Why even bother with jets?

[grizld1]

Sure there's a learning curve, Dogger. You flatten it out by doing your homework. I'm trying to give guys a realistic idea of what they can expect to deal with. BTW I know who Bob and Paul Bertaut are, and the more I see of what they claim and the way they do business, the less impressed I get. If your motor says the jets are wrong and Bertaut says the jets are right, believe your motor.

I don't mind helping somebody who gets lost in a carb job, as long as he's made an effort to help himself first. One of the things I noted in the VM section of the Carb Guide is that float level needs to be inspected and set at the git-go. In VM's this is done at the float arms where the float pins contact them. Specs are in the Sudco Mikuni Tuning Manual, and a Google search will also turn them up. If the off-idle stalling can't be cured by adjusting float level and air screws, you'll need to bump the PJ's a step. Now--what needles and needle jets did Bertaut stick in there?

 

[Dogger]

Thank you Grizld, after several months of waiting for my carbs I was starting to figure I had gone the wrong way. I wish I had dealt with 650central instead. Now I have the carbs and need to make them work.
Unfortunately with 2 kids, long hours at work, and preparing for a massive home reno, I don't have much more than an hour or 2 at a time to work with the bike. If it takes me awhile, that's fine, working on it is part of the hobby. Before I work on the carbs, I plan on rewiring the bike, fixing the pushrod seal, changing the cam seals and gaskets, plus lubing the advance mech. (it was suggested that this was related to my cold starting problem- I want to eliminate that possiblilty).
This thread got me thinking about the carbs again, but I know valves and timing must be set right before I mess around with them.
My Klx250 had the same issue with cold starts, having to gradually open the throttle until it would run at higher rpm, when I increased the main jet, and raised the needle 1mm it went away. Just a fluke?
Anyways I am sure I will need a lot more help in the future, and I appreciate the help from the guys who have already done it!

 

[grizld1]

Remember, you're working with an air-cooled engine without electronic intake controls; in cold starts you'll usually need to get off the chokes as soon as possible to avoid fouling and apply a little throttle for a short while before the engine will run on its own. And you're going about it the right way--get the ignition and valve train right so you don't wind up trying to chase those defects through the carbies. A good multitester is your friend.

 

[gggGary]

Hey I found my Yamaha J K manual today and it shows the correct float height, fuel height and measuring point technique for plastic float BS34s . Here are a few pics.



If there is doubt, I blew up the float height photo and the measuring point is the part that the tang attaches to not the step down area that curves off.
Not stepping on toes I hope, just trying to get this down right.

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[xjwmx]

The descriptions are so vague and the photos so poor that I just don't know.

As I described, the way I ran best, by a long shot, was 22 mm (a hair over) off the bare surface (no gasket) measured to the apex of the round part.

Also - since the change, with the setup I've described, I've gotten 58.6 mpg. On mountain roads and in 5th only about 2/3 of the time. That compares with what I was getting before.

 

[xjwmx]

A very interesting followup to the original post. The float needles I installed back then suddenly got unusable a couple of days ago when the rubber tips swelled up. I remembered I had the Mikuni needles and seats I took out back then with me now. I was able to fix the original problem with those seats I think by chamfering an edge with a pocket knife followed by steel wool.

Putting them back in, the bike wouldn't start - extremely lean. Lowered them a 1mm at a time until it started easy and ran right. Following the philosophy that the machine is boss I eventually settled at 19mm, as crazy as it seemed.

--Remember back then when I used the new needles with the old float setting and it smoked like crazy. 22mm was right for those new needles, 19mm for these, and I might go to 18mm. Ironically and coincidentally that is 22mm measured from the top square edge, the highest point on the float.

These are genuine Mikuni seats, and I presume the needles are too. Don't know what part number, but they do fit right.

Somebody probably used them because that's what they had. And commendably, adjusted the float and left the jets and screw alone!

If I'd changed the mix screw or jets with these needles at 22mm I don't know what I'd have ended up with! Well, they were the needles and seats I had available to me, and I'm back on the road. BTW, the original post was made in the house I grew up in, which no longer exists, and I think I am in Texas. All totally unpredictable at the time just one year ago. The only predictable thing was that Mike's needles might fritz