Re: Choke Plate Closing After 1 Hour **PICS ADDED**
Re: Choke Plate Closing After 1 Hour **PICS ADDED**
Thanks to all of you, I really appreciate the efforts people make on this forum to help each other out. I will try to answer all the questions.
HT32BSX115
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Good clear pictures!!
Thanks!
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You didn't indicate where and when you boat, but I only boat in fairly warm weather. I have an electric choke on my 454, had one on my 460 and when I had the 150 Mercruiser (with pretty much the same carb as in your pictures) I either disconnected the (electric) choke or adjusted it permanently open. Unless you're in pretty cool weather, you might be able to just go without it.
I agree. I wired the choke plate open as Charlie suggested, but it doesn't start well when warm--I have to put in throttle. I assumed this was to enrichen the mix because of the wide open plate, but now I'm not so sure. When I get a fresh load of fuel maybe we'll see a change.
I also only boat in fairly warm weather.
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Now having said that, your choke is a pretty simple device using that little piece of copper tubing to route heat from the manifold up to the bi-metallic "spring" (electrically heated in mine) you show in your picture. The spring when cold is adjusted to close the choke and when it warms up it opens the choke and takes the fast idle detent out of the picture....
Yes.
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You're obviously not getting enough heat up the tube to warm the "spring" and open the the choke once it gets running or the linkage is bent/binding and the spring cannot move it.
No, I don't think so. I've watched it three or four times now when cold, with the flame arrestor off. When cold, it starts great with the usual method--about three pumps of the throttle, leave the throttle open to maybe the 1800 rpm, turn the key and she starts immediately. The choke plate was being held lightly closed as it should be, and then it opens as the engine warms--rather quickly, in like 30 to 60 seconds actually. Then after running hard for about an hour, the plate is pulled tightly closed and the engine won't start with less than about full throttle, which engages the unloader to open the choke plate. HEY, this reminded me of something I will put in
BOLD at the end of your questions!
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The tube might be plugged or the port on the manifold it's connected to is rusted/corroded shut or it's plugged with other debris. That should be exhaust gases going thru the tubing so the little housing that holds the "spring" also probably has a small vent to allow those gases to escape so that there's a "flow" of (hot) exhaust gases across the bi-metallic spring.
When I had the tube off I blew through it--wide open, no debris. There might be debris in the manifold port, but the choke gets heat quickly enough, so I don't think so. Now the choke housing vent is something I have NOT looked into, and I think you're onto something (
bold below).
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Also, it might just be adjusted incorrectly.
Perhaps, but it was set to the same setting it was always at, and I've played with other settings with no help.
NOW HERE'S THE THING YOU REMINDED ME OF:
I apologize--I don't think I mentioned this before, because I forgot all about it. When I had the engine out and was getting ready to put it back in, I noticed the choke housing was loose! I mean, actually wiggling on the carb. I took it apart and found how to tighten it. After removing the metal baffle plate, I could access the two Phillips head mounting screws. I tightened the choke down and reassembled it, adjusted as it was before.
It was so loose that there was a small gap between the choke housing and carb--making a good vent, I suppose. So maybe I no longer have a working vent in the choke housing. Is it possible it gets so warm that the coil spring wraps once around, and the tang slips over the plate lever? It doesn't sound possible to me, but I can't find another explanation for why the choke plate ends up tightly closed after an hour of kids skiing.
Where is the choke housing normally vented?
bigskiohio
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i have to throttle mine up too, even when warm then i return it to idle when it starts. mine idles good with lever down but i adjusted my throttle cable recently.
Until now I've never had to throttle it up to warm start. I could just leave it in neutral at idle speed, turn the key for about 1/4 second or less and it would start up at idle speed.
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does yours idle? cold and warm?
Now it does this:
Cold -- As above, I have to pump it about three times and then start it with some throttle in when it's cold. I've always had to do this--and I don't mind. I leave it at 1500 rpm or a little more for a few minutes and it gets up to 130 deg. Then it idles great.
