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Unread 07-16-2012, 04:44 PM   #1
befumo
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4.2 - What affects idle speed?

I just did the Nutter on my '89 4.2. Set the timing to 12* but it still idles a bit high around 900. What effects the idle that i could be over looking? This is what i have done..

The Sol Vac is completely disconnected, plus its nuttered.
Timing has been set.
The idle screw is pretty much all the way backed out, it is barely touching.

Also it seems odd but after it warms up and i shut the engine off. Start it back up it wants to idle around 600-700 rpms.. like it should be.

I have seen people mention idle mixture screws, etc. Any help/ideas appreciated.

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Unread 07-16-2012, 05:30 PM   #2
NonRubicon
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Check the choke, it could be sticking, or simply need adjustment. I would do this before messing with the idle mix screws.
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Unread 07-16-2012, 08:56 PM   #3
Old4X
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Take the sol-vac off and put it in your tool box, it is dead weight now.

You have 2 idle speed screws, one for when the choke is on, the other for when the choke is off. On a warm engine, you should be able to back the warm idle speed screw out to the point the engine idles below 200 rpms. Set it to 650 - 750 depending on your driving style.

You should adjust your idle mixture screws for maximum RPMS and max vacuum ad idle (50 rpms lean of max speed is more proper).

Once initial timing is set, idle mixture set, reconnect the vac line to the vac advance and set the idle speed .


If you can't lower your idle speed, look for vac leaks at carb base, intake manifold, vac lines, brake booster, etc.
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Unread 07-16-2012, 09:17 PM   #4
befumo
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Yes i have the fast idle set to 1600 rpms. But it does not always idle there sometimes it will try to go up to 2,000 rpms at engine start up. I also noticed that this YJ does not come of fast idle when you give it gas at idle, it just falls right back where it was.

I did not know you could back out the idle screw like that and it will come all the way down. That would be quite the vacuum leak.

I will look into the idle screws, but i do believe something is going on with my choke.
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Unread 07-16-2012, 10:13 PM   #5
Old4X
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Quote:
Originally Posted by befumo View Post
I also noticed that this YJ does not come of fast idle when you give it gas at idle, it just falls right back where it was.

.
This sounds like the choke pulloff isn't hooked up or is not working. It is the small dash-pot looking thing on the back, passenger side of the carb about even with the bottom of the carb. It should have a vacuum line hooked to it, and drop the fast idle speed on a cold engine when you "blip" the throttle.
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Unread 07-16-2012, 11:48 PM   #6
befumo
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Quote:
Originally Posted by Old4X

This sounds like the choke pulloff isn't hooked up or is not working. It is the small dash-pot looking thing on the back, passenger side of the carb about even with the bottom of the carb. It should have a vacuum line hooked to it, and drop the fast idle speed on a cold engine when you "blip" the throttle.
Yeah probably isnt. I am sure its something stupid. That is what my last YJ did.

So does the idle mixture screws control the rpm?
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Unread 07-17-2012, 09:07 AM   #7
Old4X
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Mixture screws control quality of the idle, and will cause a drop in RPMs when mis adjusted, but they are not used to set idle speed. Idle mixture is always set first, then idle speed set with the 2 idle screws on the throttle linkeage.
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Unread 07-17-2012, 04:14 PM   #8
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Okay. Yeah i am just looking for other ways why it might be sitting high.
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Unread 07-17-2012, 05:39 PM   #9
superj
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vacuum leak is usually the reason. i always find it under the carb. even if i am extra careful when putting hte carb and gaskets on, i always get one there
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Unread 07-17-2012, 08:02 PM   #10
Old4X
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Don't forget to check the manifold heater. It is the 2" circular thing on the bottom of the intake manifold, directly below the carb.
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Unread 07-17-2012, 09:43 PM   #11
OregonNBeyond
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Pics please
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Unread 07-18-2012, 04:26 AM   #12
befumo
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Quote:
Originally Posted by Old4X View Post
Don't forget to check the manifold heater. It is the 2" circular thing on the bottom of the intake manifold, directly below the carb.
But why would this affect idle speed? Seems to be something funky going on. It refuses to fast idle properly as well.. even though it is set to 1700. (Changed it with the EGR valve hose plugged, second cam etc). It will start up to 1700 then start increasing towards 2,000 rpms.

Went through and checked all vacuum hoses today, all good.

Quote:
Originally Posted by superj View Post
vacuum leak is usually the reason. i always find it under the carb. even if i am extra careful when putting hte carb and gaskets on, i always get one there
I bet that is the problem with the fast idle issue. But as for curb idle i am not sure. I always find it odd how you can restart the engine and it will try to idle normally around 700 rpms like it should. Then when you start driving the curb idle goes right back to 800-900 rpms.
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Unread 07-18-2012, 04:27 AM   #13
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Quote:
Originally Posted by OregonNBeyond View Post
Pics please
Of what exactly, willing to go take some.
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Unread 07-19-2012, 12:33 AM   #14
OregonNBeyond
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If you don't mind that would be awesome Looking for pics of the idle screws showing which one is for choke off and which one is for choke on. Pretty much having the same problem you are having however I've only been adjusting one of the idle screws which might explain why I'm still having the problem
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Unread 07-19-2012, 12:41 AM   #15
befumo
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Not sure what exactly you mean lol. The high idle screw sits on the fast idle cam which sets when you pump the gas before you start it. Then the screws rides up the fast idle cam with the choke, or that is how its supposed to work.

For setting the fast idle go below, its the second cam step up from the bottom by the way. Made that mistake..

http://home.sprynet.com/~dale02/solvac.htm#setting

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