engine only runs with excessive choke

[gary gerber]

I have a 1970 Morgan 33 which I have owned for 35 years with the original engine. The engine starts strong on choke and runs smooth, after warm up however reducing choke she dies. I just rebuilt the carb following my Moyer Service Manual. I blew through all orifices to check for blockage and reinstalled the carb, again she runs perfectly except needs constant choke. I checked fuel bowl, tested mechanical pump, checked plugs and spark all part of my Spring tune up, even replaced all 15 gallons of fuel.

I have noted the similar forum idle comments but again, I did clear all passages in the carb. I've exhausted my limited knowledge.

[FelicityRebuild]

Sounds like fuel mixture to me. Did you try adjusting the jet?

[sastanley]

air leak?

If you are confident that you've got the carb in good shape (which would obviously be the first culprit) I would suggest an air leak, maybe where the carb goes in the manifold. I have the Indigo PCV kit (which adds a spacer & second carb gasket to the mix), and I noticed that I didn't get all the gasket material off one surface when I took mine home over the winter..it is a little hard to see the flange on the manifold since it hangs upside down. One check is to spray some starting fluid (ether?) or carb cleaner around the flange(s) to see if it sucks in any fluid thru a leak and changes the engine speed.

Be careful spraying that stuff around a hot motor..I don't think it would be a real issue, but you don't want any spontaneous combustion if it hit a red hot part

edit - FR's got a great idea too..double check using the Moyer Manual that your settings are correct.

[marthur]

Don't forget that the mixture adjusts the AIR not the FUEL. You will want to screw the mixture setting in to reduce the air and richen the mixture.

Good Luck!

Mike

[67c&ccorv]

If you are confident that you've got the carb in good shape (which would obviously be the first culprit) I would suggest an air leak, maybe where the carb goes in the manifold. I have the Indigo PCV kit (which adds a spacer & second carb gasket to the mix), and I noticed that I didn't get all the gasket material off one surface when I took mine home over the winter..it is a little hard to see the flange on the manifold since it hangs upside down. One check is to spray some starting fluid (ether?) or carb cleaner around the flange(s) to see if it sucks in any fluid thru a leak and changes the engine speed.

Be careful spraying that stuff around a hot motor..I don't think it would be a real issue, but you don't want any spontaneous combustion if it hit a red hot part

edit - FR's got a great idea too..double check using the Moyer Manual that your settings are correct.

Unless you want an on-board fire with a gasoline engine throw the ether away - if the engine won't run properly then there is something wrong and all the ether in the world won't fix it.

[thatch]

More information please.

Gary, If that is actually a picture of you at the helm of your boat I really envy you. To help diagnose the problem I'll ask a few questions and maybe we can figure out if it's a fuel delivery problem or a vaccum leak. First, while using the choke as you have been, is your engine developing normal or almost normal power? If your boat is able to attain decent speed, then you are probably getting enough fuel to the engine and the choke is merely metering the air down to keep the fuel/air ratio correct to make up for a vaccum leak somewhere between the carb and the cylinders. If on the otherhand, the engine, "under load" developes very little power, then the choke again is trying to maintain the correct f/a ratio by reducing the amount of incoming air to match what is most likely a blockage in the fuel system. If you can give me the answers to these questions then we will probably know better in which direction to look.
Tom

[Don Moyer]

Tom,

The distinction you make between returning to reasonably normal power by using choke, versus being able to restore only partial power as indicating a vacuum leak (versus a partially clogged main jet) is most interesting. When considering likely places for a vacuum leak, the manifold gasket, a broken scavenge tube fitting on the intake manifold, and the carburetor flange gasket would be good places to start.

Since restrictions within the main jet itself are so frequently discovered to be the cause of requiring choke after an engine warms adequately (I've been saying somewhat arbitrarily 99 times out of 100), we haven't spent a lot of effort looking for the exceptions. I now wonder if there might be more exceptions out there than we previously thought.

In addition to a vacuum leak external to the carburetor, I'm wondering if a review of the tech tip on "internal pressure distribution within a carburetor" might reveal a condition that could mimic a vacuum leak external to the carburetor which would respond positively to the use of choke. This would account for the (few) times I can recall when one of these choking issues resolved by replacing the carburetor, even though the old carburetor had a perfectly clean main jet.

Beyond the immediate consideration(s) of this particular thread, your suggestion also highlights the critical importance of paying close attention to "symptom observation and analysis" in the process of troubleshooting, and to not take even our most trusted assumptions too much for granted.

In any case, thank you very much for this suggestion. It deserves to be somehow highlighted, and I'm looking forward to the ultimate outcome of this particular episode.

