Car backfiring and no power

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theunz
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Re: Car backfiring and no power

Post by theunz »

Here is a quick video showing how to set static timing. It’s on a VW, but the procedure is the same on all points type ignitions. It simply gets you very close to where you want the timing so you can get the engine started and fine tune with your timing light. If your distributor slipped or your timing chain (and a 1600 definitely has a timing chain) jumped a tooth or two this will show that your engine is no longer in time. If your static timing is off substantially and you are positive that the distributor has not moved than be very careful starting the engine as if the chain has jumped you could possibly bend some valves.
If the timing is still in spec you might want to do another compression check to see if the chain jumped and bent some valves which would show up as a loss of compression.
https://www.google.com/search?q=how+to+ ... Pz_SawAk40
Mike M

Old enough to know better, too old to remember why!


1969 2000 solex mine since 1972, under resurrection. (Finally resurrected as of spring 2019!) 1969 Porsche 911s -worth more, but not as valuable!
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Gregs672000
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Re: Car backfiring and no power

Post by Gregs672000 »

You are covering the bases! Did it backfire out the carbs or the exhaust? If carbs, then it was getting lean, so that suggests a fuel delivery issue, and that may be intermittent, only one carb, etc check the entire system. If out the tail, to me that suggests too much fuel for some reason as its lighting off excess fuel in the pipes, so lack of spark via a loose wire or bad spark box . I'm imagining it not getting spark for several revolutions then sparking and that heat etc lighting off the excess fuel... bang! You said it was "still rough" before you drove it.... I'm thinking something is loose or not connected correctly causing a spark issue if it's out the tail pipe. Once it's running again, make sure it will rev up fully and not miss, wiggle wires, check initial and advance timing with a light, etc. Keep posting, well get it.

Just in case, check your firing order since you changed the leads.... 1, 3, 4, 2.
Greg Burrows
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Rob1704
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Re: Car backfiring and no power

Post by Rob1704 »

Gregs672000 wrote: Tue Oct 19, 2021 10:15 am You are covering the bases! Did it backfire out the carbs or the exhaust? If carbs, then it was getting lean, so that suggests a fuel delivery issue, and that may be intermittent, only one carb, etc check the entire system. If out the tail, to me that suggests too much fuel for some reason as its lighting off excess fuel in the pipes, so lack of spark via a loose wire or bad spark box . I'm imagining it not getting spark for several revolutions then sparking and that heat etc lighting off the excess fuel... bang! You said it was "still rough" before you drove it.... I'm thinking something is loose or not connected correctly causing a spark issue if it's out the tail pipe. Once it's running again, make sure it will rev up fully and not miss, wiggle wires, check initial and advance timing with a light, etc. Keep posting, well get it.

Just in case, check your firing order since you changed the leads.... 1, 3, 4, 2.
It backfires out of the carbs because I can see the exhaust plume out of the air intake when it fires.
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Re: Car backfiring and no power

Post by Rob1704 »

Ok I took a step back and am starting over with Keith’s tuning instructions only. I took the vacuum line off the carb and plugged it, then started the car and put the timing light on. I have a pink dot of paint between the 15 and 20 degree marks and it is hitting. But the mark disappears every once in awhile. Is that normal? Below is a link to a video of the timing light. Any other timing test I need to do at higher RPM or just at idle?

https://www.dropbox.com/s/zzjmvepfkd7by ... 9.MOV?dl=0
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Gregs672000
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Re: Car backfiring and no power

Post by Gregs672000 »

Could be a miss, though I'm not sure you can count on a timing light connector to be fully consistent. However, backfiring out the carbs is either a lean condition OR erratic timing. I just watched the video and it sounds like I hear a miss when it disappears. To test advance, slowly increase the rpms. The mark should move to the right, advancing well beyond the final mark, approximately 32-35 degrees at 3500 rpms. If it doesn't, there's a problem. Did you say plugs were Black? If so, again it suggests it could be a miss.
Greg Burrows
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Re: Car backfiring and no power

Post by redroadster »

Are the valves adjusted correctly to tight can cause a leak thru the valve, also to loose
Id see if the distr. rotor turns free one direction , gently ( your centrificall advance )
A sticking valve, slow valve condition is very common on long sitting cars
Turning torque on the engine is normal?
You need a Sun ocilliscope machines , but they are obsolete
Last edited by redroadster on Thu Oct 21, 2021 10:56 pm, edited 1 time in total.
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23yrRebuild
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Re: Car backfiring and no power

Post by 23yrRebuild »

I'll offer another opinion / idea....if you can get it to run at all, while idling, try pulling and replacing, one spark plug wire at a time, and see if there is any kind of change in idling....this might sort out which cylinder(s) is weak....IMHO...
Mike - '67 Stroker / 5-Speed
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jrusso07
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Re: Car backfiring and no power

Post by jrusso07 »

I had a bad spark plug on my #1 and it caused the timing light to miss and the engine to run poorly. I never took the car on the road because knew it wasn't right. Plug was bad right out of the box...replaced it with old plug and all good.
Joe

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Gregs672000
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Re: Car backfiring and no power

Post by Gregs672000 »

OK, so mechanically it sounds like it's ok... compression checks out and valves are adjusted.
I gather that it's running again. Now, confirm timing at idle and as it advances with rpms, vac advance disconnected. Rev it up slowly so you can watch what happens. Hold it at different rpms and observe. Watch for misses on your light that you can feel or see on the engine.

If all is sparking consistently and advancing normally then you're pretty confident of spark. Now fuel... The push pin test at idle tests if the idle mixture correct, however there's no guarantee that it's feeding enough fuel at higher demands. Rev and hold it at 4000 rpms... what does it do? Hold around 3500 and then snap rev it... again, what does it do? If it's backfiring from the carb then it's lean. If it runs kinda rough but doesn't bog down with reving try adding additional fuel with short quick shots of Starting fluid (theory here is that it's lean). If it acts boggy and does not backfire from the carbs with revs, then you're rich. Sounds like you have an electric fuel pump (I'm very familiar). Make sure it's running no more than 6lbs, with 2-4 lbs being better to not overwhelm the floats. Check the ENTIRE fuel system for blockages, especially at the carbs and float chambers, including the screens in the fuel fittings. As you rev the engine position a mirror so you can see down the carb throat and watch the piston rise, and watch for the fuel coming up past the needle. The pistons should rise equally and appear to flow fuel the same. If one backfires then there's your issue, if both then keep working backwards to find the obstruction or reason.

As mentioned it would not hurt to run a new set of plugs... you need them someday anyway and they can be useful in testing.

Are any of the components of the emissions system still on the car?
Greg Burrows
'67 2000 #588
Tacoma, WA