78 invader 440 engine not make power off of the stand

[Marisa30]

I have a 440 Invader it starts great about two pulls cold and idles great it almost seems the idle doesn't want to come down with the idle screws backed way off and it wants to creep with a new belt installed, I put an old belt on and it stopped creeping but the main issue is it has no power under load off idle from the hole shot on up and does not ever make full power and sounds flat with no crisp feel. It idles and runs great on the stand and the clutches run out full travel. I did swap both clutches out as it almost seems like something is restricting or hold the engine back like a bad roller. No help. It has good compression both sides. I am guessing that one of the crank seals is leaking (mag side) but I would like to exhaust all options before I swap out the engine and waste time when there is snow to ride on. What are the chances of a CDI box being bad, or an intake leak?

[Lloyd (ljm)]

 The CDI's are pretty dependable. Not saying it is ok, but they usually are pretty good.

 Could be an intake leak.  What are your intake boots like?

 Lloyd

[gixxer6]

If it idles too high with the idle screw adjusted out, check the throttle cable is adjusted correctly. 

[jimvw57]

Check the o-rings on the center of the carb bowls. If they leak you will have problems, might not be a bad idea to replace all the jets in the carbs. They aren't that expensive and it will eliminate a potential problem.

Also it could be the carbs are not synchronized, One side pulling more than  the other.  Start by checking compression.

[Checkmarks]

It sounds like you are only running on one piston.  Very typical symptoms to not have enough power to take off except on a jack stand.  Couple with a flat sound and I say ding, ding, ding.  Now to the why one cylinder is not combusting.  Does both sides of the manifold get hot (equally) when you first fire up the sled?  The side that is colder is the culprit with the carburetor problem.

Starts great suggests the seals are working and there is no air leak.  Change the seals or you risk not having a sled.  It cost less to change the seals than buy a cylinder and piston.  Don't change the seals and you may not get to ride your sled very long, then maybe.

[Marisa30]

  I have replaced both carb boots no help checked compression both sides are above 150 PSI. It starts on about two pulls and runs great on both sides the y - pipe indicates both sides are firing on the stand still falls off underload and will not increase RPM. While I had the plugs out of the heads but in the boots while checking compression it sure didn't seem to be much spark jumping the gap, however as soon as I install the plugs pull it over a couple times it fires right up and idles nice.

[Checkmarks]

Compression ruled out, good. 

Carburetors cleaned with new rubber o-ring? synchronized? 

What hardware is in the carburetors since you will have them apart checking for correct parts and jetting?

Starts and idles only suggests the Cdi is good but does not conclude.  Only matters if you have no spark not how much you think you have. 

New view, jetting can be out to lunch and the problem points toward the fuel metering.  Cdi is always in the maybe category.

[Marisa30]

New o rings at the main jets in both carbs fixed the issue. Thank you.