Spitting webers

[Donels]

I had a similar problems with webers on a Lotus 7. The problem was an air leak past the O seals between the carbs and manifold.

[512BB]

The O rings should be replaced if the carburettors have been removed for any reason. Flats form on them where they abut, that is not that visible if your eyesight is not as good as it once was. Sloppy maintainence if you do not.

Leslie

[billmoore42]

My 67 Elan FHC was spitting out the webers, and I found it was because it was set up for pure gasoline (not 15% alcohol like we have in California). The previous owner lived in Hawaii where he could get pure gasoline, but not allowed in CA.

I fixed this by moving up to richer idle jets, and no more spitting!

[tonyabacus]

You say the car has had the engine rebuilt and you drove without issue for six miles, which would seem to confirm that the set up of the cam timing, ignition timing are okay. The fact that it stood idling for a period indicates that the carbs are working at the lower Rev range. In rebuilding the engine, presumably you have not modified it from the spec previously?

How old is the fuel in the car, current ethanol fuels go off very quickly and can separate with water forming in the bottom of the tank, therefore as a starting point, reset everything back to normal. Then,
1. Draw out all the fuel from the tank
2. Clean out the filters and the fuel pump, check these for water content
3. Pull off the carbs and keeping them horizontal, twist the throttle spindle fairly quickly, point the carbs into free space when doing this and you should see a stream of fuel approximately nine-ten inches long emit from each barrel. This checks that the accelerator jets are working correctly, which is difficult to see when carbs are in situ
4. Check condition of the O rings at the carb mounting and replace if necessary
5. Remount the carbs and check that the Thackeray washers are all set the same
6. As you have already checked float levels all should be okay inside, but remove existing fuel which may be suspect
7. Check throttle link setting to ensure both are opening simultaneously
8. Refill the tank with fresh fuel and pump fuel through and try starting
9. Check for air leaks around each carb mounting, with engine running at tick over
10. Slowly increase revs and see if engine speed increases without spit back
11. Try opening throttle fairly quickly and see if again engine speeds up without issue

All being well the problem should be resolved, but be aware that spitting back has resulted in a number of fires in the past so always have an extinguisher to hand. If the problem persists then a suggestion missed above is get the carbs ultrasonically cleaned, as there are so many small passageways that are impossible to clean any other way. I had to ultrasonically clean my carbs three times before all the junk was finally removed.

Try above and report back
Tony

[2cams70]

Do a cylinder compression test. Sometimes if an inlet valve is not sealing correctly the combustion flame will leak past and ignite the fuel vapour in the carburettor.

[h20hamelan]

Sure its been posted many times

https://240260280.com/Tech/Carbs/Weber/ ... uning.html

I think the Progression Holes need be free too, and synchronized.

[2cams70]

If the carburettors were just removed and replaced and not otherwise touched it is not all that likely they are the cause. They may need some fine adjustment but there should not be anything significant wrong. Suggest check the cylinder compressions as it’s easy to do and report back what you find.

[h20hamelan]

2Cams70, would you think a leak down more prudent
Or a comp tells enough - go after the head?

[2cams70]

Compression test should be enough at this stage. Only takes 10 minutes for a quick diagnosis.

[nmauduit]

2Cams70, would you think a leak down more prudent
Or a comp tells enough - go after the head?

a leak-down test would tell more specifically about the rings sealing, a compression test a broader idea of head+rings

here it is unlikely that a ring has gone bad all of a sudden and starting at 2000 rpm (it's not even that likely that a piece of carbon deposit has left a valve stuck opened just in these conditions) - if the idle is as smooth as before and also upon accelerating, the synchronization is good.

The clue that a half choke (which means enrichment on a Weber) would be what I pursue more at this point (deposit in the little filters? checking/blowing the progression holes for being plugged also, as 2000 is a bit low for the idle/main transition circuit - they are on the idle circuit so that may be done in situ with air and a mirror, or a can of WD40 and with small tube?) good luck !

[2cams70]

I speak from experience about leaking inlet valves. I had the experience with a crossflow engine when the inlet valves seats were not cut properly after a rebuild. Valves don’t leak enough at idle to be noticeable but once you put load on the engine and the cylinder gas pressures increase and the leaking becomes more pronounced it most certainly does become noticeable.

Compression test is enough to do a quick diagnosis. As I said it only takes 10 minutes and you have absolutely nothing to lose.

[LaikaTheDog]

Goodmorning
Thankyou for all the great advise! It is also good to get it all in one place so I can come back in 5 years and do it all again !

I fixed the problem !

Rule no.1 : trust no-one
Rule no.2 : see rule 1

I have been bitten by this so many time I should know better.
I picked up this car as a non runner, Instead of an “oily rag” rebuild I ended up doing everything. I was assured it ran fine before it was taken apart, and I was assured that everything is there….

So i was working from a false baseline… these webers were not from this car at all !

I checked the base emulsions and jets against the default factory values …and as is normal there were variations which I had assumed were part of evolution from 4 star to … um…. Ethanol

Over the years I have gathered bits and bobs so I happened to have a set of jets. I have just moved up on mains and idles and the engine is now transformed, no hesitation or spitting. I will have to fine tune but now I can actually drive to a rolling road, Shame I can’t afford petrol anymore….

[nmauduit]

Goodmorning

I fixed the problem !

good news ! so you're actually rejetting from gasoline to ethanol (that is 85% ethanol I suppose) ? when finalized, please post your results, I'd be interested to know the required evolution, just in case... thank you !

[69S4]

Goodmorning

I fixed the problem !

good news ! so you're actually rejetting from gasoline to ethanol (that is 85% ethanol I suppose) ? when finalized, please post your results, I'd be interested to know the required evolution, just in case... thank you !

Yes me too. I'm not having any problems using E10 in my Stromberg Elan (so far anyway) but at least a couple of my old clunker motorcycles give me pause for thought and I suspect at least one of them will need rejetting. It's hard to get any concrete info about what going to be needed though, so any info would be welcomed.