Series II Fuel system questions

LarryN · Dec 26, 2011

My S-II is fitted with a Weber carb and manifold from Sunbeam Specialties. I have noticed three problems since the conversion: 1) the fuel drains from the carb and fuel line, requiring what seems like a long time and a lot of cranking to get the gas back to the carb - once it gets refilled and sputters a couple of times, it starts right up and idles nicely on the choke until warmed up (it idles fine off the choke after it is warmed up as long as I don't drive it), and 2) the engine will stall at a long stop light if I don't keep the revs up (1200-1800 rpm seems to work - so far it has re-started after a few seconds of cranking, 3) off-idle performance is really poor - the engine needs to be babied off idle and load introduced with a bit of clutch slipping, then no heavy throttle until above 2500-3000 rpm.

I should add that the fuel draining problem doesn't seem to occur unless the car sits for several days - unfortunately, I haven't been able to drive it more frequently than that lately. Am I missing a check valve or something in the fuel system which would prevent draining? Would converting to an electric pump be helpful - and what is the experience out there with converting?

The other two issues seem like perhaps a combination of float bowl and jetting, but I'm not that familiar with carburetors in general or the Weber in particular and could sure use some suggestions.

Thanks
Larry

RootesRacer · Dec 26, 2011

I doubt fuel drains from the carb unless something is wrong with it.

Fuel can drain from the fuel line with gravity down to the level of the fuel.

If you are running the stock mechanical pump, it shouldnt do this since the pump has a one way valve that should disallow flow back through the pump.
If it does, then the pump needs replaced or rebuilt.

If you have been paying attention to the many "I have fuel overflowing my carbs" threads, going electric is seldom helpful unless you also install a high quality adjustable regulator to go with it.

Bill Blue · Dec 26, 2011

I experienced the empty carb problem when running a Pinto/Weber on the 2.0. Two or three days and it would be empty. Unfortunately, this was just one of several issues with that carb that I was never able to solve.

Bill

Nickodell · Dec 26, 2011

I'm not sure how you figure out that the fuel is draining back to the pump. I can only see that happening if you have an air leak in the line from pump to carb, but then you'd get a leak. I'm suspecting fuel starvation and/or wrong mixture settings.

I think you need to check the fuel system, starting at the carb:
Float level correct;
Correct idle jets (Alpines are notorious for needing larger jets in Webers);
Idle adjustment right;
Accelerator pump working;
Block in fuel line, tank to pump/pump to carb;
Pump output sufficient;

Also check for air leak in induction manifold, either at gasket or elsewhere (I once had an air leak due to a split rubber hose to the brake booster; it was at the bottom where you couldn't see it.)

RootesRacer · Dec 26, 2011

After thinking about it, the clue to your several of your issues may be one and the same.

When you say the fuel seems to drain back AND the engine stalls for extended idle if you dont keep the revs up...
This sounds like the pump has leaky valves and the pumping efficiency may not be sufficient to provide fuel pressure sufficient to overcome the fuel head when at idle.

I'd put a low pressure gauge on the fuel line and see what it is at idle.

If its not at least 1psi at idle (1.5+psi at 2000+ rpm) then I'd replace the pump.

agmason54 · Dec 26, 2011

SII fuel pump questions

I agree with Rootes racer and might add that your diaphram in the pump may have a pin hole allowing fuel to leak into the crankcase. I can not understand why anyone would run an electric pump when the stock one works fine. I do carry one for quick fixes but have yet to use it.
Agm

puff4 · Dec 26, 2011

I can see where you guys are going on this, but I don't think 'draining back' into the pump is the issue. In fact, I've never really seen that happen. My take is very simple - the carb has old, leaky gaskets the gas is simply leaking out - either into the intake or indeed it's just making the carb 'wet' and it evaporating... and for that same reason the car is not running well - the carb is just plain clapped out. It needs a rebuild with new gaskets, diaphragms, etc., and then to be properly tuned.

RootesRacer · Dec 26, 2011

puff4 said:
I can see where you guys are going on this, but I don't think 'draining back' into the pump is the issue. In fact, I've never really seen that happen. My take is very simple - the carb has old, leaky gaskets the gas is simply leaking out - either into the intake or indeed it's just making the carb 'wet' and it evaporating... and for that same reason the car is not running well - the carb is just plain clapped out. It needs a rebuild with new gaskets, diaphragms, etc., and then to be properly tuned.

This sounds interesting but unless the carb overflows its bowls into the intake, or has a cracked case, there is no place for the fuel to leak into the intake, and this includes failed gaskets. This is because the fuel in the float bowls is on its own and raw fuel cannot be delivered to the main circuit or even the idle progression holes without engine air flow.

If the engine takes many turns before the fuel flows into the float bowls, air has replaced the fuel in the fuel lines, which means the fuel "head" level has dropped either by external (non carburetor) leak, or by flowing against the fuel pumps one way valves.

On "normal" functional fuel systems, fuel is held between runs at a fuel height just below the needle and seat. Extreme temperatures (which boils the fuel) will effect this level a small amount, but in general, the fuel pump should be able to keep the fuel head near this level for weeks until normal evaporation into the float chamber slowly diminishes the fuel line level and replaces the fuel with nasty smelling varnish.

LarryN · Dec 27, 2011

Thanks for all the feedback guys - the carb is only about 2 years old with around 3-5K miles. The mechanic who rebuilt the engine and did the carburetor conversion has considerable experience with Webers on VWs and other cars, so I think the float is probably set correctly. We decided initially to leave the jetting alone and see how the car ran - it did OK until this problem developed: idle was good, a bit of stumble coming off idle, very good mid-range performance, and not much WOT (which could be a problem with the linkage he built rather than with the carb).

Since a decent fuel pressure gauge looks to cost nearly as much as a new fuel pump, I'll give Rick a call this morning and see if he has one.

Larry

LarryN · Dec 30, 2011

Fuel pump fittings?

I got a rebuild kit from Sunbeam Specialties and rebuilt the spare fuel pump. The pump in the car has tubing nipples and the fuel lines are rubber hose with clamps. The glass-bowl pump I rebuilt has one banjo bolt and a strange looking banjo fitting. The threads look like 1/2-24 UNF.

Do any of you know what the correct fittings are? I'd like to put banjo fittings on both the inlet and outlet sides and keep the rubber lines if possible.

Thanks
Larry