One Cylinder Wont Fire at Idle

[73Satellite]

I have a 04 RX Warrior motor in my 06 chassis. The swap went great but I found that the number 4 cylinder wont fire at idle. Carbs and jets are CLEAN. Everything is hooked up correctly. It seems to be getting TOO MUCH fuel and wont fire until the throttle is opened about 1/8-1/4....then it fires and goes like hell. There is an obvious change in exhaust tone and power when the cylinder fires versus when I let off and go to idle. Could it be getting too much fuel at idle because I smell fuel through the exhaust and the oil get thinned out and smells like fuel. Any ideas????

 

[LazyBastard]

Sounds like it could be a partially fouled spark plug or other electrical problem possibly related to the coil.

 

[grader]

i know you said carbs are clean but too much fuel in one carb sounds like a stuck float. dirt under the needle and seat assembly could cause this. swapping plugs between cylinders will help determine if its spark related.

 

[73Satellite]

I have changed coils between cylinders (the coils were ok), put new plugs in, and put different (not new) fuel pumps on, when I cleaned the carbs I ensured the floats and needle valve moved freely.

Last spring the "dead" cylinder only fired until I got to about 3/4 throttle, was "doggy" and hesitated. Similar symptoms persisted then as now. This year I switched the vaccum supply to one of the fuel pumps from the "dead" cylinder number 4 to the number three vacuum port on the carb. This has improved the symptoms from 3/4 throttle firing to 1/4 throttle firing. Throttle response improved and power comes on a lot sooner. You can audibally hear a tone differance when the fourth cylinder fires and does not when you let off the throttle. An improvement but not a solution.

Any more ideas?

 

[LazyBastard]

Sounds like you could have vacuum issues. Leaky CV diaphragm? Could be the o-ring on the top is missing.

Have you done a compression test? Have you checked for vacuum leaks?

 

[rxrider]

Have you checked the o-rings underneat the main jets, the o-rings prevent fuel from escaping outside the main jets, if one or more of the o-rings are broken your sled will run like crap.

 

[LazyBastard]

If you're referring to the o-rings that seal the main jet to the hole in the bottom of the float bowl, they won't make any difference even if they're all completely missing.

 

[73Satellite]

So after swapping fuel pumps and cleaning carbs again with no change....I switched needle valves between the bad cylinder and another and so far so good. It sounds good, smells good, and runs significantly better!!! Tomorrow I will change the thinned out oil pull it out of the garage and run it down the trail to do verify its good to go. Then I will go down to the dealer and order new needles for the carbs. Hopefully its good to go after that and I can enjoy the best time of the year!!! WINTER!!! SNOW!!! RIDES!!! CAMPS!!! HUNTING!!! you get it.

 

[73Satellite]

I did in fact check to see if the diaphrams were ok and they were. The o rings of the main jet need to be replaced but that was irrelevant to my problem. But as in my previous post things are lookings good and I think the needle valve for the bad cylinder needs to be replaced. I will change them all for good measure. Thanks for all your help....it definately got the brain working.

 

[rxrider]

If you're referring to the o-rings that seal the main jet to the hole in the bottom of the float bowl, they won't make any difference even if they're all completely missing.

They won't? Why are they there???

 

[LazyBastard]

In 03 they weren't.
The 03 mountain sleds had a problem where the engine would cut out when at extreme angles due to the main jet sucking on air.

As an update for 03 mountain and as standard equipment for all sleds 04-05, the float bowl was redesigned and sealed to the main jet to allow it to continue sucking in fuel even under the conditions where the 03 mountain would have problems.

 

[rxrider]

Thanks LazyBastard.

That makes sense
I have the upgraded float bowls, that's where I remember the o-rings from, have completely forgotten how it was with the stock floatbowls.

 

[kinger]

FYI rxrider - I have ZERO o rings under my main jets runs fine. Its a flatlanders 03

 

[rxrider]

Thanks kinger

Me forgotten about the stock floatbowls as I've have run it with the upgraded mountain floatbowls for a long time.