Pilot Circuit

[strongbow]

Hello everyone,
I am new to this site but have been looking for a while and this seems to be the best vmax site I have come across. Looks like there is alot of very knowledgeable people here. I have a problem which I think is carb related. Anyway if anyone has any idea this is the problem: 1985 vmax with 45000 miles it has a K and N filter and kerker exhaust. Picked it up at what I thought was a good price about 14 months ago but still have not got it running right. I replaced 4 dodgy diaphargms and the fuel filter as well as 3 sets of spark plugs. The bike would have no problem anywhere apart from trying to cruise at between 4 and 5 thousand revs on the motorway. At this time it feels like i am running out of petrol with quite violent surges.
Since then I have fully stripped the carbs and cleaned all the jets and bodies with carb cleaner. After doing this the vmax was great until it warmed up at which time it started doing the surges at all revs up to 4000. It also does a sort of sneeze thing back though the carbs when trying to pull away. I have also noticed the mixture screws are missing their rubber o rings. It does not seem to change at all where ever I set the mixture screws which I am thinking is somethingto do the missing o rings.
Hope someone out there has an idea about this, never had a bike that was this much of a problem. Any lesser of a bike and I would have given up a long time ago but I have wanted one of these for the best part of ten years.
Any ideas would be great,
Thanks,
Al.

 

[maleko89]

If the mixture screws don't have an effect that is definitely a problem. I would get new screws or attempt to find replacements for the o-rings. I would make sure float level is set correctly and sync your carbs too.

 

[maxcruiser]

Seeing that the bike is new to you and that it's always ran bad since you've had it, I would say take the carb bank off and check what you have. What size main and pilot jets, type of needles, etc... this way you know what you have - next check all rubber intake, airbox, and vboost and the rubber vacuum plugs for cracks. Once reinstalled, do a carb sync.

Another thing to consider, is the float bowl vent tubes attached?

Good luck

Mike

 

[strongbow]

Thanks for the answers I managed to find replacement o rings as Yamaha wanted ?10.70 for each mixture screw which is a bit of a rip off for a brass screw with a spring on it. Pretty sure I have things set up properly now but I have come up with another thought. I have noticed that the stop screw on the vboost has no clearance between the screw and the vboost pulley. I looked in the manual and it said the gap should be 0.3 mm. Which makes me think the vboost is not fully closing, my question is do you think this would cause my low speed problems even if it was only open a very tiny amount? I will be sorting out the clearance but just wanted to know if I should get my hopes up that this could solve my problems.

Thanks,
Al.

 

[strongbow]

Sorry should have also said I have no vent tubes on the carbs and the rubbers look to be in good condition they were quite soft maybe not that old. Do these carbs need the vent tubes what reason do you think the old owner would have removed them?

Thanks again,
Al.

 

[4gasem]

Sorry should have also said I have no vent tubes on the carbs and the rubbers look to be in good condition they were quite soft maybe not that old. Do these carbs need the vent tubes what reason do you think the old owner would have removed them?

Thanks again,
Al.

Vent tubes HAVE to be on the bowls or you will get a bad miss at higher (interstate) speeds.

Get those back on ASAP.

Rubbers can look good from the outside but be $hit on the inside.

EDIT: Looks like you figured out your problem... The tubes are missing. My buddy did that to his bike (forgot them) and couldn't finger it out.

Cheers
Chris

 

[strongbow]

Never thought of the vent tubes as they were off the bike when I got it. I have been looking at some pictures of the tubes, can anyone tell me what the metal bit is at the airbox end of the tube? Are these tubes open ended or is there something on them were they connect to the airbox?

Cheers,
Alan.

 

[4gasem]

Never thought of the vent tubes as they were off the bike when I got it. I have been looking at some pictures of the tubes, can anyone tell me what the metal bit is at the airbox end of the tube? Are these tubes open ended or is there something on them were they connect to the airbox?

Cheers,
Alan.

If I remember right they are open but the tabs do two things... #1 they hold the tubes on the airbox and #2 they block direct wind from running right into them...

Sean Morley will have these laying around... P/M one2dmax.

Cheers,
Chris

 

[strongbow]

Nice one Chris my vmax is running like a dream now. I didnt have the vent tubes so made some up out of clear pipe and electrical mini trunking, it worked a treat. Never would have guessed them pipes would cause so many problems.

Thanks again,
Alan.