fj60 Carb adjust screws, what do they do?

2mbb

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The screw on the right side of the carb (next to the valve cover) is the idle mixture screw. The one on the front of the carb adjusts the ac idle up. The two on the back of the carb are for idle speed and fast idle speed.

The procedure for setting the idle speed and idle mixture is described in the attachment. I usually start with the idle mixture screw turned out (counter clockwise) 1 1/2 turns from it's seated position (turned all the way in). I turn the mixture screw in 1/4 turn increments (starting with counter clockwise), and wait for the rpms to stabilize, and conintue this in one direction until the rpm's maximize. I use a handheld tachometer to measure the rpm's. If I go a 1/4 turn too far (rpm's start to decrease), it's easy to find the maximum by turning the screw back the 1/4 turn. Once I'm close to the maximum I might do 1/8 turns (e.g. half as far as the 1/4 turn).

You set the fast idle screw to get the desired idle speed when the choke is pulled out.

If you set the AC idle up too high (screw it in too far) the idle will become unstable the AC is turned on. I have mine adjusted so the idle speed increase from 650 to about 1000 when the AC compressor engages.
lean drop 2.JPG
 
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Cruiserdrew

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Not to hijack, but which screw would adjust the carb for altitude?
Does not exist. The 60 has a HAC built in that I think advances the timing a bit. I've never been convinced it does much.

The way I think about the Aisin carb is that it isn't really adjustable, except for idle mixture. The main and secondary are only adjustable by disassembling the carb, and swapping out the jets. The other screws are just set screws that adjust how far the throttle opens under various conditions, like when the choke it pulled or the ac comes on. They don't adjust fuel mixture at all.
 

cbmontgo

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Does not exist. The 60 has a HAC built in that I think advances the timing a bit. I've never been convinced it does much.

The way I think about the Aisin carb is that it isn't really adjustable, except for idle mixture. The main and secondary are only adjustable by disassembling the carb, and swapping out the jets. The other screws are just set screws that adjust how far the throttle opens under various conditions, like when the choke it pulled or the ac comes on. They don't adjust fuel mixture at all.

That is what I thought too, but after I moved to Colorado, people have told me that I need to tune my carb for the altitude. It does fine up here, but I was wheelin' at 12,000' altitude a few weeks back and my engine died. Others with the Aisin who are from Colorado can go above that altitude. I am not sure what the difference is, but theirs somehow can make it higher than I can go.
 

2mbb

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That is what I thought too, but after I moved to Colorado, people have told me that I need to tune my carb for the altitude. It does fine up here, but I was wheelin' at 12,000' altitude a few weeks back and my engine died. Others with the Aisin who are from Colorado can go above that altitude. I am not sure what the difference is, but theirs somehow can make it higher than I can go.
The HAC does advance the timing, but it also leans out the primary hi/lo and secondary hi speed circuits. Maybe your HAC isn't working properly?
hac schematic.JPG
 
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Why do you think you need to adjust it? Failing smog?

If it hasn't been rebuilt ever, then take it to Mark and start there. He rebuilt mine and would recommend him.
 
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That's scary, "lean drop"?
Does this explain the method, or the result? I don't want leaned out cylinders...
 

cbmontgo

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The HAC does advance the timing, but it also leans out the primary hi/lo and secondary hi speed circuits. Maybe your HAC isn't working properly?
Yes, I am thinking that may be the problem. I am going to buy a new HAC.

I rebuilt the carb will all Toyota parts 2 years ago, and it runs perfectly. I think the HAC or something thereabouts is the problem at high altitude.
 
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Reviving this thread for a second... I live in East Texas Where the altitude is ~500 ft. I bought my cruiser in Denver where the altitude is 10x that. I've been driving my cruiser around for about a month hoping I would notice a change, but I fee like my carburetor is running way too rich. How would I adjust that? Is there a way to adjust it without pulling it apart?
 
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