1976 JD 400 Have spark, good compression won't start

[Larrytkd]

1976 JD 400 340 CCW
Have spark, good compression won't start with starting fluid.
Details: I obtained this sled last year. It was in great shape physically and seemed to have good compression, great track and everything appeared intact.
When I got it home I checked the compression 120 both cylinders.
No spark.
Replaced the CDI and had great spark.
I used starting fluid and it kicked over but wouldn't remain running.Cleaned out fuel tank, replaced lines and filter.
Cleaned carburetor.
Would not remain running after prime was used up. I know I probably have to rebuild carb.
>Primed with gas in the cylinders, attempted to start.
Engine back fired and now won't start with starting fluid either. Still has good compression
Has great blue sparks on both plugs.
SN > 55,000 bulit in 1975 but looks like it is a 1976 model
Some tech manuals say it is piston port, other indicate it may be reed valve.
Open to all suggestions.
Is this a timing issue, did it "jump" timing", or does this have reed valves and did I blow it out.

[harleysportster]

Here is some general info of your '76 400. Check your serial number to see if it falls within Serial # Range: 55,001 - 70,000. The KEC 340/22 is reed valve engine.
I would say you have carberator problems now since you have spark.

Model Year: 1976
TYPE CODE- J400E
Serial # Range: 55,001 - 70,000
Manufacture Dates: May, June 1975
Number Produced: 2400
Engine: Kioritz KEC-340/22

[Larrytkd]

Here is some general info of your '76 400. Check your serial number to see if it falls within Serial # Range: 55,001 - 70,000. The KEC 340/22 is reed valve engine.
I would say you have carberator problems now since you have spark.

Model Year: 1976
TYPE CODE- J400E
Serial # Range: 55,001 - 70,000
Manufacture Dates: May, June 1975
Number Produced: 2400
Engine: Kioritz KEC-340/22

Harleysportster,
So it does have reed valves! I had some conflicting information.
Thanks for your response but wouldn't priming the cylinders with starting fluid bypass the carburation and at least fire for a short duration? I can't even get it to fire that way. If I continue to keep pulling the starter rope I only get an occasional "fuff" from the exhaust after about 8 pulls. Like I said it would run briefly on the starter fluid until the loud back fire.
So
Larry
My sled does fall within the range you posted above it is over 55,000

[harleysportster]

Do you know when the last time the crank seals were replaced? Worn seals cause the same symptoms.

[Larrytkd]

Do you know when the last time the crank seals were replaced? Worn seals cause the same symptoms.

No I don't know when they were replaced. Sounds like I will have to pull the engine.
I was hoping there were other things to rule out.
So you don't think the backfire could have affected the timing or the reed valves?
Thanks. I appreciate your help.
I just don't understand why it would have run on starter fluid and then not after the back fire. Perhaps it was a coincidence.

[harleysportster]

The backfire probably blew out the old weak seals.

[HoosierDeereMan]

You might also check the air box and hose that bolts to the carb for a mouse nest. If it's obstructed it may not be getting air.

Troy

[Larrytkd]

Thanks Troy and Harley.
The airbox is off. I have had that problem with critters using the airbox or the exhaust for nests.
The blowing out of the seals makes a lot of sense. It was loud and toward the lower area.
I any event, taking the engine out is not a big task and I still have my 440 Cyclone which is an indestructible beast. While I have the engine out I'll check the seals and the reed valves.
Thanks!
If I were to pressurize the crankcase I should see or hear air coming out I would think.
Wish me luck!

[sledhead16]

Take a pop cap full of 50:1 mix and pour down each cylinder head then put plugs back in and pull it over. It will burn longer to pull more full than starting fluid. After that if she won't pull fuel from the carb its then the carb..

[Larrytkd]

Update:
This weekend I took the engine out, cleaned it removed the pull starter assembly, fan pulley and flywheel. Replaced that shaft seal and reassembled. Then removed the clutch, shaft seal cover and then replaced that shaft seal and reassembled. I removed the intake manifold and checked the reed valves and they all looked great and then reassembled. I then reinstalled the engine in the sled and checked for spark. Great blue spark on both plugs. At this point I am rebuilding the carburetor and hope to have it completely reassembled by the end of this weekend.
One question: I noted some fresh oil on one of the nuts on the bottom of the engine casing. Nothing else no carbon the nut was just very clean with clean oil on it. I removed it checked the site thoroughly and replaced it. Is this significant or something normal. I have great compression 120 each cylinder and there seems to be no cracks or other finding on the casing.
More to come as I complete the carb and attempt to start it again...

[JDT]

Sounds like you are making every positve progress.

Keep up the good work.

[lwb140]

I apologize on the front end here, you've been advised by the best here and I didn't read the entire thread BUT double check the cdi wires are hooked to the correct coil or the spark plug wires aren't crossed many aftermarket cdis have the red and white wires crossed also it is easy to mix up spark plug wires many sleds have both plugs fire at the same time both sides the prestolites don't . if it wont fire on either with good spark and compression and a descent plug something is up like I said I didn't read all the dialog and maybe this has been addressed just an idea, been here done this !!!! :}} I recently converted my dads 75 400 from points to cdi the red and wire wires to the coils had to be crossed from a point set-up to cdi with a dk trader 77 cdi and pick-up coil wade

one more thought, even if you have spark check the resistance of the low speed stator wire to ground it will be the yellow wire on the stator it needs to be 2.7K ish to start and run right if its much lower you could still have spark but not enough to light a fire and run right

[Larrytkd]

Thanks lwb140. I'll check into that!
I took the Walbro apart and cleaned it yesterday. I didn't put it on though. I decided to try to see if it would kick on just ether. No luck. Then I thought that perhaps the impulse tube being open might have affected it.
I will follow up on your advice. Thanks!

[Larrytkd]

Update. I took it to an 'expert" small engine mechanic who assured me he could find out the problem. It's been there since the weekend. Today I get a text message from him. "Did you have good fuel pressure? I'm thinking Carb or timing is a problem. Compression is at minimum175 to 120 I check too?? All so oump must have good vac from crankcase did you check for fuel pump vac line." I responded back to him that I rebuilt the carb before bringing it to him but didn't check if there was a good vacuum from the impulse line.The saga continues....could the crankshaft be bent?

[harleysportster]

Just a thought, bad crank seals, no impulse for the fuel pump.