Aisin carburetor idle circuit routing (1 Viewer)

[Scotty2]

Pinhead
Just to make sure…. This surface (in the pic) is the one that I can sand smooth with the 240 grit paper on a pane of glass, right? It’s the bottom side of the upper third of the carb. And then, the mating surface of the carb’s middle section? Thanks in advance.
Scotty2

 

[Scotty2]

When you depress the throttle, does the engine stall, particularly when it is not gradual but all-at-once?

The float adjustment is hard to read thru the window. In all the LC carbs I've opened up, the needle and seats were slightly different. This might affect float level? I've missed the float spec before, and it flooded the bowl. I pulled over, and the light was finally just correct, and I could see the bottom of the float in the window! I believe that I limped home with more choke, as I know that I didn't open the carb in the parking lot.

How does Scotty2's carb get vacuum for the power valve?

It’s a great time to ask since I have it laying on the bench in front of me. I’ll attach a pic. The needle valve has a small spring loaded plunger inside it. The float adjustment was pretty much perfect based on my Haynes manual, so I didn’t touch it.

 

[Scotty2]

It’s a great time to ask since I have it laying on the bench in front of me. I’ll attach a pic. The needle valve has a small spring loaded plunger inside it. The float adjustment was pretty much perfect based on my Haynes manual, so I didn’t touch it.

View attachment 3800856

And no there’s no stall. PS the window in my carb is useless, being pretty much gold and not transparent at all.

 

[Grayscale]

And no there’s no stall. PS the window in my carb is useless, being pretty much gold and not transparent at all.

Did you try cleaning it with steel-wool?

 

[Scotty2]

I’m in the middle of the carb reassembly. Nothing too noteworthy except the bottom surface of the “middle” carb section wasn’t very flat. I took Pinheads advice and sanded each surface of the top two carb sections with 240 grit wet-or-dry paper on a pane of glass.

So the surfaces are pretty flat now. The steel bottom section I looked at with a steel ruler and it was very flat to the naked eye.

But then I noticed something odd. I’m including two photos so you can see it. The bottom section of the carb has a port that opens to the idle mixture screw channels, that appears to get covered up by the gasket that came with my kit. So I’m gonna get out my trusty hole-punch and “improve it” a bit. Can’t hurt, right?

 

[Scotty2]

If I flip the gasket over it fits correctly with the port uncovered. I will put away my hole punch.

 

[Scotty2]

OK, I may have found (another) “smoking gun” for my vacuum leak. When reinstalling my carb this pm, I couldn’t tighten the two forward nuts. The studs were spinning. I pulled the studs out and ran a 8-1.25 die over them to clean the threads. (Please see photos to see the hard pieces of metal that fell out of the stud threads). I then ran a 8-1.25 tap through the holes. The tap bottoms out on the hole furthest from the valve cover. The hole closest to the valve cover has no bottom, it’s drilled and threaded all the way through.

So I have some machining questions:

1. Dare I continue to use the original 8-1.25 studs after they came out with so much material under their threads? Or should I drill, tap, and upsize the studs?

2. I can double-nut and tighten one stud down against its hole’s bottom. But to fix the other stud in place where the hole has no bottom do I just thread the stud down to its unthreaded shoulder?

3. Should I leave the two studs alone that are working just fine?

As usual, thank you all in advance for your experience and advice.

Scotty2

 

[charliemeyer007]

I would do the locking insert re thread kit. $$$ I have a small lathe and a good selection of tap/drills and dies to make a bushing to the new D&T out size with the same inside tapped hole as your stud.
You could tap the stripped hole to the next size and just use bolts.
Its aluminium have it welded and then D&T

 

[Scotty2]

I would do the locking insert re thread kit. $$$ I have a small lathe and a good selection of tap/drills and dies to make a bushing to the new D&T out size with the same inside tapped hole as your stud.
You could tap the stripped hole to the next size and just use bolts.
Its aluminium have it welded and then D&T

Thanks. I’m watching YouTube videos right now about the merits of Helicoil vs TimeSert.

 

[Grayscale]

I've had quite a bit of experience with Helicoils. They should have been in the manifold from the factory, cast aluminum can't tolerate threads like structural aluminum, and it is inferior to steel. The tang removal on a Helicoil is a bit tricky.

Whatever you do, you'll might need a bottoming tap for the two blind-holes. Basically you grind the taper off of the front of the fap, slowly, as to not ruin the tool-steel's temper.

I don't think that you should enlarge your hardware, the carb, carb insulator, gaskets, etc. would need enlargement too. It is hard enough to put a 12 or 13 mm hex nut on the studs as it is. Plus, larger fasteners need more torque to fasten with enough tension.

I secured my current carb with factory studs, hardware store low grade / class flat washers, and fresh lockwashers. The original Aisan carb wouldn't need the flat washers, because the casting is iron or steel, the OEM replacement carb is some kind of alloy. However, the lockwashers would be a good pairing for steel hardware fastened into aluminum because they maintain tension even when less torque for fastening is employed.

