Engine stalls at idle speed -- hole in choke heat tube coming off the manifold.

[jbutler67]

I have a 1988 Four Winns Horizon 200 -- quite the project boat
OMC 502APRGDP
Carburetor Info - Rochester R2-MRIN2 (#17059060)

Engine will turn over and stays running at a higher RPM but dies out at idle speed - 800 RPMs. If I throttle up to 1,000 or 1,200 RPMs, engine stays running. But, when i come back down to idle (800 RPMs) the engine will stall.

I think I found the problem. It is on the carburetor. Specifically, on the automatic choke (heat choke) -- choke heat tube coming off the manifold.The tube has rusted and has a hole in it. I am assuming the choke is closed longer than it should be without the hole in that tube.

I found a replacement heat tube. Also bought a new choke thermostat.

My question -- how do I remove the old heat tube? The "choke stove" on manifold has one good bolt and one seriously rusted bolt. Does the old tube come out of the "choke stove"? Or, do I need to drill out the rusted bolt and remove the "choke stove"?

Pictures attached.

 

[jbutler67]

No Title

 

[Grub54891]

The tube should slip out, it's sort of a press fit. Being rusted like that it will probably break, but just drill it to the proper size and fit the new tube. I'd be taling the stove off and doing whatever is necessary to clean it up and re-install.

 

[jbutler67]

Replaced the heat tube from the choke stove. Also replaced the choke thermostat. Started with choke adjusted to butterfly having 1/64 gap, almost closed, at cold. Boat takes a few try's to kick over and when it does, it won't stay running unless I throttle up to 1,000-1,200 RPMs. Engine dies 3-4 seconds after I return to idle speed. I tried adjusting choke from lean to rich (turned thermostat cover counter clockwise). Turned slightly and tried to start and idle. Repeated a few more times, continuing to adjust more a more to rich (using 1/8 turns counter clockwise each time- Lessing the springiness in the butterfly). Got to the point where adjusted it so loose that there is no spring back on the butterfly. Same result each time - it won't stay running unless I throttle up to 1,200 RPMs. Stalls as soon as I return to idle speed.

Any ideas or thoughts?

How springy should the butterfly be at cold?

 

[HT32BSX115]

it won't stay running unless I throttle up to 1,200 RPMs. Stalls as soon as I return to idle speed.

Any ideas or thoughts?

How springy should the butterfly be at cold?

Howdy,

Get the engine fully warmed up and adjust the choke completely out of the picture. (I.E. prevent the choke from operating)

THEN, with the throttle cable/actuator disconnected from the carb throttle control, adjust the carburetor for a normal idle speed.

If you cannot adjust the idle speed, you likely have an idle circuit problem (idle circuit blocked etc) Or other carburetor problem.

Time to rebuild it.

If you have to drill out those rusted bolts/screws, have at it! If you don't have a tap and die set, get a good one. Then you can clean up the threads in those holes and install new bolts. II would either use brass or stainless steel 1/4-20 bolts (etc) to hold it in. They won't get rusted in place then.

Now having said all that. I really dislike automatic chokes for this and other reasons!

Since I only boat in warm weather, I disconnected my (electric) auto-choke more than 10 years ago and never looked back. My Mercruiser 7.4L engine is not all that hard starting when first starting up in the morning. I just give it a couple of accelerator pumps and it lights right off!

Yes, it sometimes stalls and an additional try to get it started ................. I then let it warm up a little and while "taxiing out", It warms up just fine and runs great and starts great for the rest of the day.

AND, Since I have NO auto-choke, I NEVER get stuck chokes, black smoke, or soot on the transom ....etc.

ymmv......

Rick

 

[Grub54891]

ht, since you only boat in warm weather, your setup might work fine. But there is a reason for the choke on most every motor, and I disagree with removing it completely with the system. I adjust it so it will start cold, with one pump of the throttle. Then during warmup, physically look at the choke valve itself, and make sure it opens properly, and fully. From there, I adjust the mixture jets for the best idle at full warmup. If it's hard to set properly, it may need a rebuild. Not that hard to do, if you are mechanically inclined, Heck my kids were doing carb jobs at 12 years old. But then again, I just said, if you can get it to run, you drive it. And we had a big field with a few junk cars for them to mess with.......lol

 

[HT32BSX115]

But there is a reason for the choke on most every motor, and I disagree with removing it completely with the system.

Interesting though, NO carbureted aircraft engine has a choke. (in fact, NO aircraft engines have a choke)

Many have a priming system that squirts fuel directly into the intake system (in addition to a accelerator pump on some carburetors) but NO choke...........and aircraft engines will start in the coldest weather around...........

Automatic chokes are simply a one-size fits all system for making engine start and warm-up a simple "turn-key" operation. But even when adjusted correctly, they still can result in black smoke and soot on the transom.

You'll notice I did not suggest that the OP disconnect his auto choke. I just intimated what I did and how good it worked. If I were to reconnect my choke, I would probably install a cable and hide the knob so no one could find it!

Cheers,


Rick

 

[Grub54891]

I did not know that about aircraft. So the aircraft have a priming system? Kind of like a choke as it adds fuel during warmup, as does a choke. Interesting.

 

[HT32BSX115]

I did not know that about aircraft. So the aircraft have a priming system? Kind of like a choke as it adds fuel during warmup, as does a choke. Interesting.

It's really nothing like a choke at all, nor is it an enrichment system for after starting. The priming system for aircraft is usually a hand operated "pump" that will inject measured "squirts" of fuel directly into the intake manifold depending on how many times you pump the priming knob. One NEVER pumps the knob after the initial 1, 2 or 3 pumps and after priming, the knob is twisted into a locking slot so it cannot operate after the engine starts.

