Bus surging?

14platoon · Posted: Tue Oct 28, 2014 12:24 pm Post subject: Bus surging?

Hello

1974 bay window 1800cc on dual carbs
Recent purchase.
My bus feels like it is surging while in drive, if I dip the clutch the surge stops. I can only describe it as a surge / kangarooing / bouncing motion.
The engine runs great. I initially thought the clutch maybe slipping but don't think this would happen while permanently in drive.
Any ideas please, could this be clutch or something else?

Thanks

Wildthings · Samba Member Joined: March 13, 2005 Posts: 50353

What happens is you just let off on the gas for a couple of seconds and then push the pedal down again? I am thinking the carbs may not be getting sufficient fuel.

aeromech · Posted: Tue Oct 28, 2014 1:23 pm Post subject:

I'm thinking dirty fuel filter. Can you see if it's clogged? Some are clear.
_________________
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
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Capable of leaping tall buildings in a single bound

pete_the_teapot · Posted: Tue Oct 28, 2014 1:33 pm Post subject:

My bus did the same when I first got her. The culprit? Lots of rust and crud in the fuel tank blocking the filter. Start there Smile

aeromech · Posted: Tue Oct 28, 2014 1:50 pm Post subject:

I also worked on a bus doing that once and this is what was in the tank. A rag. Came out in small pieces.

Image may have been reduced in size. Click image to view fullscreen.

This was the filter

_________________
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

14platoon · Posted: Tue Oct 28, 2014 1:58 pm Post subject:

The fuel filter looks crystal clear to be honest.
When I'm driving its a constant surging or whatever you call it. During the surging I dip the clutch and hold the same accelerator position, the engine revs freely with no surge. It seems to only surge when the clutch is engaged.
The surge is quite constant or rhythmic. I believe if it was a blockage or rust etc, it would be more intermittent.

aeromech · Posted: Tue Oct 28, 2014 2:08 pm Post subject:

Well, you need to understand that when the clutch is engaged the engine has a load on it requiring more fuel. If the fuel is being metered by a plugged filter or fuel tank outlet then the engine will starve. If only you could observe the clear filter while the engine had a load on it you could see if it emptied out briefly.

If you can get your fuel tank almost empty, I'd suggest pulling the outlet off and checking the finger strainer and looking for debris.
_________________
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

Jack_O_Trades · Posted: Tue Oct 28, 2014 2:11 pm Post subject:

Is it possible the carbs are out of sync?

14platoon · Posted: Tue Oct 28, 2014 2:24 pm Post subject:

Strange you should mention carb sync, I was researching that for my next job. It is very possible the carbs are out of sync. Would this cause a fault such as mine.

Aeromech, how easy / difficult is it to get to the strainer ?

Thanks

aeromech · Posted: Tue Oct 28, 2014 3:29 pm Post subject:

Aeromech, how easy / difficult is it to get to the strainer ?

If your bus was originally carbureted then I think that it just has one drain tube. If that's the case there's a nut like fitting you remove and the drain tube and finger strainer come out. The FI tanks were different.
_________________
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

14platoon · Posted: Wed Oct 29, 2014 11:52 am Post subject:

I think it's the clutch.......
Pedal travel is 65cm before it takes up pressure!!!! Just a reminder, I just bought this so it's not my neglect.

westcoastmarek · Posted: Wed Oct 29, 2014 12:16 pm Post subject:

Hmmm, I've worn out a couple of clutches in my time (when I was younger) and I never experienced any surging. if the clutch is worn and is starting to slip under load, it doesn't suddenly grab again. if something was actually broken in the bell housing to cause this, I suspect you'd hear something rattling inside.
My money would be fuel filter or pump...
_________________
1979 Westy Auto
----------------------------------------------
sold...
1979 VW bus, 2L FI, now with a rivi top
1971 7 pass. deluxe
1974 Beetle

FreeBus · Posted: Wed Oct 29, 2014 12:27 pm Post subject:

Classic fuel starvation.

Ask an engine to work harder (eg. move a vehicle, or produce power) it asks for more fuel to do it.

Just idle an engine and rev it up (eg. no load - not asking to to produce power, just spin - they're made to do that) it wont ask for much fuel to simply spin.

Your description of Clutch-In, rev's.. under load, surges... there is a fuel delivery problem in my humble opinion.

-FB

14platoon · Posted: Wed Oct 29, 2014 12:33 pm Post subject:

Hm, damn it I thought I had found the problem. I'll obviously adjust the clutch and see what happens.
Fuel delivery ? Check filters and fuel pump, and sync carbs?

Wildthings · Samba Member Joined: March 13, 2005 Posts: 50353

14platoon · Posted: Wed Oct 29, 2014 2:12 pm Post subject:

I looked at the pedal travel measurements, mine was over double!

Tcash · Posted: Wed Oct 29, 2014 3:04 pm Post subject:

Link

14platoon · Posted: Wed Oct 29, 2014 3:11 pm Post subject:

Thanks T cash. That's exactly how I measured mine, a total of 65cm which is I believe 40cm too much!

timvw7476 · Posted: Wed Oct 29, 2014 4:21 pm Post subject: Bus surging?

the power surge is the A/F ratio changing as the carbs starve for fuel,
you should check the in-pump filter in the pump housing itself, it is behind
the six-sided plug,13mm as I recall, + the strainer at the fuel tank bottom.

timvw7476 · Posted: Wed Oct 29, 2014 4:21 pm Post subject: Bus surging?

the power surge is the A/F ratio changing as the carbs starve for fuel,
you should check the in-pump filter in the pump housing itself, it is behind
the six-sided plug,13mm as I recall, + the strainer at the fuel tank bottom.


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