Lotus Elan

Running getting worse

PostPost by: Robbie693 » Wed Mar 23, 2011 3:20 pm

Hello again,

I had a problem last year with the engine refusing to rev beyond 6000rpm and lots of hesitation/coughing.

I had the carbs rebuilt and then rolling road tuned. Whilst it was on the rollers the tuning man noticed that the engine would rev better with the aircleaner hose disconnected. He also said it was running very rich so changed the idle jets from 45's to 40's. The rev limiting rotor arm was re-set to 7000rpm and the distributor was freed off and lubricated as the advance mechanism was stuck. When i got the car back I changed the air cleaner as the old one was crushed slightly.

The car was much better after this with just a small amount of hesitation when pulling away.

Now the problem has returned with a vengance: first off it wouldn't pull beyond 5000rpm now it won't go past 4000. It also coughs and splutters in town driving. It just seems to choke up and pull no more wether I use full throttle or part.

As it feels like it's hitting a rev limiter I changed the rotor arm for a standard one but no effect. I also tried disconnecting the air cleaner hose but no difference then either.

The disributor is new (well,two years old but less than 1000 miles), coil new last year, fuel pump newly reconditioned last year.


Any ideas? I'm pulling my hair out with this!

Cheers

Robbie
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PostPost by: Old English White » Wed Mar 23, 2011 3:56 pm

Hi Robbie,
My advice ll be to put a cap on your head, and drive your car back to your tuning man.
Then, ask to set the carbs, sparks, etc, back on original specs if stds camshafts, or with the recomanded needle, jet & spark if special camshafts, and ask him to work on that and only that ... and test any solution by a 5-10mm road test.
I am sure that by checking that way you ll find the wrong element ... At the end, wrong advance angle, a worn O ring, broken tackerey washer , bad carb floater level ... can't stay hidden too long!
That if any of us hasn't allready the solution.
Christian. :mrgreen:
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PostPost by: jeff jackson » Wed Mar 23, 2011 6:04 pm

Hi Robbie,
If it's any consolation, I am in the same boat as you, ( see spark plugs again thread).
My first bit of advice never replace the rev limiting rotor arm with an ordinary Ford item, god forbid anything like a stuck throttle, and you rev to 10K and destroy your engine! please put it back.
I reckon that you may be experiencing the same problems as me, and I think that it will be down to carburation. I had the same problem with hesitation, and taking the top off the carbs revealed that the front pair floats needle valve was sticking slightly.
I have D'ellortos, maybe different if you have Webers or strombergs.
So check the float levels, 15 mm float height, 25mm droop. ( Dellorto)
Try that, see how you get on.
(Mine is better, but like you need a rolling road).

Kind regards
Jeff
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PostPost by: Robbie693 » Thu Mar 24, 2011 1:04 am

Thanks both,

I should perhaps have added that I'm running with a 43d type distributor apparently optimised for the twincam and Dellorto carbs.

Whilst awaiting suggestions I took the plugs out and found them all to look ok - reddy brown colour. I checked the timing again after setting it yesterday and it had slipped by about a degree down to 11deg, which I left as is, and the advance seems to be working. When driving home tonight the car was a bit better (I managed to pull 5000rpm before the fire went out) so it seems that the problem worsens with temperature (no traffic and cooler ambient = cooler engine). What is mystifying is why it has suddenly started to play up without me doing anything.

I've also noticed an increase in spitting back (which I gather you're getting as well Jeff? In fact we seem to have very similar problems as you say).

First off I'll check the float heights as I have read that viton tipped valves take a 'set' after a short while and need re-adjusting. Can't hurt to check anyway.

I was thinking electrics as the problem appears to be heat related, what are the symptoms of a dodgy condenser?

Thanks again

Robbie.

P.S. - I did replace the rev limiting rotor arm!
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PostPost by: Mr.Gale » Thu Mar 24, 2011 1:31 am

Have you replaced the fuel filter or checked the fuel pump?
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PostPost by: robertverhey » Thu Mar 24, 2011 6:03 am

I agree, the symptoms are consistent with

- split diaphragm in mechanical fuel pump
- sticking points in electric (su type) fuel pump
- worn points or points gap too small
- faulty condenser
- shorting low tension lead (pigtail)
- high resistance in high tension leads
- vacuum leak
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PostPost by: Frank Howard » Thu Mar 24, 2011 5:22 pm

Robbie,

I'm putting my money on your car needing new spark plug leads.
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PostPost by: Robbie693 » Fri Mar 25, 2011 12:48 am

Thanks all for the suggestions - I'll add them to the list of checks.

