High Idle troubleshoot--with video!! (1 Viewer)

[Thornton Melon]

My idle had been creeping up the past week to about 1k rpms.
I did a basic lean drop adjustment and it was sitting right where it should.
I ended up backing out both speed and mixture screws about one full turn.
Idle sat at 650 with the truck warmed up well.
Drove it away and on the first down shift into second on the test drive the idle climbed with the clutch in and went to rest at about 1500 at idle.
I tried to see if there was anymore affect with the speed screw turned out more but after a half turn it no longer had an affect.
I can put some physical pressure on the accelerator rod linkage and the speed will drop but will stumble a bit and then return to between 1-1.5k rpm.
Interesting note is when I put my hand over the carb with the air cleaner removed the idle increases significantly and it is not until I apply direct significant pressure to the opening does it stall out.
While my smog system is somewhat in tact there are several hoses not in place but they have not had an affect on the idle the past six months.
I have given the egr a good knock with a screw driver to see if the valve was sticking but this had no results.
Carb spray all around the base and every hose in connection with it has no change in idle.
If I mash around the secondary diaphragm casing the engine will bog as well.
Also while doing the initial adjustment the mixture screw was pretty torn up on the surface meaning it's been handled pretty roughly by someone previously. Just wondering if turning it from its seated position (where it had probably been for a while) could have caused a problem with that component?
The attached video is at idle and landing around 1200rpm.
It certainly seems like it is dumping fuel in there pretty rapidly.

With this info does someone have a temporary fix for me until I can do a carb rebuild (if that's the cause)?

Thank you for all that you do.

https://drive.google.com/open?id=0B8QGf6sV-dVuTWRVNlR4OF9pNUU

 

[roadstr6]

Is your idle fuel solenoid (the little electrical gizmo on the carb) working properly? With key on, unplug the connector and plug it back in. You should hear the solenoid make a click. If it doesn't, that's part of your problem. Check the wiring and/or replace the solenoid. The carb should get all of its idle fuel through that solenoid. If the truck is idling and you unplug the solenoid, the truck should cut off. If the solenoid is working and the truck does not die when you unplug it that means you are getting idle fuel from another source other than the solenoid. The secondary circuit is a prime suspect. If the secondary butterfly is cracked the least bit open the carb will pull fuel from the secondary at idle. Check your linkages to make sure the secondary is closed.

I have had the secondary butterfly to hang up on a home-made paper carb gasket before which caused me a slew of headaches. Once I figured that out, I was good.

 

[gregnash]

Hard to tell with the video as it is fairly short... Have you don't anything like rebuild the carb lately? You say that you tried the lean drop method but have you followed it specifically by the book?
What about timing adjustment?
If you put a piece of cardboard or a hand with a welding glove over the carb to try and choke it out what happens?

I am thinking it could be a couple things,
1. something is going on with your fuel cut
2. something is going on with your accelerator pump and it is sticking
3. something is up with timing adjustment and you are off.

I have a similar issue going on with my truck since I rebuilt the top end at the beginning of the year. When I did that I rebuilt the carb with a Keystar kit, which it is known that the AP is actually slightly longer than the OEM (not to mention the boot is a different material, rubber vs. leather on OEM). I do not remember if I adjust the AP throw to spec when I rebuilt the carb which would attribute to my idle issue.

 

[Thornton Melon]

Thanks for your suggestions and troubleshooting tips. I'm anxious to give them a try.
It is clear the carb was taken apart at some point though I have no idea when that was done.
Lean drop method done via the book. I've had a few carbureted vehicles over the years and in my experience I've never been able to turn the speed screw all the way out and have the idle this high, no matter what is done with the mixture screw. But this carb has a lot more hooked up to it than I've experienced in the past.

I will certainly report back when I go through some of these things later today.

Thank you very much for taking the time to respond and help.

 

[Thornton Melon]

First item checked was the idle solenoid.
And it looks like it's screwed in there but the housing and anything connected to it is gone.
If I'm correct in thinking this is it.

So I believe then I would be getting fuel from another source then? And maybe that's why it's just kind of dumping/spraying in there instead of something more regular?

 

[roadstr6]

Ding! Ding! We have a winner! Your IFS is toast. Carb is probably just dumping fuel past the solenoid. Get a new solenoid. Hook it back up and re-tune using the lean drop method. I wonder what in the world happened to that thing? It looks really crispy.

