Too much vacuum?? (1 Viewer)

[KRGfab]

1972 FJ40, original F engine and carb. Trying to get the idle down to the specified 650 RPM and vacuum to 16.5. Right now I'm currently idling around 1000 and pulling between 19-20 vacuum. I've gone through and tried adjusting the idle per my Haynes manual (i know, not the best source of info, but can't find much info about adjusting the F Carb). It runs and drives fine otherwise.

Only other thing I can think to adjust would be timing, but when I put my light on it in not seeing the BB, so not sure if it is missing, dirty, or just not seeing it. But also don't want to change too many variables at once and end up with it not running.

 

[Curt]

Your idle is set to high. With the idle at 650rpm and timing at around 10* you should be getting 18-20 inches of vacuum. you will have to adjust the idle mixture screw as well.

Carb Works Great!

 

[KRGfab]

Your idle is set to high. With the idle at 650rpm and timing at around 10* you should be getting 18-20 inches of vacuum. you will have to adjust the idle mixture screw as well.

Carb Works Great!

That's the thing, I've backed the idle setting screw all the way to the point its not contacting the linkage and it still sits around 1000-1200. I've also disconnected the throttle cable to make sure it wasn't too tight with the same result. If I push on the linkage, I can get it to drop, but that didn't seem right.

Thanks for posting the link, read through it and I'm not seeing anything I have tried though. I'm checking the timing right now too.

 

[middlecalf]

Put truck in 3rd gear or 4th if you have it, bump the rig forward by hand (I use the front tire/wheel) and with a very bright light trained on the timing hole in the bellhousing look for the timing line and ball. When you see them clean them up and put some white paint on them. That‘ll help you see them with timing light. At sea level your vacuum numbers are good. Probably need to turn in the idle mixture screw some to get the rpms at idle down, sounds like you’ve only adjusted the idle (throttle) screw.

 

[KRGfab]

Pulled the plugs, turned engine over by hand and found the BB under a layer of grime. Cleaned it and put some white paint on it. Timing is set properly. Still idling around 1000.

 

[KRGfab]

Probably need to turn in the idle mixture screw some to get the rpms at idle down, sounds like you’ve only adjusted the idle (throttle) screw.

I have messed with the mixture screw a little bit, set it to the recommended 1 1/4 turns, seems to be happy, turn it in more start to get pre-detonation pinging, turning it out seems to cause some hesitation under heavy acceleration. Really confused by this one, shouldn't be this hard.

 

[cbmontgo]

I’d really inspect your linkage for something misadjusted. It should only be pulling fuel through the idle circuit.

 

[KRGfab]

I’d really inspect your linkage for something misadjusted. It should only be pulling fuel through the idle circuit.

I'm kinda leaning to that same direction now too. Problem is finding a good reference, I'll do some digging and see what I can find. Thanks everybody for the help so far!

 

[brian]

disconnect the linkage and tune the carb, then work backwards on the linkage.

 

[Splangy]

I have messed with the mixture screw a little bit, set it to the recommended 1 1/4 turns, seems to be happy, turn it in more start to get pre-detonation pinging, turning it out seems to cause some hesitation under heavy acceleration. Really confused by this one, shouldn't be this hard.

There’s no way your idle mixture screw adjustment is causing pinging.

Is your choke hooked up? Is it causing a high idle?

 

[KRGfab]

May have found the answer, after some thorough head scratching and closer examination and comparison with exploded view diagrams. It appears there is a third "throttle adjustment screw/ idle adjustment screw" as Haynes likes to call it, tucked way behind everything. Hoping that is what is causing the high idle, so will run it up in the morning and try adjusting that.

 

[KRGfab]

Fixed! That third adjustment screw inline with the other two, but hidden behind everything was the answer. I believe it's the adjustment for the butterfly valve and was turned too far in, making the idle adjustment screw useless. Backed that out about a half turn and now the idle adjust screw is holding the cam in place. Got my idle bouncing around 7-800, will spend some time this afternoon fine tuning it.