Lotus Elan

2800 rpm tickover.

PostPost by: mickmade » Fri Jul 31, 2020 5:00 am

I have a 1966 Elan Coup.
Recently had a cylinder head refurbishment
Including guides , valves, springs etc.
I have also rebuilt the carbs with a standard carb kit for 40 dcoe's, plus new spindle bearings.
On reassembly the engine started first time after priming the carberators,but refuses to tick over below 2800 rpm.
The throttle seems to open and close correctly and if opened the revs increase.
Even closing all the
idle screws makes no difference to rpm.
Before I remove the carberators once again.
Can someone shed a little light on this
problem.
Thanking you for your help.
Regards Mick.
.
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PostPost by: sprintsoft » Fri Jul 31, 2020 8:11 am

Hi Mick,

Plenty of things need checking but I would look first at the butterflies and see where they are positioned vs the progression holes, the fact it will run with the idle screws closed tells you it’s getting air and fuel elsewhere. Are the butterflies centred? They may not be able to close fully if not.

Other secondary suspects would be timing and/or air leaks around the carb mounting o rings.

Iain
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PostPost by: Craven » Fri Jul 31, 2020 11:09 am

Two basic adjustments first, throttle stop screw and balance screw.
Best pic I can find quickly, about mid screen throttle stop ( idle speed ), very top of pic balance adjustment, this sets the amount of work each carb does.
May help.
SPRING ON CABLE.JPG
SPRING ON CABLE.JPG (66.71 KiB) Viewed 431 times
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PostPost by: pharriso » Fri Jul 31, 2020 11:27 am

Subscribed.
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PostPost by: Esprit2 » Fri Jul 31, 2020 4:31 pm

Mick,
Turn the Idle Speed screw all the way out. Does the throttle lever follow it all the way to the stop tab on the carb body, or does it stop prior to reaching the tab? If in doubt, use a feeler gauge (piece of paper) to check for contact, or a gap between the throttle lever and the stop tab. The throttle should be able to close fully against the tab.

At closed throttle, there should be a wee bit of slack in the cable. If it remains taut, then the cable is not properly adjusted and may be preventing the butterflies from fully closing. Adjust the cable.

If one or more butterfly wasn't properly centered on the throttle shaft, it can bind against the throat wall before reaching the normal fully closed position. When one butterfly binds open, it can hold all other butterflies open to the same degree. "Open" in terms of degrees of shaft rotation, not necessarily in terms of butterflies closing in the throats.

Remove the progression hole covers and look down inside. You'll see small holes drilled through the 'floor' into the carb's throat. Move the throttle a little, and you can observe the edge of the butterfly sweeping past the drilled holes. With the throttle closed, do all four butterflies align equally with the first hole. They should. All the same. If not, then one or more of the butterflies may not have been centered on their shaft during assembly, or the throttle shaft(s) may be twisted (easy to do). So, what do you see?

Regards,
Tim Engel
Last edited by Esprit2 on Fri Jul 31, 2020 6:12 pm, edited 2 times in total.
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PostPost by: mickmade » Fri Jul 31, 2020 6:00 pm

Thank you for your replies.
You were all basically right regarding an out
of centre butterfly.
Not sure how it slipped apart from the over size holes in the butterfly itself.
Now lock tited in position.
Lets see if thats cured the problem tomorrow.
Once again thanks
Mick.
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PostPost by: Grizzly » Sat Aug 01, 2020 10:34 pm

Once the butterfly is centered (best using shims in my opinion) you need to stake the screws because the solvent in the fuel will soften the liquid thread lock and you don't want a screw dropping into the inlet!!

If you stake the brass screws make sure you have some thing suitable on the head side of the screw as you don't want to bend the Throttle shaft.
Chris
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PostPost by: prezoom » Sun Aug 02, 2020 2:51 am

You can also just bugger the threads on the throttle plate screws with a small pair of Vise Grips/Mole Clamps. If the screws do come loose, they will not unthread. No strain on the throttle shafts.
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PostPost by: mickmade » Sun Aug 02, 2020 4:58 am

Thank you all for you help.
One more problem has arisen.
I had the carb bodies aqua blasted, which now seems a big mistake.
Whilst all the carbs work correctly .each one is prone to blocked jets and stops supplying fuel.
I can only assume that there is still some residue of soda powder left in the seperate carb galleries.
Please, no replies regarding my foolishness.
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PostPost by: mickmade » Sun Aug 02, 2020 3:24 pm

We live and learn, hopefully.
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PostPost by: JJ66 » Mon Aug 03, 2020 10:19 am

Hi Mick, Interesting point about aqua blasting. I bought my +2 earlier this year and have had a number of fuelling issues and last week the front carb has basically stopped working. The previous owner showed me a hefty receipt for a carb rebuild which included 'aquablasting'.

I have taken the opportunity to pull the distributor and get it reconditioned by Martin at 'Distributor Doctor' (He's very good) and I will take the carbs apart and clean them thoroughly, are there any particular points I should look at? I intend to blow through all jets and clean all cavities - I have no experience of the blasting process and so it was interesting to read your post, thanks (And don't be hard on your self, we are all capable of mistakes - He who doesn't make mistakes doesn't progress!)

Further interest on looking into the carbs, the float heights were ~8mm where they are supposed to be 15-16mm!! This may explain some of the rough running!

Thanks, Jonathan
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PostPost by: sprintsoft » Mon Aug 03, 2020 11:36 am

Hi Mick,

"... had the carb bodies aqua blasted, which now seems a big mistake...."

I don't think it's a mistake as such, it's just they normally should tell you to thoroughly clean the parts before use, aquablasting is very effective but is known to leave residues. I think you will have to strip and clean unfortunately.

Iain
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PostPost by: Craven » Mon Aug 03, 2020 12:53 pm

Aqua blasting just means the abrasive medium is within a high pressure jet of water. Sand or soda blasting is where the medium is within a high pressure air jet.
Aqua blasting often uses glass beads, a solid material very difficult to completely remove as is sand, soda on the other hand is soluble and in theory anyway, washed completely away after use.
Weber carburettors have many cross drillings within the body ideal for trapping small particles.
FWIW
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