Okay--I'm Stumped. 38/38 Starts--revs to 4000rpm. Dies.

I was having some issues with my Weber 38/38 stalling at idle under braking. So, I adjusted the float. Put the carb back together. Fire it up and it revs instantly to 4000rpm and dies. I tried again and get a "thunk." Check the carb--fuel is overflowing the bowl.

I take the top hat off--readjust the float. Pull the spark plugs, Crank and fire all of the gas out of the cylinders. Spark plugs go back in. Hat and float go back on. I check that the throttle linkage isn't binding and that all of the speed screws are back all the way out. Check fuel pressure, 3.5psi.

I give it a couple of pumps and crank. Again engine revs to 4000rpm (quite nicely) and then dies. I crank again--and it won't even sputter unless I give it a few priming pumps. When that happens--the engine revs and dies.

So, to eliminate an variables, I pull the top hat off. Fill the bowl. Leave the top hat off. Loosen the throttle cable as much as possible and prime the engine by hand. Same damn thing. Revs and dies. Note: I have the ignition and fuel pump on manual switches in the cabin.

I checked the timing yesterday and it was spot on. Fearing a hydro-locked engine and bent valve I checked compression and it came out even and within spec across the board.

It doesn't matter if the fuel pump is on--with the hat off I could see that the fuel level was good and covering the idle circuit holes. The engine only wants to run off fuel from the pump jets and then it wants to rev to four grand and die.

Ideas? Please...it not running is one thing but revving to 4000rpm and instantly dying is another. I'm kind of at the point of buying another 38/38...

Air leak? It won't rev to 4K without getting enough air to do so.

38/38 - make sure the gears that open the throttles together are meshed properly, maybe one is out of synch and sticking open.

If you ever had a sneeze back through the carb, check to make sure all the vacuum lines (PCV in particular) are still attached.

You said "Hat" if this thing is boosted, are you sure your floats are not collapsed or full of fuel (sunk). If the floats are sunk, it will flood no matter what you do.

If you adjusted the float, it is possible to have gotten it a bit out of whack and it my be hanging up on the carb body and sticking open. Watch very carefully when you put the carb top back on.

Hope this helps.

Shawn

To me, it almost sounds like a bum coil.

gjz30075 wrote: To me, it almost sounds like a bum coil.

That wouldn't explain the revving to 4k part.

I've had a fair amount of coils break down at high revs only. I would think if fuel related, the dying at 4k would be gradual, ie, sputtering, coughing, etc. If it simply quits, like turning off the key, then ignition faults would be suspected.

In reply to gjz30075:

I found the problem--the adapter plate for the Weber to the stock manifold broke, lifted, and separated. It was getting all those revs because of the massive cracks but not really pulling in any fuel because there was no vacuum.

So, I now have a reason to go 40 IDF.

Ah, that 'splains it I understand now, after re-reading your initial post, I missed the point that this happened after disassembly/reassembly. Duh. Sorry.

Two cracks formed about 1.5" apart taking out one corner of the adapter plate. There was no visual evidence of failure except that the gasket looked kind of out of place. When I removed the carb it became clear what had happened. The whole corner fell off without the pressure of the carb holding it on.

So, twin 40 IDFs are on the way. I'm in pain and pleasure at the same time. I think the whole setup is going to end up costing twice the price of the car. But--why replace when you can upgrade?

Side draft Webers are way more of a pain in the ass than they are worth.

You are going to get a new mechanical advance distributor and have it curved right?

My memory of running Weber carb on the MGB is that of tossing $100 bills at it every time I got fed up with the classic Weber stumble. Every part has to get bought in pairs, and you need to buy an assortment of each part so that you can play with the damn rubik cube number of combinations. In 20 years of trying, I never did get rid of it.

The 38/38 is already more carb than you need for a 1275 Midget engine. (Or the triumph 1500)

Have you thought of just tossing on a set of SU carbs?

In reply to NOHOME:

Don't know a thing about SUs...

The dizzy is already a no vacuum mechanical advance dizzy recurved for Webers. I can get it recurved locally for $10.

What's that saying? 99% of carb problems are ignition problems...? From my experience IDF setups where there is one barrel for each cylinder are way easier to setup. You can tune to each cylinder's needs. Plus, you have a much better manifold design. Stock Starlet intake manifolds are not the prettiest things around. The engine's 10:1 with a 290* cam. So, I think it'll be okay with the twin IDFs. I have wideband which will help and a syncrochometer.

And yes, you initially have to buy two of everything--two carbs, four stacks, four base gaskets, all sorts of fittings, and dual idle and main jet packs. I could have easily gone fuel injected or even swapped engines for less money.