Model E type II carb, choke question

[Alan]

Hello to all;
I see the intake manifold on my 80HP V4 OMC pulls air hot directly in from the tube attached to the back of the block. The hot air goes through the carb body, but not the throats.
I’m chasing what feels like starvation, at higher speeds. And, it seems to lean-sneeze a lot, in general.

I thought this tube just supplied hot air to warm the bi-metal choke, but it actually feeds into the combustion mixture.
But, I need to fight the urge to plug this, because the overall running mixture accounts for it, right? Like the EGR on an older car?
The hot air being pulled in has no fuel spray, but my guess is that’s the way it was designed, and I need to leave it alone.

All opinions welcome.
Appreciated;
Alan

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[frankr]

It heats the choke, that’s all. Of course the carb is calibrated to account for the air being pulled in through the choke stove. BTW, if the choke stove in the exhaust cover is burned through, exhaust fumes will be pulled in through the choke to the intake manifold and screw up the running. Also, some people can’t stand seeing the open fitting which is the choke stove air intake and plug it up. That also changes the air/fuel ratio entering the intake manifold.

EDIT: What I’m calling the choke stove is more properly called a heat exchanger—I think.

[Alan]

Many, many thanks, Frank R.
I’ll verify the heat exchanger isn’t blocked or burned through.
It doesn’t look blocked, and the motor doesn’t appear to have too many hours on it so I’ll be surprised if it’s burned.
But I’ll sure check.
Your continued kindness and patience are appreciated.
Alan

[fleetwin]

I’m thinking it will be easier to diagnose the high speed problem, then perhaps this might take care of the low speed problem. Does the engine RPM surge up and down at high speed/in gear? I remember you saying something about the RPM would actually pick up if you pulled the throttle back off WOT a bit. Is there any way you could post a video of the engine running at high speeds/misbehaving? Yes, I understand that audio can be deceiving, but this might help us head in the right direction. I am assuming you have found the correct OMC jet tool and removed/inspected the fixed high speed jets also.
I know you have checked the belt timing, and carb sync. Your symptom almost makes me think the carb butterflies are able to go past WOT, but this is not likely unless the roll pin was sheared off. In any event, the carb is apart now, so this is surely easy enough to check out. I know this is unlikely, but is there any chance you have the plug wire firing order/location in the cap incorrect? I’m trying to remember, but I think you said this engine used to run correctly….If so, what changed between the time it ran OK and now? Even though the belt timing and plug wires might be right, perhaps there is an ignition fault/cap-rotor problem causing a misfire which might explain this problem. Even though the plugs might be new, that doesn’t mean they are good…Again, simple stuff first. Yes, you might have a faulty/stuck/broken reed, but I wouldn’t pull that manifold off until you have confirmed all the simple stuff is OK. You can peek down inside the manifold with the carb off with a light, perhaps you can see something this way without ripping the manifold apart.

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