tockwell

Hello,

My orion is fitted with twin 40 DCOM Weber carbs. It has a facet electric fuel pump and a filter king (filter and regulator). Everything uses AN -6 fittings. The carbs have been correctly set up and rolling road tuned and the fuel pressure is 2.5psi

The flow of the fuel is (in the boot) from the tank to a filter, to the pump, to the regulator, to another filter, (in the engine bay) to the right carb, to the left carb. It is then dead-ended at the left carb.

I had these carbs rebuilt and it was running perfectly. However, after a long cold start attempt from not being started for 3 months, fuel started leaking out of the bottom of the left carb (from where the diaphragm is).

It would appear that when priming the pump for a while the fuel pressure built up was enough to override the floats and allow more fuel back in the carb. As the regulator is set to 2.5psi, why did this happen?

It worries me that there is nowhere for the fuel to go if the pump continues to pump after the float chambers are full if the car does not start.

Therefore, I am wondering if I put a return after the last carb (as a sort of fail safe), then would I still have significant fuel pressure for both carbs?

My current setup also has a return with a 1.5mm restrictor before the regulator, back to the tank so that excess fuel that the regulator denies has somewhere to go. However, this did not protect against the problem.

I am playing with the idea of having a shut off value after the last carb so that I can open it and have the excess fuel go back to the tank when the pump may be running for without the engine running (when priming).

So, to summarise, I know everybody appears to dead-head twin carb setups, but will it do any real harm to have a return after the last carb in extremis?

stevieturbo

Running a return is no problem at all with a suitable regulator.

You say it the fuel overflowed...was this at 2.5psi or is there no gauge after setup ?

It could either be excessive pressure, or simply the needle valve sticking due to dirt or other.

But if the needle valves are sealing, they should have no issues with a dead and and 2.5psi, most should handle 4-5psi.

The fact it's only one carb filling up, again, investigate float levels and needle valve condition.

tockwell

Hello,

thanks for the reply. I have just reconnected the gauges and it is producing a steady 3psi as it leaves the regulator and exactly the same pressure just before the first carb.

I have had it priming for about 4 minutes the engine off and it has maintained that pressure without leaking.

So, I am a little confused. The car has been stood for about 4 months so I suppose it is possible that the needle valve got stuck.

BigPeBe

Always when you get a flooding carb first thing to do is check the needle valve / floats as this is the most probable cause.

I also had a same problem with mine after it had been standing for few months. After carefully removing the carb top / floats and taking the needle valve apart and cleaning it (just blowing it really) and checking the float levels the problem was gone. I don't use return neither, altho my fuel pump is mechanical.

-EDIT- Only thing that sounds little weird for me is that you said it was leaking from the bottom. When my carbs flood they leak from the top. But since you have the DCOM model vs. my DCOE which I believe use the "DHLA style" diaphragm pump circuit I dunno if this makes a difference regarding what would be the first place to leak then. I would still check the needle valves/floats since it's a easy job to do.

BigPeBe

I'm gonna add that if you are actually sure that it's leaking from the diaphragm and not from the top, then I would suspect that the diaphragm itself is torn.

When these carbs flood, they usually leak from the top or from the trumpets, but it's not always easy to detect the leakage point because the thin clear fuel can run against the carbs side and drip from another point.

Sure if the leak doesn't re-appear it was probably the needle valves, so nothing to worry about at this point really.

tockwell

Hello,

This was the leak:



DCOMs do indeed have a diaphragm pump, otherwise they are much the same of DCOEs. I had the carbs rebuilt two years ago because of a similar but much worse problem. I shall see how it goes, but hopefully I wont have the replace the diaphragm again.

tkracing

Try resetting float levels and as above needle and seat need inspection

tockwell

It is still leaking! I'm getting it recovered to a specialist next week

tkracing

Last time my 40s leaked after I rebuilt them. The float was 16mm. I hadn't altered it. Needle and seat was replaced.
I stripped em back down and dropped float level to 12mm and never had problem after that.
Mines was leaking from overflow hole above to side of trumpets on dcoe....
Also made sure floats weren't sticking in bowls