Calling all G-1 Folks - Carburetors

[OgreTX]

I feel like I am being forced to finish a project I undertook almost a year ago. It concerns the continuing advice on our stock "Mikuni" carbs (pics 1,2,&3) and the Chinese knockoff "Mokini" carbs (pic4). Please excuse the blurred pics. I tried to take them all with the "up-close" camera setting.

I agree with the advice that the cheap knock offs are hit & miss. I have had luck with some, and not so much with others. So "pays your money and takes your chance." What interested me most was the thought that there might be some good pieces of the knockoffs that would help me overhaul and clean up my original Mikuni.

First my background and limitations: I am by NO means an expert. I first encountered disassembling carbs when I did a few GM QuadraJets for a couple of '72 Pontiacs I am working on (pic 5). So if you ask me a technical question, I may not have a very good answer, but I'll try. I'm just like y'all ... and old guy who love tinkering with things to see how they work, and see if I can make them work a little better.

I'll try to get some good pics and update this thread as frequently as I can.

Ogre

[OgreTX]

Right quick, while I'm thinking about it. In the stickies above, sontag1 has an excellent post on fixing his throttle shaft leakage.

This reminded me of the universal problem with QuadraJets. The throttle shaft wears and air leaks in around the shaft and makes it almost impossible to get the fuel-air mixture right, so the old QJs are usually considered junk. They can be overhauled and tuned up pretty good, IMHO.

Ogre

[JerEazy]

UGGGhhhhh the Qjet.... one of the best carbs when tuned right. Was way ahead of it's time technologically speaking. But you needed a **** PhD to properly tune it.

I like where your head is at. I would assume the jets, nozzles, floats, needles and such would interchange.

[OgreTX]

Originally Posted by JerEazy

UGGGhhhhh the Qjet.... one of the best carbs when tuned right. Was way ahead of it's time technologically speaking. But you needed a **** PhD to properly tune it.

I like where your head is at. I would assume the jets, nozzles, floats, needles and such would interchange.

That's what I am thinking too. I've got them both apart, and I will post some pics of the differences/similar parts that might be interchangeable so that the original Mikuni can be used. I already know the main nozzle (from the fuel bowl to the carb) for getting the right fuel via the venture effect, is SIGNIFICANTLY different. Not being a fluid dynamics expert, I am not sure what the eventual effect will be.

I'll try to get 'er done this PM.

BTW, the guy who wrote the book on QJs, Cliff Ruggles, is on the Pontiac forum I call home, and we had frequent conversations while I was rebuilding the two I did. Here's his book: https://images-na.ssl-images-amazon....4,203,200_.jpg

Ogre

[OgreTX]

For anybody following this thread, I should have posted the page from the G-1 AM3 repair manual which provides the nomenclature I will be using. It's below.

I know that I am not that good with the correct names, so this is where I will be getting the names of the parts.

Ogre

[OgreTX]

Ok, Next installment.

The first noticeable difference between the two carbs side-by-side is the opening from the carb to the engine (pic 1). Pic 2 shows the beefier opening on the knock off, and pic 3 is the Yamaha Mikuni. Because the outside diameter is the same for mounting to the carb boot at the cylinder, the inside is smaller on the knock off. The throttle shaft has been removed form the el cheapo.

Pic 4 and 5 show the difference in the two throttle shafts. Interestingly, the brass butterfly valve will fit on the knock off shaft. If your shaft is worn, you may want to use the knock off shaft. Use caution with the screws. The repair manual says that they have been designed so they won't come loose and flow into the piston. They will come loose ... be patient.

Ogre

[griffo002]

Thx for posting ....I am in the middle of doing up a G1.....I have picked up a el cheapo china made carb (can't get a original for love or money in Oz).Crank seals and top end rebuild kit + reeds are on the way.
So if this replacement carb is a failure i will follow your lead from this thread.
Again thanks.
Griff.

[OgreTX]

Originally Posted by griffo002

Thx for posting ....I am in the middle of doing up a G1.....I have picked up a el cheapo china made carb (can't get a original for love or money in Oz).Crank seals and top end rebuild kit + reeds are on the way.
So if this replacement carb is a failure i will follow your lead from this thread.
Again thanks.
Griff.

No sweat, Griff. I'll get to the bottom (fuel bowl) next. While I hope this will help folks keep their original, I think it might be worth buying a couple of knock offs, and getting the best parts to maybe make one decent aftermarket carb too.

Ogre

[Spicyunicorn]

Another helpful thing is sometimes the shaft and the bushing are both worn I have used the plastic bushing in el cheapos in the original carb

[mikeasis]

Good stuff here!