fast uncontrolled idle

[simon a-b]

So I started the engine today for the first time in 5 years!

 

She runs, but with a fast uncontrolled idle (3000rpm).  At that engine speed I'm getting good oil pressure which is nice to see. 

 

Any ideas why the fast idle?  Carbs have been off for a clean, O rings looked ok to me as did the rubber isolaters.  I have a gap on the carb/inlet manifold joint (where the big o ring is) and a gap between the cup washers too, not measured but by eye similar to when I took them off. 

 

I tried the main idle bolt but that made no difference, I've turned it a full turn but that's clearly not the problem as there was no change to the idle speed at all. 

 

I'll search to forum tonight.

 

cheers,

Simon

[mdw]

Do you have a throttle jack solenoid? Is ti working/ stuck on and is the bracket bent  pressing down on the lever on the carb spindle.

[andy b]

At 3000 rpm you are on the main jets the idle volume control will make very little difference to have it running that fast you have air petrol mix getting in the engine so the butterflies are open or you have an air leak on a the joint faces. But i would go with Buddsy and look for something holding open the

throttle good luck i look forward to see what you find

andy b

[simon a-b]

Thanks all so far...

So the throttle lever is against the stop, from memory when the carbs were off the shaft between the throttle lever and the butterflies is solid so if the lever is against the stop the butterflies are closed. 

I have not got as far as setting the throttle cable up, it is loose but with the lever against the stop I can't see how it is involved. 

The choke cable has been removed and the choke levers on both are pushed far right (viewed from inlet side of car) against their stops... could the choke mechanism still be active?

No throttle jack involved. 

leaving me with the air leak... by joint face I'm guessing this is between the inlet manifold and the carbs where the big O ring goes?

Looking in the manual there should be a 1mm gap between manifold and spacer and spacer and carbs.  I'll check this first tomorrow.  If I had an air leak that would mean very lean mixture, right?

Cheers all and thanks for suggestions

Simon

[molemot]

I'm with the "butterflies are open" brigade. That's the only way you'll get 3000 rpm...so something is interfering with them somewhere, I reckon. Air leaks aren't going to do it, either, imho. Try taking the plug leads off in turn....or shorting them out to ground in turn...see if it's just one of the carbs causing the engine to run fast...maybe the butterflies aren't synchronised, and one carb is shut but the other is open?  

[simon a-b]

Can the external lever the throttle cable operates be in the closed position and a butterfly be open?  I thought they were all on a solid bar... with the complex connection between the carbs aside of course.  Easy enough to take the airbox off again and have a look, which I'll do after the below.

 

I measured the gap I have and it's below the specified 1mm so tomorrow I'll ease that open a bit.

 

The only other thing I did with the carbs off was to nip up the bolt that locks the barrel in the carb housing on one of the barrels- it was loose and the inner barrel was rattling so I tightened it up.  all the accellerator pumps were working fine, I know they aren't the issue but the carbs seemed in pretty good shape. 

 

This doesn't take away from the excitement of having it run!

[jonwat]

I'm with the "butterflies are open" brigade. 

 

And me, sounds like they're way out of balance.

 

As a starting point refer to the balancing procedure in the manual. 

[Sir Paolo]

Simon,

Thinking outside the box, but have you checked your ignition timing - if it's too far advanced it will cause the engine to race.

 

At idle, it should be around 5 - 10deg btdc.

 

Good luck!

[andy b]

Pop a plug out have a look at the colour. I have seen the engine race with air leaks on a 907 in an eliteI do like the timing theory andy b

[simon a-b]

Well early indications are good.

This morning I took my home proctology kit and inspected the butterflies.  Fully closed on one carb, a slight gap on the other.  A twiddle on the adjustment screw to bring them fully closed, and I get a steady idle, at around 1600 rpm.  That's without airbox and filter so after breakfast I'll fit them to see where I end up. 

Thanks to all that offered solutions, my fingers are crossed the butterfly theory was the only issue!

[simon a-b]

air cleaner on and the idle is still stubbornly high, around 16-1800 rpm. 

I'm also getting detonation in the exhaust from time to time so it may be a timing issue too.  Would a new belt always need re-timing?  I think I got it back on the same teeth but since it's new it probably needs a re-time. 

I don't have a timing light anymore, so it will have to be static then by ear... and look out for a timing light in the charity shops etc. 

 

oh and the otter switch is leaking... so back to the forum for advice!  I'm sure I read something just the otter day about it.

 

Cheers,

Simon

[Sir Paolo]

Simon, if you're getting 'detonation' in the exhaust, there is definately a timing issue. Effectively, it is firing on the exhaust stroke i.e. with an exhaust valve open.

Or you are getting incomplete combustion, meaning unburnt fuel is igniting in the exhaust.

 

You can't really set the timing accurately without a strobe light - a static timing set will merely get the engine running.

Strobes are a worthwhile investment - incorrect timing over a length of time could kill your engine.

 

It's not necessarily the new belt that would need timing, but when you change it, all the timing marks (crank, aux drive and cam pulleys) must line up before you remove the old, and re-fit the new.

It's also worth checking ignition timing afterwards too.

This can be a real PITA as you know the dizzy lies on its side under the carbs, I find it's very fiddly loosening the securing bolt between the carbs just enough to turn the dizzy body while you check the timing with the strobe. As a micro turn too much, and the dizzy spring wants to push it out of its housing. 

Still it's all part of the fun of Lotus ownership - good luck!

[Mike6]

could it be something as simple as the return springs on the carbs not doing their job properly. A long shot I know but worth checking otherwise check all the vacuum hoses.

[jonwat]

could it be something as simple as the return springs on the carbs not doing their job properly. .

