Carb Circuits - Aisin 2F FJ60 USA - Troubleshooting (1 Viewer)

[Slow Left]

hmmm. alright, that MIGHT be a source of air infiltration, but if anything, it is going to artificially lower the vacuum in the carbs internal vacuum plenum, which in turn, should allow the power valve to open sooner than otherwise required by a motor without a possible vacuum leak, which would have you running more rich than you should be sooner than you should be...right?

So I have been attributing the symptoms (poor gas mileage, flat spot in the acceleration band at ~1,800, and stinky exhaust) more to a lean condition than a rich one. Even if the vac on the Power Piston is OK, if the spring in the Power Piston is weak, it might not be strong enough to push open the Power Valve, causing a lean condition because the Power circuit would remain closed at a time when the additional fuel is being demanded.

But couldn't these symptoms (except maybe for stinky exhaust) also be explained by a rich condition?

 

[LAMBCRUSHER]

I can't visualize vacuum leaking anywhere around that bolt. There is a gasket around every place that bolt passes.

this is what I'm thinking; glad you're confirming...

 

[LAMBCRUSHER]

So I have been attributing the symptoms (poor gas mileage, flat spot in the acceleration band at ~1,800, and stinky exhaust) more to a lean condition than a rich one. Even if the vac on the Power Piston is OK, if the spring in the Power Piston is weak, it might not be strong enough to push open the Power Valve, causing a lean condition because the Power circuit would remain closed at a time when the additional fuel is being demanded.

But couldn't these symptoms (except maybe for stinky exhaust) also be explained by a rich condition?

yes...

 

[Slow Left]

I can't visualize vacuum leaking anywhere around that bolt. There is a gasket around every place that bolt passes.

this is what I'm thinking; glad you're confirming...

I checked the bonded gasket surface on the carb base plate insulator gasket (the one that goes between the top of the intake manifold and the bottom of the carb) and there is a nice mark where the hole to that passage bolt sits. It looks like it is making a nice seal and preventing a vac leak.

So if the crush washer on the hollow passage bolt was not air tight, then the leak would have to come from behind the bolt...between the carb insulator on the carb itself or maybe even the threads or face where it threads into the Air Horn...

But until I've got the correct crush washer in hand, I'm gonna leave it be...and assume that the cause is elsewhere...

 

[Slow Left]

@LAMBCRUSHER @Pin_Head

I slapped the carb back together...everything looked fine inside. The only thing out of whack I found was I had the little arm on the Choke Breaker linkage (that gets pushed by the primary throttle link) on the wrong side before, so that is probably the reason why the CB wasn't working.

I did, however, think I solved the issue with the mid-RPM stumble (won't know for certain until I run it some more).

When I replace my 3mm vac hoses, I did not reinstall 3 orifice restrictors:
at the Air Cleaner hose on the Choke Opener circuit
before Port P at the EGR Modulator
and I can't remember the 3rd (did replace it because I only had 2 solutions and I used them above)

Anyways, I think those were causing internal vac leaks and, in the case of the EGR circuit, it was causing the EGR Valve to dance around 1,500 RPMs...

See this link for more info:

https://forum.ih8mud.com/threads/are-these-symbols-for-a-check-valve.827721/

Thanks again for the help, fellas! I figured out a couple more circuits on the carb, so I'll update the first post (the PS and DS vac ports at the front of the Air Horn that lead to the HAC Valve pull venturi vac (from the 1st and 2nd nozzles respectively)...didn't know that...)
Also confirmed that the CB pulls vac through the hollow passage bolt....

I'm gonna finish writing what I started on the first couple posts, summarizing how the carb circuits work (to the best of my understanding), and if either of you or anyone else on MUD wants to make corrections/clarifications/improvements, post em up and we'll add them in...kind of a running thread for folks rebuilding/troubleshooting carbs, it they are interested...

 

[Spike Strip]

@Rigger
@Cruiser Jimmy
@Mace

Some good stuff in this thread I've seen nowhere else....

Can it be put in the FAQ, please? (under 'Tuning and Problem solving').

 

[Spike Strip]

This hasn't been FAQ'd yet.

Do we wanna put it there?

@Rigger

 

[Rigger]

This hasn't been FAQ'd yet.

Do we wanna put it there?

@Rigger

I will get to this. I promise. Been on the run a bit lately. Sorry.

 

[Spike Strip]

Thank you! No worries.

 

[Rigger]

Added to FAQ

 

[Spike Strip]

 

[Spike Strip]

Thanks to @mwebfj60 for these posts with more information:

Aisan Decel Fuel Cut Circuit

Aisan Secondary Circuits

Carb trouble

 

[NeverGiveUpYota]

I'll add here too that on this thread a guy not on mud who does carbs is still active and his number is still accessible. I just spoke with him and am going to send the base of my carb off to him so he can pull the throttle shaft and put new teflon bushings in and resurface it.
His name is Mark Beno. Super nice and explains everything well. $60 now, 2-3 turn around.Says that the turning of the IM screw will go from 1/4 and 1/2 turns to 1/8th easily.
Need your carb throttle shaft rebushed?