78 JD spitfire 340 wont rev

[roblarss]

Just got a 78 spitfire 340 and im having some running issues. Biggest issue is I have no clue what was done before me.

Stator was out and dismantled but I reassembled it and it fires up and idles pretty decently. Give it throttle and it just bogs down. I can hold it there and it wont rev up at all. Spits gas out intake. Compression is about 90-92psi per cylinder. It has what im assuming is not the original carb. Mikuni 38mm (measuring intake side). 190 main 25 pilot needle is all the way down. Tried a second CDI that came with it and same issue. left cylinder doesnt fire as much as right but sometimes it does even out. Seems way better when i dropped the needle and let the slide down more. I am wondering if the carb is to big and flooding it out. Choke makes zero difference but I did loosen the adjustment so it seems to be fully closed as I was suspecting it was partially open.

Open to ideas. seems a decent sled for my son to drive around yard.

 

[snopro]

Could be a carb blockage but 38mm seems like a big carb for that sled. Did you look at main jets and pilot jets? Could be plugged from sitting

 

[sledneck__11]

On my spitfire the primary had seized and wouldnt shift in snd then would pull the motor down

 

[roblarss]

Could be a carb blockage but 38mm seems like a big carb for that sled. Did you look at main jets and pilot jets? Could be plugged from sitting

I cleaned the carb out pretty thoroughly. Was full of green crap. Jets are nice and clean now.

 

[roblarss]

Nothing changed with the belt off. Still idles alright but spits out the carb and does nothing but change sound when throttle is given. Tried to give fuel from bottle and also cover part of the intake with hand to see if I can find the magical formula to get some more RPMs out of it.

I wonder if it could be an issue with crank seals so its not pulling the fuel in? I cant see the stator timing being off affecting it this much. I just put the stator in the middle which is where it looks like the bolts used to be. Pulled the primary outer sheeve off but cant get the inner off to check that side. Seems to use the same removal bolt as my summit but I have alot of pressure on it and some heat.

Sprayed some cleaner around the seal behind primary and it didnt seem to change anything.

 

[snopro]

Nothing changed with the belt off. Still idles alright but spits out the carb and does nothing but change sound when throttle is given. Tried to give fuel from bottle and also cover part of the intake with hand to see if I can find the magical formula to get some more RPMs out of it.

I wonder if it could be an issue with crank seals so its not pulling the fuel in? I cant see the stator timing being off affecting it this much. I just put the stator in the middle which is where it looks like the bolts used to be. Pulled the primary outer sheeve off but cant get the inner off to check that side. Seems to use the same removal bolt as my summit but I have alot of pressure on it and some heat.

Sprayed some cleaner around the seal behind primary and it didnt seem to change anything.

As in ether or brake kleen? Ether will tell you if you have a leaky seal. Stator is probably in the wrong spot and timing is off if that’s how they time those things. I do t know much about them other than riding a JDX 4 as a kid. Try and find some info on timing for them on Google. Your local Deere dealer may have some old shop manuals in storage as well?

 

[roblarss]

I sprayed it with brake cleaner.
May have just found something. An old kohler service manual says to use a timing light to set timing. If #1 is truly the PTO side (as shown in one of the manuals) then the engine is 180 degrees out. Seems strange. Wouldnt think it would even run that way. Which side is 1 prob doesnt matter as both sides spark every rotation. Could also mean my crappy timing light is faulty...

Going to check next with a dial indicator in plug hole and see where the mark is in relation.

 

[snopro]

I sprayed it with brake cleaner.
May have just found something. An old kohler service manual says to use a timing light to set timing. If #1 is truly the PTO side (as shown in one of the manuals) then the engine is 180 degrees out. Seems strange. Wouldnt think it would even run that way. Which side is 1 prob doesnt matter as both sides spark every rotation. Could also mean my crappy timing light is faulty...

Going to check next with a dial indicator in plug hole and see where the mark is in relation.

Never heard anyone use brake kleen to check for air leaks. We’ve always used Ether

 

[roblarss]

Never heard anyone use brake kleen to check for air leaks. We’ve always used Ether

i would use ether but all out currently. Figured the brake clean burns so it should work.

 

[roblarss]

Got it figured. Moved the timing adjustment all the way and off it went. Timing marks arent even close on the stator. Must have a different backing plate or something. 8 year old is making tracks around the yard now.

