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ashman40 Samba Member
Joined: February 16, 2007 Posts: 15982 Location: North Florida, USA
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Posted: Wed Dec 08, 2021 6:28 pm Post subject: Re: I cant figure out why it's sputtering, backfiring and hesitating |
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All good points made above. Follow their advice.
I would add that the distributor end of your vacuum hose is frayed. While the rubber under the frayed end may be fine, by the time they look like that the rubber is often cracked, resulting in a leak. If this is the case with your hose, trim the end off so you have a clean cut and nice flexible rubber. If the rubber hose is stiff and brittle, replace the entire hose length.
The vacuum advance canister diaphragm is very sensitive to liquid gasoline. To prevent liquid fuel from dripping down from the carb to the vacuum canister, VW routed the vacuum connection between the carb and the distributor up before going down. This was done with a segment of metal tubing in the shape of a "hook" called a Shepherd's Hook. Here's a pic.
You can make one with a small segment of metal tubing, or just find a way to route the rubber hose up above the carb before going down to the distributor. If you were running a stock air cleaner you could just loop it thru one of the clamps. _________________ AshMan40
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'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!} |
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ashman40 Samba Member
Joined: February 16, 2007 Posts: 15982 Location: North Florida, USA
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Posted: Wed Dec 08, 2021 7:12 pm Post subject: Re: I cant figure out why it's sputtering, backfiring and hesitating |
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WojoBeetle wrote: |
Thank you for additional feedback. I have tried 3 separate distributors and caps, so if the dizzy were to blame, I’d see a difference between each of them, but there was absolutely none. |
It's not only the distributor. I asked which models and how you set the ignition timing. If you set the timing incorrectly, or used the wrong timing setting for all three distributors the engine would run badly... not because of any issue with the distributors, but because you were using the wrong ignition timing for the model you have installed.
One common mistake... setting the ignition timing based on the model year of your car. This works great, only if you have the original distributor and it is working correctly!
If you are running a different distributor you often need different ignition timing. Set your ignition timing based on your installed distributor model. The vacuum canister on your distributor looks very new so I would guess it is not an original VW distributor? Does it have a VW/Bosch model# stamped into the body?
Your vacuum advance distributor appears to be an SVDA. I can't say for sure because you have yet to ID the model#. The OE SVDA distributors were timed at either TDC or 7.5BTDC. Again, depending on your distributor model.
This timing was adjusted at idle (800-950rpms) with the vacuum advance hose disconnected and plugged. Did you set your idle timing with the vacuum hose connected?
If for example, you left your vacuum advance hose connected to the carb as show in your pic (rear facing carb port) and tried to set your idle timing to 7.5BTDC at idle... you would actually be setting the initial timing to 4.5ATDC ~ 0.5ATDC! The vacuum port you are connected to produces strong vacuum at idle. This would force the vacuum advance to max. It would cause the vacuum canister to advance the idle timing by 8-12deg. 4.5ATDC initial + 12deg of advance appears as 7.5BTDC at idle. You would be measuring the idle timing at initial + full vacuum advance instead of just the initial timing.
Even your mechanical advance would be impacted as it adds to your initial timing of 4.5ATDC, not your idle timing. This would results in only a feeble 15BTDC total mechanical advance instead of 28BTDC.
This hypothetical scenario could easily result in what you have described... hesitation and no power.
You see, how you set your ignition timing can have significant impact on your engine's performance.
So, what model distributor are you running... and how have you set your ignition timing? Be specific and detailed please. _________________ AshMan40
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'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!} |
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WojoBeetle Samba Member
Joined: April 04, 2012 Posts: 18 Location: Chicagoland
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Posted: Tue Dec 14, 2021 2:38 pm Post subject: Re: I cant figure out why it's sputtering, backfiring and hesitating |
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Thank you all for your critical review of the pictures I posted. All excellent points and I loved that you did not leave anything "unaddressed." To be honest, the pictures I took were in the middle of my triaging efforts, so I switched to another carb and distributor cap and I tried different vacuum ports. When the engine ran well, I had all tinwork properly installed, OEM air filter and heating channels in place. So, after much trial and error, I've got to say that ashman40 had the answer. I was setting my ignition with a strobe gun, but without removing the vacuum line, so my reading was off. In the past, I used to adjust ignition advance by ear and feel, but someone gave me the gun recently and so I used it to set the timing to 7.5 deg BTDC. Clearly, it was too delayed. For now, I just advanced it by feel and the motor is already running better and is drivable again. I feel silly for not researching the proper way to set timing with the strobe light, but looks like I will be in good shape going forward. My dizzy is indeed an EMPI SVDA. You guys are the best! |
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