Poor / no running - Weber Carbs

[Gizze]

Hi,
I'm ....hopefully..... nearing the end of an extremely long restoration. Everything's looking great except I can't get the engine to run for more than a minute or so!
Engine - rebuilt, compression checked all ok.
Electrics - new coil/condenser/points/leads/plugs. Static timed to 10 deg
Weber Carbs - Stripped and cleaned.
Symptoms- I did initially have the engine running to the point where I've driven it about 20 miles after it's MOT, but it wasn't great to say the least. Now a few months later and a couple of minutes is all it will last. With engine start spray I can get the engine running, although not smoothly. It coughs and splutters and then after about a minute at most dies. There's plenty of petrol in the float chambers and the petrols 'fresh'.
I think there's something not right with the carbs since I've gone through the electrics a couple of times and everything's new as such.
Any suggestions would be welcome.
Cheers

[ericbushby]

Hi,
Take this a little further.
For instance, when it starts to die, can it be kept going with starter spray in which case it would point to fuel shortage. Or feed the carburettors with a short piece of tubing and a funnel.
When it has died, is there fuel in the float chamber immediately after it stops. You do not need the jet cover to be on or the large jet tube assembly fitted in order to run at low power.
Kieth Franck of `Sidedraft central` says the first and most important thing to do with Webers is to set the fuel height to 25mm , plus or minus 1mm below the top of the float chamber. For me this is easier measured as 41mm from the rim of the jet cover. A small rod and a torch works well for me.
If you have a Strobe timing light, leave it on any plug lead to see if the spark is regular until the engine stops.
Have you got permanent 12 volts to the coil, before and after it stops.
Best of luck
Eric in Burnley
1967 S3SE DHC

[mbell]

Are you sure the ignition components you fitted are good quality? There a lot of issues with low quality replacement ignition parts.

Eric's advice to check the fuel level is very sensible. Have you also pulled the plugs to see if it looks rich/lean?

[Certified Lotus]

I would ask the same question, what do the plugs look like? If any concern at all, replace them.

[paul_adamson]

I had a similar problem on the for the MOT.
The car ran fine for the first 5 or 6 miles then started to run badly defore stopping.
It would run again after a short while but would die out again shortly after.
After a tow back home i stripped the webers and found them to be full of crud.
I have a feeling that nasty ethonol petrol may be the cause.
I'm currently cleaning the webers and have replaced all the ignition but i will drain at least some of the fuel before i prime the carburettors again.

[Sea Ranch]

Could be, Gizze, that as per Paul's experience, your carbs have ingested some new crud. Been known to happen

All other advice above seems very sound to me and worth pursuing.

My own personal experience is that I had a bad coil new-out-of-the-box. Finally replaced with a known-to-work used coil from someone else's car and mine went from crazy-bad running to perfect (well, you know . . . )

Keep us up to date with your testing and experiences . . .

Randy

[nigelrbfurness]

Definitely replace the coil with a known working example. The symptoms you describe are typical of ignition coil failure.

[Apx]

I have just had a similar problem with my plus 2. Tried all the standard routes but had a feeling that it would be electrics as i noticed that when the engine stopped / struggled the rev counter went to zero quicker than the engine, but it felt like a fuel problem. Did everything above and found crud in petrol line but when resolved made no difference, i found a poor almost broken joint at the starter solenoid and on replacing it it made an improvement. however the problem remained and in frustration i began by checking all wires and components on the ignition system. I found a corroded joint at the security device and removed it, but it wasn't until i began replacing the exposed wires in the engine bay that i solved it. The issue was the white yellow wire from the Tacho to the coil, which i presume has a break/partial break in it, as when i bypassed it the engine ran fine. The wire has been repaired and i have had no more issues. Hope this helps, Cheers Neal

[vxah]

Neal, was that White/Yellow not a ballast resistor wire? As in itself being the resistor, It was on my 72 plus 2, maybe you had a 12v coil running on the 9 volt supply to it?

[Gizze]

Many thanks for the advice, definitely some items here that I'd not though of or thought of but dismissed but can see logic behind checking them again - back into the breach (garage) once more!
Will let you know, but in the meantime really appreciate the feedback

[RichC]

ah takes me back to when i put mine back on the road...
first can i ask you is yours a +ve earth ? i.e mid '68 or earlier ? looking at the rev counter should tell u if u don't know ....

[Apx]

Neal, was that White/Yellow not a ballast resistor wire? As in itself being the resistor, It was on my 72 plus 2, maybe you had a 12v coil running on the 9 volt supply to it?

No, the ballast resister is a capsule attached to the coil. The fault was in the run of wire itself. Cheers Neal

[Gizze]

Update from the garage......

- Took the plugs out, all of them were black, so cleaned them all.
- Put one of those in line flashing lights onto one of the plug leads.
- Confirmed there is power at the coil with a bulb and lead.
- Checked the static timing at 10 BTDC.
- Tried to start engine with help of engine start spray.
- Measuring the petrol height from the top rim of the carb, has not been very successful. The petrol being very clean is hard to see on a steel rod. I think it's 35-40mm, will see if I can get some card to use instead.

-The engine tried to fire a couple of times, but almost nothing, even with liberal use of the engine start. In line flashing light was always flashing. Finally it now seems worse then ever - hardly any sign of firing at all, engine just spins over.

-Because I think I've flooded the engine a couple of times I've had the plugs out more than once and they're now spotless having been washed with petrol and wiped a few times. No longer black at all.
- I've also noticed petrol gathering in the air box back plate. I've now taken this off, and when I've taken the venturi out they are also soaked in petrol, as are the apertures they sit in leading up to the butterfly valves.

So it seems I have a spark, it seems I have petrol, but still nothing. Any further advice would obviously be most welcome!

[mbell]

You need to make sure the fuel level is correct, if its too high the fuel will run directly down the throat through the jets.

The best way to check is to mark a pointer screwdriver at 25mm. Remove the jet cover and main jets, insert the pointer and with a torch pointed down the jet watch for the shimmer from the fuel as the pointer touches it. See if the 25mm is level with the top of the jet holder.

Are you running the standard fuel pump or an electric one? If an electric one you need to make sure its not too high pressure and overcoming the fuel inlet valve of the carbs.

[roblotus79]

Ok, I know almost nothing, but in the past I had a choke stuck open that would slowly flood the engine and kill it. Are your chokes good? Also, do you know what fuel pressure you are running into the carbs. After replacing the fuel pump I had to install an inline fuel pressure regulator and set it at 1 - 1.5 I think as the new pumps run too much pressure on their own???