Getting frustrated, need help with engine running issues

[Barnsley-mark]

Stevens car, I appreciate that could be blasphemy in this forum but it's a carb turbo so a bit of a rarity in the 'other' side.

after almost 8 years it's almost back in. Running order but I have some running issues which is puzzling me.

starts no problem, high tick over for first few minutes, during which time it appears to run pretty well.

when the RPM drops to, it still idles fine but will not Rev at all, struggles, pops bangs or cuts out etc.

figured it must be carbs so had them rebuilt b specialist, still the same. (Appreciate they will need setting up).

noticed the problem was much less when plenum box was not fitted so maybe turbo? - nope, that's ok.

all hoses and vac pipes are new and in right place, just feels like I'm running around in circles and it's getting frustrating because I'm so close to it being drivable again.

any suggestions guys?

 

[molemot]

Diagnosis. Always the first thing....(!) Getting the carbs rebuilt by "a specialist" isn't going to help much....if it's not them at fault. Or maybe, even if it IS..

So what to do now? Check the sparks...see if the distributor centrifugal advance and retard system, the bobweights and springs, is working freely and correctly. Look at the plug leads...could be losing sparks from them. See if there is a good fat spark at the plugs... Check the timing; both ignition and valve timing, easily done with the dots on the cam pulleys. 

Get the book out and check the float heights in the carbs are correct. Inspect the jets and ensure they are clean and clear...might be new, after your specialist has been at them...make sure they are correct; the standard jets are marginal and anything smaller or any varnish coating on them can cause problems. Don't forget the turbo car has pressure carburetters and these use different gaskets...

The rubber mounts between the carbs and the inlet manifold can perish and leak air... Balance the carbs and check the mixture. Don't assume that anything that has been done has been done correctly, either....much frustration can be due to not checking stuff for this. I'm just rambling on with random thoughts..hopefully they might be useful. Always difficult to do this sort of thing in absentia!!

Good luck with it.....I'm about to put the new exhaust manifold and sundry other bits on mine......all good fun!!

[jcslocum]

I'm by no means a lotus expert. As you are checking the above, check fuel pressure and then flow. If you have a later car with early engine, you could have a Fuel Injection fuel pump which I would think is too high pressure. Check filters for cleanliness or replace. Last, leave the fuel filler cap off or loose. Sometimes a tank vent can get blocked and a vacuum in the tank will keep the gas from flowing.

Other than that is spark......

 

[Barnsley-mark]

New fuel pump, filters, breathers, tanks cleaned and sealed etc.

just noticed something very weird, the high idle for first couple of minutes is not by the jacking solenoid because it's not even close, so something else, timing etc is holding high idle for so long. While in high idle it will Rev no problem, as soon as idle drops (can't see why it would time-out etc) then it won't Rev at all.

i can usually fix most cranes and other technical machines in minutes but this is baffling me at the moment

[Paul Coleman]

I had endless problems with my S1 popping and banging. I rebuilt the carbs but it made no difference and in desperation I bought a replacement distributor. That made no difference either and it turned out to be... the distributor!! As somebody once said "90% of curburettor problems turn out to be timing" I bought an exchange distributor from SJ and it cured the problem. The replacement distributors don't have the internal O ring which stops it filling with oil as it's lying on its side.

[mdw]

Does the distributor use the ab14 amp unit. These sometimes fail.  I fitted I new Chinese distributor from Simonbbc on ebay. no amp needed and works fine. 70ish all in from memory.

[Paul Coleman]

Mine also came from Simonbbc and didn't have the internal O ring and it also had the wrong advance curve. I sent it back for a refund.

[Andyww]

Later cars have the vac advance on the distributor which is controlled by a temperature switch. So it sounds like the timing is correct when the vac advance is activated during warm up and goes out when normal hot running. 

Seems like a case of checking the timing when hot, and the advance curve. Must be something to do with that. I dont know exactly what the specs are as my service notes dont cover that version but I am sure someone else on here will know more.

 

7 hours ago, Paul Coleman said:

I had endless problems with my S1 popping and banging. I rebuilt the carbs but it made no difference and in desperation I bought a replacement distributor. That made no difference either and it turned out to be... the distributor!! As somebody once said "90% of curburettor problems turn out to be timing" I bought an exchange distributor from SJ and it cured the problem. The replacement distributors don't have the internal O ring which stops it filling with oil as it's lying on its side.