If it was lack of spring pressure then pressing down on the lever would slow the idle.

[molemot]

I assume it's the adjustment screw on the linkage joining the two spindles together that you have adjusted...so that all the butterflies are fully closed together?

When you fit a new belt, several things are essential. Firstly, the auxiliary pulley that turns the oil pump and distributor has a tendency to rotate easily once the belt is off...and that is going to change the timing. I have marked this pulley on mine with a line which coincides with the edge of the casting when it's in the right position...makes it easier. Secondly, The cam pulleys have to have the timing dots pointing at each other ....and then the belt itself has to be installed so that the belt is tight from the crankshaft pulley to the exhaust cam, then tight across to the inlet cam, then tight to the auxiliary pulley...and finally all the slack is taken up by the tensioner, and the belt tension set. A rule of thumb is to set the tension so that the belt will just twist through 45 degrees on the length between the inlet cam and the auxiliary pulley....get it set accurately with the proper equipment as soon as possible.

Checking the cam timing is easy, just ensure the dots point at each other.... but the auxiliary pulley alignment requires squinting at the front of the engine, or up from below, setting the timing mark on the auxiliary pulley..next to the dimple...to align with the line joining the centre of the crankshaft with the centre of the auxiliary shaft.

Setting up the static timing accurately will suffice at this point....use the timing marks on the flywheel, removing the cover over the access hole (if you still have it fitted!) The distributor shouldn't need to turn very far...loosening the nut holding the distributor clamp to the block will enable you to rotate it enough for this, and means that the distributor cannot move out of it's housing far enough to come out of engagement. If it ever does come out of engagement, it can only fit back correctly as the coupling as assymmetrical.

 

Fun, these, aren't they??(!)

[simon a-b]

That's right John, the adjustment I made was between the two carbs allowing them all to be shut at the same time.  I can adjust this to the point of lowest idle (around 1600 rpm) at which point I reckon they are all closed. 

 

I'm fairly confident I got the belt on right, and that the aux pulley didn't move.  I had the lump out to do the job and took copious photos with straight edges as guides held through the pulley centres and the dots, and once all done up it was the same as the old belt. 

 

I tensioned with a freqency analysis app on my phone, from memory I settled on multiple readings of 114Hz.  I'll re tension after a 'run in' period. 

 

I'd be surprised if the timing didn't need adjusting with the new belt though (I clearly have problems still and the detonation in the exhaust shows it). 

 

I'll see if I can get hold of a timing light, from internet research the type with a clamp onto the plug lead and separate power from the battery is the best?

 

And I clamp onto the lead for cylinder 1?

 

Cheers all, I drove her around the property (taking Mrs and daughter for joyrides), first time the car's moved under power for over 5 years.  The Mrs can't call it a 'coffee table' anymore... just the right height for a coffee to sit on, never went anywhere etc...

[Sir Paolo]

Simon, another thing that would affect idle speed is of course fuel/air mixture.

I don't know if the adjustment screws were s disturbed at all during cleaning, but it's worth checking.

If the mixture is too rich, this can also cause high idle speeds.

You can check plugs for fouling, but long periods of idling will cause this anyway.

It's better to adjust the mixtures with the engine running.

You could try turning the idle mixture screws in half a turn at a time with at least 30 seconds between turns to let the engine settle, and only turn one at a time.

Keep a mental note of how much you've turned each screw so you can return to the current setting s if there's no improvement.

Leaning off a rich mixture will lower idle speed. Carb tuning isn't really a black art, as you can make improvements yourself. But I've always taken the car to a known expert for final adjustment- even though I'm armed with Des Hammil's bible Good luck.

[Sparky]

Don't touch anything else; follow Paul's advice.  Golden rule - if you change a belt, the very first thing you do is verify dynamic ignition timing.  Anything else is just wasting time and potentially causing further issues.

[simon a-b]

That's my plan; get hold of a good timing light and go from there.  No screws were touched on the carbs while they were off the car, apart from the aforementioned locking bolt for one of the inner barrels.  The carbs were separated, which could allow for the difference from carb to carb on the butterflies.  Car was running very nicely before so within reason (different exhaust for example) the tune should be OK. 

Thanks

Simon

[simon a-b]

timing was pretty close, but with a tweak idle is now improved, except for the rear two cylinders not firing at idle.  they are fine off idle, just not at idle, so I'm getting around 1000 rpm off two cylinders.  it will idle just on one cylinder!  I discovered this while pulling leads off to see which cylinders weren't firing...

I've responded to a thread about this issue in this part of the forum so if anyone has any ideas, please put them there.

Thanks again

Simon

[simon a-b]

Success!

 

Anzac day, so off to the march in the morning.  Then some time to play with the car in the afternoon.  I've ordered vacuum spigots from the web, but I thought I'd take another look.  I ended up taking the carbs off again and put them on the bench. 

 

I discovered that there was no way with the adjustment between carbs to bring them even close into sync.  I don't know how it happened but the lever between the carbs must have got bent when I took them off. 

 

Looking at the angles there was no doubt about it, so I carefully re-bent the tab on the end of the lever to bring the screw adjustment into play...

 

re-mounted the carbs, and immediately got an even, smooth, all cylinders firing idle. 

 

I'll still do a balance when the spigots arrive, but a very happy result!

 

cheers,

Simon

[Mike6]

Nice one. Bet you are smiling ear to ear.

[Sir Paolo]

Well done Simon.

When I had a dyno session last year, the guy crimped the joining bracket as he reasoned that the springs were loosing some of their clamping effect. Ultimately it meant that the butterflies weren't opening equally when the throttle was opening, but it was at idle.

You can tell I was impressed with his attention to detail!