TO-30 Backfiring

phil(va) · Mar 12, 2015

TO-30, converted to 12 volts, starts easy, sometimes runs smooth, other times it backfires and sputters, acts like a plug wire is out of place or timing is way off. Then it will smooth out and run good for awhile. Cleaned carb, reset points, set timing. Drained gas and replaced fuel. I'm thinking trash in fuel line, but I don't know. What say you? It started after a cold spell. No water in oil, no oil in radiator. I did replace plugs, which needed it (AL 3116), but still popping and sputtering about half the time. When I cleaned the carb i did not have full kit, but I did have a good main gasket and new needle and seat. I did find trash in bottom of carb. Only thing I can think of is more trash somewhere, but interested to see what you say.

Jason S. · Mar 12, 2015

Check the advance weights in the distributor. Also check the distributor for excessive play in the bushings.

Tony in Mass. · Mar 12, 2015

To me, backfires all always electrical.
You swapped plugs? Got em all back in order? I bought a v8 ford van years ago that ran ok much of the time, backfired a lot, two plugs were crossed.
Cracked or some other way damaged dist cap. Maybe a short in there?
I wouldn't waste more time chasing fuel. good luck.

phil(va) · Mar 12, 2015

Plug wires are back on correctly. It was popping
before I replaced plugs. But I like your idea of
cracked cap. I did not replace the cap, although
I did look at it and did not see sign of a
problem. I think I have an old cap I can swap out
to try as a test without buying one.

phil(va) · Mar 12, 2015

I guess I'm not up to speed on how to check the
weights. I know where they are, but how do I know
if they are ok? As for bushings, would I see play
in the shaft if the bushings are bad?

Dieseltech · Mar 12, 2015

Dist timing lite should show advance at flywheel as engine speed is increased, and retard back to base idle timing when slowed down. I usually check the advance curve on the dist test machine for best results.

Grandfatherjim · Mar 12, 2015

Rotor and condenser are two other possible culprits that are easy and in expensive to replace.

Steve@Advance · Mar 12, 2015

A simple test of the advance weights is to gently turn the rotor CCW, it should turn a few degrees, then spring back when released.

If it won't turn, it's rusted in place. If it is hard to turn and sluggish to return, it's dry. If it moves and doesn't try to return, the springs are broke or missing.

If any condition exists, the distributor will need to be disassembled, inspected, the weights and shaft cleaned up and lubricated. Not a difficult job.

The side play in the bushings can be checked by pushing side to side on the distributor shaft. There should be very little movement. Any excess wear in the bushing, and the point setting will be impossible to keep set.

Worn distributor bushings is a very common problem. If the bushings are worn, and you want to keep points, the bushings will need to be replaced or buy a rebuilt distributor.

Or... Install an electronic conversion kit, eliminate the points. The kit will work well with a worn distributor.

phil(va) · Mar 13, 2015

Rough day today. Went to tractor to work on it and it wouldn't start. Not getting fuel. Ended up pulling sed. bowl which was clogged. Gasket bad, so had to get another. Went to TSC and got another (new) sed. bowl and it was bad. No fuel would come through it with valve open even with enough fuel in tank to go into tall input pipe. Pulled it and took it apart and it apparently has a burr in an orifice somewhere. Did get tractor running briefly and still popping with new dist. cap. Wouldn't run long enough to check timing. Rotor springs back so weights must be ok. Don't feel any play in shaft. Any more ideas? I'm going to get another sed. bowl and the look carefully at distributor.

16-30 oilpull · Mar 13, 2015

phil,despite what one man said popping is not always electrical. an engine starved for fuel will pop (which is not really a backfire).

RandyB(MI) · Mar 13, 2015

I agree with 16-30 below. Your problem is lean mixture as apposed to elect. Take plug out of bottom of carb and should have good full stream of fuel. If so then go inside...float level? I've seen new China floats hang up on bowl sides...prove passage- ways are clean. If it is popping at idle or fast idle then check for sloppy throttle shaft bushings. Does it help to choke it slightly? If it can suck air, it won't suck fuel = lean mixture = popping. Check for cracked intake manifold or warped gasket to head surface.. I will disagree with the guy below...most popping is lean mixture. Now if it backfires enough to blow your muffler off then it's electrical/timing.

phil(va) · Mar 14, 2015

Got a new Sediment Bowl. Probably be Monday now before I can install it and get it "running" again to test other suggestions. Thanks for replies so far. I'll post back.

Spudm · Mar 14, 2015

Problem could be in your 12v conversion if not done properly.

Jerry/MT · Mar 15, 2015

Phil,
Depending on what you are doing with the throttle, it could be that your carb needs a thorough cleaning especially the small passage for the off idle fuel.
It"s also possible that your distributor needs some work. Too much play in the bushings or stuck distributor weights, damaged springs, etc; something that"s causing a retarded spark.

It"s hard to tell from here but you said there was crud in the fuel bowl and there could still be some crud in some of the metering passages. The most important part of a carb rebuild is a thorough cleaning of all the passages.

phil(va) · Mar 16, 2015

OK, here it is guys: drum roll.... Installed new sediment bowl, blew out fuel line, rebuilt carb, put in some gas, and voila, she fired up and ran pretty smooth. Not perfect. It probably does need some electrical tuning now, but no popping or back firing. It's usable as is now, at least good enough I can set the timing, etc. The carb still had some brown color in the gas, even after I had cleaned it once before. I'm thinking the gas tank might have some crud. I tried to peer in there, but that's tough to do. The baffle is loose, I do know that. Thanks for all your help.

Tony in Mass. · Mar 17, 2015

So the carb work cured the 'popping' and spuddering. Good.
I, and other fergie guys were on about curing a 'backfire'.
I think we need to define the word 'backfire','popping'and a 'spudder'. As in desables?
Today I started the MF30 I rebuilt a few years ago. Gas all dried up, so starving... popping, weezing, setting itself on fire with my dollar store ether.... then roared to life. 20 minutes later purrs smooth as a kitten.
Not quiet, just typical gas Perkins rumble. Last year a tree branch took out its dist cap, it backfired in an unmistakable sorta noise, like a 10 gauge in a tin shed? I was deaf for two hours. I never found the end piece of the vertical exhaust it launched either. Textbook backfire in my book!!
I was taught a backfire was too much unburnt fuel igniting at the wrong time. Mine was a classic example.
A noise from too little fuel... should be a sucking sound shouldn't it? But yeah they pop what little lean gas mix they try to make the cylinder move with.
So how loud was the backfire??? Bet it wasn't like mine!

TO-30 Backfiring

phil(va)

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Jason S.

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Tony in Mass.

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phil(va)

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phil(va)

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Dieseltech

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Grandfatherjim

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Steve@Advance

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phil(va)

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16-30 oilpull

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RandyB(MI)

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phil(va)

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Spudm

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Jerry/MT

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phil(va)

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Tony in Mass.

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