Newly built carb fuel leak (1 Viewer)

[hodol88]

I got my carb built by JimC. Everything looks good, and I get 11 mpg (I got 8 mpg before this). I have been checking everything under hood very often. Then, I noticed small fuel leak from the carb show in the attached photo. When I compare to the old carb, there used to be a rubber ring there. Do you thin kthat JimC forgot to put the rubber thing there? Should I bother fixing this?

 

[Slow Left]

Then, I noticed small fuel leak from the carb show in the attached photo.

That plunger is called the Secondary Slow Cut Valve. That valve is usually 'off' (closed), preventing fuel from the fuel bowl from entering into the second barrel of the carb through a small hole in the wall of the below the secondary butterfly.
But, at WOT (Wide Open Throttle), the linkage in the carb does two things. First, it kicks open the secondary butterfly on the throttle, creating a vac at that small hole in the wall. Second, it opens that plunger (the Secondary Slow Cut Valve), allowing fuel to pass. The vac created at that small hole then draws in gas into the second barrel, adding additional fuel during the opening of the secondary.

When I compare to the old carb, there used to be a rubber ring there.

That rubber boot was just a dust boot. It has no effect on whether that valve is leaking or not.

Do you thin kthat JimC forgot to put the rubber thing there?

No, those pesky dust boots are most likely torn...they're 30 yrs old...

Should I bother fixing this?

Yes, that's a good idea. For what it's worth, the exact same thing happened to me (although I rebuilt the carb myself). Before I rebuilt the carb, that valve was not leaking. After the rebuild it started leaking. You don't want that raw gas flowing out of that valve...and onto the hot manifold below...a spark would cause a fire.

I don't think the valve assembly is still available...or if it is, it's gonna be ridiculously expensive.

There is a modification that consists of removing the valve assembly (it's simple, there are two screws holding the valve assembly to the side of the carb - be careful not to loose or tear the figure 8 gasket inside the assembly, you'll have to reuse it), pulling that plunger, taping the hole in the casing that held the plunger and then J-B Welding in a bolt to plug up the tapped hole.
After the mod, the secondary will draw fuel on demand...no longer needing the mechanical actuation of the plunger...

Do a search here in the 60s section of MUD for 'Secondary Slow Cut Valve' and you should find threads on this topic.

But I would contact Jim and let him know. He might have a better suggestion on how to deal with it.

 

[Stumpalama]

There is no replacement for the cap, nor any way to reseal the plunger.
As Slow Left stated, the fix for this is to gut the plunger assembly and tap it for a 4mm or 6mm short bolt (I can't remember which one I used) to plug the hole.
it works fine and I can't tell if it affected anything either way.

 

[cwwfj60]

Had the same problem, do some searching for the exact details, it's pretty simple and I noticed no difference in performance

 

[Spike Strip]

This is what you do with it, using a 8mm bolt.


They are available from Toyota, but something around $150

.

 

[cwwfj60]

are you sure they are available spike strip? I did alot of checking a couple years ago and found nothing, had one parts guy tell me they were discontinued, but I didn't have the expertise of beno on my side....may be one of those things where you need a knowledgable toyota parts guy to find one on some dusty shelf somewhere.

 

[Spike Strip]

You're right. Looks like it has come to a discontinuation.

 

[hodol88]

Thank you all for your replies. I plugged up the lower holes with epoxy, and it does not leak anymore.

 

[Dan Singhbere]

Thanks for the great pictures, I'm waiting for my carb from him, I"ll be ready with the parts to fix it.

 

[Slow Left]

Thank you all for your replies. I plugged up the lower holes with epoxy, and it does not leak anymore.

Which holes, exactly, did you plug? See image below (a cross section of the innards of the Secondary Slow Cut Valve assembly can be seen at #11).

Also, will gasoline eat the epoxy you used? What type of epoxy did you use and how do you know it can withstand gasoline?

 

[Slow Left]

Thanks for the great pictures, I'm waiting for my carb from him, I"ll be ready with the parts to fix it.

Be careful not to strip the phillips heads on those two screw that hold the Secondary Slow Cut Valve assembly to the side of the carb. If the carb is unistalled from the vehicle, it might be easier to crack them loose using vice grips grabbing around the circumference of the screw heads...