Warm -- It will not start at idle setting. I have to start with throttle open pretty far. Then it takes too much cranking, like it's trying to start. Then it finally sort of starts, then the rpm's climb slowly while it "clears its throat" or something, then it gets up to around 1800 rpm or more and the running smooths out. THEN it will idle just fine. I really hope this is a bad load of gas, but I don't think I'll be that lucky. As I've said, I now think I have two separate problems--one causing the choke plate to go tightly closed when really warm, and the hard starting when warm. Both are new. They may be symptoms of the same problem, or not.
gene8084
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There's something wrong here. While disabling the choke is an option, knowing it used to work, I'd go back to the drawing board.
I agree.
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You need to find the assembly and adjustment instructions take it a apart and start at the beginning.
The Mercruiser Service Manual on page 4B-9 lists only this:
AUTOMATIC CHOKE ADJUSTMENT
Normal setting of the choke is such that scribed mark on cover is in line with long case mark on choke housing casting.
No adjustment of fast speed is provided.
Page 4B-4 and 4B-5 show how to disassemble the choke. I've done that, but have never removed the choke piston and linkage from inside the housing. Page 4B-7 covers choke reassembly (one short paragraph for what i've done).
I also have a Clymer manual (I know, I know...) that actually does a better job of describing the choke adjustment.
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Why deal with throttling up to start, that's what the choke is for? Let it do the work for you.
I agree with that. When warm, I want to just turn the key to start at idle. With kids wakeboarding and skiing, the engine is going off and on all the time, and I want to know it will start when a kid is out in busy water waiting to go.
smartwork
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Question: At the one-hour mark, is the tension on the choke plate the same as when the engine was cold? More? Less?
It is much, much more. When cold, it is where I adjust it to--lightly closed per the manual (some say to use an 1/8" drill bit, that's fine, this isn't the issue). Once it's hot and the plate is closed under a lot of tension, I'm pretty much stuck until I loosen the choke cover (it spins hard) and reset the choke setting. So I can't say what happens if I just let it cool once it happens--I needed to get back to the dock!
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Reading through the thread, one thing stuck with me: You said that it was after a length of time at WOT and that you probably couldn't replicate it on the muffs. To me, that means that something has got to be heat-related... maybe even extreme heat.
I would've said no, that the engine is staying at about 135 to 140 deg tops (usually 135 deg, I'd say). But, per the discussion above, I think the inside of the choke housing may be getting very hot. I don't understand how that's supposed to be vented.
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I don't know if this is possible... but, here's a hyphothisis. The reason the choke coil contracts and expands with temperature is because it is made from two materials that contract and expand at different rates. When the choke heats up, that difference causes the coil to contract (which allows the choke plate to fall open with gravity acting on the plate and linkage). Well... (here's the part I don't know is possible)... what if the coil got SO hot from running WOT that the difference in those two materials reaches a plateau (maybe from defective coil), equilibrium, or reverses. I don't know if that's possible, but if it reaches reversal, the coil would then start expanding again... pushing your choke closed.
Yes, I've wondered if my choke coil is bad. Is there a test, like for a thermostat, where you can put a choke coil in water on a stove, and it should uncoil a certain amount at certain temperatures? I guess I have to get the coil from an auto parts store, if I want to pop in a new one to test it. But it looks and feels good, and I think it's related to me tightening the choke housing onto the carb and now it's not venting to release the heat (?).
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Has it done it at any time other than when the engine has been run hard?
No. This weekend was the first time it happened. It was the first time I was able to run the boat on the water since I had the engine out to replace the coupler. Except that it was on the water for a few minutes the weekend before, when I trashed the impeller and the engine got to 190 degF. So I've replaced the water pump and impeller since then. Cooling for the engine is now good, 135 degF running temp.
Today when I first looked at the carb, the plate was actually closed tightly. It probably went into that position on the way to the launch to be put on the trailer and driven 3 hours home.
All I can think of is that:
1) tightening the choke housing closed the venting; or
2) I bent something in the linkage when hoisting the engine (I don't think so, but maybe).
(I know, loosen the choke housing and try it again... the boat is on a trailer here at the house. I can't get back on the water for another 2+ weeks due to other commitments to my kids. I'd love to have both issues--carb closing and hard warm starting--resolved for next time, if possible.)
Any new thoughts?
Thanks!
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