The Stovebolt Site Forums The Shop Area Engine Shop Changed back to the Rochester 1 bbl; still have problems

As mentioned in my previous post I changed back to the Rochester 1 bbl carb. that came with the 235 I swapped in the 1941 pick-up I working on from the 216 (Carter) carb that I was using and having trouble with. Now I'm getting a loud hissing sound from this carb. and it won't idle without having the choke partially on. It seems to be sucking in a lot of air. I tried different timing settings and checked for vacuum leaks to no avail. Does this mean I have a fuel delivery problem? If so would this be most likely related to 1) too much restriction in the fuel line/filter, 2) a bad fuel pump, 3) an improperly set idle mixture, or 4) a combination of the above? The engine ran fine with this carb when I got it but it was set up differently with a newer style fuel pump, no fuel filter, and the 235 intake/exhaust manifold which I couldn't use because the outlet orientation was wrong for a 1941 pick-up.

Thanks for any help.

What procedure did you use to adjust the carburetor?

How did you check for vacuum leaks (and what locations did you check)?

If it ran fine before you changed the intake, i would check the gaskets on the intake manifold. It doesn't take much for a misalignment of the alignment rings on the intake manifold to create a vacum leak.

Like the other guys, I would guess that you've got
a whoppin' big vacuum leak.
Denny G

Take a shop towel & hold it at various places around the carb. If you get it over the leak the sound will be muffled.
There is a small plug along the fuel discharge channel on the inside of the top part of the carb on the model B Rochester. If that falls out it causes those symtems.

Seems to have a vacuum leak around the throttle shaft upon further inspection. Does anyone sell a kit to re-bush these yourself?

Chevs of the 40s

That seems like a lot of money just for a throttle shaft. Seems to me like brass or bronze bushings would be a better way to go anyway because the wear qualities would probably be better than a steel shaft in a cast iron throttle body. I'm going to call Mike's tomorrow and see if he can fix me up with some.

If the engine "ran fine when you got it" with that 'B' then what
do you suppose happened to the throttle body while it was
sitting, Maybe the mice got to it and chowed out the bore for
the shaft or erosion of some sort??????

Unless that throttle shaft is REALLY loose, that carb should run
just fine if it did before, might be a tiny bit rough at idle
if it's worn a lot, but still should be near normal. Put a few
dabs of grease around the shaft to seal it up and see if it
will idle ok and if the "hiss" goes away.
I think you have other problems.

Denny G

Yes, I was thinking that too. I was just basing my assessment of the throttle shaft situation on the fact that when I wiggled it back and forth it seemed to change the sound of the hissing.

What about a leak around the carb's fuel inlet? The engine seems to run better when I spray carb cleaner right around this fitting. I noticed it was very loose when I screwed it in like the threads in the carb's inlet were worn out. I just used some thread sealant on it, but maybe that wasn't good enough to prevent a vacuum leak. I don't have a fuel leak there however. Can I be getting a vacuum leak even though I don't have any fuel leak? Is it even possible to get a vacuum leak there?

That's not a vacuum source, spray some carb cleaner around the intake manifold while it's running, you will find the vacuum leak.

I've sprayed almost a whole can of carb cleaner around the carb and intake and I can't tell much difference in the way the engine sounds or looks. Having said that something tells me I'm not going to get this engine to run right until I put the 235 intake and exhaust manifold back on it. Trying to run this engine with a mismatched set of intake parts - 235 carb on a 216 manifold on a 235 engine - does not seem to be working. I wished I would have never tried to put a newer 235 in this '41 pick-up; I should have just fixed up the 216 that was in it and been done with it.

Did you use the alignment rings when you installed the intake manifold?

Yes.

I have used a propane torch to find vacuum leaks. You DO NOT light the torch! I would not use it around an extremely hot exhaust manifold. You just open the valve a bit and move it around until you hear the engine rev up, there's your leak. Make sure the air cleaner is in place as this will allow you to hear the increase in rpms better, and possibly hear the vacuum leak. The nice thing about propane is that it is heavier that air so it doesn't drift around and end up in the top of the carb, giving you a false reading. It works best if you turn the idle as low as possible and still have it run smoothly. That way you can hear the increase in rpms more easily. To get an idea of what to listen for when the propane hits the leak, aim the torch at the air intake of the carb and listen for the rpms to increase. You have already tried the "swap and hope method of auto repair" with the carbs without success. I would recommend that you find the real problem by checking all of the suggestions provided to you so far by members of this site before you swap and pray for the manifold to be the problem. There is no reason that a properly installed 216 intake won't work on your 235. I feel your pain, diagnostics can be frustrating. It is a matter of conclusively eliminating each possible cause at a time until you find it. Keep in mind that it may be more than one malfunction causing your trouble. Take a break, eat some red meat (vegiguy?) to get your mind right , and sort it out.

I'll ignore that last comment. Can't we all get along and respect each other?

My apologies for offending you. It was a misguided attempt to lighten the mood. No disrespect intended. I am an old, fat, bald guy who should not cast stones. I wish you the best of luck in mastering your troubleshooting skills and getting to the bottom of your engine problem.

I don't suppose it could be a leak in the vacuum wiper line, motor,or a bad diaphram in the combination vacuum pump on the fuel pump (if mit has one)? Or the line going to the vacuum advance on the distributor or the vacuum advance diaphram itself?? Just guessing.

John

John's musings are the reason that I also carefully do the unlit propane-torch tests on ALL connections leading-to, coming-from, and connected-to the carburetor on a low-revving/idling running engine (as nicely described by Carl).

For what it is worth, I also use a lit propane torch to beautifully sear/brown the outside of rare steaks and of tastey sliced grilled oiled vegetables (the torch adds wonderful browning control).

I don't want to make this more confusing but I have two concerns;
First, how does a 235 carb sit on a 216 intake manifold? I thought the bore diameters were different, as are the stud widths.

Second, you say you used the alignment rings but I thought the diameter of the intakes of a 235 were slightly larger than the 216. In fact, there are aftermarket rings with stepped down diameter for this purpose.

On my COE I used a 216 updraft manifold because it was the only non-cracked one I could find and attached it to a '58 235. I could not use the 235 alignment rings so bolted it up without any rings. No problems so far, but subsequently found the modified rings on Ebay. If I ever remove the manifold I have these ready to use.
Kent

Kent,

Who is the seller of those rings on eBay? That info would allow us to search for the rings.

Thanks,

Tim,
I couldn't find them on Ebay today either. The rings I have are sitting in a drawer up at my shop but I won't be there for awhile. There are still in the original packaging so I hope the seller/maker contact info will be there. If so, I will share.

As I recall, the intake ports of the 235 are 1/10 inch larger diameter than the 216. I am just concerned that Vegieguy may not have a good seal with a mixed 216/235 manifold to engine. In my situation I only had 235 rings and I could not mount the manifold without obvious gap, so I chose to not use rings at all. Later I found the custom rings, but I have had no problems in any case.

Kent

Larrowe & Sons used to sell those adapter rings. The only website I can find for them is odd?

I know the bores are different on the B for the 216 (1.5") and the 235 (1.5625"), not sure about the stud spacing though. Someone should know.

John

The intake/exhaust manifolds-assembly-to-head bolts are the same bolts, in the the same locations, for all 216/235/261 engines.