Also, the trick to the whole modification (after you have removed the assembly from the carb and popped out the brass valve from the aluminum assembly housing) is to thread the inside of the hole in the housing where the valve just came out of with a tap. Off the top of my head I can't remember the size tap I used, but do a search here in the 60 series section, there should be plenty of posts from folks who have done this.
I then used JB weld (a thin coat) on the thread of the bolt going into the newly threaded hole.

Be sure not to tap too far down in the hole, or use too much JB weld, because you want those two holes on the face of the carb and the face of the valve assembly housing to be open, because that is the circuit through which the gasoline flows...and you need that gasoline to flow freely through the circuit after the mod...the only thing you are doing is removing the valve and plugging the top of the hole where the valve used to be with the JB weld on the threads of the bolt that goes in there...

 

[Dan Singhbere]

What else should I be prepared to fix once I get the carburetor back from JimC?

 

[Slow Left]

What else should I be prepared to fix once I get the carburetor back from JimC?

Pretty much the standard stuff. How familiar are you with working on carbs? Have you got any mechanical understanding?

 

[Dan Singhbere]

I had the impression from reading his website that he tested every carb he rebuilds on an engine, adjusts the mixture. The website made it sound like I could bolt it on, adjust the linkages and be on the road. I didn't expect I would be checking for gas leaks, seems like vacuum leaks are another concern.

 

[Output Shaft]

website made it sound like I could bolt it on, adjust the linkages and be on the road

You can.
If it turns out that there is a problem. Let him know.
A slightly weeping secondary slow cut valve is not really considered a "problem" with these old carbs. They now all weep a little bit to some degree due to the worn seal. Little bit of fuel = No big deal. Lots of dripping fuel = Problem.

 

[Stumpalama]

I had the impression from reading his website that he tested every carb he rebuilds on an engine, adjusts the mixture. The website made it sound like I could bolt it on, adjust the linkages and be on the road. I didn't expect I would be checking for gas leaks, seems like vacuum leaks are another concern.

The best person to answer these types of questions for you is @FJ40Jim. I didn't see where the OP brought up his issue with Jim before posting.

 

[hodol88]

Be careful not to strip the phillips heads on those two screw that hold the Secondary Slow Cut Valve assembly to the side of the carb. If the carb is unistalled from the vehicle, it might be easier to crack them loose using vice grips grabbing around the circumference of the screw heads...

Also, the trick to the whole modification (after you have removed the assembly from the carb and popped out the brass valve from the aluminum assembly housing) is to thread the inside of the hole in the housing where the valve just came out of with a tap. Off the top of my head I can't remember the size tap I used, but do a search here in the 60 series section, there should be plenty of posts from folks who have done this.
I then used JB weld (a thin coat) on the thread of the bolt going into the newly threaded hole.

Be sure not to tap too far down in the hole, or use too much JB weld, because you want those two holes on the face of the carb and the face of the valve assembly housing to be open, because that is the circuit through which the gasoline flows...and you need that gasoline to flow freely through the circuit after the mod...the only thing you are doing is removing the valve and plugging the top of the hole where the valve used to be with the JB weld on the threads of the bolt that goes in there...

I guess that I closed the channel. I thought that I could disable this without a problem. I just plugged the two holes with the steel reinforced epoxy. I haven't noticed any difference yet. When does it get used? I can drill holes again to make the channel.

 

[Slow Left]

I guess that I closed the channel. I thought that I could disable this without a problem. I just plugged the two holes with the steel reinforced epoxy. I haven't noticed any difference yet. When does it get used? I can drill holes again to make the channel.

If you look again at the image in post #10 above that shows the cross-section of Aisin carb circuits, you can see the Secondary Slow Cut Valve assembly (#11 in the image) mated to the side of the carb.

