Carb Circuits - Aisin 2F FJ60 USA - Troubleshooting

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LAMBCRUSHER said:
IIUC, the power valve gets its vacuum internally via that hollow bolt...
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Pin_Head said:
Manifold vacuum is anywhere below the throttle plates. In the case of Aisan carbs it is obtained through the hollow bolt.
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OK, so consensus here is that the manifold vac generated to operate the Power Piston is generated through the hollow bolt...

EDIT: there is a hole in the wall of the primary throttle body housing between the hole in which that hollow bolt sits and the primary barrel...that is how the hollow bolt gets manifold vac...


So, if the gasket that I reused on that hollow bolt is leaking, then I might not be getting enough vac on the Power Piston and the Power Valve is open giving 'rich' condition...
 
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yep, that's the spot...the spray will show the way...
 
Pin_Head said:
You can just look at it and see daylight between the primary bore and the hollow bolt well. On some years (75-78?), the base lacks this hole perhaps because the is external vacuum control of the power valve.
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this is true of ealier vintage 2F carbs. in 80, the power valve got its vacuum internally...prior to, there were a couple different configurations of how and where the PV got its power from...for instance, the 77 carb and 78 carb had different inlet for this, at different points on the carbs...
 
Slow Left said:
EDIT: there is a hole in the wall of the primary throttle body housing between the hole in which that hollow bolt sits and the primary barrel...that is how the hollow bolt gets manifold vac...
Click to expand...
LAMBCRUSHER said:
yep, that's the spot...the spray will show the way...
Click to expand...
Pin_Head said:
You can just look at it and see daylight between the primary bore and the hollow bolt well.
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Yep. It's a pretty big hole, easily confirmed by looking through it that it connects the 1st barrel to the hole with the hollow screw in it. Makes sense now.
 
Pin_Head said:
On some years (75-78?), the base lacks this hole perhaps because the is external vacuum control of the power valve.
Click to expand...
LAMBCRUSHER said:
this is true of ealier vintage 2F carbs. in 80, the power valve got its vacuum internally...prior to, there were a couple different configurations of how and where the PV got its power from...for instance, the 77 carb and 78 carb had different inlet for this, at different points on the carbs...
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OK, looks like we've got some different configurations for different carb designs.
The carb I'm working on is an '81.
I think the first production year for 2F FJ60 USA was 1980, so if LAMBCRUSHER is right, then can we safely assume that all 2F FJ60 USA carbs use this 'hollow bolt' configuration? Including those post 4/1985?

If so, I just might make a note at the bottom of that section describing the Power Piston/Power Valve circuit that earlier 2F (earlier than the 1980 FJ60 USA) carbs might have a different configuration...and if someone, say from the 40 & 55 section wants to cross link/elaborate, then it can be more specific.
 
Any ideas how I can test to see if that reused gasket I have on the hollow bolt is not leaking?

Or, off the top of your head, do either of you guys know if the Hygrade kit comes with the correct gasket for that hollow bolt?

EDIT: there is a copper gasket and a fiber gasket in the Hygrade kit that are slightly smaller than the ID of that hole in the housing...but I wouldn't know for sure if they will fit over the bolt unless I remove the bolt...
 
uncertain...but I'd guess that with bolt in hand, one could source copper washer for this at their FLAPS, or online. unless that gasket has deep gouges in it, or it isn't tight, then it's prolly not leaking. have you done compression check and valve adjustment?
 
lovetoski said:
Nothing to contribute, other than to admit that I now realize I know way less than I thought I did about how a carb works. Very humbling.
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Yeah, it is humbling...that's why I think it's important to sort through it all...and by logging it here on MUD, hopefully it will help someone else answer some questions, too.
 
LAMBCRUSHER said:
uncertain...but I'd guess that with bolt in hand, one could source copper washer for this at their FLAPS, or online. unless that gasket has deep gouges in it, or it isn't tight, then it's prolly not leaking.
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Yeah, it would be easier if I had either a spare OEM gasket in hand or a sample hollow bolt.
Gonna think about this a bit more...
LAMBCRUSHER said:
have you done compression check and valve adjustment?
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Just did a valve adjustment and have noticed an increase in performance. Don't have compression numbers since...my compression gauge froze up on me, so either I'll have to borrow one or clean/fix (I think it's just rust, so a Seafoam bath might dissolve the issue)...