 

[snopro]

Got it figured. Moved the timing adjustment all the way and off it went. Timing marks arent even close on the stator. Must have a different backing plate or something. 8 year old is making tracks around the yard now.

Enjoy! Those were one of the coolest sleds ever built.

 

[roblarss]

Well it was short lived. He got about 10000km driving around the yard. Was not running as great today and then i went to start it and it acts how it did before i cranked the timing i think as far advanced as i can. I wonder if the stator still has an issue. Anyone have a spare stator? Ebay has some but will take a month. Or a reliable place to rewind one around red deer or Edmonton. Sled did run amazing but earlier today it seemed sluggish at top end. Now it just idles and wont do anything when i hit throttle.

 

[roblarss]

Still working on this sled. Still bogging when you take it off idle. Strangely i was showing the issue toa friend and it fired and reved right up. Put together the next day and ran fine. Did a few yard laps and parked it. Started up the next day and was bogging again. I was moving wires around an got no difference. started pulling plug caps back and forth to see if it was running on both cylinders and then it started to rev up again. Kid did a few laps (was very dark) and we parked it. Today same issue. I noticed the right cylinder will get hot and the left not as much. pull and plug cap and it will stay running no matter left or right. Compression is about 105psi on both cylinders. Any ideas? I am stumped. I am doubting its a spark issue. 105psi should be enough plus when it works it works until its parked. Has a 190 main jet. book shows a 210 but i dont think that should make much of a difference.

 

[brian h]

So am I understanding it correctly but sounds like after it warms up some is when it starts to run fine. For every morning or next day it acts up

 

[roblarss]

It doesnt seem to matter if its warmed up or not. Its more just random if it runs or not. Majority of the time it doesnt. I havent really tried running it and then letting sit for a few hours to see if it works again. I havent been home enough to test that. Usually if it runs when I get home from work the kid drives around for an hour or 2 until dark.

I was playing with it in the shop for a week or 2 and couldnt get it to rev. My buddy showed up and i cold started it and it reved fine. Later that evening it was fine so I pulled it out and now its not. Maybe its temp related but I was trying it for a week inside and I had no luck until he showed up.

 

[roblarss]

im going to get a new set of plug wires and caps tomorrow to try. The current ones have a bit of leakage (shocks you when you touch them). May have to get an entire coil as Im not sure if the current wires come out. Appear to be glued in. Dont think this is the main problem though as I should see arcing to the engine if they were grounding out. Should be changed anyways.

 

[kenvb]

PLUS 90 LBS COMPRESION ISNT ENOUGH, PUT NEW PISTONS AND RINGS IN IT.. WE HAD 2 SPITFIRES FOR FEW YRS, KIDS DRIVE HELL OUT OF EM. NEED A MIN OF 125 TO RUN DECENT,,150 IS TOP SHAPE. GET A COMPLETE GASKET AND SEAL KIT,.REBUILD AND RESEAL IT..THEN RUN 20-1 PREMIUM , WILL LAST LONG TIME,

 

[roblarss]

PLUS 90 LBS COMPRESION ISNT ENOUGH, PUT NEW PISTONS AND RINGS IN IT.. WE HAD 2 SPITFIRES FOR FEW YRS, KIDS DRIVE HELL OUT OF EM. NEED A MIN OF 125 TO RUN DECENT,,150 IS TOP SHAPE. GET A COMPLETE GASKET AND SEAL KIT,.REBUILD AND RESEAL IT..THEN RUN 20-1 PREMIUM , WILL LAST LONG TIME,

Thanks for the info. Im starting to think that it needs a rebuild also. Gasket set is on the way. Need to look for a piston/ring set. Compression did come up to 105/cylinder with some riding. Its so strange that when it wants to run it seems to run great. Also fires up instantly and idles. Carb also seems way to large being a 35mm. You say 20:1 mix? at 40:1 it smokes like an old locomotive.

 

[roblarss]

pulled cylinders and measures the ring gap. .010 and .019. .019 was the cylinder that was not getting as hot. Prob explains the running issues. Now I need to figure out where to find new pistons/rings. Cylinders appear fine. I herd they may be plated. Easy to work on as you only need a 1/2" to take everything apart.