half way through my build i started my bike up with a custom wiring harness, straight pipes, uni filters and a pma/pamco swap. I have since changed over to the vm 34's with 175 main jets and 15 on the pilots. i have 2 sizes up and 2 sizes down on the mains and a size up and down on the pilots. I can not get the bike to start now. there is spark, i went through and checked the pamco and coil with a meter and everything seems good. When i spray starting fluid into the carbs it will fire momentarily but will not stay going. my guess is its not getting enough fuel. If this is correct, should i go up on the pilots? raise the needles? or something else?
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wont start with new carbs
- Thread starter j_dubbb
- Start date
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- bobber carburetors engine
Would like to see your bike, your pictures are too small.
Have you disconnected the fuel line from the carbs to check the fuel flow? Also, there could be an air lock in the plumbing, to fix that, remove the fuel cap, blow into the fuel tank, it doesn't take much to move the trapped air. Don't inhale the gas fumes, that can make you stupid.
Scott
Have you disconnected the fuel line from the carbs to check the fuel flow? Also, there could be an air lock in the plumbing, to fix that, remove the fuel cap, blow into the fuel tank, it doesn't take much to move the trapped air. Don't inhale the gas fumes, that can make you stupid.
Scott
Are you using the choke? Have you read the Carb Guide for VM carbs that is in the Tech Section?
Richardg
XS650 Member
Start with stock jets on the 34 as your base line. Once you know those carbs in the stock config will run the engine then you can make the jetting changes. A common mistake people make is to make several changes at once without running the engine, which makes it is difficult to figure out which one caused the problem.
weaselbeak
XS650 Junkie
My money is on the floats.
There is no stock jetting on the vm's for an xs...you might be thinking he is running bs carbs.
Richardg, there are no "stock jets" for that application; it's not a stock carburetor.
j dubb, ignore the guesswork above. Read the VM section of the Carb Guide; go to the Tech section and find the link, I'm not going to play "Write it again just for me." There's a jetting baseline there. Here's a freebie: those #15 PJ's are too lean to work, period. In fact, your 1 step up to 17.5 isn't going to work.
j dubb, ignore the guesswork above. Read the VM section of the Carb Guide; go to the Tech section and find the link, I'm not going to play "Write it again just for me." There's a jetting baseline there. Here's a freebie: those #15 PJ's are too lean to work, period. In fact, your 1 step up to 17.5 isn't going to work.
24 mm. +/-1 mm. This is a tuning range, not a tolerance. Measure from the carb body surface where the float bowl gasket seats to the point on the brass float arms where they contact the horizontal pins on the floats. If the gasket is stuck, leave it in place and reduce the spec. by 1 mm. Adjust by slightly bending the float arms. Your elevation does not require leaned out jetting; you'll probably wind up with 22.5 or 25 pilot jets. Pay attention to ALL of the brass: correct jet needles and needle jets are expensive but critical. Do yourself a favor and buy the Sudco Mikuni Tuning Manual.
This thread has lots of VM lore including setting float height. There are several types of VM floats depending on how old they are IIRC
http://www.xs650.com/forum/showthread.php?t=6570
A link to the Mikuni manual on the XScafe site.
http://www.xs650.com/forum/showthread.php?t=6570
A link to the Mikuni manual on the XScafe site.
Yeah, I've read that thread a couple times now, good stuff. I'm guessing that the sudco manual is the one on mikes. It doesn't list the vm 34s specifically. And these puppies are brand new from the Tc bros. And have had the proper changes to go from 2 stroke to 4. I suppose I'll pick up some pilots from Mikes while I'm there. Please say a prayer for my bank account.
Ok, bumped the pilots up to 25 and made sure my floats are at 24 +/- 1 and we have lift off. Couldn't do any adjustments tonight but it's dying when I let go off the throttle and blowing white exhaust. Will be spending time in the garage tomorrow with the tuning manual.
The manual on XScafe isn't the Sudco Mikuni Tuning Manual and contains some specs that are questionable at best.
The needles and needle jets are the heart of the carburetor. If those components aren't within a viable range, nothing is going to be right. Some vendors cheat on this and send out "pre-jetted" carburetors with fat factory NJ's and leaned out pilots and mains, and some buyers take short cuts and never look at anything but pilots, mains, and clip position. That's a recipe for frustration.
The needles and needle jets are the heart of the carburetor. If those components aren't within a viable range, nothing is going to be right. Some vendors cheat on this and send out "pre-jetted" carburetors with fat factory NJ's and leaned out pilots and mains, and some buyers take short cuts and never look at anything but pilots, mains, and clip position. That's a recipe for frustration.
I'm trying to figure out what needles/needle jet they installed in my carbs but they keep telling me I shouldnot mess with them and won't give me the sizes..... do i have to measure the needles to determine the size? In the meantime I'm doing the retorque on my engine. My exhaust is lined with burnt oil and it's all over any object the exhaust is facing. I had a leaking issue with a gasket before but this is new. I was juggling the idea of a rebuild buthe it's looking like it's imminent. I'm getting to know this bike more than I was planning to...
