Weber Issue

[LL]

Guys,

Had my car in my mates garage now for 6 months and still got problems. Car has had a new ignition (Lumenition), head had been pressure tested, new guides fitted, valves done etc. Great compression wet and dry. Just fitted new spacers and O rings as the spacers had holes in them where the O rings fit but still I have the same problem. The jetting in the webers has been confirmed as correct. I don't know the cam profile personally, but the cam clearances have been reset. I have receipts showing the cams show be 30/70 type.

OK, so what appears to be happening is this. The car has to be set up very rich to run, and when it is below normal operating temperature the car runs quite nicely, smooth progression off idle and up the rev range. As soon as the car gets close to operating temperature any acceleration at all causes the car to backfire and miss badly.

My mechanic friend has 30 years experience tuning cars, webers etc and knows what he is doing. He is stumped on this one though and our only thought is that there is an internal blockage in the progression side of the carbs.

As a bit of a background, the car has been sitting pretty much for 11 years - in heated storage and has only been driven about 1000 miles since in that entire time.

As for me, I am at the end of my tether and my wife who's car it is will shortly sever a part of my anatomy.. Our last resort appears to be to replace the Webers, however, if it comes to that, I will convert it to EFI myself as I have some experience in the area. My concern is that the fault is not in the carbs, but somewhere else and if I convert to EFI I won't be solving the problem. However it will give me a better idea of what is going on with a wide band sensor installed etc etc.

Sorry for the long post, but thoughts appreciated!

Cheers,
Neil

[LL]

I forgot to add the car has a big valve twin cam running dual DCOE 40's. The carbs have been dissasembled and cleaned with carb cleaner and an airline twice.

[twincamman]

sounds like a timing problem to me ---either the distributor or mechanical timing --try new plugs or clean the old ones with carb cleaner - or a carb balance problem --- ed

[gjz30075]

I don't understand. You said the jetting is correct but the car has to be setup rich to run? Are you changing jets to do this? What jets?
Actually, it sounds as if the coil is breaking down when its warmed up. An easy swap.

Greg Z
'72 Sprint

[tdafforn]

The other classic problem that can give this effect is a bad condenser...
Otherwise I have heard of cracked intake manifolds that leak only at high temps..
Cheers
Tim

[triumphelan]

What about Distributer cap and rotor arm

[triumphelan]

Try going back to points it may be the Luminition at fault

[miked]

Dizzy cap is a favourite for me. I am now back to a lower voltage coil due to spanking them with 40kv. My symptoms went worse with heat.

Keith pointed me on this. I also read quite a bit about the SAE for the stadard cap and max Volts. Lucas gold DLB 105 is max at 35Kv for the black bakalite (whatever cap).

Mike

[reb53]

Assume all the HT leads are OK.
Having a look under the bonnet on a dark night will quite often show up any that are breaking down and jumping to earth or each other.
This problem can come and go in the early stages.

Ralph.

[twincamman]

if you have had the carbs off you probably didn't get them balanced and set up properly-----find a unisyn and perform that test first --then back the idle jets 1 1/4 turns out from bottom -80% thats the problem --remember when its all set up---carburetter is French for LEAVE IT ALONE- -ed

[LL]

Thanks for all the ideas.

The mechanic has pretty much tried and tested all of the above. The inlet manifold could be a problem but it's overfueling so I doubt it's that either.

All the igniton system components have been tested and replaced where faulty thats the frustrating thing. Carbs were cleaned out, jet sizes checked, rebuilt, synched and reset - still no luck. I don't believe in replacing components if they are not found to be faulty it can introduce new problems but the only area we can hazard a guess the fault could lie is in the webers. My mechanic worked as a Ferrari mechanic and he's been around more than a few webers!!

When I get it back from him I'll do it myself, but I've decided to inject it instead. I can't be bothered with replacing the Webers, the cost of this comes close to an EFI system. Webers I don't think will ever drive the way I want them to for the wife. I've had loads of Weber equiped cars in the past and most of them were rubbish about town driveability wise, WOT awesome but it's not my car and EFI will suit her better, I'm sure y'all know what I mean.

If anyone is interested I'm converting the car to injection with a Surge tank in the boot, using the Weber/Jenvey DCOE style throttle bodies and running it with a Megasquirt. Building it myself as I do a bit of electronics and I'm a software developer. Ignition will be wasted spark using a coilpack and trigger wheel. So, I hope to improve the ignition side and the fuel side. Idle wise I'm going to try and build in an idle control valve circuit to help on that side. I'm going to run her up first on ignition only and go from there.

Cheers,
Neil

[twincamman]

wellll good luck ---I have run webbers for 40 years on 3 motors and 2 separate marques both British and Italian and have had some of the problems you have until I figured it out -- but when webbers are set up properly with correct jetting they are reliable as all get out for daily driving or competition stuff ---the problems occur when the points wear or the dwell isn't correct or the timing isn't correct mechanicaly -- the first thing every one does is fiddle the carbs --then you have 2 problems to solve and webbers received a a bad name for reliability --------------seems like its answering a lot of questions that haven't been asked---------------- but good luck --- ---ed

[LL]

Car has had a new ignition (Lumenition),

Points? Dwell? Sorry is it my turn to ? Do you know how a standard Lumenition operates? Dwell/points gap is not variable as there are no points to vary. But hey I'm sure you knew that just didn't bother to read my first post.

If all you can do is cast dispersions and make generalisations and assumptions then please post on another thread. You have no idea as to my background or my knowledge of mechanics let alone the test procedures we went through to get to this point. If you really wanted to know, you would have asked and this might have remained constructive.

[twincamman]

you know what ----- guys like you ask questions and then have all the answers ---if you know it all don't ask --no wonder Kieth quit the site -- : ---fuck you and your worn distributer bushing -ed

[M100]

Regardless of whether they have already been replaced, chuck out the lumenition regardless of newness it might be faulty, fit new points, condensor, distributor pigtail, distributor cap, coil, HT leads and spark plugs. Feed it from a direct battery connection with a good earth direct to a front cover bolt or similar.

Check TDC on front cover with reference to true piston position

Set static timing with a test light.

Check the jetting in the carb again by reference to the holes in them not the numbers on them.

Set the float height

Start the engine and set the mixture screws to give the fastest running

Synchronise the carbs

Don't drive the car just let it warm up

Check for equal rpm drop on each cylinder

Check hot compression or preferably perform a leakdown test.

If the engine stalls as it warms up remove the spark plugs and check for wetness

If it still misfires then either swap to known good carbs or go back to basics and learn how a Weber carb works. But in that respect you are probably knackered because the published texts are wrong, your mechanic friend doesn't know and the expert has left the forum.

Oh and FFS calm down it isn't going to get your car running any better.