72 fj40 revival after sitting for 41 years

[JohnMerk]

Got the wheels on and currently waiting on exhaust pipes to ship for it. Been messing with the carb since it just didn't run quite perfectly.

Got a rebuild kit and went over it to the best of my ability but still have issues, everything I can find on tuning the carbs in is either for a 2f or only partial info. My issue seems to be that I can't get it to idle down low enough, right now according to the tachometer it's 900-1000.
I saw mixture screw out 3-4 turns and to adjust from there but even with it so far out I can have both idle screws all the way out and it still won't idle down far enough.

Also getting on the gas pedal it drops rpm before revving up. I've set a bunch of Atv and dirtbike carbs but never a big one like this. If anyone would be willing to take the time to write it out or direct me to a write up on it that explains it like I'm dumb I'd greatly appreciate it!

 

[greenbeasty]

" explain it like I'm dumb"
Now there is an instruction I can relate to!! Well said.

 

[JohnnyC]

IMO sounds like a vac leak… did you check around intake… carb gasket… brake booster? Carb have any vac ports not capped ?

 

[JohnMerk]

IMO sounds like a vac leak… did you check around intake… carb gasket… brake booster? Carb have any vac ports not capped ?

Now the brake booster has been problematic but I can't gaurntee the one that was on it or the one I swapped it with was the reason because neither work . I had read that just covering the carb with a piece of cardboard when running and if it revs up before it dies it's a vacuum leak, I tried that and it just died out without any change.

I can go over it tomorrow and spray it all down and see if I can find any leaks. I guess it's not a bad idea to just go ahead and replace all the vacuum lines regardless if they need it or not.

" explain it like I'm dumb"
Now there is an instruction I can relate to!! Well said.

Information can too easily be lost when it's assumed that someone already knows something, id rather someone tell me something I could already know just for the sake of incase I don't.

 

[Pighead]

I saw mixture screw out 3-4 turns and to adjust from there but even with it so far out I can have both idle screws all the way out and it still won't idle down far enough.

make sure you have the right idle speed screw, sometimes they can be hard to see. Maybe disconnect the throttle linkage from the carb, make sure the linkage isn't hanging up somewhere. Check your timing too, too much advance can make it idle fast

 

[JohnMerk]

make sure you have the right idle speed screw, sometimes they can be hard to see. Maybe disconnect the throttle linkage from the carb, make sure the linkage isn't hanging up somewhere. Check your timing too, too much advance can make it idle fast

I saw two on the firewall side of the carb and both of them backed out till not touching anything and still high idle, I don't know if it's the linkage, it all seems like it's in place of where it should be and hitting where it should as well, cranking the mixture screw in to like 1ish turns out it will drop the idle but I don't think it should be screwed in that far?

I have yet to check timing, tha could be a possibility. Are there any good write ups on that on how to do it properly?

 

[RevISK]

make sure you have the right idle speed screw, sometimes they can be hard to see. Maybe disconnect the throttle linkage from the carb, make sure the linkage isn't hanging up somewhere. Check your timing too, too much advance can make it idle fast

My first thought was timing.

Start there.

 

[Pighead]

I saw two on the firewall side of the carb and both of them backed out till not touching anything and still high idle, I don't know if it's the linkage, it all seems like it's in place of where it should be and hitting where it should as well, cranking the mixture screw in to like 1ish turns out it will drop the idle but I don't think it should be screwed in that far?

I should have said cable, not linkage. Maybe disconnect the cable at the carb, see if you have full range on whatever it attaches to. Is the return spring weak? give it some help manually. That linkage looks a little rusty too. I leave my idle air mix screw alone until the end.

 

[sogafarm]

Check the choke adjustment screw and make sure sure its not touching the bottom plate.

 

[diesellibrarian]

I've just been through this with my '72 - especially the little rpm drop or stumble when you first hit the throttle. In the end it was timing/ignition.

Are you still running the original distributor? Mine was, and it's a vacuum retard unit. My theory is that the mechanical advance was not working properly, so when I put some pedal into it, the distributor was only retarding, which is of course the opposite of what you want. I swapped out the distributor for one from a '76 and it's now running very well.

 

[JohnMerk]

I've just been through this with my '72 - especially the little rpm drop or stumble when you first hit the throttle. In the end it was timing/ignition.

Are you still running the original distributor? Mine was, and it's a vacuum retard unit. My theory is that the mechanical advance was not working properly, so when I put some pedal into it, the distributor was only retarding, which is of course the opposite of what you want. I swapped out the distributor for one from a '76 and it's now running very well.

I'll be going over the ignition tonight, I assume it's original I'm really not too sure tho. I am sure I have others to pick from tho if it is more beneficial to swap to a different one? I should have a bunch of 2f ones but I'll have to see what looks the best.

I should have said cable, not linkage. Maybe disconnect the cable at the carb, see if you have full range on whatever it attaches to. Is the return spring weak? give it some help manually. That linkage looks a little rusty too. I leave my idle air mix screw alone until the end.

Pushing the linkage back it bottoms out one one of the linkage rods, I think it is working properly linkage wise. They are not rusty enough to interfere but I will spray they with some lubricant later to make sure they actuate nicely

Check the choke adjustment screw and make sure sure its not touching the bottom plate.

I had that one backed out as far as it goes I believe.

 

[diesellibrarian]

I'll be going over the ignition tonight, I assume it's original I'm really not too sure tho. I am sure I have others to pick from tho if it is more beneficial to swap to a different one? I should have a bunch of 2f ones but I'll have to see what looks the best.

Assuming you're still running the OG vac retard distributor, the conventional wisdom on this forum is to pinch the vacuum line that goes to the distributor. I think many folks permanently plug it. Might be worth a try, to see if it makes any difference. I'd start by setting the timing per the service manual though, so you know it's not way off to begin with.

 

[diesellibrarian]

Also, is this hose plugged?

 

[JohnMerk]

Assuming you're still running the OG vac retard distributor, the conventional wisdom on this forum is to pinch the vacuum line that goes to the distributor. I think many folks permanently plug it. Might be worth a try, to see if it makes any difference. I'd start by setting the timing per the service manual though, so you know it's not way off to begin with.

I'll try that

Also, is this hose plugged?

View attachment 4204723

yes it is plugged up

 

[JohnMerk]

Checked it out, it was indeed off on timing, points look terrific and checked out good, got the timing back where it should be. Kept fighting with it as soon as I got timing set because it kept getting harder and harder to start and then just wouldn't.
It ran out of gas
Anyway with a fresh tank of fuel I was able to get my idle down lower but I think I do indeed have a vacuum leak in the vacuum timing advance line because it doesn't seem to work as it should. I pulled a vacuum with the distributor apart and it does move but doesn't seem to when it's running. I'll get new hoses later today and keep going at it

 

[JohnMerk]

Just trying to tune in my 71 fj40, this was before I noticed my vacuum advance hose being sucked closed | John Merkey

Just trying to tune in my 71 fj40, this was before I noticed my vacuum advance hose being sucked closed

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Not sure if that link will take you to my facebook reel, I can't add a video here so that's my next best option.

I got it running significantly better than it did previously. The vacuum advance hose had not been sealed up real good. Got a new one on just a temporary replacement till my other one comes. Also ordered a new throttle cable.

I hadn't noticed when I took the video but it sucked my vacuum hose closed so that could have something to do with the (in my mind pretty sick) backfires but new hose is ordered and on its way. Next is going to be the brakes. Real stiff pedal even with swapping another brake booster into it