Lotus Elan

Fuel starvation.

PostPost by: dougal9887 » Mon Jun 29, 2015 9:39 am

Rebuilt engine, carbs, fuel pump. Dellortos, glass bowl pump.
Filled carbs with fuel to start up.
Rev's suddenly dropped after a minute or so.
Problem traced to no fuel in front carb.
Checked banjo tee fitting, banjo filter, passage to needle valve, needle valve operation, float height and floats empty of fuel - no faults found.
Checked fuel flow with engine running - about .5ltr in 30 seconds or so. No way of checking pressure however.
Bypassed Filter King to eliminate problems there. No difference.
Before I remove the carbs again to get at the fuel pump, is there something else that might stop a carb filling?
It is strange that if it is a fuel delivery problem, only one carb is affected and that it's the front one which I'd have thought would receive any fuel first.
The Filter King remains only a quarter full so this may indicate lack of pressure.
I haven't yet checked the pump filter. It's also possible that the pump rebuild had a fault although it appeared to work satisfactorily when tested.
Any suggestions, other tests etc appreciated.
Dougal.
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PostPost by: RotoFlexible » Mon Jun 29, 2015 1:37 pm

My favorite way to induce intermittent fuel starvation is to introduce little blobs of silicone sealer into the fuel tank when I install the fuel gauge sender. Said blobs are just the right size to get sucked into the intake pipe and block it for a while. Make sure that fuel can flow easily out of the tank. I now carry a MityVac in case I didn't get all the blobs out.
Andrew Bodge
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PostPost by: collins_dan » Mon Jun 29, 2015 1:42 pm

Check the filter. I just spent a couple of hours in the building supply parking lot to eventually figure out that the lack of fuel the carbs was due to a clogged in line filter. Dan
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PostPost by: dougal9887 » Mon Jun 29, 2015 3:41 pm

Thanks for the replies.
I'll need to have a look at the fuel pump and the inlet flow.
I still can't figure out why both carbs wouldn't get an equal, if reduced, quantity of fuel. And why the first carb in line is the starved one :? .
Dougal.
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PostPost by: collins_dan » Mon Jun 29, 2015 4:14 pm

I'm not sure why either, but I was initially convinced that one of the jets on one of my carbs was clogged, as that is how the problem manifested itself. Eventually, the flow was reduced to so little that neither worked and I was able to figure out that it was the fuel filter. Good Luck. Dan
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PostPost by: Galwaylotus » Mon Jun 29, 2015 5:05 pm

If it's only the front carb, I'd check the hose that connects the two carburetors. Possibly the inner collapsed. It isn't unheard of! :shock:
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PostPost by: EPA » Mon Jun 29, 2015 5:19 pm

Could be that the float is catching on something and therefore not hanging correctly thus keeping the needle valve closed.
Best of luck
Ed
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PostPost by: dougal9887 » Mon Jun 29, 2015 5:59 pm

Well, I swapped the carb tops front to rear and the problem followed!
Another look at the offending top revealed a slightly angled float which was fouling the chamber and so not able to drop with the fuel level.
At least it was a simple fix.
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PostPost by: Galwaylotus » Mon Jun 29, 2015 6:58 pm

Don't you love it when a plan comes together? :lol:
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