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Function of this?

Old 03-26-2020, 10:26 PM
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Default Function of this?


What does this braided tube that goes to the carb do?
Old 03-26-2020, 10:33 PM
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Choke operating device.
Old 03-26-2020, 10:35 PM
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Heat tube

As the engine warms up it pushes hot air up the tube to pull the choke off,behind that black cover is a wound spring that opens or closes the choke thermo spring of sorts.

On newer motors they switched to an electric choke,you can convert that but no need if it is working.

loosen the 3 screws on the black plastic thing to adjust the choke turning the black cover left or right to open or close sooner or later.

If it goes bad and you are stuck with the choke closed,in a fix,loosen the three screws,turn the cover until the choke opens all the way,tighten the screws,and it will get you home.

Very simple system but sometimes that tube gets carboned up and plugged.


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Old 03-26-2020, 10:51 PM
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Originally Posted by Rjh1960 View Post
Heat tube

As the engine warms up it pushes hot air up the tube to pull the choke off,behind that black cover is a wound spring that opens or closes the choke thermo spring of sorts.

On newer motors they switched to an electric choke,you can convert that but no need if it is working.

loosen the 3 screws on the black plastic thing to adjust the choke turning the black cover left or right to open or close sooner or later.

If it goes bad and you are stuck with the choke closed,in a fix,loosen the three screws,turn the cover until the choke opens all the way,tighten the screws,and it will get you home.

Very simple system but sometimes that tube gets carboned up and plugged.
The engine just won’t start if this tube is plugged? Or are there other symptoms that occur when it’s plugged?
Old 03-26-2020, 10:58 PM
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Normally just hard to cold start and maybe run a little off when cold initially.
Old 03-26-2020, 11:09 PM
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When the engine is cold the thermo spring behind the black cover will close the choke.

When the engine starts up the vacuum will open the choke a little and as it warms up the thermo spring will slowly open the choke all the way.

If the thermo spring is defective it will either hold the choke closed by not opening or it will stay open all the time.

When the engine is cold you can test it,before cranking,full throttle all the way to set the choke then pull back to idle. Then start the engine.

Yes if the engine is warm and the choke is closed it will stop it from starting by being to rich.

Then you can push to full throttle and crank it to clear out the richness.Pull back on the throttle as it starts.

With the air filter off,engine cold,choke closed,start the engine.

Watch the choke (butterfly) as the engine warms up it should slowly open up as the engine warms up.

That tube connects to another tube inside the engine,honestly if the tube is plugged inside the motor it is way easier to just convert it to electric.

The electrical one is the same for GM from the late 70s all the way up into the 90s.

Easy to hook up with a key on positive wire.

Are you having starting problems and asking about this as part of the diagnostics?


Last edited by Rjh1960; 03-26-2020 at 11:18 PM.
Old 03-27-2020, 05:29 AM
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The tube itself, is, a steel line with insulation
Old 03-27-2020, 11:27 AM
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It’s called a bimetallic spring, made of two different materials that expand and contract at different rates that so it moves the choke rod.
Old 03-27-2020, 11:49 AM
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we always just called it a stove pipe
Old 03-27-2020, 03:03 PM
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It sounds like you're still having a rough running/stalling problem. If you think it's the choke, when it's warm, take the flame arrester off and adjust the plate on the choke control where that tube goes, so the choke is wide open. If it runs ok then, you know you isolated the problem. You said you cleaned the carb and changed all of the filters. You did change the filter in the inlet of the carb behind the fuel line, didn't you?
Old 03-27-2020, 04:02 PM
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Originally Posted by mikie View Post
It sounds like you're still having a rough running/stalling problem. If you think it's the choke, when it's warm, take the flame arrester off and adjust the plate on the choke control where that tube goes, so the choke is wide open. If it runs ok then, you know you isolated the problem. You said you cleaned the carb and changed all of the filters. You did change the filter in the inlet of the carb behind the fuel line, didn't you?
Yes, I inspected/replaced all filters in the fuel system.
Old 03-27-2020, 08:16 PM
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Your problem is probably going to end up being the carb. I've never had any luck cleaning, rebuilding or having carbs done by somebody else. Usually end up with a new carb which solves the problems. I'm sure a bunch of guys will jump in saying how easy it is to rebuild and clean carbs, I've just never had any luck with it. You could try taking the carb back off, disassembling and totally soaking it in cleaner for awhile. Then blowing it out and try it again. Sounds like a fuel problem and you've stated that you replaced everything else. Good luck.
Old 03-27-2020, 08:28 PM
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When the engine is cold, take the flame arrestor off. The choke plate should be closed and have a 1/8th inch clearance between the plate and carburetor horn. Anything less and it still flood and be hard to start. Once it starts, it should gradually open as the engine heats up. You can use a 1/8 drill bit to set it.
Old 03-27-2020, 08:36 PM
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I've set up a bunch of marine engines and we just abandoned the choke. Wired it open, whatever. For cold start, just "twiddle" the throttle to get some accelerator pump action, within 30 sec of running it had warmed up enough to be stable enough for pushing the boat reliably.

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