Car backfiring and no power

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Rob1704
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Car backfiring and no power

Post by Rob1704 »

Ok folks here is the situation. 1970 1600 with SU carbs I am trying to get running after sitting for 10 years. New plugs, wires, and Electronic distributor. I had it running, timing was spot on. Balanced the fuel/air mixture so that the engine sped up a bit when raising the pin under the carb and then stabilized, and carbs were balanced to pull the same amount of air. It was still running a little rough but I decided to try and test drive it. Got it out on the road and it started back firing at higher RPMs and lost all power. Then it died and would not restart. Wouldn’t even cough. We checked and It still has gas to the carbs and spark to the plugs. I’m at a loss.
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theunz
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Re: Car backfiring and no power

Post by theunz »

I would check static timing to see if perhaps the distributor slipped.
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Bwk2000
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Re: Car backfiring and no power

Post by Bwk2000 »

Might also want to consider:
Bad coil, condenser (or their connections),
Contaminated gas,
Valve train (clearances, looseness, etc),
Timing chain jumped, or
Plugged exhaust.
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redroadster
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Re: Car backfiring and no power

Post by redroadster »

Start with a cold compression test easy to do check s plug color etc. I like to run it in the dark to see arcing wires
Also what's the vacuum guage on at idle
A spark gap tester check the gap strength
It good to eliminate major components 1st
Then all of the other above slides free?
Sure it flowing gas free ?
Check the centrifical advance for normal operation
Last edited by redroadster on Wed Oct 20, 2021 5:23 am, edited 1 time in total.
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Gregs672000
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Re: Car backfiring and no power

Post by Gregs672000 »

What's true is always true... you must have spark, fuel and compression. With all three in the right amounts and time it HAS TO run. You have confirmed spark and fuel, and most likely compression didn't suddenly change (but a compression test is a good idea regardless: All plugs out, good battery, throttle wide open, 10 cranks.).
So, what do the plugs look like? Black, white? Uneven between 1-2 and 3-4? Smell like gas? Bad, ugly smelling gas? Will it run on another source of fuel, like starting fluid? Spark... good and strong? (The EI dizzy sparks strong, you should see a nice spark). Correctly timed (timing light required) at idle, and advancing normally (assuming you get it running again)?
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Rob1704
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Re: Car backfiring and no power

Post by Rob1704 »

theunz wrote: Mon Oct 18, 2021 8:47 pm I would check static timing to see if perhaps the distributor slipped.
Static timing? Can you explain, I don’t know what that is.
Rob1704
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Re: Car backfiring and no power

Post by Rob1704 »

Bwk2000 wrote: Mon Oct 18, 2021 9:00 pm
Might also want to consider:
Bad coil, condenser (or their connections),
Contaminated gas,
Valve train (clearances, looseness, etc),
Timing chain jumped, or
Plugged exhaust.
New coil, no condenser since switched to EL dizzy, drained and filled with new gas, valves recently adjusted, no timing chain on a 1600, I can check the exhaust but it had been running sitting in the garage
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Re: Car backfiring and no power

Post by Rob1704 »

redroadster wrote: Mon Oct 18, 2021 9:55 pm Start with a cold compression test easy to do check s plug color etc. I like to run it in the dark to see arcing wires
Also what's the vacuum guage on at idle
A spark gap tester check the gap strength
It good to eliminate major components 1st
Then all of the other above slides free?
Sure it flowing gas free ?
Compression test last week had all four between 147 and 155. Plugs were black but we had been running it and making carb adjustments so we cleaned them and put them back in. I can pull again and check but since we had been doing more adjustments it may be an old indicator.

How do you test vacuum?
Plugs were gapped when replaced
What do you mean by slides free?
Yes we have gas. Took the line off the front carb and turned on the pump
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Re: Car backfiring and no power

Post by Rob1704 »

Greg- that’s the crazy thing is I have all three! We did compression test last week, all between 147-155. Confirmed fuel pumping to carb. Confirmed spark at the distributor and spark at the plugs. Unless somehow we flooded it and fouled the plugs? I guess I’ll know if it starts up again tomorrow but then why would the fuel/air mixture test say we were in target?
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Re: Car backfiring and no power

Post by notoptoy »

If spark at the plugs, and fuel and compression, that pretty much only leaves timing. Do you have a timing light? The timing light should fire even while cranking to at least see if you are firing steadily and not intermittent.
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Habitat.pat
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Re: Car backfiring and no power

Post by Habitat.pat »

You said the engine sped up when you lifted the carb pistons. That indicates a rich mixture. You may have fouled the plugs.

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Rob1704
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Re: Car backfiring and no power

Post by Rob1704 »

notoptoy wrote: Mon Oct 18, 2021 10:57 pm If spark at the plugs, and fuel and compression, that pretty much only leaves timing. Do you have a timing light? The timing light should fire even while cranking to at least see if you are firing steadily and not intermittent.
Timing is spot on. We had the light on it just before we took it out
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Re: Car backfiring and no power

Post by Rob1704 »

Habitat.pat wrote: Mon Oct 18, 2021 11:02 pm You said the engine sped up when you lifted the carb pistons. That indicates a rich mixture. You may have fouled the plugs.

Peace,
Pat
My SU tuning manual says that the engine should speed up and level off when you lift the pin. It says if it keeps speeding up it is too rich and if it stumbles it is too lean. If I get it running again I could try leaning the mixture
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redroadster
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Re: Car backfiring and no power

Post by redroadster »

Rob1704 wrote: Mon Oct 18, 2021 10:50 pm
redroadster wrote: Mon Oct 18, 2021 9:55 pm Start with a cold compression test easy to do check s plug color etc. I like to run it in the dark to see arcing wires
Also what's the vacuum guage on at idle
A spark gap tester check the gap strength
It good to eliminate major components 1st
Then all of the other above slides free?
Sure it flowing gas free ?
Compression test last week had all four between 147 and 155. Plugs were black but we had been running it and making carb adjustments so we cleaned them and put them back in. I can pull again and check but since we had been doing more adjustments it may be an old indicator.

How do you test vacuum?
Plugs were gapped when replaced
What do you mean by slides free?
Yes we have gas. Took the line off the front carb and turned on the pump
With a vacuum / & pressure guage kinda hard to find these days to a big vac port on the intake some techs set timing by vacuum not a timing lite on this era of car
70 s like mine had a S bend in the line right off the tank , and will starve it for fuel with just a bit of calcium in the tank ,,yeah you look good on compression though
It sounds like a high voltage leak / break down too you might run it in the dark to check ,sp wire , dist cap
If the carbs are unbalanced that can give this condition
I fought it on mine , it was mostly running on the frt carb
The carb slides = the dash pots that lift the fuel needles
You should view the wiki thread here on that
Last edited by redroadster on Tue Oct 19, 2021 11:46 am, edited 3 times in total.
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jrusso07
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Re: Car backfiring and no power

Post by jrusso07 »

I recommend that you read Keith's SU tuning write up in the tech wiki here: http://www.311s.org/pmwiki-311/pmwiki.p ... sNewSuTech.

IMO, it's either carbs or timing. Have you checked the distributor vacuum advance with your timing light?
Joe

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