Now Hands-On Help Needed Carb cleaning in Tampa Fla.

[Jeffintampa]

took a step backwards

I miss riding to, I took a step backwards yesterday will 2 steps so not only do I have my carbs in Pa my gas tank at a painter, my cams setting on the work table, my mufflers and oil pan are off lol should just be calling it a rebuild lol

[Rasputin]

Just look back at what you knew a few weeks ago, and then now, and think about how much you have learned and how much more you will appreciate your ride when you get her all done.
I feel that the more one puts into his ride the more he gets out of it. Any arsehole can buy a bike and ride it, it takes some intestinal fortitude to stick it out and make a silk purse out of a sow's ear.
Congrats on sticking with it. Soon you will enter the guru status due to all of your experiences.

[Schming]

First let me apologize for the blurred pic but I think you can see the shorter length of the "new" float needle on the left, that Jeff supplied, and the stock Mikuni on the right:



Now look how they fit in the bores of the valves, the clip on the left/new one bottoms and gives a light seal and the stocker has room to seal tightly, another possible problem point:



I don't know if the octy was working or not but it will get some much needed love also

[Jeffintampa]

needles

I got the new needles from a dealer too.....

[TopCatGr58]

Hey Schming,

That's a very astute finding with regards to the aftermarket needle and the float clip...so even though the overall length of the aftermarket needle appears to be the same...the little float plunger is longer on the aftermarket and like you said, the wire clip is fitted LOWER on the needle which appears to interfere with the full travel/depth of the needle within the seat!

Whodathunk?

Will have to add this to the collective database against aftermarket carb parts vs. Mikuni!

T.C.

[Schming]

Hey Jeff carbs are 99% done just need to bench synch and test for leakage which will be done today.



BUT, (there's always a but) I ordered, from Ron Ayers Motorsport, the Genuine Mikuni 42.5 pilot fuel jets, using the recommended part # 4G0-14142-42-A0 , I received jets without air bleed / emulsion holes. As per my phone conversation with their tech Yamaha has discontinued the 6 hole pilot fuel jets... BUT... Jets R Us has them and I should have them Monday.

As mentioned in the previous posts the difference in the float needles may have contributed to leakage through the bells. Here a pic of the new Mikuni one installed, notice the clip clearance:



All floats, but one, were bent and needed straightened so measurements can be made accurately:





I check measurements on this tower of milk crates so I can see comfortably:



Using the white paper behind helps to see any gap:



Trimmed the gaskets:




New O-rings for the Tees:





Also three of the four float pins were bent so I dug through my stash and found some. The shoulders on them have been filed to fit the posts with a slip fit.
IMHO your floats and needles were the main problem along with 30yr. old corrosion and crud. I cleaned and installed a new diaphragm in the Octy valve also. You'll need inline fuel filters to keep any nasties out.

As soon as I receive the pilot fuel jets I get them shipped back to ya.
Thanxs for your patience

[Jeffintampa]

carbs

Cant wait to get back on 2 wheels

Thank you thank you thank you

Jeff

[Rasputin]

Jeffintampa.
Just have to say that when I joined this forum I had no more experience than you do. I spent over $800 on getting my carbs adjusted, and it ran lean. It was also the very reason I joined this forum!
These guys talked me through and now I can do my carbs with no issues at all. It is kind of too bad that you are not a bigger part of the carb fix so you understand more about how they work and then you can enjoy the bike more and not be sidelined every time a carb acts up.
Your choice, but I would learn everything I could about these bikes, so I could be a rider, rather than an owner!

[TopCatGr58]

BUT, (there's always a but) I ordered, from Ron Ayers Motorsport, the Genuine Mikuni 42.5 pilot fuel jets, using the recommended part # 4G0-14142-42-A0 , I received jets without air bleed / emulsion holes. As per my phone conversation with their tech Yamaha has discontinued the 6 hole pilot fuel jets... BUT... Jets R Us has them and I should have them Monday.

Hey Schming,

After I sawed a bunch of carb bodies in half both length wise, and crosswise,
"WE" learned that the pilot jet circuit doesn't get the AIR into the circuit until way AFTER the point of fuel flow well after the pilot jet. See photo:





SO...that's partly why the sideholes in the pilot jets are MOOT. Before we thought that the wrong # of side holes in the K&L/Aftermarket jets was the cause for their poor performance/overly richness...but after later analysis, it was determined that K&L and others used a different measurement for the sizing of the central HOLE in the metering end of the jet...that they are LARGER than the same stated size jet in the K&L brand.

Great work on your work on his carb bank and figuring out the fault in the float needle and pins!!

T.C.

[Schming]

"WE" learned that the pilot jet circuit doesn't get the AIR into the circuit until way AFTER the point of fuel flow well after the pilot jet."

T.C., doesn't the later carbs with no passage from the main to the pilot and no rubber cap get air from the pilot air jet and the 6 holes in the pilot fuel jet are necessary ?

[TopCatGr58]

Hey Schming,

Here are the photos of the 80-81 carbs sliced:

Here you can see the Pilot jet tower and note the mounting screw threads for the jet, and then the angled end of the jet whole where the head of the jet seals/stops against the carb body...so there's NO place where any AIR can get AROUND The pilot jet.



In this image you see the "Y" channel ABOVE the pilot jet. In the left half the left upper branch of the Y channel is capped off at the top of the carb body, it matches up with the right upper Y channel of the right body, and the large hole near the top is the inlet from the pilot AIR JET.

On the left half body, the vertical tunnel going from the right upper half of the Y channel is what goes up to the pilot circuit that goes forward to the channel that feeds the 3 little holes in the top of the carb throat, as well as the pilot jet screw. That vertical channel is also sealed where it goes to the vacuum slide diaphragm chamber.



So...you can see that ANY air that gets into the pilot jet fuel flow comes into the flow WAY after it flows thru the Pilot Jet itself way down deep in the carb, so the aeration holes in the Pilot jet are MOOT for these carbs!

T.C.

[Schming]

You Are Awesome T.C.

Thanxs T.C., for the pics and taking the time to explain the fuel flow.

I've read your "Anatomy of the Carbs" thread must not have been on receive oops

So the 4G0-14142-42-A0 pilot fuel jets (no air bleed holes) 42.5 size, will work in our carbs with no ill effects.

[3Phase]

Yamaha's 'new' 4G0-14142-42-A0 part is a Mikuni N151.067 series.

Hopefully they saved enough money buying jets with no bleed holes to make it worth rewriting a thirty-year-old obsolete spec' and parts list.

.

[Schming]

Yamaha's 'new' 4G0-14142-42-A0 part is a Mikuni N151.067 series.

Hopefully they saved enough money buying jets with no bleed holes to make it worth rewriting a thirty-year-old obsolete spec' and parts list.

.

Yes Scott, that's is how they're listed on Jets R Us site and they
exclusively list the 6 hole jets also. No other site to date seems to have the 6 hole genuine Mikuni, least I haven't found so yet.


Jeff, I bench synched your carbs "Trbig style" and set your fuel levels, equal, with the floats measuring 24.5mm 'cause I just wasn't comfortable with where the fuel level ended up with them set at 23mm . . . BUT . . . you'll now need to install them, with an inline fuel filter before each Tee and perform a running synch and mixture adjustment at the least.

Primary leak test:



Static fuel levels:



#1& 2:



#3 & 4:



I'll get them boxed along with the engine mount rubbers from Mack and out to ya Friday morning.

[Jeffintampa]

cant wait

wow thanks again cant wait