Popping in Carb

Deleted User · Post by **Deleted User** » Sat Nov 18, 2006 9:52 pm

Hey,
I got my 72 JD Model 600 running but it pops through the carb regardless of needle settings. I've also changed the timing incase it was too advanced but this doesn't seem to make much difference, is there anything obvious that I'm missing?

Thanks,
Craig

400brian · Post by **400brian** » Sun Nov 19, 2006 4:22 am

Has anything been done to the carb? Cleaning, rebuilding?

Deleted User · Post by **Deleted User** » Sun Nov 19, 2006 11:27 pm

I did just rebuild the carb, it is the same as before the rebuild. Are there reed valves that could cause this? It runs OK now, just not well. I can't seem to kill it by enrichening the main needle, this worries me...
Craig

400brian · Post by **400brian** » Mon Nov 20, 2006 3:57 am

Lets make sure what we are talking about here.

JD started building the 600 for the '73 model year.

If your sled is a '73, it should have a KEC 440/4 CCW engine, which is piston ported ( no reeds ) The carb should be a Walbro WDA-32

I'm not sure you should be able to "kill" the engine by screwing the mixture needle out.

The base settings according to the service manual are:

High speed needle ( the one on top ): 7/8 turn open
Idle mixture ( the one on the side ) : 1 turn open

There are no doubt more than one reason why you might be getting popping back through the carb. I have seen this myself with a Mikuni on a 340/5 engine. In that case, the carb was jetted way too rich. It ran best when the engine was cold, but would start popping back through the carb when it was warmed up and running faster than idle.

Something isn't quite right. I suppose you could have a mechanical issue, an ignition issue, or some sort of fuel delivery issue.

When you rebuilt the carb, did you check the metering lever setting? Generally, it seems if it is wrong, it is more likely not allowing enough fuel in. In those cases the engine may not even run, which makes it easier to diagnose.

The service manual does not seem to give any trouble-shooting advise on a situation like this. If you can give us more info about this, perhaps someone will come up with a good idea.

Danzig · Post by **Danzig** » Mon Nov 20, 2006 10:45 pm

In my opinion, this is all related to the timing.

Craig please explain how you went about retarding the timing.

JDFanPa · Post by **JDFanPa** » Tue Nov 21, 2006 12:58 am

I think Danzig has a good point here......could also be a bad air leak even crankseal like.......specialy with the high side issue........I had this happen on a cat motor with great compresion etc and it had a piston skirt broke off and the exhaust was coming out the carb........I think we need more info on your problem

Deleted User · Post by **Deleted User** » Sun Nov 26, 2006 7:01 pm

Hey,
Well its a Model 600 that has a build date of 1972. Likly a 1973 model. The popping has been more or less stopped with the addition of fresh fuel. The issue that I see it bogging, with the track jacked up if I bar it, the engine doesn't really pick up RPM's well. It will ocasionally fire back through the carb but what is really happening is that air/exahust/fuel blows like a stiff wind from the carb when its bogging. It I add more fuel with quick start when running it picks up RPM's well.

I have looked at the metering setting and its good. It was level with the carb body and I even pulled the setting a little lower and this made no difference.

As for timing, I've set the points and verified the operation. The timing was changed by rotating the stator and this made little difference, would this cause the wind from the carb if too advanced? I also think that at times I can hear detonation, would this also indicate too advanced?

I think that the crank seals are good because I get great fuel pump operation and if I spray ether around the seals I hear no difference at idle.

Thanks,
Craig