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ForestVW
Samba Member
Joined: September 08, 2018
Posts: 24
Location: Florida
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 Posted: Sun Dec 05, 2021 1:04 pm Post subject: Engine stumbles and coughs |
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My 1600 engine in my buggy will cough and stumble when I shift from 1st to 2nd and 3rd when giving it gas then will pick right up and run fine------
The engine 1600 new long block
new 34 pict -3
new pertronix vacuum advance
bosh blue coil
new plug wires and bosh plugs
Timing set at 5 ATDC
As of now it starts right up idles fine - revs up fine no hesitation or cough --put it in 1st take right off just fine put it in 2nd get cough stumble then takes off fine same for 3rd and 4th----oh yes I put the larger jets in, that came with the carb
I would like to thank any input that anyone has on this. Harvey
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ashman40
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Joined: February 16, 2007
Posts: 15982
Location: North Florida, USA
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| Posted: Sun Dec 05, 2021 1:18 pm Post subject: Re: Engine stumbles and coughs |
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| ForestVW wrote: |
The engine 1600 new long block
new 34 pict -3
new pertronix vacuum advance (distributor)
bosh blue coil
new plug wires and bosh plugs
Timing set at 5 ATDC |
These two highlighted things are not compatible.
The Pertronix vacuum advance distributors are modeled after the VW 205/034 SVDA distributor from the '74 Beetle. This distributor was timed at 7.5BTDC @idle with the vacuum hose disconnected and plugged.
If you don't have a 7.5BTDC timing mark on your crank pulley... measure the distance from the TDC dimple to the 5ATDC notch. Add a pencil mark the same distance on the other side of the TDC dimple. This will be 5BTDC. This mark should be CW from the TDC dimple. Split this distance in half and add a permanent mark this much further from the 5BTDC mark. This will be 7.5BTDC.
The other way would be to remove the crank pulley and lay a paper degree wheel over the pulley lining up the timing notches you have with 5ATDC and TDC and then add the proper 7.5BTDC mark. You should also add a mark at 28BTDC and 32BTDC. These could be useful when adjusting max total advance.
Your ignition timing should be based on the distributor you have installed in the engine, not the original timing specs for a distributor you are no longer running.
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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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ForestVW
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Joined: September 08, 2018
Posts: 24
Location: Florida
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| Posted: Sun Dec 05, 2021 1:39 pm Post subject: Re: Engine stumbles and coughs |
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Will try setting at 7.5 btdc and will ck total advance - tomorrow- Thank you
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sjbartnik
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Joined: September 01, 2011
Posts: 5995
Location: Brooklyn
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| Posted: Sun Dec 05, 2021 1:42 pm Post subject: Re: Engine stumbles and coughs |
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Listen to ashman!
Yes the 5˚ ATDC idle timing spec was an emissions control measure for distributors that had both vacuum advance and vacuum retard. If you are running a distributor that does not have a vacuum retard function, then you do not want to set your timing to 5˚ ATDC.
7.5˚ BTDC should be a good starting point for a distributor without vacuum retard.
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VW_Jimbo 
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Joined: May 22, 2016
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Location: Huntington Beach, CA
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| Posted: Sun Dec 05, 2021 2:09 pm Post subject: Re: Engine stumbles and coughs |
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And be sure the throttle plate is set correctly!
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Jimbo
There is never enough time to do it right the first time, but all the time necessary the second time!
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Starbucket
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Joined: April 30, 2007
Posts: 4025
Location: WA
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| Posted: Sun Dec 05, 2021 2:35 pm Post subject: Re: Engine stumbles and coughs |
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| Check and make sure the accelerator pump jet squirts AS SOON as you move the throttle if not adjust it. |
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ForestVW
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Joined: September 08, 2018
Posts: 24
Location: Florida
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| Posted: Mon Dec 06, 2021 12:48 pm Post subject: Re: Engine stumbles and coughs |
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Ok --I have set timing (vacuum hose off and plugged) at 7.5 btdc
Total advance with vacuum hose off-----26
Total advance with vacuum hose on -----36
I have a degree pulley on the engine
The engine starts right up --idles fine and revs up fine --have not test drove it.
I believe 36 is to much---- now do I back up the timing to get the total advance of 30 ?-----------Thank you for your help
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sjbartnik
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| Posted: Mon Dec 06, 2021 1:42 pm Post subject: Re: Engine stumbles and coughs |
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To do that, you rev the engine up to 3000 rpm (or wherever the timing stops advancing - with vacuum hose connected) and turn the distributor body until the timing light shows the max advance number you want.
Then you leave the idle timing wherever it happens to land after that.
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Last edited by sjbartnik on Sun Dec 12, 2021 8:37 pm; edited 1 time in total |
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KTPhil
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Location: Conejo Valley, CA
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| Posted: Mon Dec 06, 2021 2:18 pm Post subject: Re: Engine stumbles and coughs |
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| sjbartnik wrote: |
To do that, you rev the engine up to 3000 rpm (or wherever the timing stops advancing - with vacuum hose connected) and turn the distributor body until the timing light shows the max advance number you want.
