Engine cutting out at low speed.

[RogerFrench]

I'm posting this in a couple of Europa places as well, but since the engines are pretty much the same as Elan's, maybe someone here can help.

My Europa Twin Cam has developed a bad habit. It starts and runs fine, but after a while, say 10 miles or so, it cuts out and is a devil to re-start.
It has Stromberg carburetters, is a Federal spec engine with the emission stuff removed (cross-pipes, redundant throttles, etc.).
Ignition is Pertronix in a new distributor, good coil, wiring all new.
Fuel pump is electric (Facet).
It only stalls if I let the revs drop - if I keep it above 1,500 rpm or so when stopped at a red light, say, it stays running.
There seem to be no performance issues when on the move, as long as the revs stay up.
It "feels" more like fuel starvation than over-richness, and using a bit of "choke" (which only operates on one carb) seems to help it to start.
Ambient temperature around 95deg F, 35 C.

I'm thinking carburation, maybe an Air Valve (piston) sticking in an "up" position, but before I rush out tomorrow and attack, I thought I'd ask collective wisdom if they had any better ideas.

I have done forum searches, but haven't quite found the same symptoms.

[Higs]

One easy one to try is a new / different coil (although you say it is good). One failure mode of the coil is a short that occurs when it gets hot. Easy to test and eliminate.

Richard

[promotor]

I agree with the above post - when i first read this thread my thought was coil overheating - always a cheap way to find out provided you try another similar spec coil.

[robertverhey]

If it runs above 1500rpm but dies below, might be worth checking the idle circuit, maybe blocked jets....oops stromberg I see.... Something about the needle then? Not my area of strength.....

[twincamman]

fuel pump starting to fail ?? or an air leak at the intake manifold ---ed

[miked]

May be wrong but If it were heat related to the coil, cap or rotor arm surely it would be a pig on the higher RPM, in my opinion. I would agree with ED on an air leak. What about the temp compensators. They weaken the mixture as I recall when you get higher under hood/bonnet temperatures. Running in 35 ambient is pretty hot. Are they both seated property with their 2 little seals. Are they set right (been fiddled with). Could be opening prematurely. A lot of people over tension them so they never open. What about balance pipe ?O? rings and any leaks. Also the 3 bolt (O ring) and 4 bolt gaskets fastening part on each carb. Have seen nuts shaken off and air leaks here.
NB Stromberg?s are not known for good hot starting at the best of times. Last thing needed is some extra air to prevent pulling fuel that long distance from the needle jet.

[types26/36]

Is the fuel tank breather/venting system OK.....possibly blocked or partially blocked?

[RogerFrench]

Thank you all for taking the trouble to reply.

I don't think it's anything electrical or fuel feed. If so, The problem would be worse at high speed, but this is a low-speed issue.

Temperature compensator sounds like a good place to look though - it sure has been hot around here lately!

[rgh0]

Hi Roger
Is the engine cutting out because it is over rich ( float valves leaking and causing it to flood) or because it is over lean ( air leak through somewhere?). Understanding why it cuts out will tell you where to look next.

cheers
Rohan

[69S4]

I've had far more problems with low speed / idling issues with Strombergs over rich than running lean. Almost exclusively the running lean issues have been due to air leaks with the main culprits being the "O' rings and more recently a split "T" piece on the front vacuum tank. That usually manifests itself as a very uneven idle where the engine speed cycles up and down over a 3-400 rpm range over about 10 secs or so. I've had the temperature compensators all over the place and not noticed much difference - certainly not enough to cause the symptoms described.

I've had exactly the symptoms you describe but caused by carb icing in the winter - probably not a likely cause in 35C heat

I've had severe running rich at idle issues with Strombergs for ages on my S4 and had cutting out problems in eg traffic but usually you get plenty of warning with stumbling, coughing, spluttering etc and normally a few blips on the throttle will clear it for a while. If it does cut out it'll normally start again if you don't leave it more than 10 -20 seconds but more than a couple of minutes and it'll be hours before it'll go again until its cooled down. You can usually smell the petrol by this stage though. The cure for it was a complete carb rebuild replacing needles, jets etc.

How are the diaphragms? I've not experienced a split or a hole that would cause the carb to work properly for 10 miles and then leak but you never know.

[RogerFrench]

Hi Roger
Is the engine cutting out because it is over rich ( float valves leaking and causing it to flood) or because it is over lean ( air leak through somewhere?). Understanding why it cuts out will tell you where to look next.

cheers
Rohan

I think it's starvation - the last time it happened operating the "choke" seemed to help it to restart. Points to air leak or sticking piston I think.

[gav]

I am struggling with a similar problem with my twin cam which has run fine for years but last time out, ran onto 3 cylinders and was a pig to restart. Checked the obvious items (although the coil is at least 10 years old - do they go off over time?)
I was wandering if the fuel which has been in the tank for a long while now can go off. Is this possible and does bad fuel create problems like this?.
I'm on Webers and the only thing to play with is floats. I'll check them again but last time I looked they were fine.
Could it be the misabs?
There are so many possibilities finding a sensible start point can be a little overwhelming.
What is the correct diagnostic trail?
Thanks
Gavin

[ricarbo]

Sorry, lost me, what are misabs?
Richard

[ardee_selby]

Sorry, lost me, what are misabs? Richard

HIH - Richard