The Stovebolt Site Forums The Shop Area Engine Shop 235 runs rough and little power

My 235 idols just fine but it has started to run rough on acceleration and will back fire on occasions. All the plugs look just a bit on the black side. Would this be a timing issue or a fuel issue. Could the vacuum advance be out of adjustment?

Thanks,
Charlie

Could be any of the above, but I think I would start at the carb. Make sure the accelerator pump is giving a good squirt, remove the air cleaner look down the carb with engine off pump the throttle and look for the fuel stream coming out of the accelerator pump circuit. With the engine running, blip the throttle and see if the distributor turns, that will tell you if the advance is working

Charlie,

I think that your path of diagnosis is as Bolter2 stated, and you're already on the way: Fuel delivery, timing, vacuum advance, vacuum leak, exhaust restriction.

Plugs that are over-carboned would indicate a rich condition, though I'm not certain that would lead to backfiring? If they're oily black, well, that's oil in the combustion chamber. Fouled plugs will certainly cause bad acceleration, but again, not certain of the back-firing. "just a bit" on the black side may mean usual wear on the plugs, with a slight rich condition, but isn't related to this problem. On the other hand, a lean condition will give the poor acceleration you describe, and could cause backfiring.

Check for that accelerator pump squirt, and whether the distributor rotates as stated (this is easier with an assistant in the driver's seat). Report back on your findings. Also, describe the backfiring in more detail. Is it "popping" out the tailpipe, a bunch of rapid pops, or one big whammo? Or is it clearly back through the carb?

-Michael

Findings thus far:
Distributor moves, vacuum advance seems to be working
Looks like a good solid stream of fuel from accelerator pump
Seems to be back firing through the carb and not the exhaust

The point gap/dwell is the most likely thing to deteriorate routinely and normally.
Wear of the cam follower closes the gap and reduces dwell very gradually and the timing gets later and performance suffers in sometimes strange ways-- but that is the FIRST thing to check when performance is noticibly down.

Have you adjusted the valve lash? How?
Have you adjusted the timing? How?

If your coughing out of the carb, timing is the first thing I would check. Then Dwell. Then finally the valves.

I would focus on timing and valve lash. Make sure you run the truck for at least 30 minutes to normalize the engine temp when checking valve clearances.

OK lets reason a little here guys.
I made my statement about checking point situation first based on personal experience with these older engines non-professionally maintained until necessary and I find:

* timing is unlikely to change in normal use unless points close up or (rarely) the distributor slips it's restraint.
* valve setting are slow to change and usually exibits increased noise and until very loose don't effect performance very noticibly.
* dwell changes normally only when point gap changes.
*vacuum advance malfunction only affects acceleration when a small air leak is created by the ruptured diaphragm and really only effects performance at light loads because it starts to retard as load is applied/decreasing vacuum strength.

My case rests.

Mr. Enginenut

All of your points are very valid provided with the fact of having an engine that was working fine with a sudden or gradual decline in performance.

In this case it appears that the engine is not running correctly. Since none of us are sitting under the same shady tree as this particular engine and can only offer assistance based off the infomation given, all of the points posted before you are good ones.

I have gotten many old engines to run like a top and I approach all of them with the same path. First determine if the engine is getting fuel, spark, then see if its getting them when in needs (timing).

Your first point is often the reason for not starting a newly rebuilt engine. The timing is set, then the clap isn't tightened completely or at all and the engine slips out of time. When this happens, more often than not, it will backfire out of the carb.

it seems to be back firing more through the exhaust.....sounds like a pop corn popper

There is more than 1 ailment with your described symptoms and, in lack of a reliable "crystal ball", you have to provide the necessary feel for what your engine is telling you.
Then we can quit guessing and try to interpret the symptoms.
Please try to describe the vehicle, it's recent history, how it acts under what conditions and of course what you have determined in testing it.
Your more recent statement brings to mind the simple problem caused by NOT CLEAN (fouled) spark plugs trying to digest our current available fuel-especially on a intermittant vehicle use where the fuel has a chance to degrade while in storage.Our gasohol changes quickly in storage and will short out plug insulators readily during operation when the engine is not warm and mixture is rich.

Here is what I know so far...my 1937 1/2 ton with a 235 was running like a top until a week ago. It now starts and idols just fine but when I go to accelerate it seems to lose power and backfires through the exhaust....sounds like a popcorn popper. It always seemed to be a little cold blooded but once it was warmed up it use to run great. I have checked the plugs...dry and a bit on the black side. Vacuum advance seems to be working correctly. I have good fuel flow from the accelerator pump. I have checked the exhaust and there doesn't seem to be any blockage. Nothing has seemed to change with the timing as well.

