Another DC carb question

[ISITRUSTY]

After I got the tractor running, it ran great just running with no load. If I started to work it, it would have a backfiring fit and just barely pull itself until it cooled. I got a rebuilt carb for it. It was obvious that it needed it. It now runs great until you put it under load and it starts having the backfire issue again. Gas flow seems fine. Not sure what it is telling me. Thanks in advance for the help.

 

[chuck machinist]

I think it is great that a new carb is bought and installed, Although, sometimes carbs, just because they are new are not necessarily built correctly. You have checked that you have sufficient fuel flow from the gas tank?CM

 

[rustred]

FIRST check compression, then u checked the valve lash and set it. a carburator does not cause a backfire. you have valve problems. its the standard thing to do on a complete tune up.

 

[Denny K]

Have you aqdjusted the power needle? You may have to open it up another 1/4 turn at a time until it runs fine when pulling.

 

[Denny K]

Have you adjusted the power needle? You may have to open it up another 1/4 turn at a time until it runs fine when pulling.

 

[ISITRUSTY]

Thank you everyone! I do appreciate your advice. This is the tractor that the engine was stuck and came free when I put it in the barn. I did not check compression or the valves. That makes sense, that that would be my issue. A friend told me that if the tractor was running lean, that would cause backfiring. So I was focusing on on the carb. What is surprising to me the tractor ran better and had more power when I first got it running. I will check the valves and compression tomorrow. I live on a hill so I drove up it to have a load. I then adjusted the needle the quarter turns. I think the carb is adjusted about as good as I can.

 

[rustred]

Also is it backfiring out the exhaust pipe or carb. ? Dont get missing mixed up with a back fire. Carbs do not cause a backfire. It could be tight valve. Once engine gets hot metal grows and cause a no valve clearance keeping it open a bit.

 

[ISITRUSTY]

It is backfiring out the carb for sure. It has blown the oil out of the air cleaner.

 

[LPakiz]

Sticky valves can cause this, as well as a faulty distributor cap.
When you apply a load, the carb butterfly opens up and lets more charge into the cylinder, which raises compression pressure, which is more difficult to fire. Then spark may jump in the cap to a plug which fires easier.
Make sure the cap is dry inside. Moisture likes to accumulate in there, also causing cross-fire.

 

[fixerupper]

Battery ignition or mag? In my mind your symptoms just scream bad condenser. Its definitely not a bad idea to run an overhead on it. Properly set valves can smooth it out even if tight valve setting isnt causing the backfiring.

 

[ISITRUSTY]

I put new coil, points and condenser it it but I didnt replace the cap. I will check the valves and I think go ahead and replace the cap.

 

[Ron Sa]

I don't know why but many year age my uncle had a similar problem with his F20 Farmall. It idled good, cranked good with seemly normal and equal compression on all cylinders. Under load is would spit and sputter and backfire. After working thru the carb, mag, and spark plugs with not change, finally, he ground the value and that fixed the problem. I have never figured that out.

 

[ISITRUSTY]

Well the distributor cap may have been the issue. I checked to see if there was any moisture in it. It was dry but the tractor has stopped backfiring. It actually sounds good. I am still going to check the valves though. The issue now, the governor doesnt open when the tractor is under load. The governor worked fine with the original carb. Now the tractor just bogs down.

 

[fixerupper]

Probably just simple binding in the linkage. Or the throttle plate is sticking. Glad you found the dist cap problem. As others can testify a new condenser can be bad out of the box. They arent made as well as they used to be.