Calling all G-1 Folks - Carburetors

[smallblock450sl]

I've seen my share of "Mokuni's". Seems my biggest complaint is the brass float needle collar inserted into the carb base. Seems like everyone I've encountered, the float needle does not slide open and closed well. Stuck float/needle...gas in oil and starts to smoke or engine failure when engine kept running that way.

[OgreTX]

Originally Posted by smallblock450sl

I've seen my share of "Mokuni's". Seems my biggest complaint is the brass float needle collar inserted into the carb base. Seems like everyone I've encountered, the float needle does not slide open and closed well. Stuck float/needle...gas in oil and starts to smoke or engine failure when engine kept running that way.

You're the expert and right on as usual Dave. I'll get to the fuel bowl and the float needle, valve seat, et al next. BTW, the Mokuni's obviously used the original carb for creating a mold for casting. Sadly their casting material and some of the casting is junk and will crumble under pressure. I'll also get to that. The valve seat and float needle problem may be because of the crappy casting in that area.

My first one leaked fuel all over my garage. I couldn't get the needle to shut off the gas, and it also wouldn't seal the bowl very good. Gas everywhere ... lol

And Spicy, there are a few different ways (like sontag1) to seal off the throttle shaft. Some of the Mokuni parts can be used, and I also modified sontag1's method to make it a little easier. I'll also cover that.

Again guys, I am NOT an expert. Smallblock and others have more knowledge than i will ever have. I just hope my tinkering will help some and make others think about better ways for us to keep our G-1s running SMOOTHLY.

Ogre

BTW, if I get too far into the weeds, somebody call me out and tell me to get back up to 30,000 ft. I have a tendency to get way too detailed. THX.

[smallblock450sl]

Originally Posted by OgreTX

You're the expert and right on as usual Dave. I'll get to the fuel bowl and the float needle, valve seat, et al next. BTW, the Mokuni's obviously used the original carb for creating a mold for casting. Sadly their casting material and some of the casting is junk and will crumble under pressure. I'll also get to that. The valve seat and float needle problem may be because of the crappy casting in that area.

My first one leaked fuel all over my garage. I couldn't get the needle to shut off the gas, and it also wouldn't seal the bowl very good. Gas everywhere ... lol

And Spicy, there are a few different ways (like sontag1) to seal off the throttle shaft. Some of the Mokuni parts can be used, and I also modified sontag1's method to make it a little easier. I'll also cover that.

Again guys, I am NOT an expert. Smallblock and others have more knowledge than i will ever have. I just hope my tinkering will help some and make others think about better ways for us to keep our G-1s running SMOOTHLY.

Ogre

BTW, if I get too far into the weeds, somebody call me out and tell me to get back up to 30,000 ft. I have a tendency to get way too detailed. THX.

Your a very valuable member at BGW. You ask questions, post procedures and fix's. What more could we ask for. Am I an expert, no way, bat after 35 year's ...wait "I've forgotten more then I remember.

[OgreTX]

Before I get started this morning with my carb "compare and contrast" epic, I want to let those following this thread know that if you have a question about a part please ask. While I have the carbs stripped down to their basics I can easily get more pics. It may be more difficult a couple weeks down the road when they are re-assembled.

As I have stated, I am only trying to help other G-1 folks get our aspirated carts humming. (And I am educating myself also.)

Ogre

[OgreTX]

Let me start off with more info on the question from Spicyunicorn. Pic 1 below is a close up of the two throttle shafts. [As an aside, I think there may be more than one knock off ... some things may be different on this one than others on the market.]

This picture was taken during my first attempt to complete this "Masters dissertation" (LOL). The Mokini (on the left) has a white plastic bushing below the rubber sealing o-ring. If I remember correctly the knock off casting was drilled out to allow for the plastic bushing, so when it is removed the rubber o-ring will be good enough for sealing the Throttle shaft (I think). Sorry to be so fuzzy. I also found that the rubber caps for capping small lines will sometimes fit the shaft to reduce any air entry.

Pic 2 is a side-by-side comparison when I was preparing to replace my original carb. My original did not have the overflow tube now present on the knock offs. Note the top of the throttle control arm attachment to the shaft. the original is a solid connection, and the knockoff appears to be a "smashed" down end of the shaft. The connection is not that good, and you can actually rock the control arm back and forth (slightly). This could cause the knockoff to surge a little from the vibrations of the engine.

Also the oil injection (if you still inject, vs. mix) is moved to the opposite side of the knock off.

More later.
Ogre

[OgreTX]

A quick update, before I get back to installing (MAJOR CONSTRUCTION) a new Sleep Number bed. You can't just lay the box springs down and put the mattress over them and be done. Enough of my whining.

