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[geniusloerts]

here is the challenge of the day!

my bike was running great unil this week. it appears that the number 1 cylinder is not firing.....I have spark, compression, but it seem that fuel is not being sucked into the cylinder...i do have 30psi of vaccum at idol......when i am in upper RPM's it fires.

What do you all think?

-Genius

[TopCatGr58]

Vacuum leaks really SUCK!

Hey Genius,

We've seen this before. A vacuum leak, either the carb boots to head fitting, or the synch port cap, where there's enough of a vacuum leak to not allow it to be able to draw the fuel/air mixture thru the Pilot circuit, but once the rpms get up a bit, then there's enough vacuum to pull the fuel thru the mains! Oh wait, you said you measured 30 PSI vacuum at idle, I'm assuming at the synch port. So unless the synch port cap is hardened, brittle, then I suspect below!

OR...the pilot circuit is clogged, so fuel can't be drawn thru it at low rpms, but higher rpms engages the mains!
T.C.

[skids]

Re: Vacuum leaks really SUCK!

I am betting it is due to a broken-off pilot screw (mixture screw) tip.

Originally posted by TopCatGr58
OR...the pilot circuit is clogged, so fuel can't be drawn thru it at low rpms, but higher rpms engages the mains!
T.C.

[mro]

OR...the pilot circuit is clogged

mro
BTW,
what's the condition inside tank and how old are the fuel lines?
Do you have in-line fuel filters?

[geniusloerts]

I have put new carb holders on, new sync plugs, jets (mains, and primarys) are new, fuel lines are fairly new, the inside of the tank is in alright condition(shiny metal) and ifigured something is plugging the carbs so i put the inline filters on last night.....

I did pull the carbs and pulled off the float bowl and jets and sprayed out the orfaces on the #1 cylinder.......I didnt mess with the mixture screw.....maybe i Should? Pull and clean?

[TopCatGr58]

Not just the mixture screw, but the PILOT JET as well, and the spritz inside it a lot to make sure the pilot circuit is clear! IF it's not too big a pain, would recommend doing this to ALL 4 carbs since you have the bank off, since you JUST put the inline filters on, there could be junk lurking in the bowls of the other carbs just waiting to be sucked up into the pilot jets and clog!
T.C.