Bay bus 2000cc backfiring

[BobbyDEE]

We checked for vacuum leaks,checked compression,adjusted valves .Regaped plugs .Stiil when you give it gas backfiring . no power on any type of hill. Just was wondering if it could be CAM ? Need advice Bad We just rebuilt this engine 2 yrs ago. Only has about 1000 miles on it. It was a new long block that had been sitting in bus in garage fir 12 yrs before that. We tore it all apart and rebuilt with new rings bearings seals and so on . Help Thanks

[TomWesty]

What type of induction do you have, and what type of ignition?
_________________
If you haven't bled on them, you haven't worked on them.
Visit: www.tomcoryell.com and check out my music!

[Tcash]

[SGKent]

as others have said, FI or carb & if so what kind.

Has it ever run right after the rebuild?
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[BobbyDEE]

1973 bus 2000cc / the guy I bought it from bought a new long block so don't know what yr it is.i am assuming 77 -79 I have progressive new carb on it Was rebuilt 1000 miles ago since it sat for 12 yrs in bus in a garage . don't know if it could be cam or what .? rebuilt it in 2106 ran great . till started it this winter in garage and it sputtered some .cleared up Took it to car show last wk ran great then bang started back firing electric fuel pump back firing thru carb 009 dist.

[SGKent]

Did you do something to make it happen or did it start on its own?

*Check the dwell and timing in case the points broke.
*do a cylinder balance test at idle to see if one cylinder is affected more than the others.
*check the valve clearances cold and if one is radically different do a compression test
*look for vacuum leaks
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[BobbyDEE]

started on it's own Rally frustrating knowing I might have to pull motor Just wonder if carb went hay wire ? it was brand new never had any problems with it but never know

[aeromech]

I hate to say but you are doing like a bunch of us do and that’s always think the problem has to be the hardest, most expensive fix. In all actuality it’s probably something simple. Start with the simple things first. Do one thing and try it. Dont go ripping and tearing or you could induce more problems. The chance it’s your cam is very very remote. Most likely a hose came off or you have a gummed up carburetor jet
_________________
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

[BobbyDEE]

Trying not to go crazy.wish it had bug motor vs the pancake I have . But they went to pancake motor then. I have a 79 last yr super beetle no problems 59,000 original miles on it thanks for the help

[Tcash]

Backfiring through the carb could be.
Valve adjustment
Do u have hydraulic or solid lifters?
Lifters Hydraulic or Solid ?
https://m.youtube.com/results?search_query=Type+4+valve+adjustment

Distributor condenser failed.

Lean condition.
Tell us u drained the gas tank and added fresh gas before you started it after sitting for two years?
Glogged gas tank.
Bad fuel pump.
Bad excelerator pump
Test the fuel pump max delivery

Vacuum leak.
Finding vacuum leaks with smoke (smoke test, tester)

[Abscate]

If its idling a bit different, then backfiring at revs

....you might have messed up plug order when gapping.

Check by removing the wires, confirming Number 1 TDC, rotor position, then put in 4-3-2 accordingly.

Dont confirm with just a visual
_________________
.ssS!

[BobbyDEE]

idling good when you ref it up starts back firing . nothing changed in wiring from fall driving.mechanic checked gap.idle dwell, we re adjusted valves ,hydraulic lifters we checked every thing we could think of Thanks for the input

[SGKent]

What is your dwell?

Put a timing light on it and verify that the timing is advancing properly with RPM and falls back when the RPM's fall back.

Next look for a vacuum leak. Use propane or a flammable carb spray (sparingly so not to start a fire).

Next check that your fuel pressure is holding
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[BobbyDEE]

dwell is good we did everything you are talking about . tried it all

[Mispeld]

9 times out of 10, ignition timing causes backfires. What causes bad timing? Worn points, vacuum advance, loose distributor, crossed plug wires, bad distributor cap, bad rotor, bad distributor etc. Something is causing it to spark at the wrong time.

[BobbyDEE]

I am changing all points ,plugs ,condenser ,dist.cap wires just to make sure .. going to try every thing before I pull it,that is for sure.will have to work on it in the evening's.have to work day shift all wk in 3 months will be off work for 6 months. so maybe have it done by then. Hoped to go to a lot of vw shows this yr. But looks grim Thanks for the input form everyone . Glad to get different views of the problem

[Tcash]

You will be pulling the engine for nothing. A worn cam would not cause back firing through the carburetor. The only way the cam could cause it is if it had a bolt on gear and the bolts came loose and with a type IV engine that is highly unlikely.

[Stuartzickefoose]

[SGKent]

X2 - couldn't agree more with TCash. 99% of the backfiring is either fuel or ignition. In a T4 bus one can drop an intake valve seat but if you looked over the valves to be sure none changed with their adjustment it won't be that. Really common in a T4 bus to drop a valve seat.

The dwell question was really a trick question. It was to see how adept you were at adjusting your distributor and reporting facts. "Its Ok" wasn't the answer I was looking for. If everything you checked over was Ok the bus would be running fine. You are our eyes and ears when asking for help on a forum like this. Without specifics we (the bay community) can't do much except list possible causes and throw out new ideas. On the other hand if you report specifics and post photos we are in a better place to help. Hang in there you will find it.
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[ac78]

I would certainly do this before dropping the motor...

One thing i added to my tool kit is a $20 endoscope on amazon that plugs into your phone. Take your plugs out, drop it in each one and manually rotate the motor. I confirmed a sunken valve pretty quickly(and cheap) that way. I was backfiring too, but im setup a different than you.

Good luck!
_________________
78 Westy 2.0l hydr. FI

VW Campmobile
For people who believe a family's
car should be it's castle !