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flightofphx
Samba Member
Joined: September 11, 2017
Posts: 114
Location: AZ
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 Posted: Mon Dec 16, 2019 11:39 am Post subject: backfire/popping at 2000 rpm |
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I am having trouble diagnosing a popping/backfire issue. It's a 1776 with a Weber 32/36 DGV and a K3 turbo from a Scirroco running 6lbs of boost. I was driving down the road the other day, engine running great, and suddenly got some hesitation and then a popping. I figured it may be an intake or exhaust leak, I check both and no leaks. Then I check valves and set clearances, all good. I checked timing and it was good and hadn't changed.
Since it doesn't pop at idle or above 2500 rpm, I thought may a clogged idle jet was causing it to run lean from 2000-2500 rpm. I cleaned both and still have the popping in that RPM range.
Kind of stumped on this one. |
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hobbybob517
Samba Member
Joined: June 02, 2011
Posts: 1194
Location: Netherlands
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| Posted: Mon Dec 16, 2019 1:13 pm Post subject: Re: backfire/popping at 2000 rpm |
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what ignition are you running?
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THE BUILD http://www.thesamba.com/vw/forum/viewtopic.php
| SBD wrote: |
3 million rpm? Well there's your problem! No wonder it blew up! |
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flightofphx
Samba Member
Joined: September 11, 2017
Posts: 114
Location: AZ
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| Posted: Mon Dec 16, 2019 1:24 pm Post subject: Re: backfire/popping at 2000 rpm |
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| hobbybob517 wrote: |
| what ignition are you running? |
Horrible - an .009 centrifugal with Pertronix points, blue coil, NGK long reach as I have big valve heads on it. I am seriously considering going to a CB Magnaspark unit. |
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nextgen
Samba Member
Joined: August 19, 2004
Posts: 6022
Location: CONGERS, N.Y.
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| Posted: Mon Dec 16, 2019 1:54 pm Post subject: Re: backfire/popping at 2000 rpm |
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After reading your post, it reminded me of my back firing problem. Car ran great but at about the same RPM as yours it back fired and seeing I have duel exhausts I asked my wife to follow me and tell me if she see fire out of one of the exhaust pipes. It was out of both!! Did all you looked for and shot starting fluid all over every thing looking for leaks. Did not drive it much, ruined half my summer fun. Was worried I was gong to blow my exhaust apart.
Car ran great otherwise. It was time to send my carbs out for rebuild after 10 years from when I did it. Wanted it done by a trusted pro and got some great reviews , so I sent them out to Rich Hunt. In Simi, Calif. Car never ran so good. Backfire was gone???
So I think you looking into ignition and Fuel is the correct thing to do.
I still have no idea what it was but rebuilding the duel Dell 36’s was the answer for me , not bad at $120 per carb.
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hobbybob517
Samba Member
Joined: June 02, 2011
Posts: 1194
Location: Netherlands
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| Posted: Mon Dec 16, 2019 2:18 pm Post subject: Re: backfire/popping at 2000 rpm |
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| flightofphx wrote: |
| hobbybob517 wrote: |
| what ignition are you running? |
Horrible - an .009 centrifugal with Pertronix points, blue coil, NGK long reach as I have big valve heads on it. I am seriously considering going to a CB Magnaspark unit. |
see if you can borrow another distributor so you can try that.
_________________
THE BUILD http://www.thesamba.com/vw/forum/viewtopic.php
| SBD wrote: |
3 million rpm? Well there's your problem! No wonder it blew up! |
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VW_Jimbo 
Samba Member
Joined: May 22, 2016
Posts: 9944
Location: Huntington Beach, CA
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| Posted: Mon Dec 16, 2019 5:42 pm Post subject: Re: backfire/popping at 2000 rpm |
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Popping out the intake or popping through the exhaust?
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nextgen
Samba Member
Joined: August 19, 2004
Posts: 6022
Location: CONGERS, N.Y.
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flightofphx
Samba Member
Joined: September 11, 2017
Posts: 114
Location: AZ
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| Posted: Wed Dec 18, 2019 12:51 am Post subject: Re: backfire/popping at 2000 rpm |
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| VW_Jimbo wrote: |
| Popping out the intake or popping through the exhaust? |
I am fairly certain it is through the exhaust. It is kind of hard to tell what is going on in the intake because of the turbo. |
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