Don

[thatch]

Don,
I am honored by your posting a reply to my suggestions and I completely agree with your "well seasoned" observations. In Gary's case since he seems to have done a reasonably thorough job of carburator cleaning and filter servicing, it might be best if he could just borrow a "known quality" carb for a test to verify or put the carb question to rest. I know this sounds like a rather simplistic suggestion but since there are so relatively few A4's around these days it might be difficult to find a willing doner. Maybe another forum viewer in his area could help out with this.
One other area which is with us these days and can affect, particularly A4 vintage fuel systems is the presence of alcohol in our fuel. I have seen fuel lines which have swelled almost completely closed because of it's effects.
Again, thank you for your comments.
Tom

[67c&ccorv]

I have a 1970 Morgan 33 which I have owned for 35 years with the original engine. The engine starts strong on choke and runs smooth, after warm up however reducing choke she dies. I just rebuilt the carb following my Moyer Service Manual. I blew through all orifices to check for blockage and reinstalled the carb, again she runs perfectly except needs constant choke. I checked fuel bowl, tested mechanical pump, checked plugs and spark all part of my Spring tune up, even replaced all 15 gallons of fuel.

I have noted the similar forum idle comments but again, I did clear all passages in the carb. I've exhausted my limited knowledge.

Not trying to be smart but when you re-intalled the choke and choke cable are you certain (buy removing the flash arrestor and looking) that the choke is "on" when you think it is "on" and "off" when you believe it to be "off"?

It is pretty easy to confuse the setup.

Secondly, did you check/set the float angle during the carb rebuild?

[gary gerber]

Thanks for the responses, you are all correct. I had to wait for the engine to cool so I wouldn't burn my hand but I did adjust the idle jet. I posted the thread before I went back to the boat to move her for the season from the marina to our dock at the house. She started perfectly, ran perfectly without the choke , we had a great sail and brought her into the slip under power, feathering her motion to stop on a dime right at the dock.

My 1970 Morgan has the original engine, I only replaced the carb from Moyer and rebuilt the mechanical pump with a Moyer kit.
Moyer Marine is absolutely essential to us Atomic Four owners.

[gary gerber]

I have to LOL, yes that is me at the wheel in the picture, but I'm steering a Beneteau 50 in the Windward Islands chasing another Beneteau 50 flying a French flag... I caught him and passed him. USA, USA

My 1970 Morgan 33 has a tiller.

[sastanley]

Gary,
Great picture..(glad you got the engine running!)

[off topic]
Where in the Windwards did you go?

In 2003, we did the Leeward Islands Grenadines loop (starting in Grenada) and making it to Mayreau and back, in a forgettable 43 footer with another couple. I proposed to my wife in Salt Whistle Bay.

This spring, we went to Antigua & Barbuda with 3 other couples and chartered a Lagoon 44 (the huge cat that looks like a tank!)

Absolutely beautiful down there!

[Matridium]

I have the same problem! I need help please

Hello
I'm new here, and I found this forum searching for a problem like this.
This is what I have:
Johnson 25 hp 1972 outboard

Here is the problem:
The motor only runs when the chock is completely closed, and when the chock is opened the motor dies.

I rebuild the Carb last year, and did not have a chance to get it out on the water till this year, due to major family problems. However I followed the instructions in the original service manual on rebuilding and put it all back the way it was taken apart. Second thing was I replaced the slow speed needle because it was badly worn down. I also replaced the slow speed needle bushing, however, the one that came with the rebuild kit was way too big, almost as if it was the wrong size, if would not fit. So I ordered a new bushing from iboats.com and I got the original part, however it too was way too big. I ended up cutting the bushing down with a razor blade in order to make it fit. I hope this is not the issue. I have checked all the lines and I can see no leaks..
I ran the motor our of the water ( in a trash can of water) for a few minuets to see if it will worked after the rebuild and it worked fine, however I did not get to winterize the motor, and I'm worried all my work on the carb is down the drain due to slop in the jets, and bowl.

Any ideas here? I just need some direction, my last resort is to take it to a dealer.

thanks for the help!

Mike

[ndutton]

Why did you rebuild the carb in the first place? Running problems? You didn't say but I assume you've adjusted he jet to its limit.

If it ran OK before the carb rebuild and poorly after, that's where you need to look. Jet issues? Carb float set at proper height? Massive air leak?

Your choke is compensating for an excessively lean mix.

[Marian Claire]

Let’s see: rebuilt carb and tested and it ran fine, put away un-winterized for several months, now it will only run with the choke on. Is that right? If so, pull the carb and clean it. I have been dealing with a similar problem on a 3.3 hp. Welcome to the forum. Dan S/V Marian Claire