I'm determined to go through this on thing at a time to hopefully identify the cause, sorry if this starts to resemble a blog!

Driving this morning revealed slightly different symptoms. I noticed that if I applied full throttle I got the cut-out at 4500rpm but if I lifted off a bit I got a few more revs before it choked up again. At this point a got a pop from the exhaust so I changed up and cruised.

I checked the float levels today and found two things - first being I don't know what I'm doing! I measured the float height with the carb top perpendicular to the ground, like the diagram, and they looked a bit out so I 'adjusted' them by bending the 'u' shaped bit that goes around the valve plunger. Starting to doubt my methods I had a look on the 'net and realised that, in the pictures of the how-to guides, this bit doesn't contact the needle valve at all and I should be measuring when the float arms are just touching the plunger within the needle valve and adjusting by bending these arms. I think (?). Please advise if I've got this wrong too.

The problem I had was that in the strictly vertical position the floats were compressing the springed plunger so I had to measure slightly off vertical and gauge when there was no pressure on the plunger but still contact with the end of it. If that makes any sense.

Now I've convinced you all of my ineptitude :oops: , I'll go on.

I set the float height to 16.5mm as recommended in the Dellorto service kit for Viton tipped needle valves. After all this faffing about I'm afraid there is no improvement. In fact I thought I'd made it worse as, on start up, there was a great deal of spitting back, which I find disturbing, but this subsided after it warmed up a bit. I checked the timing again too and found it had advanced a bit from yesterday (9deg) so I re-set to 12deg. So no progress so far unfortunately.

I checked the filters in the carb inlets and they are clean, as are the fuel bowls. The gauze filter in the pump looks clean too.

Next I'll get new points and condensor and try that.

Frank - I have a spare set of leads and cap so I'll try swapping those too, although the ones on the car are about the same age as the distributor it's definitely worth a try.

Cheers and thanks again everyone

Robbie
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PostPost by: oldelanman » Fri Mar 25, 2011 8:44 am

Hi Robbie,
Looking through your posts I wonder if your distributor advance mechanism is still sticking when it gets hot......

Robbie693 wrote:the distributor was freed off and lubricated as the advance mechanism was stuck


Robbie693 wrote:I checked the timing again after setting it yesterday and it had slipped by about a degree down to 11deg


Robbie693 wrote:I checked the timing again too and found it had advanced a bit from yesterday (9deg) so I re-set to 12deg


Regards,
Roger
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PostPost by: Robbie693 » Fri Mar 25, 2011 9:23 am

Good point Roger.

How do I check the advance the advance is free with the distributor out? And do I have to dismantle to free/lubricate?

I think you might be on to something here. I did find a deposit of black greasy stuff around the top of the distributor and a bit inside the cap.

Thanks very much

Robbie
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PostPost by: oldelanman » Fri Mar 25, 2011 12:32 pm

Robbie693 wrote:How do I check the advance the advance is free with the distributor out? And do I have to dismantle to free/lubricate?


Hi Robbie,
With the distributor out, hold the gear with one hand and turn the rotor arm anticlockwise against the advance springs - you can't overdo it as there is a stop at max advance - when you let it go it should return freely and fully. If it is gummed up you may be able to free it without dismantling with a drop of WD40 down the centre of the cam where the retaining screw is (take off rotor arm first) but if the distributor is out anyway it's a simple job to take it a part and clean it up thoroughly - workshop manual describes what to do, just note where everything goes as you dismantle it.
It's a good idea to lubricate periodically with a drop of thin oil down the centre of the cam to keep it from siezing.

Hope this helps.

Regards,
Roger
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PostPost by: Robbie693 » Fri Mar 25, 2011 12:53 pm

Thanks Roger, I'm off to the garage now!

To lubricate after I've taken apart and cleaned up, do I use grease or oil? (sounds like a trunnion question!)

Regards

Robbie
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PostPost by: oldelanman » Fri Mar 25, 2011 1:05 pm

Robbie693 wrote:To lubricate after I've taken apart and cleaned up, do I use grease or oil? (sounds like a trunnion question!)


Use oil - engine oil will do fine - definitely not grease.

Good luck.
Roger
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PostPost by: Frank Howard » Fri Mar 25, 2011 2:38 pm

Robbie693 wrote:I did find a deposit of black greasy stuff...inside the cap.
That can't be good.
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PostPost by: oldelanman » Fri Mar 25, 2011 2:57 pm

oldelanman wrote:It's a good idea to lubricate periodically with a drop of thin oil down the centre of the cam to keep it from siezing.


I knew I'd seen it somewhere........

Distributor 001.jpg and


....but I don't think it's written on the rev limiting rotor arm.....or is it?
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