Another Aisan Carburetor question

[CHCP]

I recently cleaned and put a kit in a 77 FJ40 2F Aisan so I could swap out my current 78 FJ40 2F CDN Aisan that has a power problem and fix it.
The CDN pulls 19 inches of vacuum steady, when I install the 77 vacuum drops to 15 and erratic with no idle screw adjustment, I have replaced intake to heat shield gasket, heat shield to carb base gasket but still get low vacuum for the 77. Is there a way to bench test a carburetor for vacuum or air leak? The only differences between the carbs is the 77 has the egr spacer which is capped, the 77 has two ring venturis on both primary and secondary sides, and the primary and secondary slow jets are the same length. The 77 has a 1.50 main jet and 1.71 secondary main jet.
The CDN losses fuel on long hill climbs and towing a trailer, but on short climb hills I can actuate the secondary and accelerate from 50 to 60, so I can't believe its a fuel delivery issue from the tank to the carburetor. Any help appreciated especially about bench testing.

 

[Splangy]

Joe, it sounds like your running off of your primary circuit instead of your idle circuit at idle. Possible culprits could be a defective idle stop solenoid or a gummed up idle circuit. Or perhaps the idle speed screw has to be turned in too far to keep it running because the idle mixture was too far off when you first ran it. It’s also possible you have a vacuum leak somewhere.

 

[FJ40Jim]

There may be other issues, like a vac leak, but ultimately a stock 77-78 US spec carb slow jet is too small. Even with the idle mix screw maxed out (4-5 turns out), it is still too lean for best idle quality. The slow jet needs to be about 15% larger.

 

[CHCP]

Thanks Splang and Jim for your insights. Interesting enough the good idle CDN carburetor idle mixture screw is out
4 turns. By my calculations the .75 primary slow jet of the 77 needs to be bored out to .8625 mm and using a 1/32 fractional bit should be right on. I see the next closest slow jet would be .90 but used in the secondary (21024-61010) good luck in finding one of those.
Just a thought, what does the slow jet do in the secondary?

 

[GA Architect]

CHCP - The Keyster carb kits have slow jets in them. I'm not sure what sizes go with which kit, but I think I have a few slow jets left over from a few builds. I'll check my stash and report back.

@cruiseroutfit - maybe could shed some light on which main & slow jets are in which Keyster carb kit?

 

[thebigredrocker]

Here's a link to FJ40Jim's posts on the subject of secondary slow jets—>

Search results for query: secondary slow

forum.ih8mud.com

 

[CHCP]

Here's a link to FJ40Jim's posts on the subject of secondary slow jets—>

Search results for query: secondary slow

forum.ih8mud.com

Thanks! That's some great info, we're fortunate to have JimC amongst our ranks!

CHCP - The Keyster carb kits have slow jets in them. I'm not sure what sizes go with which kit, but I think I have a few slow jets left over from a few builds. I'll check my stash and report back.

@cruiseroutfit - maybe could shed some light on which main & slow jets are in which Keyster carb kit?

I just looked on Keyster Carb Kit site and could only find one kit for TLCs that listed the sizes for its main and slow jets
it was kit K11-352A 1969-75 #50 and 200 mains, and #90s. I don't know if that's what included in the many other kits but I just sent an email to sci@siriusconinc.com which is the parent company of Keyster (sirius consolidated) asking for a more definitive list of its offered
main and slow jets in each kit, if I ever hear back from them I'll relay the info

 

[FJ40Jim]

SCI is the canadian importer of Keyster products.

You would have better luck asking somebody at Cruiser outfitters to check the sizes of slow jets in Keyster kits, then you could buy one and report the findings here.

 

[CHCP]

SCI is the canadian importer of Keyster products.

You would have better luck asking somebody at Cruiser outfitters to check the sizes of slow jets in Keyster kits, then you could buy one and report the findings here.

Well, take the wind right out of my sail.
I'll check with Cruiser Outfitters not to be mixed up as JT Outfitters.
Drill bits cost less.

 

[cruiseroutfit]

Not all Keyster kits offer jets. We stock ~20 different kits and it’s been a longtime goal of mine to develop some tidy bill of materials on them. I do have some jet note at the shop and will be back Monday after a few weeks of travel.

 

[CHCP]

SCI is the canadian importer of Keyster products.

You would have better luck asking somebody at Cruiser outfitters to check the sizes of slow jets in Keyster kits, then you could buy one and report the findings here.

Well, I've found that both slow jets were plugged up, can't believe that got by me. The slow jets seem to be identical even in length, the primary slow is marked 75 but excepts a 3/64 drill bit but not a 1/16 which is over 1.19mm but smaller than 1.587mm, now I'm confused maybe the PO opened these up years ago.

Not all Keyster kits offer jets. We stock ~20 different kits and it’s been a longtime goal of mine to develop some tidy bill of materials on them. I do have some jet note at the shop and will be back Monday after a few weeks of travel.

Thanks Kurt for helping with this, it seems a lot of individuals look for jets from time to time.

 

[CHCP]

SUCCESS.....in a fashion, the replacement 77 Fed Carburetor runs great, adjusted the idle mixture screw by vacuum, seemed to be a lot easier then the drop lean method especially with an analog tachometer, plenty of power but now it periodically losses idle circuit acts just like a loss of vacuum. Idle solenoid?? Pricey little devils!

The major success was that it gave me some time to troubleshoot the 77 CDN Carburetor, THIS IS What I Found: In 2017 after a total rebuild of my cruiser I bought the CDN to replace a Weber (the Weber would no longer fit because I also installed a 78 brake booster)
I bought two Aisan carburetor kits, one from Mike's Carburetors (K4422) and one from Rockauto (Standard Mtr Products 791B) I added new gaskets and a float valve assembly. Now I can't substantiate this because I can't find the OEM valve assembly but when I removed the assembly on the CDN I found that the OEM fuel filter screen (which I had put on the new valve assembly from one of the aforementioned kits) was crushed, it bottoms out in the valve assembly carburetor well causing a fuel restriction; enough fuel for level flight but not enough for an increase of power. I would suspect that the OEM and kit valve assemblies are not the same length. I've taken the screen out, reinstalled the CDN and it runs great, no more stumble on hills. But I have yet to put a loaded trailer on it.
I had thought that the problem could be too small of a primary main jet after JimC recommended increasing the OEM 1.36mm by 15% but I found that the CDN has a 1.50mm in it. That's interesting because the 1.50mm (90999-41150) is not listed as a North American primary main jet size but is used in Asia and European markets.

My thanks to all for their help and also because it has given me the the confidence to tackle cruiser Aisan carburetor problems which don't seem to be so much rocket science as before!