Tuning the carburetor in a 77 fj40 (1 Viewer)

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I am new to the 2f engine having a 327 in my 74 and know that . You guys have really helped me lately on these forums getting my cruiser up and running good, thanks for all the advice. I have an fsm for the 77 year coming soon too. I need it to run better before the fsm gets here. I put in my new dissy from an 84 and it runs like a champ. Only problem was that after I put it in the idle speed was like 1,600. Like and idiot instead of finding out first what each screw did in back I messed with them, well I did look in my haynes manual and it didn't show much. I backed off all three screws. I have done some searches and found that the one facing the valve cover is the Idle mixture screw. Is there a process (just with the carb. for now, I will do the valves etc. in the future) that I can do to tune the carb with just these three screws for now. I am going to send my carb into Jimc in the future but want to get it running good for now. I had to turn up the idle to get it to stop hesitating from the get go. I read that one thing I can do is to turn the idle mixture screw all the way in to make sure it gets the idle circuit gets gas. I was just going to try this but thought that if I could get a process from you guys first, or just a thread where it has been done I would be golden. My carb is the original for that year, I don't know non asian or asian. I will send a picture.

Thanks guys for your help and sorry for the long write up. I find when you know more then you can help me pinpoint without further delay.

Mitch
IMG_0768.jpg
 
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What the Hell is that wire going to the secondary diaphragm for?:confused:

If that thing is holding the secondary open you have idle problems for sure.....
IMG_0768 copy.jpg
 
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One rule I learned a long time ago with carbs. Always screw in the adjusters to lightly seated counting the turns. Then you know where you were and can always go back.
Cant help ya on the later carb. Mine only has a idle mix and speed.
 
Joined
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Wow that helped out a lot.

Right in front of me and didn't even see it. Like I said I am new to this carb and motor. I just bought it in Dec. and am bringing it up to the new millenium. I cut it and my idle went to like 400. I tightened up some of the other screws, especially the one that I think is the idle mixture screw, see pic. below. It runs much better but I still want to know what the other two screws are and maybe a process to get them adjusted to an optimal running level. Thanks agian, I do have a vacuum tested available to help me here.

Help me with the pic. and identification. My FSM will help a lot too when it gets here.

Thanks everyone for looking and helping.

Mitch
 
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Here is the picture of the back of the carb.

Back of carb. help
IMG_0791.jpg
 
Last edited:

65swb45

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In order of your listing

Top:Throttle Positioner-used to hold throttle partially open during start up

Middle: Choke adjuster screw-brings idle up as choke is applied

Bottom: Idle speed-sets basic idle speed

[not shown]Idle mixture-on the inboard side of the carb [facing the valve cover]

This is a VERY HELPFUL PICTURE to have on MUD. Thank you for posting it. If you could re-label it, it will be useful info for many others who ask the same questions.

Best

Mark A.
 

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