the choke on. Checking the exhaust temps with an IR heat gun, it looks like it is only running on 2 cylinders....cylinders 1 and 2 are firing but nothing out of 3 and 4.

Spark is present on all cylinders and I have replaced all the spark plugs as well.

I have not checked the fuel pump output. I'll search for a procedure for that.

Trying to avoid needing to pull the carbs off for overhaul but maybe that is inevitable. This is what I get for letting the bike sit....even non-ethanol fuel has been used. The bike is full of 100LL now and that's what will be in from now on....

 

[Batlet]

If you think the problem is in the carburettors of cylinders 3 and 4 and you don't want to disassemble them, you can try blowing with a compressor through the carburettor drain hoses, before blowing through the hose you have to loosen the drain screw. If the high and low jets are not very clogged, you may be able to revive them without disassembling the carburettors. Before doing this it is better to disassemble the upper cover of the carburettor and remove the membrane and the guillotine. Important, you have to blow before the carburettor's fuel tank empties.
Sorry for my English, I don't know if I explained myself well.
This can work, but if you want to do it right, you have to disassemble the carburettors no matter what.

 

[82ndCowboy]

I had the same issue for a while. Ended up being 2 bad accelerator diaphragms and a broken mixture screw oring.
Print out the parts diagrams for the carb set, and individual carbs. Take lots of pictures before you disassemble them and even number and mark positions with a sharpie.
Inspects soak and clean all the parts and jets. Use a screw driver that fits in the slots in the jets perfectly. No wiggle room and seats all the way down in the slot. Inspect all diagrams for pin holes and cracks, up to a bright light.
And most importantly make sure when you are reassembling the 4 carbs back together, make sure they are sitting on a true flat surface when tightening the brackets back up. A miss-alignment will give you problems.
Trust me. Been there done that.
It sounds scary tearing apart carbs, but it really isn't. Worst thing is stripping out a jet slot. Hence the screw driver advice.
You can do it if you keep track as you go and do it in a place where there is no chance dropping parts in places you cant find them when they fall off the workbench or in the dirt.

 

[82ndCowboy]

I'll also add, never use anything hard in the jets or mixture screw seats like a steel pick. I've had good luck with copper wire strands.

 

[Zeus36]

My bet is it's your pilot jets inside the carb jet block as others have suggested. Try the Shotgun again with just compressed air, no carb cleaner, but this time REMOVE each pilot air jet #1 (PAJ1 is #2 in the diagram below) to get maximum compressed air flow to the pilot fuel jet. (When I say compressed air, I'm talking about shop air at around 90 PSI and a blowgun tip.)

The diagram shows pilot air jet number 1 inline with the pilot fuel jet (Item #15). Direct compressed air into every orifice with the carb drains open, you want to try to get an air stream through the pilot jet and out to atmosphere. You could even try air into the drain lines with the drain screws open. When mine was dying at idle when the choke was turned off and stalling with any throttle, I did this modified Shotgun and it fixed what ever was in the pilot jet(s). If this doesn't work, you will need to open the carbs and clean the pilot fuel jet manually with a super fine wire.