 

[FJ40Jim]

Also, the linkage on the backside of the carb is OOP, which will bind, preventing idle.

 

[gregnash]

Yup your ICS is toast and PO probably rigged the choke so that it was on just enough to keep the truck idling.
Unfortunately, for a NEW ICS this was the only option I was able to find. Solenoid, Idle You want the bottom one.

 

[roadstr6]

Also, the linkage on the backside of the carb is OOP, which will bind, preventing idle.

Nice catch, Jim.

 

[Thornton Melon]

Thank you very much guys.
Luckily I live close to Cool Cruisers. Picked up a new solenoid and connected it up.
Loosened the choke cable so the choke is not engaged at all.
But now I'm not getting a response from my mixture screw. It can be screwed all the way in and back out without effect. And fluid is still spraying out the main jet I believe, like the video shows.
So I'm chasing a significant vacuum leak if I'm reading some other posts correctly.
Too many hoses.

 

[Thornton Melon]

And the idle solenoid is currently not having an effect of the idle. I can plug it in and unplug with no no engine cut off.
I'll have to test the switch later but from the outside look of things there's nothing off.
The secondary looks pretty dry from the inside. And slowly revving up the engine to about 3800 rpms the secondary rocker arm thingie never comes in contact with the throttle linkage. I know my technical jargon is off there. It hopefully that makes sense. Hard to tell from the pic but the secondary cylinder just looks dry. And this truck has been used on the highway with frequency.

 

[gregnash]

Try the redneck test on the carb... if you have a welding glove or something similar, get the truck running then place the gloved hand over the top of the carb (with the air cleaner removed). It SHOULD choke out, sputter and die. If it does not then you have a significant vacuum leak somewhere.

 

[Thornton Melon]

And the idle solenoid is currently not having an effect of the idle. I can plug it in and unplug with no no engine cut off.
I'll have to test the switch later but from the outside look of things there's nothing off.
The secondary looks pretty dry from the inside. And slowly revving up the engine to about 3800 rpms the secondary rocker arm thingie never comes in contact with the throttle linkage. I know my technical jargon is off there. It hopefully that makes sense. Hard to tell from the pic but the secondary cylinder just looks dry. And this truck has been used on the highway with frequency.

View attachment 1328503

Sorry for the multiples.
Egr test confirms the valve is working.

 

[gregnash]

For the secondary, my understanding is that it should be dry as it is only used in high load situations (e.g. freeway driving, going uphill, etc.). There is documentation to test that your ICS circuit is working properly but basically, you should be able to have the ICS unplugged and turn the key to the ON/RUN position, not actually start the engine though. When you plug the ICS in you should hear and/or feel a significant CLICK come from it. (hopefully that makes sense). Try that test and let us know what happens.

 

[Thornton Melon]

Try the redneck test on the carb... if you have a welding glove or something similar, get the truck running then place the gloved hand over the top of the carb (with the air cleaner removed). It SHOULD choke out, sputter and die. If it does not then you have a significant vacuum leak somewhere.

Shop towel over my hand.
As I place it over the top the engine revs for half a second, maybe 500 rpms or so then sputters and will die if I leave it covered up.

 

[gregnash]

Ok so it is choking out the engine. Does it actually die if you let it?

 

[Thornton Melon]

Ok so it is choking out the engine. Does it actually die if you let it?

Yes.
Now, I have a Weber that I just installed on another truck and if I put my hand over that it comes up and grabs me with significant force.
This carb isn't necessarily pulling my hand down. And really if I just gently place three fingers over the top of it, then the engine kicks up its idle and smooths out.

 

[gregnash]

Yeah a weber is a completely different beast and not recommended for these trucks. You wont run much better than with the AISIN carb. Something is telling me that your carb has been modified internally. Just seems to be running quite strange, @FJ40Jim is the carb whisperer though.

 

[SteveH]

Unless you know that the intake/exh. manifold gasket has been changed lately, I would suspect a leak there. The average 2F clattering around in the US has a manifold-to-block leak, in my experience.

 

[FJ40Jim]

Restricting air intake with hand & idle increases = mixture is very lean.
Look for restricted passage in carb, bad ICS, vacuum leak(s)...