When mated to the side of the carb, the Secondary Slow Cut Valve acts as a mechanical valve interrupting the flow of gas through the circuit.
When the SSCV is mechanically shut (which is it's standard state) it does not allow gas to pass through that secondary slow circuit.
When the SSCV is mechanically opened by the throttle linkage (when you stomp on the gas creating a condition of Wide Open Throttle (WOT)), it allows gas to pass through that secondary slow circuit.
But, being open is necessary but not sufficient for gas to flow into the second barrel of the carb. The secondary butterfly valve must also be cracked open, creating a vac at the opening of the secondary slow circuit at a hole in the wall inside the throat of the second barrel.
The secondary butterfly is cracked open by the throttle linkage at the same (or close to the same) time as when the SSCV is mechanically opened.

After the secondary butterfly valve is cracked open, the gas that is drawn into the second barrel through the secondary slow circuit is supposed to provide additional fuel for combustion "in transition"...meaning, the amount of fuel delivered through the slow circuit is minimal compared to the amount that is going to come from the venturi (see #3 for the secondary venturi and #5 for the primary venturi), which draws it's fuel from the main jets (see #10 for the secondary main jet and #17 for the primary main jet).

By plugging those two holes, you stopped the leak (presumably coming from a gap between the SSCV and the SSCV housing as a result of wearing down over time - it is not a serviceable part...no parts for the SSCV are packaged in carb rebuild kits and Toyota no longer sells the SCCV assembly new...) by plugging the top hole so that the gas from the fuel bowl can no longer reach to the SCCV.

Here is the secondary slow circuit outlined in red:

The mod, as described above, removes the SSCV from the aluminim SSCV housing, threads the hole in which the SSCV used to sit, and then JB welds a bolt in place of the SSCV, without blocking the continuous flow through the secondary circuit.
After the mod, fuel will flow into the second barrel through the second slow circuit "on demand"; meaning whenever the secondary butterfly is cracked open and a vac is generated at that port in the wall of the second barrel.

Now, after having plugged that circuit, fuel can no longer flow through the secondary slow circuit. Therefore, fuel is not being pulled out of the port in the wall of the second barrel right when the secondary butterfly is cracked open (at WOT).

So, the question you are asking is, what are the implications on performance for not having fuel delivered through that circuit under those circumstances.
That is difficult to measure, but the theory is that the slow circuits deliver fuel at idle (in the case of the primary slow circuit) and in 'transition' (in the case of both the primary and secondary slow circuits)...'in transition' means right at that point that the secondary butterfly cracks open...

It will not affect idle, since that is controlled by the primary slow circuit.
It will only negatively affect the performance under conditions of WOT if the second barrel cannot pull the fuel it requires directly from the second venturi in the short amount of time it needs. This depends on how important the fuel from the second slow circuit is in creating the necessary vac to initiate the minimal amount of flow of air through the second barrel to create vac on the second venturi, which in turn draws out the fuel through the second main circuit.

Insufficient fuel delivery means fuel starvation which means a slight hesitation. I would suspect that as long as there is sufficient vac at the second venturi to pull fuel through the second main circuit, the affect of not having fuel delivered through the second slow circuit during 'transition' is minimal.
If you drive the rig and create a condition of WOT (stomp the pedal to the floor) and you feel the secondary open up...you're safe to assume that there is minimal affect of having plugged that circuit.

This is how I would see it, anyways...

 

[Output Shaft]

& more validation of Slow's excellent explanation:

86FJ60 leaking fuel at Carb

fj60 Secondary Slow Cut

 

[FJ40Jim]

The rubber dust boot on the SSCV is always hard as a rock after 10 years of underhood exposure. The slightest touch and it crumbles apart, if it was even still there (this applies to all carb, not OP specifically). There is no practical replacement of the boot. The bit of fuel that may ooze out around the plunger is only the fuel that is in the vertical passage above the SSCV. IOW, it can't siphon/leak all the fuel out of the bowl.

When the secondary is inop (normal condition for all 10+ year old carbs), fuel is never drawn up & over to the SSCV, so it never appears to leak. After the roached seconday diaphragm is replaced and the vacuum system is modified, the secondary goes from being a dead end, to a major air & fuel supplier. Fuel is seeping out now because the secondary barrel is actually working.

Plugging the valve so it stops leaking, but also stops flowing fuel, will cause a secondary tip-in hesitation.

HTH