Lotus Elan

Webber carb balance

PostPost by: l10tus » Wed Oct 15, 2014 9:05 pm

I just started my rebuilt engine for the first time.

The Webbers have been cleaned and reset.

Aldon ignition and rebuilt dizzy.

New fuel, electric pump.

Standard Big Valve.

Timing 10degrees BTDC ( just to get it running)

Problem:

Using the balancer that you stuff into the bell mouths, the reading (at fast tick over is :-

Cylinder 1 = '2' on balancer
Cylinder 2 = '6'. ". "
Cylinder 3 = '6'. ". "
Cylinder 4 = '6'. ". "


When I blip the throttle / increase the revs anything above tick over, they all balance at '30' or so, all exactly the same vacuum.

Q: Any ideas why 1 & 2 are not the same, or why Cylinder 1 is low?

Also noticed that the headlamps aren't lifting with the vacuum switch, so wondered if this had any bearing on the issue.

I had to wrap up without finding any reason for the imbalance, and wondered if anyone has suffered similar issue?

Any Thoughts gratefully accepted !

Regards,

Phil.
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PostPost by: UAB807F » Wed Oct 15, 2014 9:15 pm

Possibly the vacuum take off for the servo/headlamps leaking at the tubing or non return valve ? IIRC that's at the front inlet tract on the head isn't it ?

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PostPost by: l10tus » Wed Oct 15, 2014 9:29 pm

Brian,

Yes it is.

I was thinking along those lines but thought it would tend to rev higher if there was an air leak?

However, there is a connection problem somewhere with the vacuum headlamp lifters, so I hope it's connected, as it should be an easy fix?

The original H/L vacuum switch seemed to work ok, it's a new Chassis ( so the vac tank should be ok?, ) new pipes, so I'm hoping it's just either a leak or incorrect connection somewhere?

Then hoping that will be the cause of the carb issues also.?

What did you say ? - you love a man with imagination !!

Nothing on a Lotus is that easy is it?

Thanks for the thoughts - I'll let you know if it cures all!

Regards,

Phil?
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PostPost by: bill308 » Wed Oct 15, 2014 10:09 pm

What balancer are you using?

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PostPost by: l10tus » Wed Oct 15, 2014 10:28 pm

Bill,

It's the Snycroniser,

The one with a Grey body with louvres and and a black rubber carb Venturi grommet.

The type that you jam into the Venturi, one carb at a time, and note the swing needle reading, as you adjust the balance.

It's very consistent, does not affect the air intake, and is made specially for Dcoe's and presumably Dellorto's?

Available for ?33 on that auction site.

Great bit of kit, totally reliable, dead easy and quick to use, must add it's not mine, only borrowed from another Lotusist !

Regards,

Phil.
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PostPost by: Plus 2 » Thu Oct 16, 2014 3:13 am

Hi Phil,

Your symptoms sure indicate a typical problem on the vacuum line attached to the manifold at no1 inlet.

However typicaly this also usuallycoincides with poorer starting but the pipe run to the chassis box section joins a T piece and this can easily come off from the metal tube on the chassis into the box section.

Also thoroughly check the condition of the T piece as they perish and split. Small splits or poor connections show up more at low/no vacuum and as the suction starts to create the vacuum leaks can actually almost temporarily self heal by the vacuum contracting the pipe and pulling small splits/joints together so can then appear ok.

The simplest test to check condition of the vac line is to see how long your lights stay up (down if failsafe) when you put them on and then just cut the engine. The fact you say yours are not even lifting indicates an open/incorrect circuit

Also whenever tuning the carbs I always clamp off the vac lines either side if a servo fitted too.

The synchroniser is a great tool for fine tuning especially if you are not astute to the noise of the air induction with a simple tube to your ear. The figures you quote though I would expect to be picked up even by ear.

Focus on your vacuum line though to start with is best advice.

Regards

Steve
Last edited by Plus 2 on Thu Oct 16, 2014 3:30 am, edited 2 times in total.
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PostPost by: bill308 » Thu Oct 16, 2014 3:19 am

Thanks Phil.