Since smallblock reminded me of the fuel leak, I looked back at my info. It was not year ago, but 2015!! I bought the el cheapo to replace my '81 G-1 carb, because I could not get it tuned right. The mokini leaked gas and I had a problem getting the fuel bowl off to adjust the float, and couldn't get the fuel bowl back on tight enough to seat with the rubber o-ring gasket. It was then that I realized it was junk.

After calling to complain I was told they would send me another one (oh goodie). They seemed to know of that problem, so I said ok and I would send this one back. They said just keep it ... What? Are these just throw away carbs!!?

Got the new one and it did work better, so I decided to disassemble the junk carb and see why they were junk.

I'll be back after trying to finish my major construction of something to sleep on. Boy do I feel stupid.

Ogre

[OgreTX]

Continuing with the theme of Junk Carbs, for the most part, the castings dimensions seem to be pretty good. The outside dimensions are very close. The outside for connections to the carb boot and air box hose are close enough (with minor deviations) that there is no problem just swapping the carbs. The largest discrepancy is the length of the junk carb which is approximately 1/2mm shorter than the original. (no big deal)

As I mentioned to smallblock, the material seems to be inferior to the original. Perhaps that is why they had to make the throat walls thicker; so they wouldn't crack under pressure.

The outer screws (pilot adjusting, throttle stop, and pilot jet) are threaded similar(?) and the tapping of the holes appear to not have been cleaned very well. For instance I would recommend using caution when removing or re-inserting the screws. On my original, you can finger tighten (good matching threads on the screw and the hole) all of the screws, even against the spring load. On the junk, the screws do not want to go easily in, or out. I'm going to guess that after tapping the holes, nobody cleaned them out and small particles are still present. (For throw away carbs, QC was probably not a high priority.) The screws and associated springs can be used on our good carbs, and seem to thread fairly well.

The pilot jet is smaller on the junk (pic1). The original is a #45 (parts manual calls for #45 0 1). The junk is a #38.9. What does this mean? Sorry, my fluid dynamics degree has expired. Pic2 shows that the threads are the same, but the junk is slightly longer (bad pic), and the orifices are smaller.

Finally for my outside comparison, Pic 3 is the pilot adjusting screw. Threads are good and it will fit our originals. And if the point on yours (from years of in-and-out adjustments) is not sharp you might want to try the junk screw.

I'll get to the insides of the fuel bowl next.

Hope this is still helping,
Ogre

[JerEazy]

So general carb question: if I wanted to go up a jet size or something. What would I be looking for? Is there bigger jets we can use as we make performance adjustments and such?

[OgreTX]

Originally Posted by JerEazy

So general carb question: if I wanted to go up a jet size or something. What would I be looking for? Is there bigger jets we can use as we make performance adjustments and such?

I would not even try to answer that one, JerEazy. Some of the experts on here have talked about re-jetting, but I can't remember if it's for the G-1 2-stroke carb or other complicated carbs.

Ogre

[OgreTX]

I'm going to try finish this thread today, and make some brief suggestions on what might work as our Yamaha Mikuni carbs wear out.

HEY ADMINS/MODS: James, Roady89, and moderators I apologize for using so much space with my diatribe and jpegs. If you need to delete this thread, please feel free to do so. I will keep a copy of it on my computer, so that it can be provided for future members.

So much for the external workings/parts of our G-1 two-stroke carbs by Mikuni. The internals (accessed through the fuel bowl) are not that exciting either. Pic1 and 2 show the "removable" internals. Ok, that's it ... any ??? Alright Pic 3 and 4 show a closer look at what is removable when the fuel bowl is removed ... now I'm done !

The first "CAUTION" I need to mention is that the cheap knock off uses paper washers rather than the good phenolic (I think) washers on the Mikuni. When you remove the bolts (fuel bowl attaching, and valve seat bolt) they will probably tear apart. (Note: See the red paper around the bolt on the fuel bowl bolt, and the red paper on the valve seat is also ripped.) I have noticed on later junk carbs, someone has started to put better washers on, so just be aware of the problem.

The float, valve seat, and float needle all seem to be in good shape and within size limits of our original carbs, so I will make the "brash" statement that they can probably be used in our good carbs. Check the flanges on the float which can be bent to set up the correct cut-off float level. Note that if the long flange hits the side of the bowl cavity, the small flange will not shut off the float valve. Check it out well.

Finally the Main Jet (small threaded jet next to the valve seat). See Pic 5 (a little blurry) and you will see the difference in original and knock off jets. The parts manual calls for #100 jet, and the knock off is a #95. Also notice that the brass is VERY soft. I really didn't have to apply that much torque and the brass was disfigured.

I'll take the next post to wrap it all up, and explain how our simple carb works.

Ogre