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Stumbling/stalling at part throttle when cold: ideas?
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2014/1/18 5:51
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My engine's been starting and running a little rich, so today I checked the fuel level in the float bowl (about correct), and took apart the automatic choke to make sure it's working right.
I adjusted the auto choke so it's definitely closed when the engine is cold. I push the throttle pedal once to shift the lockout so the choke does close, and that pretty much floods the engine. It takes a LOT of cranking to suck the gas through (and the car reeks of raw gas) and then finally it starts. Until it warms up, I just have to sit at idle, because if I get on the throttle at all, it'll sputter and die.
In contrast, if the car's run, like, yesterday, and I don't push the throttle (so the choke is still mostly open) the car will start and I can get to fairly full throttle, but it still stumbles badly below like 2000 rpm.
As soon as the water temp is off the peg, the car behaves perfectly.
It also appears that the choke is opening fully well before the engine is warm, and I'm wondering if that's why it's stumbling so badly, although as noted I think it's running rich not lean, so when I open the throttle a bit I'd expect it would get closer to lambda and run better.
The accelerator pump is definitely working. I can see it spraying in fuel. I feel like it's working too well. (Kinda kidding: it works just fine when the car's warmed up.)
I'm a little tempted to put a manual choke on there for a while and see if I can adjust it to perform better, or whether it's not the choke but something else that's the problem.
Timing (with the vacuum removed) is right on, and pulling vacuum advances the timing, so as long as that tube's not leaking, I think the timing is okay.
It's weird. I mean, I'm glad it works fine when it's warm.

Posted on: 2022/4/4 4:50
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Re: Stumbling/stalling at part throttle when cold: ideas?
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Strange behavior


So you
* set the choke (one pump with engine off). It is closing all the way
* fuel does spray out with the pump


Does it start right away? With foot off the accelerator pedal?

If it is flooded it will only start if you hold the pedal down while cranking

On the other hand, if you have your foot on the pedal during a cold start, that introduces another variable. Best to get it start with the foot off

My guess is that the Choke Pull-Off is bad. As soon as it starts (foot off) the pull-off is supposed to open the choke approximately 3mm Otherwise the engine will start, and then flood out

you can test. with engine cold, and choke set, pull the linkage. Does it open 3mm? Good. Next pull hose off the Pull-off, pull linkage and put your finger on the port. Let go of linkage and it should stay. If the linkage goes back even with finger blocking the port, the Pull-Off diaphragm is bad

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Now that's just starting. If it begins to stall as the engine is warming up, the choke spring may be worn out an opening the choke too soon. You can swap on another Hitachi choke cover

Posted on: 2022/4/5 3:00
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Re: Stumbling/stalling at part throttle when cold: ideas?
Just can't stay away
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I went through this again.
First thing I was wrong about : the choke wasn't closing fully. I thought it was until I got in and messed with it a bit.
Second thing, you're right, the choke pull-off isn't working. The hose to it is cracked.
So I'll sort those out.
TBH I'm kinda thinking about just reverting to a manual choke.
But thank you for the suggestions: I learned some already and if I can get the choke to consistently close all the way I'm sure it'll work better.

Posted on: 2022/4/12 5:33
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