FJ55 f engine Carb tune issues (1 Viewer)

[Tomba]

Back at the fine tuning again. I've read up on this topic quite a bit and also did some additional work to get the motor and carb running the best its been since I started working on this pig. That said, I am still not convinced the carb is functioning 100% correctly.

I am questioning if I still may have a partial idle circuit /transition blockage. I am getting 18 in.hg vac reading and have set the idle to about 800 rpms when fully warmed up. When I adjust the mixture screw I do get an increase /decrease in rpms but requires a full rotation to get any effect. If i shut the mix screw all the way off the motor still runs.. I also cant tell if the fuel is coming out of the idle and transition slots or the primary throttle. when I throttle it I see gas coming out from the top hole on the primary emulsifier but before that, nothing and I do see fuel going in while idling but cant tell from where . Runs and idles fairly well but occasionally dies when I come to a stop. Starts back up right away though. Feel like I am very close but not perfect.

Any thoughts on this?

 

[Tomba]

This is becoming routine. brush teeth, wash face , remove carb. Blowing compressed air through the idle and transition holes from the base of the carb didnt do the trick. Removal again and take the airhorn off it is. Hoping it would be easier. That said , she runs very well just not perfect ... yet

 

[65swb45]

The idle circuit delivers fuel below the throttle plate/butterfly. Therefore, if you can see gas, it’s not coming from the idle circuit.

Back the idle speed down to 650. That is low enough that the primary should stop dribbling, and the engine run exclusively on the idle circuit IF there is sufficient vacuum to operate the circuit.
No amount of cleaning will make the idle circuit work properly without good vacuum.

 

[Tomba]

Thanks Mark. I'll revisit this afternoon. I may have to advance timing a bit to get there. Will report back-

 

[mattressking]

Note that when tuning, if you can soft seat the mixture needle and the engine continues to run, your primary jet is too large. Mark is right though, 800rpms is too high, back it down to factory 650 or start at 690 if lean dropping.

Did you sort the mixture screw out with a replacement?

 

[Tomba]

Note that when tuning, if you can soft seat the mixture needle and the engine continues to run, your primary jet is too large. Mark is right though, 800rpms is too high, back it down to factory 650 or start at 690 if lean dropping.

Did you sort the mixture screw out with a replacement?

The primary , secondary stock sizes. Did not replace the mix screw, it's in good shape. When I rebuilt carb I kept all stock. I starting doing the lean drop yesterday but got interrupted. yeah, I'll back it down a bit and continue . Thanks-

 

[mattressking]

The primary , secondary stock sizes. Did not replace the mix screw, it's in good shape. When I rebuilt carb I kept all stock. I starting doing the lean drop yesterday but got interrupted. yeah, I'll back it down a bit and continue . Thanks-

Incorrect - mixture screw is damaged. It has been hammered down too tight, way too many times. The tip needs to be a smooth, no step at all. If you're in a bind, chuck it in a drill or similar and shape the tip to a triangular point without step. There are a number of styles of mixture screws in rebuild kits and you have to ensure it actually seals up correctly when closed.

What jets are in the carb - did you actually verify the numbers and if anyone drilled them out? There's a lot to this unfortunately and assumptions make the resolution take longer.

Short answer though, once the truck is at 650rpms, measure vacuum. If it's under 16, fix your leaks and get it above 18. Also make sure that if you are at sea level, your timing should be under 10*. I'd recommend base 7* to fault find your issues. If at sea level, for a smooth running motor, you want 18inHg minimum. You can tune 16-17inHg out mostly, but I'd recommend fixing all leaks if that is the case.

 

[Tomba]

Incorrect - mixture screw is damaged. It has been hammered down too tight, way too many times. The tip needs to be a smooth, no step at all. If you're in a bind, chuck it in a drill or similar and shape the tip to a triangular point without step. There are a number of styles of mixture screws in rebuild kits and you have to ensure it actually seals up correctly when closed.

What jets are in the carb - did you actually verify the numbers and if anyone drilled them out? There's a lot to this unfortunately and assumptions make the resolution take longer.

