Help!

I've been at this problem for weeks. The bakelite spacer between the carb and intake manifold seems to have a leak and will not allow the engine to run smooth.

When I start the car, the engine runs well for a few minutes, then starts to idle rough. I can hear see little puffs of smoke coming out from under the spacer. So I took the spacer off, sanded it down on a perfectly flat surface. Same problem. I've changed carburetors, thinking maybe one has a bad mating surface, same issue. I haven't changed gaskets yet, but the gaskets are new.

Is there anything else I can do, to get those parts to mate and be air tight?

I had this same issue for a while and it think it wound up being a combination of a non-flat carb flange and a leak on the top bowl cover of the carb. Step one was having the carb flange machined true at a local shop. That helped a little, but the issue remained. I tore the carb down and noticed the bowl cover didn't appear perfectly flat either. So I lightly sanded the mating surfaces on a work bench and replaced the gaskets. That helped even more. I finally tracked down a minor leak on the fuel inlet pipe. It's a press-fit brass hose barb that was loose in the carb. I pulled it out, cleaned all the surfaces, sanded the outside of the fitting, lightly coated it in JB Weld, and pressed it back in. The JB Weld sealed up any gaps, left a small bead on the outer joint, and I've been leak/issue free ever since.

These little carbs can be a royal PITA - I took mine on/off probably 5-6 times to trouble shoot it. This time, it's been in situ for about two years with no issues, so I may have finally cracked the code (tocca ferro)

Surely if there was an air leak, the engine would idle rough all the time, not just after a few minutes.

Are you sure the engine isn't flooding due to a faulty float valve/incorrect fuel level in the carb. This might also explain the little puffs of smoke.

Al.

If you are seeing little puffs of smoke (or something) then you clearly need to eliminate that first. You may have made the spacer flat but the carbs are prone to deflect on the flange also. A nice fresh sheet of wet and dry on a flat surface and a bit of patience will sort that out. Also a straight edge like a 6 inch steel rule over the head where the spacer sits is and easy check for any deflection there.


If you can see an issue you need to remedy that before looking for something else.

The float in the float chamber is also prone to crack, which allows fuel to enter the float, thereby altering the float level. This is a problem more noticeable when the engine is hot and doesn't need any extra enrichment. When you next have the carb off, check the float---if it 'rattles' there is fuel in it. It is just about impossible to get the fuel out so get and fit a new float. At the same time check the float level vis-a-vie the needle valve. With the carb top held vertical (and the float hanging down) the clearance between the gasket and the float should be 7mm. The easy way to check this gap is with a drill bit of the appropriate size.

Thank you guys! Great suggestions.

1. I agree that I have to solve that puff of smoke coming from the spacer first. That is definitely causing additional air to enter the combustion chamber, fouling up my mixture.
2. I did not consider the float as ever being an issue, but I think its worth checking that out. I have two carburetors that I am going back and forth between. The original and a new one. Both are true Webers, not Chinese, BUT the original one is an IMB 4 and the new one is an IMB 10. The original also seems to be worn in just right and works relatively better than the new one. Non empricial observation.
3. I might have a broken idle mixture screw! I just got an order in for parts and compared the idle mixture screws and one seems to be missing the tip! I think...I will double check today.

Looks like my idle mixture jet is a problem

tminus3 said:

Looks like my idle mixture jet is a problem

Click to expand...

I've heard of this happening, there used to be a warning against over-tightening this idle mixture screw in the workshop manuals.

It might be worth checking that the broken screw tip isn't still lodged in the orifice (that's a fancy word for a hole )in the carb. Also check that there's no damage e.g. burring or cracking, to the orifice that this screw tip enters.

Have you cleaned the idle jet? This is removeable without stripping the carb - it's a slot-headed brass screw on the side of the carb, just above the idle mixture screw iirc. When this is removed, the actual idle jet can be separated from the brass screw and blown through - there's a fine, metered hole in the chamfered end and a larger cross drilling - you should be able to see clearly through the small hole.

Al.

Al...thank you for those tips.

My observations today....

1. The broken idle mixture screw is from the old carb and I'm rebuilding a new carb body. So I don't have to worry about the tip being stuck in the orifice (fancy word for a hole! )

2. So once I was done rebuilding the carb, I decided to install it. Well that is when I noticed the bakelite carb spacer was cracked. This explains why the car idles fine when cold and then starts to idle rough when it warms up.

3. So I've ordered 2 new spacers and while I wait for them, I will use some high-heat and high-pressure epoxy to seal and fuse that crack. This test will hold me over until the new ones arrive.