A real conundrum!

colt250ss · Post by **colt250ss** » Wed Jan 07, 2009 1:14 am

Hello all,
A friend of mine is working on a 1978 JD Spitfire with the 340 Kohler F/A motor in it. The sled is acting very strangely. It has many new parts in it such as:
CDI Box
Coil
Seals
Carb cleaning and trying a known good carb
150 LBS of compression in each hole.

It starts up fine and will idle all day long. However, that is all that it does. It will never rev up or increase in RPMs at all. It just runs the same no matter what. He has checked the seal by spraying starter fluid at it, with no change. Also, we fixed a small air leak in the intake, with no change. The exhaust is not plugged either. If we pull the exhaust, there is no difference. The smoke is also horrendous. It is just running pig rich and blackening the plugs. There are four professionals on the job ( ranging from factory trained sled mechanics, veteran auto techs, and an engineer). They can not figure this out! It is driving us all nuts? Does anyone have any idea what it could be? Fuel, spark and compression (three things that we have) are what I thought it took for an engine to run. This is what is so baffling! Another thing that they did was look at the pistons through the ports, and the pistons are in one piece, and un-scored.Thanks so much for assistance. If anymore information is needed, I will respond right away. Thanks again! Forrest

400brian · Post by **400brian** » Wed Jan 07, 2009 3:31 am

Does it have the correct carb for the sled?

What does it have in it for jets?

What happens if you slowly open the throttle?

Does it spit back through the carb?

speedy295 · Post by **speedy295** » Wed Jan 07, 2009 4:32 am

My El tigre does the same thing. Its the stator, those two sleds have very similar ignition systems. 77-78 340f/a jags, 77,78,79 4000,5000, and 6000 eltigres have the same setup too. maybe a lynx as well.

Don't buy a kimpex stator for it, they are built wrong.

speedy295 · Post by **speedy295** » Wed Jan 07, 2009 4:33 am

put a timing light on it and see what its doing. My guess, it that you'll see that it is an ignition miss.

JDT · Post by **JDT** » Wed Jan 07, 2009 8:05 am

Bad CDI Box. Common problem.

Rodimus Prime · Post by **Rodimus Prime** » Wed Jan 07, 2009 10:11 am

Try the simple thing first have you checked fuel pump to make sure it doenst have a pin hole leak pushing extra gas into crankcase?

ChickenRat · Post by **ChickenRat** » Wed Jan 07, 2009 10:40 am

What? Rodimus Prime? Next thing you know, Stebner will be back online!!

Robb

jdsledhead · Post by **jdsledhead** » Wed Jan 07, 2009 11:06 am

Sounds like the timing is wrong, ie a bad cdi or the stator is not lined up...take as much load off the motor as possible, best way would be to remove the belt, and do like brian said, try to slowly rev it up and check to see gas spitting back out. Also, make sure the choke cable is adjusted properly, this does have a mik. round slide on it right?

Spitfire79 · Post by **Spitfire79** » Wed Jan 07, 2009 1:19 pm

Welcome back Rodimus. Been wondering where you disappeared to!
Mine was doing the same. It was the CDI. Start with the simple items. Fuel, timing, etc

Jeff

speedy295 · Post by **speedy295** » Wed Jan 07, 2009 5:57 pm

First off, he allready replaced the cdi. Secondly, unless the cdi is bad, the timing cannot be adjusted enough to make it not run.

JDT · Post by **JDT** » Wed Jan 07, 2009 6:06 pm

Just because the CDI box was replaced does not mean it is good.

Two experiences with bad CDI right out of the box lead me to say this.

And if he replaced it with a used one chances are even less that it is good.

Best test is to install a known good box on fire it up.

Forrest do you have access to another Spitfire?

colt250ss · Post by **colt250ss** » Thu Jan 08, 2009 3:00 am

Hello again,
Thanks for all of the ideas. The motor is now out of the sled, and on the bench being torn down. I think you are on to something with the fuel pump. Also, this has a Mikuni butterfly/floater carb. No matter what one does with the throttle, it runs poorly. The belt has been off the whole time. We are going to tear it all down, clean it up, and start over again. Thanks so much, Forrest

speedy295 · Post by **speedy295** » Thu Jan 08, 2009 3:50 am

Props, for ignoring the one who actually has the same problem, with a sled that uses the exact same ignition system!

jdsledhead · Post by **jdsledhead** » Thu Jan 08, 2009 10:35 am

did you actually figure out your problem? and actually its not exactly the same system. if it was you could use a CDI from an el tigre and put it on a f/a 340?? havn't heard about that one. If you are talking generally, about the fact there is a coil, cdi, stator, then yes, the systems are the same.
I believe since he has tore into the engine now, there is no need to argue about what was causing his problem until the engine is running again.

Forrest, I don't know what kind of spare parts are available to you, but I would try what Todd said and barrow a known good CDI. (after of course checking out the engine to make sure there was no internal damage)

JoeRainville · Post by **JoeRainville** » Thu Jan 08, 2009 2:40 pm

speedy295 wrote:Props, for ignoring the one who actually has the same problem, with a sled that uses the exact same ignition system!

Speedy: Please check your attitude. Some of the guys you are discounting have been paid factory snowmobile mechanics, and have also rebuilt Spitfires. Voice your opinion, but we are all here trying to help Forrest out.

Forrest: I owe you a phone call buddy, sorry, just been buys as usual. Do you have the factory service manual for the Spitfire? If not I can drop mine on a copier for you.

It does sound like an ignition issue to me, and Speedy may have a point about the stator. My 99 Cat lost a stator at a SnoCross race back in 2000. I was sure it was a carb problem since it seemed to have spark. Tried swaping them side to side with no change.

The only other really wierd problem I've seen is a slipped crank that put one of the pistons out of time and ran very badly. But, since you idle well, have good compression, that seems to rule out a base motor problem. Remember that a bad stator can mess up a good CDI box, and as others have noted, some "new" or NOS boxes can still be junk.

I have an NOS stator if you need one. Drop me a line at home if I can be of any help.

-Joe Rainville