My suspicions are still ignition irregularities.
Lets prove/disprove it by observing spark strength/regularity.
Pull the coil high voltage lead from the distributor with the engine running and quickly, so it doesn't die,hold the end close to the dist socket so the spark can be observed as it goes to the dist rotor.
Bring the engine speed up to the point where the popping /missing starts-- observing the spark it should: be regular--be strong enough to jump a gap of 1/2 inch.Move the wire to open the gap to the point of misfire/stall and see how far it can jump.
Weak or intermittant spark can be a bad coil wire or point spring broken, loose condensor, dist-coil primary wire problem, cond wire problem, dist internal ground wire problem,POINT GAP closed, dist not well grounded and maybe someone can fill in some blanks.I have experienced all the above.
I don't think a cap/rotor problem would allow smooth idle and lood low speed performance.
You didn't mention if the choke had any effect on the off idle running.
Don't guess-test.

I recently had a problem where the condenser was bad. I was suspecting fuel but when I was using the timing light, it "went out" every time the engine stumbled. An obvious indicator it was electrics.

So i decided to just replace all the spark plugs and see where that got me and it seemed to solve all problems I was having. I am guessing I had a bad plug. Thanks for the help and keeping me on the right path to trouble shooting this problem.

Charlie

Great Charlie, and thanks for the feedback--now maybe someone can benefit from your experiences.
As I said this is very common these days with the modern fuels coupled with driving habits that don't allow quick use of the purchased amount, or full engine warmup or heavy loads that will allow the normal cleaning of the plug by burning off deposits.
The people working on small engines see this a lot and recognize the popping, spitting, but the plug will fire when checked outside the engine.
Some cures might be: minimal choking for warmup, 1 step hotter plugs if your expected work load is light, a little more RPM during warmup, use the fuel up quicker, fuel additives???, hotter ignition source probably not-in fact I've seen evidence that the high voltage equipment will allow shorting of the insulator by deposits where the old point type factory system would have cleared right up.
I explain that by the THOUGHT that as the voltage potential has increased the amperage of the spark has decreased, so is actually cooler.
I reference experience with carburetor equipped GM's with the first HEI systems.If over choking by improper action of the crazy choke pulloff system occured, even good fuel would short the plugs and you would probably NOT restart without a plug change.Admittedly most of these cases were trucks used in stop and go short run use on a plant site but it was a notable change in maintenance needs.

Great Charlie, and thanks for the feedback--now maybe someone can benefit from your experiences.
As I said this is very common these days with the modern fuels coupled with driving habits that don't allow quick use of the purchased amount, or full engine warmup or heavy loads that will allow the normal cleaning of the plug by burning off deposits.
The people working on small engines see this a lot and recognize the popping, spitting, but the plug will fire when checked outside the engine.
Some cures might be: minimal choking for warmup, 1 step hotter plugs if your expected work load is light, a little more RPM during warmup, use the fuel up quicker, fuel additives, hotter ignition source probably not-in fact I,ve seen evidence that the high voltage equipment will allow shorting of the insulator by deposits where the old point type factory system would have cleared right up.
I explain that by the THOUGHT that as the voltage potential has increased the amperage of the spark has decreased, so is actually cooler.
I reference experience with carburetor equipped GM's with the first HEI systems.If over choking by improper action of the crazy choke pulloff system occured, even good fuel would short the plugs and you would probably NOT restart without a plug change.Admittedly most of these cases were trucks used in stop and go short run use on a plant site but it was a notable change in maintenance needs.

So, SWEET's common sense advice prevails. Check the simplest/cheapest/easiest things first: good spark - plugs & ignition wires.

Back in the day (60s/70s), when a friend bought a "new" old truck (or, a VW), they'd come to me for help. I would not touch a thing until they got new plugs, points, condensor, rotor, distributor cap, ignition wires, oil, oil filter, fuel filter (if equipped) and valve cover gasket (for setting the valves).

Might as well eliminate the simple things first.

Glad to hear you solved your problem.

My truck also ran rough until I pulled the plug wires off one at a time to determine if it made any difference in the way it ran.
Got to the 5th plug and when I pulled it off the engine didn't run any worse, so I pulled the plug, put in a new one and fired it up. Ran like a top.

The plugs were Delco R45's and had probably 50 miles on them. Bad plugs can happen even if they are new. I never would have thought it.

Thanks for all the trouble shooting ideas. I love when things are a simple fix and trust me that is not usually how it goes with most things I touch. I will have to keep this fix in the back of my head for next time.

thanks again and as usual this site proves to keep these classic trucks on the roads and running!!

Charlie

I'd maybe take things another step and see why the plugs were black and needed to be replaced.....