78 bus with dual 44 empi/solex carbs

[63RAGTP]

I have a 78 bus that has dual empi / solex 44 mm carbs installed on it. I have a popping/backfiring back through the carb on the left side.

I am running a 009, timing is set and valves are good.

any suggestions? before I switch to a single progressive carb.

[aeromech]

Try to synch them. First, watch each carb as you move the linkage from idle to full throttle. They should both move at the same time. You may want to learn about the procedure first.
_________________
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

[Randy in Maine]

I trust you have been here?

http://www.aircooled.net/synchronize-dual-vw-carburetors-103/

[63RAGTP]

Here is an update, I pulled the dual carb setup off and installed a single progressive carb.

Valves and timing are set as they should be. Idles great. I still get a steady backfire through the intake on cylinder 4 when reving up the engine. its a constant pop, like the intake valve is open at the time of spark ignition on that cylinder.

I pulled the head on that side, and didn't see anything wrong with the valves, checked them for leaks, all were good

Any ideas?

The bus is running a pertronix vac advance distributor. I did notice that while setting the timing, vac unplugged, that the engine, timing, wouldn't advance as I raised the RPMS.

Could the dizzy be bad?

[mnskmobi]

[vic74westy]

If the problem definitely seems related to cylinder #4, I would pop the valve cover off, have someone crank the engine and check that the exhaust valve seems to be opening. Just visually compare the movement of the rocker arms between cylinders 3 &4 and see if they look the same. An exhaust valve not opening can cause a backfire through the intake. Just food for thought. Definitely want to get that distributor sorted out too!

[63RAGTP]

ok so here is where things are, I put a new SVDA distributor in to rule out the old one.

Still no increase in RPMs past around 2500, even when secondary barrel opens on the carburetor.

Im at a loss here, Any pointers?

I have had other buses with the same carb setup run just fine.

[aeromech]

Take a heat gun and while the engine is running, warm up the intake runners. Come back and give us the results
_________________
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

[Tcash]

Popping through the carb can be a lean condition.
check your fuel pressure and capacity

Lifters Hydraulic or Solid ?

Triple check that the plug wire are on correct and make sure your timing light is on #1.
Finding TDC #1/ Installing Drive Gear and Dist.
Timing

Good luck
Tcash