Need help with mystery engine miss

[aeromech]

Jumping in here without reading all the posts...

A massive leak in the brake booster vacuum line has caused problems with #3 on other buses.
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[fifteenduth]

EUREKA!!!! Morning update:

Late last night (early this morning) I reinstalled the cleaned up vacuum check valve with new rubber sleeves. Then I added more SeaFoam to the fuel tank since I had filled it up yesterday morning to dilute any potential bad fuel. Then I added about 120mL of SeaFoam to my engine oil. I started the engine and ran it for about 2 minutes just because (!!!???). Then I called it a night.

This morning I checked the new messages on this topic (thanks folks) and then I hooked up my timing light to check #3 ignition wire and started her up.

Normal! No miss, no backfire, just smooth idle. Checked the #3 with timing light anyways and confirmed no misfire in that wire at all.

Took her around the block for a quick test to get engine up to operating temp and came back home and listened. Purrs like the beauty she is. Scratched my head for about 5 minutes.....

So I guess it could have been;

- slight leak at the back connection of my check valve, as it did come off very easily and was quite tight when I reinstalled with the new rubber sleeve;

- sticking valve at #3 that was helped with the SeaFoam I added to the fuel tank, or the SeaFoam I added to engine oil;

- I had a batch of bad fuel that resolved when I diluted it with fresh fuel (and SeaFoam);

- maybe had a plugged jet that the fresh fuel and/or SeaFoam cleared out.

I can't thank enough those that took the time to post ideas for solving this issue and I hope that someone else will benefit from this discussion in the future. As well, I now have some more ideas for troubleshooting future issues I may encounter.

I will pay close attention to this potential #3 valve issue going forward to be sure there are no long term effects of this incident as much as possible.

I think I like SeaFoam even more than I did before!!

I hope this is the end of this issue and it doesn't rear it's ugly head again any time soon.

Thank-you to all contributors!
Ronnie C
_________________
'74 Westy - "Josée"
2014 Beetle GSR - "Ozzy"
2006 Jetta TDI - "Jerry"

[aeromech]

I'll bet your neighbors loved that seafoam
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[fifteenduth]

Is that what that smell is!!!
_________________
'74 Westy - "Josée"
2014 Beetle GSR - "Ozzy"
2006 Jetta TDI - "Jerry"

[Tcash]

Might be worth it to hook up a vacuum gauge, so you can get a base reading. In the event it happens again, you will know where the reading was when it was running correctly.
Congradulations
Tcash

[fifteenduth]

Ya that's a good idea Cash. I am not quite clear on where exactly to hook up the gauge but I'm thinking I need to set up a T with a smaller hose to connect the gauge in line with the vacuum system. I read a few spots about it and looked at some of the diagrams but I'll try searching more specific instructions for bus type 4 set up
_________________
'74 Westy - "Josée"
2014 Beetle GSR - "Ozzy"
2006 Jetta TDI - "Jerry"

[Tcash]

Vacuum Gauge Hooking up the Gauge

[fifteenduth]

I have stock dual Solex's and an ACN SVDA so could I use the retard port on the left carb throttle plate where I have it plugged with a closed piece of vacuum hose?
_________________
'74 Westy - "Josée"
2014 Beetle GSR - "Ozzy"
2006 Jetta TDI - "Jerry"

[Tcash]

[fifteenduth]

Do you mean the fitting where the rubber elbow attaches between the vacuum tube that comes through the firewall and the manifold base?
_________________
'74 Westy - "Josée"
2014 Beetle GSR - "Ozzy"
2006 Jetta TDI - "Jerry"

[Tcash]

[fifteenduth]

Got it. Thanks a lot
_________________
'74 Westy - "Josée"
2014 Beetle GSR - "Ozzy"
2006 Jetta TDI - "Jerry"

[whatdoesthisbuttondo?]

I had the exact same symptoms, see the last page of thread:

https://www.thesamba.com/vw/forum/viewtopic.php?t=603715&start=180

I haven't had time to try fixing yet but all my money is on the brake booster vacuum or diaphragm having a leak as posted above. I'm thinking the latter as when I plugged the vacuum hose at the back of the diaphragm, I finally got noticeable idle drop at #3.
_________________
Orange 1973 Campervan. Rebuilt 1700cc with dual Solex carbs. Pertronix electronic points on stock distributor. Engine rebuild in progress (fall 2023).

[fifteenduth]

My experience would suggest that before you go into the major job of rebuilding the whole vacuum booster system I would start from the engine, at the elbows connecting #1 and #3 manifold with the vacuum tube and make sure there are no cracks in the rubber elbows. Replace if in doubt. Then make sure the connection at the front of the firewall where the vacuum tube goes through the firewall, then check the connections at the check valve. Move on foreward along the vacuum line to check each connection you can access until you get to the booster. While you are doing this I would disconnect each fitting at each connection and replace the rubber sleeve at each one to be sure you don't have several small leaks that are adding up. The time you spend at this could save you major work with the booster rebuild. As one of our greatest posters always says, "Start with the simple stuff first" when troubleshooting!!!

I believe you can get the rubber sleeves from Germansupply and I'm sure other sources are out there as well.

Good luck
_________________
'74 Westy - "Josée"
2014 Beetle GSR - "Ozzy"
2006 Jetta TDI - "Jerry"