Aisan carb question, the final chapter.

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Joined
Oct 20, 2008
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I have another link out there with carb questions, but I think I am down to two final questions.
What is the correct way to set up the Idle mixture adjusting screw? (I'm not sure if I'm understanding correctly as explained in my haynes book)
What is the correct way to set up the Throttle Positioner connection link? (I put this back together as it was but would love to know if that is correct)
If it is needed, this is for the carb off a 72
Thanks again for all the help on this project.
 
I did but there was no reply so I worried about too much info/replys that someone wouldn't want to read through it all to get to my final questions.
 
I total agree I'm trying to make it easier rather than wade through all the questions I have had, everyone has been so very helpful, I just want to make it as easy as possible.
 
If people are interested, they will follow the thread, no matter how long :) Hardest thing for me is getting a thread title that people will click on. By keeping one thread rolling along, it often times contain better overall info like D'Animal pointed out.

You can keep the thread on the first page by posting yourself, or keeping good updates on it.

I think you are darn close to getting a sweet running carb, hang in there. I suspect the photo posted in your other post helped on the linkage. Also good instructions on setting idle mix. But you will need a timing light, do you have one? That's the best way to tune it up right. You can use an electronic timing light to get RPM's, then set timing and etc... also. Idle speed will make your timing vary, as you set idle with the carb. So each thing will have to be tweaked and checked.

One thing I do when setting idle speed and idle mixture is set the primary butterfly to where a thin card, match book cover thickness is evident between the butterfly and bore wall. There is an exact spec for this, but hard to measure in the FSM. To have an engine idle correctly, you only want the primary opened up enough to provide vacuum to make the idle curcuit hole flow gas. The idle curcuit comes in below the primary butterfly. If the idle palte is opened too far, you will see gas being pulled from the passages above the plate at idle, and it is not as effecient. This equtes to only a turn or two of the idle set screw on the back of the carb, after it makes contact with carb linkage. The idle mixture screw then adjust the mix of gas and air in the idle curcuit passage. However, the only way to see where gas is getting pulled from is with the aircleaner off, which is not recommended, as it changes the settings some. You have to dial it in with the aircleaner on, so the vacuum is correct, as it would normally run that way.

If the primary plate is open too far, you are bypassing the idle curcuit, and adjusting the idle mix screw on the valve cover side of the carb will have very little if any effect on idle speed and performance. Remember this, if the idle mix screw does nothing to idle speed, then the primary needs closed some, and idle mix opened up a bit. A little bit goes a long ways too.

This may have been the issue all along with bad accel too, at least a contributing factor. All the curcuits have to work together, one fault in a curcuit can effect the others. And as you have probably found out, the idle curcuit passage to the base of the carb is pretty small and can plug up.

Sorry, windy, good luck
 
Thank you so very much
I just replied in my other thread but we have sucess. I put the carb on the cruiser and it fired right up, it idles, etc. I don't have time to do the adjusting but your comments will be perfect to fine tune it. Everyone has been so extremly helpful, it just renews my faith in man kind.
I'm out of here before I start to cry.
Again, thanks to all
 
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If people are interested, they will follow the thread, no matter how long :) Hardest thing for me is getting a thread title that people will click on. By keeping one thread rolling along, it often times contain better overall info like D'Animal pointed out.

You can keep the thread on the first page by posting yourself, or keeping good updates on it.

I think you are darn close to getting a sweet running carb, hang in there. I suspect the photo posted in your other post helped on the linkage. Also good instructions on setting idle mix. But you will need a timing light, do you have one? That's the best way to tune it up right. You can use an electronic timing light to get RPM's, then set timing and etc... also. Idle speed will make your timing vary, as you set idle with the carb. So each thing will have to be tweaked and checked.