.
In fuel injected aircraft engines, the system is a "continuous-flow" system. if the electric boost pump is on, fuel will continuously flow through each injector.

For starting, you turn on the fuel boost pump briefly for 2 or 3 seconds, then turn it off, then crank the engine. The engine driven fuel pump then takes over normal running. Some systems use the boost pump to "back-up" the engine driven pump during landing and takeoff only.

A "choke" is just a butterfly valve on the air-intake side of a carb. It's usually got holes in it or it doesn't completely cover the hole or close tightly so it at least allows some air in. I don't think there has ever been an aircraft carburetor certified with a choke. Aircraft carburetors are usually jetted so they'll produce maximum power at WOT @ sea level.

A manual cockpit mixture control will lean to maintain a proper mixture at higher altitudes based on observing exhaust gas temp or charted fuel flow in fuel injected engines.

 

[vasy]

With rust this bad, why not just get a new carb?
I see it on eBay for just under $300.
Save yourself a bunch of work taking out old rusted out screws and other parts that may need to be replaced in the process.

 

[HT32BSX115]

With rust this bad, why not just get a new carb?

It's not the carb that's rusty. It's the heat pipe. The auto choke housing is aluminum.

Another way to fix it is to just change the autochoke to electric. There's kits for the conversion.

 

[jbutler67]

I found a replacement heat pipe for $20.

909580 — TUBE, HEAT EXCHANGER

Had to drill out a small piece that broke off but it came out and new heat pipe fit in great. (Used a shot of compressed air to blow out any drill shavings. )

I suspect the stalling problem is related to the fuel. Changing fuel filter, fuel water separator. Also, I haven't added any Seafoam to fuel after any fill ups.

 

[HT32BSX115]

I found a replacement heat pipe for $20.

909580 — TUBE, HEAT EXCHANGER

Had to drill out a small piece that broke off but it came out and new heat pipe fit in great. (Used a shot of compressed air to blow out any drill shavings. )

I suspect the stalling problem is related to the fuel. Changing fuel filter, fuel water separator. Also, I haven't added any Seafoam to fuel after any fill ups.

That'll fix your choke as long it will move freely. Then just make sure it's adjusted so that when fully heated up is completely "out of the picture"

Stalling near idle (if not ignition related) is a fuel (delivery) problem in the carburetor. Seafoam is just light mineral oil, alcohol and Naphtha. Adding any type of "Mechanic-In-A-Can" Snake oils (like Seafoam) will not rebuild your carburetor for you.

 

[jbutler67]

Stalling near idle (if not ignition related) is a fuel (delivery) problem in the carburetor. Seafoam is just light mineral oil, alcohol and Naphtha. Adding any type of "Mechanic-In-A-Can" Snake oils (like Seafoam) will not rebuild your carburetor for you.

Thanks. Rebuilding the carb is something I eventually want to learn. But not at the cost of more of time on the water lost.

Boat is with marine mechanic right now.

 

[HT32BSX115]

Thanks. Rebuilding the carb is something I eventually want to learn. But not at the cost of more of time on the water lost.

Boat is with marine mechanic right now.

Be sure to come back and let us know what the 'fix" actually is!!:thumb::thumb:

 

[jbutler67]

Certainly. Will do.

 

[jbutler67]

Boat came back from the mechanic. A good news, bad news situation.

Good news -- it runs well again. Starts on first turn and idles fine even when cold. Throttles up nice and smooth and back down to idle with no hesitation or stalling.

Bad news -- during changing of the fuel filter, some fuel was spilled in bilge. Then starter sparked and started a small fire. Luckily no one was hurt and they put the fire out right away. (One would think the battery would be disconnected during any fuel system work, or any spilled fuel cleaned up and blower run before reconnecting the battery?)

Repairs included; fixed wire ends on starter and ground wire on back of block above starter (sparks coming from starter area), replaced fuel filter, points conditioned, cap and rotor, timing adjusted, choke on carb adjusted.

I cleaned the bilge with soapy water. I have been going over everything in the corner where the fire happened (starboard side toward bow end) and under the engine. Also checking all the hose, electrical wires, any rubber parts, etc. Fire burned the paint off the fuel pump (ugh). And the rubber hose from the fuel tank to the fuel filter bracket / fuel filter is starting to show some very small cracking. I plan to have that replaced. Oh what fun.

 

[HT32BSX115]

Bad news -- during changing of the fuel filter, some fuel was spilled in bilge. Then starter sparked and started a small fire. Luckily no one was hurt and they put the fire out right away. (One would think the battery would be disconnected during any fuel system work, or any spilled fuel cleaned up and blower run before reconnecting the battery?)

Glad no one was hurt! This can happen very easily! I even added a second bilge blower in my boat for this reason!

Good thing is, it happened on his (the mechanics) watch? He's on the hook for the repairs?

 

[jbutler67]

No Title

Back to the mechanic.

Took the boat out Saturday. Cruising up river 15-20 mins at about 1,200 RPMs - in a no wake zone. Suddenly, the engine stalled. Couldn't get it to start again. Starter was cranking but it wouldn't turn over.

Repairs just completed last week included: fixed wire ends on starter and ground wire on back of block, replaced fuel filter, points conditioned, cap and rotor, timing adjusted, choke on carb adjusted.

During above listed repairs, the boat caught fire at the mechanics. While changing the fuel filter they spilled gas in the bilge and the starter sparked. Burned all the paint off the fuel pump. I can only imagine what that does to a 25 year old fuel pump.

I'm willing to bet the problem now is the fuel pump. Oh what fun.

 

[jbutler67]

New fuel pump installed this week. Been out twice with no issues. Boat starts on first key turn. Idles great. Carb needs a cleaning after sucking up all the fire extinguisher dust. But, back in business and boating again.