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Author: Subject:  "poping" small backfires (video linked)
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posted on December 10th, 2011 at 05:01 PM
"poping" small backfires (video linked)


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posted on December 10th, 2011 at 05:29 PM



hmm. whats ur timing at? no single ignition lead in the incorrect position?

Just given the way it kicked back when trying to start, either a hint ignition is too advanced or a spark is going to a cylinder when its not meant to be.
mind you though, during running, too advanced ignition should pop in the intake, hence if its poping in the exhaust i would be checking the 1-4-3-2 sequence.




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posted on December 10th, 2011 at 05:30 PM



certainly sounds like a lean "miss" to me.

pull your plugs and see if all of them are white

You are either under jetted on the idle circuit, blocked idle or a bad leak some where




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posted on December 10th, 2011 at 08:02 PM



leads are in the sequence 1-4-3-2, compression of the motor is 130psi per cylinder, spark plugs are black. What should my timing be for this year model beetle?
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posted on December 10th, 2011 at 08:52 PM



You've got timing way out on that.
Is that a vac only dizzy?
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posted on December 10th, 2011 at 09:35 PM



what the hell happen in the end of the video? looks like it just abruptly locked up.



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posted on December 11th, 2011 at 07:56 AM



Mate, that engine isn’t kicking on all 4 any time throughout that run. Listen to it hissing as you crank it over, that’s not right. Do a compression test, all the plugs out, crank it and test each cylinder. My bet, you’ve fly cut the heads and not had the head face cut too. One of them is sitting up on the barrel’s fin castings and not sealing on the top of the barrel. I’ve seen it before. It blows out and sucks in, causes popping and missing etc. You get a similar effect with a valve out of adjustment, not closing.
My money’s on a leaking head, place your bets.
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posted on December 11th, 2011 at 10:10 AM



Joel: yes its a vac only dizzy, big dizzy for the 40hp.
Bevoracing: ok, so what do i need to do to fix that? i did a compression test, it holds 130psi on all cylinders. All that has been done to the engine is: Pulled apart, clean up, and put back together.
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posted on December 11th, 2011 at 12:24 PM



Not a compression leak IMO, but not running on all cylinders either. Set timing to 32* total advance, I think 7.5* BTDC for the 40hp dissy. Double check your valve clearances and timing is my suggestion, carb tune won't go astray, neither would tailpipes. No exhaust leaks??



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posted on December 11th, 2011 at 12:48 PM



no no exhaust leaks, new gaskets all round. On the dizzy, there is a line marked on the outside rim, that is where the rotor is meant to be pointing on TDC right? pretty sure it is from what i remember :?:
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posted on December 11th, 2011 at 04:40 PM



That's right but it's not guaranteed to be there if the distributor drive gear was not installed correctly. Check if the rotor points there when no 1 is at tdc. From the video, it sounds as if only 3 cylinders are firing.

As Matt said, try setting the timing to 7.5 degrees btdc. Also have you checked the spark on each plug?




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posted on December 11th, 2011 at 05:33 PM



Quote:
Originally posted by rob53
That's right but it's not guaranteed to be there if the distributor drive gear was not installed correctly.


Doesn't matter how far out of alignment the dizzy drive is installed, the rotor will always line up with the #1 notch but the trouble is then things like the vac can hitting the fuel pump if it's too far out.


Quote:
Originally posted by vwbugsrule
On the dizzy, there is a line marked on the outside rim, that is where the rotor is meant to be pointing on TDC right? pretty sure it is from what i remember :?:


Well there is probably the main source of your issues, the early vac only dizzys are timed at 7.5BTDC and some are even 10BTDC so make sure your pulley is the right one and has 7.5BTDC

If you have it at TDC that's why it's so doughy and popping.
Check it with a test light.
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posted on December 14th, 2011 at 08:24 PM



Mate, there’s just something silly going on there. You’ll have to start double checking everything, even the new stuff. Start with the coil, cap, rotor, plug leads, plugs etc. I’ve seen brand new coils, leads & plugs that just don’t work. Double check, everything.
Then, try taking the carby and the fan housing off, remove the rocker shafts, so that all of the inlet valves are shut at the same time, then put your mouth on the manifold and suck, see if you can find a leak.
There’s something wrong, it’s just a matter of finding it, double check everything until you do.
Now you know why mechanics seem to charge a lot for some jobs and not others.
Good luck, make sure you let us all know what it is when you find it, we can’t wait. It all looks great by the way, well done.
Cheers
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