carb question

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LSUfj

LSUfj

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I've spent hours reading up on old tune-up posts related to the carburetor.

I have a desmogged 75 that I just replaced the distributor/coil with an electronic fj60 set up. I bench tested the coil and distributor and its good to go. I put it in, with carb set to the base settings outlined in the FSM. I got it to start, but cant get it to stay running unless i keep the pedal down (approx 1500-2k rpm) It stalls almost immediately when I let it drop below 1500ish. Fuel tank, lines, filter are all new. Fuel level in carb is slightly above mid level. Accel pump is working. After all of the reading I have done, I came up with a few ideas and would like your input:
  • idle mixture setting isnt allowing enough fuel in to idle. By keeping my foot on the pedal, it is running off of the main(??) jets
  • there are some clogged passages that arent allowing fuel in under idle conditions.
What do you think?

Thanks, Bret
 
Trollhole said:
Idle solenoid?

Sure it's getting 12v? Can usually feel it click.
Click to expand...

It isnt connected, but I think that the tip of it was removed internally. Does anyone ever do this to the solenoid as part of a desmog? I will certainly try hooking it up, but I think it is modified to work without being powered. Any other ideas??

Thanks for the input Trollhole, if all else fails I will be ordering a carb from you. I assume your carb will work with a vacuum advance dizzy....
 
Last edited:
Yes it will but you should try to fix the junk you have first.

Modified? Need to see pics?

The whole carb sounds suspect.

No desmog I have ever seen has had this done.
 
Sounds like a vacuum hose is loose.
 
Yes, I do know you can defeat the purpose of the fuel cut-off solenoid by chopping the plunger off...on an early carb, like my '74. I looked at my buddy's '76 carb and it had a different solenoid, didn't look so easy to do on his. I'd pull out that solenoid and take a look at it.
 
I just got done going through my carb-Also on a 75. It ran like garbage even after I got done. So I got to looking around and realized that the PO had cut the juice to my idle solenoid. I think that they did it when they desmogged. I hooked it back up and it made almost all the difference in the world. Runs smooth and I can turn the idle down to where it should be. Here is a link to tuning the idle screw and idle mixture screw: https://forum.ih8mud.com/40-55-series-tech/266151-adjusting-tuning-my-77-fj40-carburetor.html

I know this works if the idle solenoid has juice and is working. I however, have no idea how this works in relation to a modified solenoid. Hope it helps!
 
Pighead said:
Yes, I do know you can defeat the purpose of the fuel cut-off solenoid by chopping the plunger off...on an early carb, like my '74. I looked at my buddy's '76 carb and it had a different solenoid, didn't look so easy to do on his. I'd pull out that solenoid and take a look at it.
Click to expand...

I snapped a photo of the solenoid. It doesnt work as it should, but the tip was removed. I am thinking that it allows fuel to flow all the time now. Let me know if you guys think otherwise. I will order a new one and give that a shot anyway.



Thanks,
Bret
idle solenoid.webp
 
I pulled the carb off again to go through the idle circuit. I removed the idle mixture screw and cleaned out the passage. I cleaned one of the jets but cant get the other out. The one in the bowl, on the secondary side isnt coming out easily, so I moved on. So here is my question,

  • The diagram in the FSM shows the carb split in half, does this represent the primary and secondary barrels?
  • In the attaches picture, is this jet the one that feeds the idle circuit?
  • What does the power valve do?
Thanks,

Bret
carb top1.webp
 
Yes, the primary main jet subsequently feeds the primary slow jet. Since the carb runs at 2000RPM, we know the pri main is not plugged up. Remove the slow jet and the idle mix screw and blow through the idle passages w/ carb cleaner and compressed air. Reinstall idle mix screw 4 turns out.

The chopped off idle solenoid is not a problem.

There are many wrong ways to connect vacuum hoses on a 75 carb & dissy. We need pics of the vac hose routing.
 
I removed the carb...again. Everything seems to be in order internally. I noticed a patch-job on the inside of my intake manifold, so I suspect it to be leaking. I am going to try to source a replacement. I got it to run for about 30 seconds at a decent idle, but eventually it stalled. I had the choke out at that time. When it stalled, I checked the fuel level in that carb and it was still normal. I dont think I am running out of fuel at the carb, but thats what it seems like. I will post some pics of the vacuum routing, but here is a temporary explanation:
-aux accel pump??? to connection at thermostat housing
-power valve to manifold vacuum
-throttle positioner?? to manifold
-ported vacuum at base to fj60 dizzy
-other thermostat housing port to manifold
-brake booster to manifold



I think thats it.
carb pass.webp
carb front.webp
carb driv.webp
 
Last edited:
Mine did this a couple years ago ('79 2F). I left it in storage for over a year, and it wouldn't start. I'd prime it, and it would start and then die. I figured the float was stuck, so I primed it with fuel (poured in via a mason jar), cranked it, and tapped on it with a hammer. Problem fixed. It took a few good whacks, but it has worked 100% for a couple years now since I tapped it. Probably not the safest way to do it, but it worked.
 
tx4guns said:
Mine did this a couple years ago ('79 2F). I left it in storage for over a year, and it wouldn't start. I'd prime it, and it would start and then die. I figured the float was stuck, so I primed it with fuel (poured in via a mason jar), cranked it, and tapped on it with a hammer. Problem fixed. It took a few good whacks, but it has worked 100% for a couple years now since I tapped it. Probably not the safest way to do it, but it worked.
Click to expand...

Ha, I tried this not too long ago and it backfired.....enough to split the muffler in half....
 
I'm pretty ignorant about this stuff. My only carb experience is with my motorcycle, but I'm with igotta40. It sounds like a vacuum issue. Do you have a vacuum gauge to see if you have enough pressure (unfortunately I don't even have enough knowledge to tell you which port to check)? HTH. Good luck.
 
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