Lotus Elan

Stumbling Dellorotos

PostPost by: frogeyesimon » Sat Oct 22, 2016 11:51 am

My +2 has DHLA45s fitted. It has always been a bit stumbly below about 3000rpm when the throttle is floored.
Yesterday I was out and about, mixture of town driving and open roads. Pottering around town was fine. Once on the open road I booted it and all was fine. After a couple of miles of hardish driving, I encountered some serious stumbling. The car was virtually undrivable above about 30mph and when I cruised to a stop the engine stalled (it has never done this before). Started OK but I had to very gingerly use the throttle to get home.

Today I have blown out all of the jets and emulsion tubes (one of the latter had some crud in it). The fuel filters in the carb inlets are clear, the fuel levels in the float chambers seem ok, The needle valves in the float chambers seem to be operating ok. There is fuel coming through from the pump and the plugs all look ok (brownish with white electrodes).

So I took it out for another run, filled the car with fresh super-unleaded petrol (which I always use) and initially it seemed better, but on my return home it started stumbling again, not as bad, but not much fun to drive. I guess that I'm going to have to take the carbs off the car and have a closer look, but I'd be grateful for any pointers that anyone may have.

Simon
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PostPost by: toomspj » Sat Oct 22, 2016 12:40 pm

One cautionary comment I'll make is that in my experience, many carb related problems turn out to be electrical - particularly if they show up as the car warms up. So, i'd also consider rotor arm, distributor cap, and coil amongst other things. Spark plugs and leads can be an issue too.

Paul
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PostPost by: john.p.clegg » Sat Oct 22, 2016 1:04 pm

..and don't forget the condenser.

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PostPost by: richardcox_lotus » Sat Oct 22, 2016 1:32 pm

I'd add to Paul's advice. Don't assume it's carbs.
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PostPost by: vincereynard » Sat Oct 22, 2016 4:43 pm

"Stumbling Dellorotos"? Sounds like a country band.
Last edited by vincereynard on Sat Oct 22, 2016 7:09 pm, edited 1 time in total.
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PostPost by: Mr.Gale » Sat Oct 22, 2016 6:21 pm

I had a similar problem a couple of weeks ago and it turned the problem was a partially blocked inline fuel filter.

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PostPost by: RichardHawkins » Sat Oct 22, 2016 6:26 pm

Simon,

I agree with Paul. Back in the days before engine management there was a mechanics phrase that said something like "90% of carburation problems are electrical"

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PostPost by: vincereynard » Sat Oct 22, 2016 7:16 pm

I tend to agree with the others. If it ran OK for a time then there is probably nothing fundamentally wrong with the carbs. It is probably electrical problem that only happens when hot or spasmodically (cracked dizzie cap etc) or a fuel supply problem.

For instance. I once owner a TR that would run fine for days and then throw a major wobble. Cut out, refuse to start, stutter and pop. In the end it turned out that some kind soul had stuffed a pile of paper in the tank. Ata certain, unpredictable times this would block the tank outlet. Car stopped or stumbled. I had the same, years later, with an awful Escort 1300 E.
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PostPost by: frogeyesimon » Sat Oct 22, 2016 9:02 pm

Thanks chaps for your advice. On reflection it seems more than plausible that it's an electrical rarher than fuel problem. Wide throttle opening leads to stumbling when engine is hot. Will swap out condenser and coil and see what happens
Simon
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PostPost by: Elan45 » Sun Oct 23, 2016 2:56 pm

And if you still have points, check the gap. I had some driveability issues last year that turned out to be points gap barely opening.

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PostPost by: frogeyesimon » Sat Oct 29, 2016 11:49 am

An update:-
I have fitted a new coil, rotor arm, distributor cap and a powerspark electronic ignition system (I have had one of these in my frogeye for years). Initial impressions were that the car is much smoother and better. However after 5 miles or so of hardish driving (full throttle up to 70mph ish!) and the stumbling has returned. I had to nurse the car back home with very gentle use of the throttle.

Could it be accelerator pump? or maybe fuel supply?

The problem seems to be when the engine is under load. It revs quite freely and without hesitation when there is no load. When it initially started to stumble, I dipped the clutch and the engine stalled. Came back to life when I let the clutch back in.

Whilst it was in stumble mode I was able to (very gently) ease the car up to 60mph or so and it was fine, but open the throttle more than a little and the stumble was back.

I'm hoping that there will be someone here who recognises these symptoms. I'd be grateful for anyone's thoughts.

I will go out again in an hour or so and see whether I get the same behaviour and report back

Simon
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PostPost by: frogeyesimon » Sat Oct 29, 2016 12:03 pm

Another update:-

Car sat on drive for half an hour (so it was still hot) and I took it out again. It was fine for a mile or so before the stumble came back. Whilst stumbling there was some noticible "popping" from the exhaust when on overrun - weak mixture perhaps?

Simon
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PostPost by: frogeyesimon » Sat Oct 29, 2016 6:33 pm

Perhaps stumble is a poor description.
When it's in "stumble mode", flooring the accelerator is like turning the ignition off. Backing-off the throttle and normality resumes (sort of)
Simon
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PostPost by: frogeyesimon » Mon Oct 31, 2016 8:51 am

Another update:-

OK, had a fun day yesterday dismantling carbs & fuel pump. Have blown out / rodded all jets again. Accelerator pumps all seem to be working as they should.
Fuel pump (original AC delco type) had some crud in it but otherwise nothing obviously wrong. What I did notice was that once re-assembled, it took maybe 10-15 seconds of engine cranking to fill the fuel pump glass bowl with petrol. Does that seem like a long time? - any views?

I ran out of time and didn't get the chance to road test the car, but I will try and take it out for a spin this evening.

Simon
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PostPost by: alan.barker » Tue Nov 01, 2016 6:10 am

Clean and make sure accelerater pumps are not seized in bottom of carbs
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