The Stovebolt Site Forums The Shop Area Engine Shop COE won't idle / poor running

Hello Gents,

Got to go and look at a COE with an idle problem tomorrow. This is a late '40s truck but apparently with an early '60s engine in, size unknown but possibly a 235. Carter BB updraft carburettor.

Apparently it was given to a guy to do some work on including replacing the exhaust manifold which was cracked. It sounds as though he has had the inlet and exhaust manifolds off. He has also been inside the carburettor and changed the float, perhaps done other things but isn't admitting it.

Truck now won't idle or run below about 1500 - 1800 rpm. Apparently it is also running lean, and adjusting the idle mixture screw makes little or no difference, though both of these symptoms might just be because it's running so fast it's on the main jet not the idle circuit.

I'm going to start by checking the obvious - air leaks, manifold sealing, simple carb faults - but has anyone any suggestions to anything else I should be looking at?

Thanks

The idle circuit in the Carter BB-1 has TWO idle tubes, not just one. The one in the top casting is in plain sight. The one in the lower casting is hidden in the same passage that the the one from the top casting fits into.

Failure to remove the lower tube and clean the passageway beneath the tube will often result in the idle circuit being non-functional.

Jon.

Jon, thanks for your quick response.

I had a look at it this morning. The carb has multiple issues even on a quick glance. The top has been off and re-sealed with the old gasket and silicon sealant, some of which has detached into the float chamber. The throttle butterfly is loose and the upper idle tube is either off centre or bent. The accelerator pump rod sticks as it is returning which prevents the throttle flap closing smoothly.

I've brought the carb back here to strip, clean and inspect in detail. I didn't get involved in looking for other problems until the carb is sorted out!

The engine code (from the pad next the distributor) is FI28J - can anyone shed any light on the meaning, as I can't find a guide online that mentions it?

Well, the full catalogue of woe is:

Throttle flap loose
Idle tube bent
Accelerator pump sticking
Top gasket damaged and glued back together with silicon sealant
Sealant traces in float bowl and fuel galleries
Wrong carb to manifold gasket blocking the vacuum port
Bleed holes in main nozzle blocked
Float level wrong
Someone's chewed up the slots on the jets so I can't unscrew the idle or power jets or the pump intake valve
At some point the carb's obviously had a lot of water sitting in it, so there's a lot of (loose) rust in the bottom
Loose flaky rust in the fuel galleries
The carb is a 517 which I believe is for an early 216 not a late 235

The owner has another carb which is in better condition but for a different vehicle, so all the jetting will be wrong. Going to go on the hunt for a gasket set and see what I can do with it!

Jon, quick question for you. The venturi on these carbs has a land which is slightly proud of the mating face of the top half casting, presumably so bolting the carb together clamps the venturi in place.

Looking at the old gasket and photos of replacement gaskets, the gasket should not be clear of this land and is trapped between the land and the carb body, is that correct?

On one of the carb tops, the land is just fractionally proud of the mating face. One the other, it's significantly proud - 0.5mm or so, if not more - which looks as though it's going to prevent the two halves of the carb coming together properly and allow air leaks around the idle tube. I'm going to use the former top and venturi as they go together more cleanly (they're both 34 venturis) - does that seem reasonable?

Thanks

BE CAREFUL IN MIXING PARTS FROM DIFFERENT CARBS!

Carter made dozens of different BB carbs. There are several different tops, and several different lower castings. They are NOT necessarally interchangeable.

As to your question: without pulling a carb apart, I cannot say. There are several different venturii, in at least 3 different styles:

(A) Ridge on venturi holds body gasket in place
(B) Two separate ridges on venturi used with 2 round gaskets, independent of the main body gasket
(C) Venturi held in place by drive pin, independent of gasket.

The castings are machined accordingly.

EDIT: the 517s has a mounting bolt spacing of 2 11/16 inches, while the later carbs used on the 235 have a spacing of 2 15/16 inches.

Jon.

Thanks Jon.

I realise I wasn't clear - I am keeping carb top, body and correct venturi together, using the assembly that seems to me the better, or more correct, fit.

What I can't be sure of is whether someone has already mixed them up - in both carbs, the venturi has been rotated 180 degrees, so someone's been in there. However, they all appear to be the same design.

Both carbs have what sounds like your second item. The venturi have two ridges, top and bottom, which locate with corresponding lands in the carb top, each with a thin round gasket.

Checked the print.

517s does use the two venturi gaskets.

Jon.

Jon, thanks again for the information. I'd probably have come to you for a carb, or at least a kit, but I don't think you ship to the UK.

Comparing the carbs, I'm pretty sure they're both the same - or at least, the same variant. The 'spare' is marked 0-456 on the throttle body and stamped 456 on the mounting face, which the original isn't. The tops are a fairly lousy match to the bottoms on both carbs, but all the internals seem to match OK - the castings just don't match cleanly on the outside, but looking at photos this seems to be common.

Anyway, the spare carb seemed in better condition and wasn't corroded in the bottom, so I rebuilt that using the venturi that came with it and the jets / nozzle from the original truck carb.

Put it back on, the truck fired up and idled cleanly immediately. Picks up cleanly too. Haven't driven it yet, so we'll see how it goes.

I haven't read all of the responses above, but my first thought on this is the original engine in any cab over is going to be a low oil pressure primitive 235, not a 216. Any two ton truck was going to have a 235 until they came out with the 261 later on. I know the 216 intake manifolds had smaller intake ports than the 235's. I wonder if you have a 261 and the intake manifold is just too small and not able to move enough CFMs. You are working with the original UPDRAFT caburetor and manifold system correct?

Jason, thanks for your thoughts. Yes, it's the original updraft carb as I mentioned in the first post.

I don't think the problem could be intake restriction; if the intake was over-restrictive, it's likely any problem would appear at high revs when a lot of flow is needed. The problem here is the opposite; it wouldn't idle but would run at high revs. Even a very restrictive manifold should flow enough air for it to idle.

As I say above, although it hasn't been back on the road yet, with the carb rebuilt the truck immediately idled smoothly and picked up cleanly, so it's likely the multiple carb faults mentioned above were the problem.

Just to add to this, I had a call from the owner the other day - he is absolutely over the moon with the truck, which is now apparently running better than it ever has done. Kept telling me how pleased he was with it - in fact, he said it was the best it had ever been.

Job done, I think. Thanks for the input.