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Type 4 FI backfire/sputtering
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dabble
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PostPosted: Thu Jun 14, 2012 8:45 pm    Post subject: Type 4 FI backfire/sputtering Reply with quote

I just timed my 78 FI with Pertronix at 7.5* BTDC, but it runs like crap. It has a very rough idle and backfires when not on the accelerator. I checked all the spark plugs and wires, and they all seem fine. Pertonix so no need to adjust the points. It has hydraulic lifters so I haven't adjusted them.


When I use my timing light and advance to about 20* BTDC it runs better, but there is still hesitation and backfiring, although not as bad as at 7.5* BTDC. Should this be happening?

I believe that I followed the Bentley correctly - what could be going on? I don't have a tachometer so I'm not sure what my idle currently is. I could adjust the lifters, but I don't think that would cause such hesitation and backfiring, right? Anyone in the Seattle area willing to lend a helping hand for some beer?

Hoping the Samba gods can help me once again... Shocked
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1973 Westy with a 78 FI 2000cc
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Daverham
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PostPosted: Thu Jun 14, 2012 9:10 pm    Post subject: Reply with quote

Sounds like what I did once - it would barely run - it was because I had mistakenly put the timing light clip on the #2 cylinder wire EVEN THOUGH I DOUBLE CHECKED! The #1 and #2 wires did this tricky crossover thing and fooled me. Just one possibility....

Define "Seattle area." What part of town you in?
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Daverham
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PostPosted: Thu Jun 14, 2012 9:16 pm    Post subject: Reply with quote

Also... did it run fine BEFORE you did something? What did you do?

I have the day off tomorrow. Will be working on my bus. Might be able to help.
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dabble
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PostPosted: Thu Jun 14, 2012 9:25 pm    Post subject: Reply with quote

It wasn't running very well before I adjusted the timing - still backfiring and running rough. Now I can make it idle a little better with timing adjustments, but it still runs like crap. I'm in Madison Park.
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Stuartzickefoose
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PostPosted: Thu Jun 14, 2012 10:11 pm    Post subject: Reply with quote

BEER? Very Happy


im local too, and more than willing to lend a hand if i can. im about an hour or so north of you, in edmonds. maybe a half hour without traffic... when would you like me to swing by?
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Wildthings
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PostPosted: Thu Jun 14, 2012 10:29 pm    Post subject: Reply with quote

Forget trying to set your timing at idle, haven't a clue why VW went in that direction when their original timing spec was at full mechanical advance, 27 BTDC at 3500+ rpms hoses off. This is where you still want to be, but most give it a degree to more extra. Get it set at 28-30 BTDC at 3500+ rpms hoses off and it should be right.

Your spitting and sputtering could be a valve problem or you could be running very lean. Make sure on more time that your wires are in the correct order.
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Westfabulous
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PostPosted: Thu Jun 14, 2012 10:53 pm    Post subject: Reply with quote

I agree with WT re: being too lean. Check for vacuum leaks, and here is one that tricked me for the longest time on my wife's bus: the EEC valve had failed and was compromising the mechanical advance of the distributor (probably the Fuel Pressure Regulator too). I fixed that and enriched the mixture a touch, after addressing all potential vacuum leaks, and she runs like a charm now.....the bus that is, not the wife.
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dabble
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PostPosted: Sat Jun 16, 2012 10:11 pm    Post subject: Reply with quote

Westfabulous wrote:
I agree with WT re: being too lean. Check for vacuum leaks, and here is one that tricked me for the longest time on my wife's bus: the EEC valve had failed and was compromising the mechanical advance of the distributor (probably the Fuel Pressure Regulator too). I fixed that and enriched the mixture a touch, after addressing all potential vacuum leaks, and she runs like a charm now.....the bus that is, not the wife.


I'll check all of my vacuum lines to see if they're connected. I looked before, but I couldn't find anything amiss.

When I pulled the vacuum hose off of my distributor nothing changed (that I could tell). My strobe light didn't show any change when I had a neighbor hold the accelerator. Does that indicate a problem with my dizzy?

I'm starting to go crazy...
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tootype2crazy
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PostPosted: Sat Jun 16, 2012 10:34 pm    Post subject: Reply with quote

Backfiring is a telltale sign of crossed spark plug wires. Check that too.
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SGKent Premium Member
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PostPosted: Sun Jun 17, 2012 12:04 am    Post subject: Reply with quote

vacuum leak. The lean mixture requires longer to burn cause the molecules are farther apart. Find the leak and 75% of your problems will be gone.
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dabble
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PostPosted: Mon Jun 18, 2012 9:18 am    Post subject: Reply with quote

Replaced plugs, wires, cap, and rotor. Set my idle and timing at 7.5* btdc and 28* at full vacuum advance.

I found my vacuum line that attaches to the deceleration valve was off. That fixed my sputtering/misfiring feeling but it is still backfiring.

It still is backfiring when I let off of the accelerator. Why? It goes away when I depress the clutch. Thoughts?
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Stuartzickefoose
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PostPosted: Mon Jun 18, 2012 10:40 am    Post subject: Reply with quote

dabble wrote:
Replaced plugs, wires, cap, and rotor. Set my idle and timing at 7.5* btdc and 28* at full vacuum advance.

I found my vacuum line that attaches to the deceleration valve was off. That fixed my sputtering/misfiring feeling but it is still backfiring.

It still is backfiring when I let off of the accelerator. Why? It goes away when I depress the clutch. Thoughts?


have you tested for vacuum leaks yet? spray carb cleaner all over while it idles and if the idle changes, pinpoint where you sprayed to get the change. they fix the leak that you just found.
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weswsimpson
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PostPosted: Thu Jul 28, 2016 2:32 pm    Post subject: Re: Type 4 FI backfire/sputtering Reply with quote

I had a problem with my hydraulic lifters, so don't assume your valves don't need to be adjusted. You can read up about them at:

http://www.ratwell.com/technical/HydraulicLifters.html

If they leak down, they won't open the valves, causing all kinds of problems, backfiring, lack of power etc. I refused to check them myself for a while... but sure enough they were an issue! It's not hard to remove them and check them. Takes about 1/2 hour, assuming your lower tin bolts come off easily. You can pull your push rod tubes thru the heads and then fish the lifters out.

If you have an inspection camera you can stick it down the spark plug holes and watch your valves open and close as you push your van forward and backward in forth gear. It's a good way to determine if you're on top dead center for each cylinder and you can see if you have an issue with a valve as well. Harbor freight sells them cheap.
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