Diagnose this engine problem if you can

[rustred]

check the compression when it is acting up. like thats the thing to do if you have repalced a pile of parts. why not check it first then post back , it might be that simple, tight valves. that the heart of the engine. plus your playing with timing,.. why not just set it to the factory spec.?

 

[rustred]

spits sputters and backfiring is valves, check that compression.!

 

[parisspringstom]

Could you have the fuel line running to close to the exhaust manifold and causing vaporization.

 

[rustred]

and also have u confirmed the firing order is correct? 1 3 4 2 , i have seen people trying to run an engine with the plug wires on wrong!!!

 

[Bruce from Can.]

Way out there, but I have seen this happen. Is the distributor wore and loose? If it can jiggle back and forth it will affect the timing and how the points are set. I had a similar issue with a 430 I had many years ago, and swapped out the distributor , and solve my problem. Really a timing issue for my tractor I guess.

 

[rustred]

and also a low hr engine? original or just redone? if redone the guy had no clue how to set valves and there u go. just because they are moving means nothing. they must be set to the factory specification. do you know how?

 

[JMOR]

oil leaking out of cylinder around plug seal, but compression doesn't?

 

[oldwrencher]

have you checked the air filter?. I have a m f 135 in the shop now that would run good only with some choke. I pulled the air filter, opened the choke and it cleared up and speeded up some to run as it should. Date on the filter is 95. Doesnt mean installed then, but was not made since then

 

[geok]

Had a ford 900 that wouldn't run well most of the time. Replaced the wiring from the battery cable to the switch then to the ignition coil and distributor. It ran like new. Old wiring seem to build up resistance over the years

 

[Hobo,NC]

Whut do the spark plugs look like ?

 

[sixbales]

Jon,

If it's running rich, maybe the fuel pump is overpressuring the system, forcing fuel through the (closed) carburetor needle valve??

 

[Steve@Advance]

Exhaust backfire is almost always intermittent or erratic spark.

Loose connection, failing ignition switch, worn distributor shaft, pinched, chewed,burned primary wire to coil, poor connection from coil to distributor, distributor housing not properly grounded (rare but happens).

 

[Janicholson]

Put a timing light on it and watch the front pulley. Not for timing, but for stability of the rotation. If the flash is inconsistent on the wheel, the distributor cam bushing is worn and making the timing as much as 20 degrees advanced or retarded! Jim

 

[caterpillar guy]

Junk the Gasser and drop a diesel in it problem solved.

 

[used red MN]

Uncle Tom asked ..Is the needle and seat not holding and flooding enough to make it rich?.. You say the mechanical fuel pump works good, maybe in a way to good. Maybe whatever controls the amount of pressure the pump puts out is stuck or faulty. Then the higher fuel pressure cannot be held by the float needle valve and the fuel bowl level gets to high. In the photo is a method to test the level as it is running, showing a small engine carb but the method is the same for many gas engine if the carb configuration allows it. It requires some clear tubing and a hose barb for the carb drain. Also what springtom says about fuel vaporization commonly called ..vapor lock.. may be aggravating this as well. If this check can be done it would clear up several things that may be to blame as far as the carb goes. Just trying to point out different angles to a couple of things mentioned.

 

[gene bender]

as always start with compression check

 

[Geo-TH,In]

It would be easier to remove the radiator cap, back the old swather out and put the old radiator cap on a new swather?

Backfiring out the exhaust is a sign of a bad exhaust valve or too much gas in the exhaust.

 

[sms]

And check mechanical advance. I've seen the weights hang up or just be stiff and move erratically. If so timing will be off and cause backfire.

 

[sms]

Forgot to add that this can happen if it is not run often.

 

[r.w.b.]

check valve clearence. had a tractor run good,let a load hit it n it would act up like that. valves were too tight