Thats right, our distributors are special, they have a machined recess in the inside of the body to accept an oil seal. I changed mine a couple of weeks ago as oil was coming out of the hole where the wires exit and was covering the right hand side of the engine with oil. Many people seem to confuse this with the O-ring located on the shaft which is standard. 

[Barnsley-mark]

Ordered workshop manual and electrical diagrams from SJ.

dont know why I didn't get them ages ago

[marcbria]

Don't see how oil getting past the seal in your distributor could be your problem but maybe I'm missing something. When my distributors oil seal failed it resulted in an occasional hiccup where it wouldn't fire because the contacts in the distributor cap were oiled up.

Brian

[andy b]

On my 91 excel the vacuum advance advances the engine by a lot making the engine run fast idle it worked when cold but when the engine warmed up the vac advance reduces and the disi base plates move back to normal ignition and my car would cut out i removed the disi and put a little wire  between the two base plates and that cured the problem there is a little bush that becomes oval and looses the earth connection that could be the problem it will cause misfire hope this helps

andy b 

[Barnsley-mark]

This is sounding possible, I've been trying to work out why it seems ok for a few minutes, then revs drop and runs poorly when warmed up.

 

[Sparky]

Have you confirmed the valve timing is correct?  I stand to be corrected, but I can't find acknowledgement of this in the thread.  Check flywheel - NOT crank pulley - and cam sprockets.  Have you checked static/dynamic ignition timing?  Above, Andyww references something that means timing would be the very first thing I'd investigate, given your symptoms.

[molemot]

I'd forgotten about that pesky temperature switch.... prime suspect, as far as I'm concerned!!

[Barnsley-mark]

2 hours ago, Sparky said:

Have you confirmed the valve timing is correct?  I stand to be corrected, but I can't find acknowledgement of this in the thread.  Check flywheel - NOT crank pulley - and cam sprockets.  Have you checked static/dynamic ignition timing?  Above, Andyww references something that means timing would be the very first thing I'd investigate, given your symptoms.

Flywheel and cam timing appear right, I thought it was carb trouble but now looking more like ignition timing, I still don't understand why it changes after a few minutes of warming up and idle rpm drops. Thought this was jacking solenoid but it's the same with throttle Jack taken out of the equation so must be something else that changes with temp or a timer?

21 minutes ago, molemot said:

I'd forgotten about that pesky temperature switch.... prime suspect, as far as I'm concerned!!

Is there a temp sensor that interacts with ignition timing?

if so it would explain the dramatic change after a few minutes warming up.

[Sparky]

Read Andyww's post!

[Sparky]

Smoking gun?

http://www.thelotusforums.com/forums/topic/74157-camshaft-identification/#comment-571974

[molemot]

Hi Mark....Andyww and I have been around this hamsterwheel before. Tracked it down to here...

 

All you need should be in this thread...I copied the pages from the manual, too, so I hope it's clear. Could very well be your problem; let's hope you get it sorted quickly...

[Barnsley-mark]

54 minutes ago, molemot said:

Hi Mark....Andyww and I have been around this hamsterwheel before. Tracked it down to here...

 

All you need should be in this thread...I copied the pages from the manual, too, so I hope it's clear. Could very well be your problem; let's hope you get it sorted quickly...

Thank you, hopefully get chance later on this week.

[greentengu]

Does this car have a heated Oxygen sensor? 

--Scott 

[Barnsley-mark]

7 hours ago, greentengu said:

Does this car have a heated Oxygen sensor? 

--Scott 

I'm going to say no, i haven't seen anything like that.

 

[Andyww]

11 minutes ago, Barnsley-mark said:

I'm going to say no, i haven't seen anything like that.

 

It wont have as its a carb car. But is the problem still there?

[Barnsley-mark]

7 minutes ago, Andyww said:

It wont have as its a carb car. But is the problem still there?

Been away so haven't had chance to re look at timing and the valve thing in right quarter panel.

workshop manuals and electrical diagrams on back order from Lotus unfortunately so I'm working on limited information.

[greentengu]

Ah! You're right...what was I thinking? No injection = no sensor. 

Here in the US, I have copied and sent .PDF files of the electrical diagrams of my (pre-'90) Lotus notes. Maybe someone here can pipe up with the diagrams / schematics you seek and send them to you as you wait for your order to arrive.

Cheers, and please keep us posted,

Scott