View attachment 3757922

Hot damn I need to get my eyes checked, good find! I confirmed the numbers on the jets but not sure if anyone before me tampered with them.
I used the new ones in the kit only if they were the same numbers as the stock ones, I do remember the power jet? was off so I reused the original after cleaning it. I'm not sure I have the skills or the eyes to reshape this screw. Maybe there one in the rebuild kit, if not I'll p/u a new one.

 

[Tomba]

Incorrect - mixture screw is damaged. It has been hammered down too tight, way too many times. The tip needs to be a smooth, no step at all. If you're in a bind, chuck it in a drill or similar and shape the tip to a triangular point without step. There are a number of styles of mixture screws in rebuild kits and you have to ensure it actually seals up correctly when closed.

What jets are in the carb - did you actually verify the numbers and if anyone drilled them out? There's a lot to this unfortunately and assumptions make the resolution take longer.

Short answer though, once the truck is at 650rpms, measure vacuum. If it's under 16, fix your leaks and get it above 18. Also make sure that if you are at sea level, your timing should be under 10*. I'd recommend base 7* to fault find your issues. If at sea level, for a smooth running motor, you want 18inHg minimum. You can tune 16-17inHg out mostly, but I'd recommend fixing all leaks if that is the case.

View attachment 3757922

Looking back earlier in this thread, Matt called that the mix screw was NOT perfect but I didn't quite catch it at the time. Damn.

 

[Tomba]

Just warmed it up got it to about 650 and pulling 15+hg. NO sign of vac leaks tho, spray bottle and also piece if card board over the carb kills the engine. At 650rpm I can still see fuel spewing in from the primary. is 15hg enough to pull fuel from the idle circuit?

 

[mattressking]

15inHg means you are missing about 6-7inHg from a tight motor. 21.5-22 is a tight motor.

You’ve got leaks to fix first…start at manifold and work your way out.

 

[Tomba]

15inHg means you are missing about 6-7inHg from a tight motor. 21.5-22 is a tight motor.

You’ve got leaks to fix first…start at manifold and work your way out.

I recently replaced the manifold gasket, adjusted valves, tinkered w timing , set point gap, rebuilt the carb and more.

hmmmm. might take a closer look at my vac gauge line, its a bit jankity. maybe that's the source of the leak. Using. spray bottle and water i couldn't find any leaks... head scratcher

 

[65swb45]

Points?

 

[Tomba]

Points?

I set the point gap , yes. The dizzy is a as you said a, "time bomb" Delco Remy

 

[Tomba]

Some progress. Vac tube was leaking. Zero evidence of leaks elsewhere tho.

 

[65swb45]

I set the point gap , yes. The dizzy is a as you said a "time bomb" Delco Remy

Point gap is an approximation of what you are really after, which is dwell, the amount of time the points are closed. As distributors get old/worn, it is often necessary to close the gap on the points to reach the appropriate dwell.
Insufficient dwell =weaker spark=lower vacuum.

 

[Tomba]

Point gap is an approximation of what you are really after, which is dwell, the amount of time the points are closed. As distributors get old/worn, it is often necessary to close the gap on the points to reach the appropriate dwell.
Insufficient dwell =weaker spark=lower vacuum.

 

[ToyotaMatt]

W/O a dwell meter, how much smaller should I make the gap ? a few hundreths to see if that makes a difference?

here is the nomenclature on a 1972 FJ55

@65swb45 / uncle Mark can better explain why some Land Cruisers came with a set / 2 / pair of additional JETS that were simply threaded into the back-side of each of the JET Service Plugs ?


any time i have seen this , there ALWAYS a different Spec. / orifice ID , but NOT all Land Cruisers have this little feature ?


.

.

 

[Tomba]

here is the nomenclature on a 1972 FJ55

@65swb45 / uncle Mark can better explain why some Land Cruisers came with a set / 2 / pair of additional JETS that were simply threaded into the back-side of each of the JET Service Plugs ?


any time i have seen this , there ALWAYS a different Spec. / orifice ID , but NOT all Land Cruisers have this little feature ?





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When I rebuilt my carb, I found that mine did in fact have extra jets. Maybe for tuning at different altitudes?

 

[Tomba]

The throttle cable was tight causing fuel from the primary to interfere w/ tuning. Once I backed off the cable.
Got it to work /tune properly