Then you leave the idle timing wherever it happens to land after that. |
And then make a paint mark where the static timing ends up, so after this you can find that point without a timing light. Use a color other than white (which is often used for TDC) like yellow or orange. |
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ashman40
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Location: North Florida, USA
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| Posted: Wed Dec 08, 2021 6:39 pm Post subject: Re: Engine stumbles and coughs |
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| ForestVW wrote: |
Ok --I have set timing (vacuum hose off and plugged) at 7.5 btdc
Total advance with vacuum hose off-----26 |
So you are saying that with the vacuum hose disconnected and plugged the timing marks never go higher than 26BTDC at ANY rpm? This is your Total Advance; made up of the initial timing advance + max mechanical advance. You want to see this setting never exceed 28-32BTDC. This is the safe max advance based on engine rpms. You would up your idle timing by 2deg so you reach 28BTDC. Test drive at this timing with the vacuum hose connected and see how it runs. Listen closely for knock or pinging on hard acceleration, especially at high rpms when the timing is maxed out.
You can work your way up 1deg at a time until you reach 32BTDC Total advance. Many engines cannot run this much advance so don't feel you need to push the limit. You can happily stay at 28BTDC if you like. Just note what the works out to at idle (with hoses disconnected and plugged) and you can use that as your ignition setting for future tune ups.
There is no recommended timing setting for that distributor with the vacuum hoses connected so don't worry what the timing is with the hose connected. The vacuum advance adjusts for engine load and will raise or lower the timing advance as needed when it senses low or high load on the engine. Under load, the engine will not produce vacuum so the vacuum advance is disabled. The only advance is from the mechanical advance, which is why you want to confirm that the mechanical advance never takes you above 28-32BTDC.
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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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ForestVW
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Location: Florida
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| Posted: Sun Dec 12, 2021 8:26 am Post subject: Re: Engine stumbles and coughs |
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Ok--first I would like to thank youall for the input. As of now the settings are 3 degrees BTDC at idle. and total advance is 30 degrees BTDC at 3000 rpm with vacuum hose on . It now runs like champ . I never had to monkey with A petronix disturber this much before ( I have 3 other rigs with same set up) they all were plug and play just set timing with strobe light at recommend timing at Idle and go. Thanks again
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ashman40
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| Posted: Sun Dec 12, 2021 1:22 pm Post subject: Re: Engine stumbles and coughs |
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| ashman40 wrote: |
| So you are saying that with the vacuum hose disconnected and plugged the timing marks never go higher than 26BTDC at ANY rpm? This is your Total Advance; made up of the initial timing advance + max mechanical advance. You want to see this setting never exceed 28-32BTDC. This is the safe max advance based on engine rpms. |
| ForestVW wrote: |
| As of now the settings are 3 degrees BTDC at idle. and total advance is 30 degrees BTDC at 3000 rpm with vacuum hose on…. |
No. With the vacuum hose connected you are measuring initial advance + mechanical advance + a variable amount of vacuum advance. The 28-32BTDC target at high rpms is for initial + mechanical-only. There is no suggested timing advance when you add vacuum advance into this mix. Vacuum advance can add anywhere from zero to 12deg of timing advance depending on the vacuum level. Vacuum level varies based on many different conditions. This is why ALL instruction for setting timing at high rpms are with the vacuum hose disconnected and plugged. You missed this point.
Redo your ignition timing. You are running your ignition timing with too little advance.
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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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ForestVW
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Location: Florida
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| Posted: Sun Dec 12, 2021 4:57 pm Post subject: Re: Engine stumbles and coughs |
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Ok will do -tomorrow---and will let you know
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sjbartnik
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| Posted: Sun Dec 12, 2021 8:36 pm Post subject: Re: Engine stumbles and coughs |
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My bad, I realized I gave bad info above - I wrote to rev it up with vacuum hose connected when, as ashman40 pointed out, it should be vacuum hose DISconnected to measure only the mechanical advance.
This is why drinking & posting is a bad idea. 
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ForestVW
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| Posted: Mon Dec 13, 2021 2:06 pm Post subject: Re: Engine stumbles and coughs |
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well here is the results-----vacuum hose off and plugged----
Idel -- 7.5 -8 degrees BTDC
3000 rpm --26 - 27 degrees BTDC----total advance
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with vacuum hose on
idel -- 7.5 -8 degrees BTDC
3000 rpm -- 38 degrees BTDC ---total advance
ran the rig around my property never got out of 2nd gear -- ran very strong and did not stumble at all
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KTPhil
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| Posted: Mon Dec 13, 2021 2:40 pm Post subject: Re: Engine stumbles and coughs |
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| That should be fine as long as the vac can hose is connected to the correct port on the carburetor. |
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mukluk
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| Posted: Mon Dec 13, 2021 2:54 pm Post subject: Re: Engine stumbles and coughs |
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| KTPhil wrote: |
| That should be fine as long as the vac can hose is connected to the correct port on the carburetor. |
The advance numbers the OP posted with and without the vaccum connected look to me like ported vacuum has been used. I'd expect to see some advance at idle over the non-vacuum stats if manifold vacuum was used.
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