JD300 has one plug a bit leaner than the other.

grasscutter97 · Post by **grasscutter97** » Tue Jan 23, 2007 12:24 am

Did a 195 miles on my JD300 over last 2 days. Put it in garage to do some check over stuff. Track, plugs, etc.

Compression tests 135 both sides. About 500 miles on complete engine rebuild (seals, crank, pistons, everything). Plugs were nice brown on MAG side, and definitely VERY light, lean on PTO side.

Took a look at the fuel filters. The check ball filter in tank looks good, the clear inline filter looks clean.

Carb screws were: top high speed at 1 1/8 out. Idle mix on side was: 1 out.

Fires up in about 2-3 pulls from cold, and runs a steady 40 mph all day.

How do you go about fixing a lean plug on one side, when only one carb feeds both cylinders? If I richen it (screw out the high speed needle a little at a time), I found that it makes the sled much harder to start. Anything else to do?

I do not have the rubber intake tube that connects to the airbox. Is this a necessity?

Danzig · Post by **Danzig** » Tue Jan 23, 2007 12:32 am

Did you pressure test the engine prior to the install?

grantnelson00 · Post by **grantnelson00** » Tue Jan 23, 2007 12:34 am

same plugs on both sides?

bpmailman · Post by **bpmailman** » Tue Jan 23, 2007 12:35 am

Are you drawing in air around a gasket on that side?

grasscutter97 · Post by **grasscutter97** » Tue Jan 23, 2007 12:59 am

Found it! I think? After looking it over, I found the 2 little screws that hold the throttle/choke assembly to the carb. There is one that is screwed directly into the top of the carb. It was about to fall out. (both were loose). I put a tiny dab of locktite on both of them and srewed them down tight.

That would be a cause of a lean condition for both sides right?

Check all intake gaskets. All are good, tight and no warpage anywhere. Both plugs are the same. I'm gonna run it 2morrow and see if that makes any difference. I know the pto side on dual carbs are usually jetted richer. So, if I can reduce the lean condition (which I think I did), it might bring the PTO side a closer to normal brown, and probably bring the MAG side a bit on the rich side.

That would be fine by me. I'll post after tomorrows riding.

Danzig · Post by **Danzig** » Tue Jan 23, 2007 1:14 am

I would not think that the loose screws would be the problem, if they needed to seal I would think that the carb would have came with a seal on these screws and in the rebuild kits. Hey, I am troubleshooting problems also!! Good Luck!!

JDFanPa · Post by **JDFanPa** » Thu Jan 25, 2007 1:42 am

If it were those screws it would lean both cylinders. Most likely you have a crank seal failing but could also be a intake gasket or even where the crankcase halves seal.

grasscutter97 · Post by **grasscutter97** » Fri Jan 26, 2007 10:43 pm

Ok. Update:

I should be more clear about the 2 little throttle bracket screws. The top one was out. How it didn't vibrate and fall some where I do not know. It was out of the carb but was in the hole in the throttle bracket.

The other one was so loose that the whole throttle bracket was about to come off completely.

It looks like only the top one would suck air. Bad!

So, took it out for some runs and the plugs are definitely browner! The PTO side is still a bit leaner than MAG, but it is brown! So, I played with the high speed needle adjustment a bit and found the book states 1 1/8 turns out. I put it to 1 1/4 out and it browned the plugs just a bit further.

So, next time I plan on doing a 100+ mile trip I might turn out the high speed another 1/8, just for safeties sake.

The only downside I noticed to richening up the high speed (turning high speed screw out) was that it got a little bit more difficult to start after warm.

Example: 1-2 pulls cold. After gets nice and WARM, after a lot of WOT, it takes 5-6 to re-start.

Would there be any adjustsment to make to the idle screw to compensate for screwing the high speed needle out a little bit more?