 

[charliemeyer007]

So I had another thought about those "loose" stud threads. Most of my round dies are split - by turning in the screw you can cut oversize threads (opens the die). Take the next size up stud, reduce the diameter and cut oversize thread to fit in the intake manifold, the other end is then turned down and threaded normal size.

As a kid I would make firing pins from aircraft bolts with an egg beater drill and a file plus a hacksaw. I think the term was Hispanic Milling Machine.

 

[Scotty2]

I got my thread repair kit this pm, so I’ll be fixing the two stripped studs soon. But I found an old ih8mud post that discussed the evils of using the two gaskets on the carburetor base spacer. There were some very definite opinions about NOT using the gaskets. The spacer does appear to have a gasket layer applied to it.

I would appreciate your opinions on whether to use the gaskets or not. (Please see the attached photo.)

 

[charliemeyer007]

I would put a gasket on each side of that phenolic block. I have one of those man-a-fre tungsten mixing screen units in there too,

 

[Scotty2]

I installed two thread repairs (Helicoils) for my intake manifold carb mounting studs, and installed the carb. Phooey! No change in the idle problem. (Since I leak-checked the base of the carb 4-5 times this shouldn’t have been a surprise to me I guess.)

Tried installing the carb with the base spacer gaskets AND without. No difference.

Bottom line:

I still have my best, lowest idle at 1000 rpm with 12 in Hg vacuum. Of course, with the choke Off.

The IMS still has little effect. I see fuel spraying in the center ring (emulsifier?) of the passenger side carburetor barrel.

It drives low speed like a bucking bronc. Timing is not even visible in the window.

Misc:
I cleaned the PCV valve and it works. My new one from Amazon didn’t fit. Oh well.

During the carb disassemble/ re-assemble I sprayed all the passages with carb cleaner and pushed monofilament thru them. Also 240 grit sanded the flanges.

I triple checked all the linkage connections using SOR photos to make sure I was in the right holes.

I really really hate to admit defeat, but I’m stumped.

Maybe I’ll see if there’s a reputable FJ40 mechanic in the Jacksonville Florida area who can figure this out. I’m outta ideas.

I’m very appreciative to all of you who have contributed your knowledge and experience.

Since the Idle Mixture Screw has little effect on idle, and since I still see fuel being sprayed down the carburetor throat on the passenger side, everything seems to point to a vacuum leak. I just haven’t been able to find it.

 

[Pighead]

Timing is not even visible in the window.

Then make the timing mark visible in the window.

 

[Scotty2]

Then make the timing mark visible in the window.

I’m gonna try that this afternoon.

Two questions from the “nube”:
What’s the best way to check to see that my throttle plates are completely closed?
And
When I look at the SOR photos of carburetor linkage (attached) all of the samples shown have a linkage from the diaphragm operated device to an arm. My carb is like the one at upper right, and I’ve circled in red the arm. My carb has neither the rod nor the arm to which it connects.

Did the carbs mutate a bit over time? Why am I missing this apparatus?

Thank you again. I’ve learned a lot from your posts on Mud.

Scotty2

 

[Grayscale]

Likely, a PO deleted the Choke Breaker / Throttle Positioner diaphragm on your carb. It is not necessary equipment, but, it makes for easier starting.

I'd like to see a few more carb pics.

Your throttle plates will be closed when the idle speed screw is backed-off. It is hard to see on the truck, but, you can shine a light thru the primary throttle (valve cover-side) and look at the throttle plate below.

 

[Pighead]

Why am I missing this apparatus?

It probably wasn't working. Those diaphragms end up leaking. I took mine off too, don't miss it.

 

[thebigredrocker]

here's a thread with pics of a secondary throttle plate open, I still wonder if your primary is cracked too far open: Carb Tuning /ignition question 78 2F ignitor - https://forum.ih8mud.com/threads/carb-tuning-ignition-question-78-2f-ignitor.1058227/#post-11664251

while fiddling around I'd have unnecessary vac connections like the VSV plugged/capped. brake booster also.

early in this thread 65swb45 listed valve adjustment as a possible thing to do. There are a couple great threads on how to do that. Also Mark's Off Road(65swb45) mentioned your distributor could be an issue. Proper spark timing does wonders to improve vacuum. Not sure why the rig was bucking while you drove it but bucking can be fuel starvation. I cleared my plastic sight window up by wetsanding the orangish layer off. Then you can kill the engine while it's bucking and see the fuel level. I got the impression you bent the float tab and weren't 100% on correctness. Something to ponder. Another thing later on might be to have your intake manifold planed and reseal it to the head.

 

[thebigredrocker]

Also you lost the discharge weight. I wonder if that needs addressed down the line.