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eengel1

ignition or carburettor

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Hi

My 85 Esprit is still juddering under load, even when revving up the engine without load it is obvious.

The rpm is not perfectly stable at a constant gas pedal position. It feels like there are minor interrupts from time to time.

Have been fiddling with the idle jet settings and with the ignition for a while.

Have measured the ignition voltage today with a home made setup.

Looks like I have something around 20kV for each cylinder. - Guess that's ok ?!

Have also tested CO level, but only with car standing

rpm CO(%) boost (psi)

900 2.5 0

2000 0.3 0

3000 0.4 0

4000 0.5 0

5000 1.5 2.5

6000 2.3 5

Can you derive anything from those values measured at idling?

The car doesn't seem to be running lean, and it also looks like I have an ignition that is strong enough.

Still problems. :-(

Any ideas ?

Cheers

Marc

Edited by eengel1

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Upgrade today to remove Google ads and support TLF.

If it's present and at similar engine speeds under load and no load then I'd say ignition, although that depends on the engine speed this occurs at.

Your idle jets will be a major contributor to carburation at 2.5k rpm under load but it will also get some input from the main jets, That engine speed under no load would be purely idle jets, and hardly any throttle.

Thus if the issue is at anything other than idle for both load and no-load you can normally say it's not the same carburation issue (unless you're unlucky enough to have two issues with carbs, rule them out).

I'd say ignition, possibly the mechanical components of the dissy that generate the advance mechanism.

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thanks Andy !

the bad thing with the dizzy cap and its advance mechanism is that it is impossible to get to.

maybe I'll have to remove both carb. for that.

attached the pics I could not post yesterday

the self build setup to get an estimate of the ignition voltage is based on the gunson flahstest, the calibration values as well.

I still have a spark at 12mm electrode distance - that should be something around 20kV

have to figure out a way to check the advance setting then.

ignitiona.jpg

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I love the inginuity to test the spark potential.

You can get the dissy cap out between the carbs and the end of the engine then get the whole dissy out between the carbs and the starter, it just takes a lot of patience.

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Andy

just come back from another test drive

I can smell fuel from time to time, engine is juddering, but not always, that would indicate ignition is faulty - wouldn't it ?

cheers

marc

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marc,

If you smell fuel, one thing to check is the accel pump for leaks. With engine off give the accel a few pumps via the carb linkage and see and smell if fuel is coming from the accel pump diaphragms. I had this problem on mine. Scary part is it leaks right on the dizzy!

Jeff

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Thanks for the hint.

I better check that then. The smell is pretty obvious inside.

Have a feeling I will dismount the carburettors soon :-) , access to the dizzy is also easier then.

Cheers

marc

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Marc

I have just had a problem with severe juddering under load following a carb rebuild. Initially the float needle valves were not shutting off fully resulting in the fuel bowls over flowing into the carb intakes. Have you checked whether the fuel pump stops ticking with ignition on but engine not running. If it doesn't stop and you're smelling fuel check inside the intakes. If they're wet with fuel then your fuel bowls are flooding.

On resetting the needle valves I incorrectly set the float heights too low which created even worst juddering under load. After much fiddling to get the float heights right its now running without so much as a hiccup.

I've also experienced similar problems when it turned out to be the ignition coil failing.

Hope this helps as these faults are sometimes difficult to trace. Just need to eliminate one at a time.

Graham

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Graham

thanks for your input

I have the impression my fuel pump is always running, think it never stops, have to check that.

Marc

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Hello

Have been working further through the labyrinth.

Checked timing of ignition pulses, they seem to come regularly, HT voltage checked earlier also seems to be correct.

HT check setup

htvoltagetestsetup.jpg

Timing

setups.jpg

timingo.jpg

advance

advance values measured with timing light are the following

at 800 rpm +/- 10 deg

at 2000 rpm +/- 20 deg

at 3000 rpm and above +/- 25 deg

picture below at idling (+/-800rpm)

advance.jpg

So it looks like the ignition side is ok - I dont' see anything special.

Started to dismantle the first carburetor, to check the float level.

It is around 25mm from the top.

cimg5412.jpg

cimg5416.jpg

Is 25mm from the top enough ?

Difference between float lever and cover is 15mm. (vertical position)

Ideas, suggestions ?

Thanks

marc

Edited by eengel1

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Graham

thanks for your input

I have the impression my fuel pump is always running, think it never stops, have to check that.

Marc

Marc, your pump is fine. you should hear a constant buzzing from the fuel pump when the ignition is on whether the engine is running or not.

Les

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Float levels are checked by measuring the gap from the gasket face to the top of the float, with the carb top held so that the float arm just touches the float valve, without moving the spring on it. I can't help with the fuel level you find in the carb...it'll be different once the floats are floating in the fuel, as they displace their own weight of fuel, bringing the level higher...apologies if I'm stating the obvious!! I made a cardboard gauge to help set the float levels without having to refer to measuremnents,scales etc. My beast has never liked holding constant revs without a load..but runs fine on the road, now I've got the idle jets clear!!

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Marc,

I believe the fuel level in the chamber should be 27mm once the floats are removed. Your 25mm would indicate a rich misfire and alter the point at which the carbs change from idle to main jets.

Trevor.

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27mm is the correct level. the float hight is a starting point, and yes 2mm will make a big difference.

This is a very good site:

www.sideways-technologies.co.uk/forum/Blah.pl?m-1201970113/

Edited by AJay

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thanks for all the info guys !

also checked the float level in the second carb. It was exactly 27mm !

readjusted the floats in the first carb. slightly and first impression was that the car reacts a better.

as the roads were wet yesterday I could not test full throttle.

will keep you updated !

cheers

marc

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Update

Yes ! the car reacts better now, I am not yet fully satisfied, but it's a lot better.

I'll open the front carb. if I have time, to check if the fuel level has really changed.

Finally a positive experience :-)

cheers

marc

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