Lotus Elan

Stromberg spitting fuel/ engine running rough and dying

PostPost by: Evante » Thu Jun 04, 2020 7:55 pm

Hi All,

I am looking for some help.

My 1972 Federal Elan with Stromberg Carbs and Petronics Ignition was running fantastically on the highway whereupon decelerating for an exit ramp it started to pop through the tailpipe. The engine started running really rough, missing, bucking, and losing power. I bearly crept home. I changed the wires, rotor, cap, coil, and fuel filter.

After taking the airbox off, I noticed there was gas around the rear carb spilling onto the footwell. I took off the carb and checked the float and float valve. Both were fine. The car will start but runs really rough stalls and the carb is wet with gas.

Any thoughts?

Thank you for reading and considering this situation.

Jay S.
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PostPost by: Matt Elan » Thu Jun 04, 2020 8:17 pm

Sounds like the timing has slipped. How’s the distributor fixing bracket and bolt?
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PostPost by: Evante » Thu Jun 04, 2020 8:38 pm

Right, so I thought that as well. The car would not run so I did a static timing on it. Still would not run so I advanced the timing bit by bit until it would run but it is still incredibly rough. The timing also does not explain the gas coming out of the carb, I don't think.
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PostPost by: s28ven » Thu Jun 04, 2020 9:35 pm

Evante wrote:Right, so I thought that as well. The car would not run so I did a static timing on it. Still would not run so I advanced the timing bit by bit until it would run but it is still incredibly rough. The timing also does not explain the gas coming out of the carb, I don't think.


I had an issue with 1 cylinder spitting fuel back out the carb (Weber) and it turned out to be the timing.

When I read your initial post I thought you distributor must have slipped.

I would try advancing a little further while it’s running and see if it improves. Was the distributor tight when you started?
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PostPost by: Neil D » Thu Jun 04, 2020 9:42 pm

Third time attempting to post!
I've just been fixing a similar problem on a Stromberg S4. Eventually found fuel coming out of the rear carb float chamber vent (top hole on the carb front face). The problem was a fuel pressure regulator failure and an electric pump providing too much pressure. The failed regulator parts were found in the fuel filter.
Hope this helps. I thought it was ignition until I found all the fuel!
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PostPost by: Chrispy » Thu Jun 04, 2020 10:37 pm

I had very similar on mine (with webers though) and it was timing. Didn't notice any fuel, but could be possible if it's spitting.
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PostPost by: wotsisname » Thu Jun 04, 2020 10:57 pm

I've not touched a Stromberg for many years, so hopefully this won't be nonsense. And I am assuming all Strombergs are pretty much the same.
What condition is the diaphragm in ? although I would think a weak mixture if it has failed.
There is I think a fast idle screw.. is this mechanism returning home as I could see this flooding the carb... otherwise I would look again at the floats and any related seals.. my first thought was timing along with others.
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PostPost by: Evante » Thu Jun 04, 2020 11:24 pm

Diaphram. Have not checked this yet but the carb was rebuilt 2 years ago. I will check it.

I advanced the timing several times and each time it started better but eventually not so much. It still runs rough and sounds like not on all cylinders. It eventually dies in about 5 seconds.
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2005 Elise, sold
1988 Evante 140TC, sold
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PostPost by: SENC » Fri Jun 05, 2020 12:32 am

AC mechanical fuel pump, or electric? If the latter, too much pressure?

Can you tell where the fuel is coming from on/in the carb? Is it weeping from the choke valve on the back carb? Makes me wonder if there is a blockage somewhere. When you get it running without the airbox on, is the piston in that back carb behaving as expected when you throttle up?
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PostPost by: rgh0 » Fri Jun 05, 2020 2:10 am

Get a timing light so you can accurately set and check the timing advance curve otherwise your shooting in the dark trying to diagnose the issue.

cheers
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PostPost by: elansprint » Fri Jun 05, 2020 7:39 am

Check the float does not have a pinhole allowing it to fill with petrol so never closing the needle valve had this on Webers allowing petrol to poor out the air intake
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PostPost by: Evante » Mon Jun 08, 2020 1:17 pm

Thank you all for your ideas.

I will let you know the outcome after I get the car timed properly.

Best to you all,

Jay S.
Jay S.
1972 Federal Sprint, Colorado Orange/White
2005 Elise, sold
1988 Evante 140TC, sold
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PostPost by: Evante » Fri Jun 26, 2020 7:24 pm

Follow-up!

Finally got the car running properly! It turns out that the Petronics electronic ignition was not working properly. I know people say that it either works or doesn't but I just could not get it to start with the Petronics. it would just cough, backfire, and sputtered out. I put in a new Powerspark distributor and whamo; it started with just a little fiddling. I then found an air leak in the rear carb that I think I created when taking it off and replacing it. New O rings and Thackery washers solved that problem and it seems to run great.

Thank you all once again for your invaluable help!

Jay S.
Jay S.
1972 Federal Sprint, Colorado Orange/White
2005 Elise, sold
1988 Evante 140TC, sold
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PostPost by: Matt Elan » Sat Jun 27, 2020 1:32 pm

That’s great and well done - it’s always tricky to diagnose these things remotely and not too easy on the spot! As an aside, I’ve not used Petronius electric ignition but on my Classic Triumph and bsa bikes I used to fit Boyer Branson electronic ignition. The units were very reliable but had one fault - if the battery voltage dropped too much they would go onto full advance for some reason which could do significant damage to an engine.
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