One thing I do when setting idle speed and idle mixture is set the primary butterfly to where a thin card, match book cover thickness is evident between the butterfly and bore wall. There is an exact spec for this, but hard to measure in the FSM. To have an engine idle correctly, you only want the primary opened up enough to provide vacuum to make the idle curcuit hole flow gas. The idle curcuit comes in below the primary butterfly. If the idle palte is opened too far, you will see gas being pulled from the passages above the plate at idle, and it is not as effecient. This equtes to only a turn or two of the idle set screw on the back of the carb, after it makes contact with carb linkage. The idle mixture screw then adjust the mix of gas and air in the idle curcuit passage. However, the only way to see where gas is getting pulled from is with the aircleaner off, which is not recommended, as it changes the settings some. You have to dial it in with the aircleaner on, so the vacuum is correct, as it would normally run that way.

If the primary plate is open too far, you are bypassing the idle curcuit, and adjusting the idle mix screw on the valve cover side of the carb will have very little if any effect on idle speed and performance. Remember this, if the idle mix screw does nothing to idle speed, then the primary needs closed some, and idle mix opened up a bit. A little bit goes a long ways too.

This may have been the issue all along with bad accel too, at least a contributing factor. All the curcuits have to work together, one fault in a curcuit can effect the others. And as you have probably found out, the idle curcuit passage to the base of the carb is pretty small and can plug up.

Sorry, windy, good luck


Digging up an old thread…



Just kitted the carb on the 78 and it wont idle without the choke pulled out just a smidge. The mixture screw has no effect at all and when it is ‘’idling” all the fuel is driping from the primary Venturi.

pulled the idle cut solenoid and it appears to be working.

The idle mixture needle is bone dry pulled immediately after running.

This implies a plugged idle circuit…

Where do i look first?
 
“This implies a plugged idle circuit.” Possibly, but probably not. The most common cause is a vacuum leak somewhere resulting in you (or someone else) needing to turn up the idle SPEED screw to get it to idle or pull the choke a little. That gets it to idle alright, but the result is that the throttle plate is open too far and the idle circuit inside the carb is effectively bypassed. When you find and fix the vacuum leak, the idle will magically increase and when you then reduce the idle with the idle speed screw, the mixture screw will work as it should. And you won’t need the choke.
 
“This implies a plugged idle circuit.” Possibly, but probably not. The most common cause is a vacuum leak somewhere resulting in you (or someone else) needing to turn up the idle SPEED screw to get it to idle or pull the choke a little. That gets it to idle alright, but the result is that the throttle plate is open too far and the idle circuit inside the carb is effectively bypassed. When you find and fix the vacuum leak, the idle will magically increase and when you then reduce the idle with the idle speed screw, the mixture screw will work as it should. And you won’t need the choke.

YUP !!!

There is a leak between the throttle body and the EGR spacer. The Carb kit didn't include those gaskets so I cleaned and carefully reused what was there... Unfortunately I failed!!!

Letting the truck cool down now and the carb is coming off again.

What does everybody use to fix this condition as the OEM gaskets are bonded in place?
 
There is no reliable ‘fix’ other than complete replacement of the offending part. I got mine from City Racer for about $100.

IMG_6984.webp


IMG_6986.webp


IMG_6987.webp
 
There is no reliable ‘fix’ other than complete replacement of the offending part. I got mine from City Racer for about $100.

View attachment 3365717

View attachment 3365718

View attachment 3365719
My spacer/heat-shield is in good shape and have gaskets for both sides...

Its the EGR spacer between the cast throttle body and the venturi plenum that I dont have gaskets for.


Just pulled it apart, used some spray permatex and will try it.

If that doesnt work it looks like there are other carb kits that include those gaskets.

Was trying to keep the $$$ in the Mud community so I went with a different kit than what Pinhead shows on the videos...
 
Ah, very good. Carry on and good luck with your repair.👍
 
My spacer/heat-shield is in good shape and have gaskets for both sides...

Well that was more of a wish than anything else...

Pulled everything off, used gasket adhesive, put it all back together and the leak is worse.

It moved from the carb body to the spacer/intake junction so I have that going for me.
 
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