But I will add that I'm pulling 22 inHg at idle and the vac gauge shows that the engine is performing as it should under all conditions...
 
Pin_Head said:
I don't recall that there is a gasket for the bolt. Doesn't it have a lock washer like the other bolts. It has been a long time since I have seen one in the wild.
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The carb reassembly procedure in the FSM specifically calls for a new 'gasket' (aka crush washer). I guess this is what caught my attention, that the FSM explicitly states this and does so in bold type...?

from page 6-18 in the Fuel System chapter of the 2F Engine Repair FSM:

upload_2014-12-21_14-5-12.webp
 
Pin_Head said:
OK, so I had to go get out my box of junk carbs and check and sure enough, early 2F carbs use a lock washer and not a gasket.
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So when Toyota began using the hollow passage bolt at the manifold vac source on their 1980 on 2F FJ60 USA carbs, it appears they needed a gasket there to replace the lock washer so that the bolt head is sealed in order for sufficient vac to operate the Power Piston. Makes sense...

Pin_Head said:
I can't imagine reusing a metal gasket would be a problem.
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I came to the same conclusion during rebuild, but now I'm second guessing myself. Maybe Toyota explicitly states to install a new gasket in the FSM because they made the design change from lock washer to gasket...not in response to some failure study...

I wonder if these gasket are available through Toyota...I'd feel more comfortable having the correct one in hand instead of pulling the bolt and going on a hunting expedition....
 
I'm still not certain where vacuum could or would leak to or from ifn that gasket wasn't sealed...I mean, the bolt is hollow, right? the whole shebang is sealed under the carb from atmosphere; only exposed to same vac that would be via primary barrel port, right?
 
LAMBCRUSHER said:
I'm still not certain where vacuum could or would leak to or from ifn that gasket wasn't sealed...I mean, the bolt is hollow, right? the whole shebang is sealed under the carb from atmosphere; only exposed to same vac that would be via primary barrel port, right?
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The leak of a failed gasket on that hollow passage bolt would come from a space between the top face of the throttle body housing and the insulator/spacer above it (the insulator/spacer that goes between the lower and middle carb 'plates')...as far as I can tell.

Right, so it needs to make a seal so that the hollow bolt only draws from the manifold vac, not from a possible air gap between the insulator plate and the throttle plate...
 
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? aren't there gaskets between the bowl and spacer and base that should prevent air from infiltrating that passage?
 
The Choke Breaker draws it's vac through the hollow passage bolt, too. (see red lines tracing the circuit in the image below)

I can blow air through the CB vac port in the Air Horn and feel/hear it come out down at the hollow passage bolt.

The fact that my CB diaphragm holds vac for a long time when Mighty Vac applied to it on the bench, but the CB does not work on the vehicle under operation, is an indicator of a vac leak through the hollow passage bolt.

EDIT: It took more than 3 inHg of Mighty Vac for the CB to 'break' open the choke plate (this was a bench test...I twisted the link where the choke cable connects, holding the choke plate fully closed and applied Mighty Vac to the CB diaphragm until it 'broke' open the choke plate)

Still trying to figure out what additional vac circuits draw vac from the hollow passage bolt (so far we've got 2 definite: Power Piston/Valve, CB; and 1 maybe: 2nd diaphragm)

Choke Breaker Vac Circuit 2F FJ60 USA carb.webp
 
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LAMBCRUSHER said:
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?
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Agreed. If there was a leak that was causing weak vac through that passage bolt, then the Power Valve would probably be open more than it should be if the vac leak was large (so that vac was less than 3 inHg, since that is the estimated value of pressure needed to release the Power Piston which would allow the Power Valve to open)...
LAMBCRUSHER said:
aren't there gaskets between the bowl and spacer and base that should prevent air from infiltrating that passage?
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No gaskets on the stock insulator (or if so, then bonded gaskets on the insulator) but I installed the two gaskets that came with the Hygrade kit...one on each side of the insulator...
 
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