A little help would be great

[jonjonwells]

Ok, working on a 750 sl. When I start it it idles on 1st cyl. but when i pull that plug cap off the rear two will fire. Now for the crap, when the rear ones fire it rockets to high rpms without any throtle. I checked the plates in the carbs and they are not stuck and the throtle cable works fine. Why would it do this?? I made sure all the carb settings were at stock and this still does it!!! Please tell me that this has happened to someone!!

[delagem]

Ugh, that sounds like an air leak....

When were the crank seals last changed? Have you done a leakdown test?

Have you tried swapping the spark plug wires around? See if the problem follows the wire, or stays with the cylinder?

[Bernie]

Have you looked down the throats of the carbs and operated the throttle to make sure they are in Sync with each other .It has to be getting air/fuel from somewhere .Try swapping plugs over and check it again .It may be that it needs a stronger spark to fire the richer mixture .When you removethe boot it gives the spark more time to build up hence stronger spark .

Cheers

Bernie

[jonjonwells]

Am in the middle of swapping carbs off of a known good ski. With any luck, it will run. If it doesn't, then main seals? CDI?

Oh well, back to work.

[jonjonwells]

OK, Good carbs installed. Started and reved to the limit. So whats the verdict???????????????

[xplayer2885]

Do a leak down test. Pull the carbs an the pipe off. Plug up the intake an the manifold. I used packing tape for this an it worked just fine. The pull the pulse line, hook up a compressor. I dont remeber how many psi i had pumped into the case. But the motor must hold the psi for a few minutes. Probally leaking at the crank seals.

[ph2ocraft]

If I'm not mistaken you just assembled the engine correct?
I think it may just need a little run time to properly fill the lines, carbs etc..
If you have a primer, pump it while running to get the RPM's down.
If you have a choke, choke it enough to where it brings the RPM's down.
Let it run a moment or two on the hose and see if it settles down.

[jonjonwells]

Unfortunately, this is not a fresh rebuild. We (thesepaperwings) currently working on two polaris', polarises, polarisi, etc....

[xplayer2885]

Al's very correct on the idel part. If you crack the throttle while running on the hose it takes a few seconds too settle it self back down becuase there is no load being applied to the engine.

Sorry too jump the gun Al!!!!

[ph2ocraft]

Mnnnn, try what I suggested for giggles at least you know if it brings the RPM's down with the extra fuel, you're too lean and of course most likely due to an air intake leak.