I have a couple of BK (SK's are slightly smaller and probably more appropriate for DCOE40's) Synchrometers that measure mass air flow and are very good, but I much prefer a multi bank manometer system that measures intake manifold vacuum. Synchrometers see only the air that flows through them. They do not see leaks through faulty O-rings, vacuum hoses or carb shaft bearings.

One of the things you want to do at idle is shorten the throttle cable enough so it is the only thing controlling the idle speed setting. back off all stop screws so none are touching. Now set your balance using the carb-to-carb balance screw. When happy, just nip up the single, master carb idle speed screw, not the slave idle speed screw even if present.

Balance adjustment within barrels of a carb depend on the carb model. One will have to twist the shaft of 40 DCOE18's and 31's to equalize balance. Later 40DCOE151's have a special air balance circuit to equalize air flow between barrels of a common carburetor. One of these balance screws should always be closed. One opens the balance screw of the lower flowing barrel to match the higher flowing barrel. If the end result is higher flow than the second carb, one adjusts the carb-to-carb balance mechanism to compensate.

I hope this helps.
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PostPost by: l10tus » Thu Oct 16, 2014 10:41 am

Bill, Steve,

Thanks for sticking with me on this one!

I'll be having a closer look at the weekend, so will check it out and hopefully post a result then,

Keep your eye on this one will you ? - your knowledge will be invaluable!

Many thanks,

Phil.
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PostPost by: Galwaylotus » Thu Oct 16, 2014 7:00 pm

It certainly sounds like a vacuum leak symptoms, especially as No. 1 is the one reading low. I found a gross leak there when I put mine back together. In my case the line into the manifold has a tee that went to the headlamps and to the servo. As I had removed the latter a few years ago I must have had a plug in that line that came out. My fix was to get a short length of fuel line, plug one end and hose-clamp the other to the tee branch.

I recently purchased a Synchrometer and used it to check the balance that I'd set on my carbs. It was spot-on and no adjustment needed! :shock: :D Flow at idle is 5 kg/h. I did find, however, that with the inlet air horns on my carbs that I could not get the Synchrometer onto No. 1. There isn't enough space between the inlet and the inside of the wing. That didn't bother me as the instructions say to measure the flow at the middle two throats only. It runs ok anyway. In my case I rebuilt the Webers, installed electronic ignition and installed a Stealth BlackBox controller so I'm still playing around with the advance curve. 8)
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PostPost by: AHM » Thu Oct 16, 2014 10:04 pm

Phil,

You are ok! I have just checked and carb balance is not part of the MOT test. So you can get your car going and fiddle with the carbs at leisure afterwards! Lord knows you will need to anyway!

The simplest check for leaking hose on no.1 is to remove the pipe and block it off Then you are comparing 4 equal barrels.

How near are you to roadworthy?
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PostPost by: l10tus » Thu Oct 30, 2014 8:30 pm

Gents,

Sorry for the delay in answering, apologies.

Work got in the way.

I had a quick look at the vac pipe lines, there should be 2 x non return valves yes?
( one in each of the headlamp pipe and one in the servo pipe ?)

Well the brass one that goes to the H/ lamps is leaking (I think?) -replacement on its way !

The second one was in the wrong way round ( plonka!) !

All the rest is brand new ( T piece, poly tube, rubber hoses connections ) all clamped and PTFE tape jointed together -so should work to lift the lights next time I start up the engine ?

I was also thinking that the No. 1 carb butterfly may be twisted on the shaft ?

So, a couple of possible contributory. Items there to try !

Weekend is approving so will try then, after re-fitting the fuel tank after repairing the sender unit.

Never ending fun !!
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PostPost by: Mick6186 » Fri Oct 31, 2014 8:32 am

Hi,
Why not eliminate one problem at once. Remove the vacuum pipe, replace it with a short blocked length of tube then set up the carbs with no external problems.
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PostPost by: Galwaylotus » Fri Oct 31, 2014 8:56 am

That's exactly what I did. :wink:
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PostPost by: AHM » Fri Oct 31, 2014 11:21 am

That's exactly what I said :) ... and did!
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