Question about Jetting

I've been working on the 81 kz750 I bought about three weeks ago. I have pulled the carbs off so many times I can do it with my eyes closed. It had pods on it when I bought it, and I have been trying to get it running right.
it has cv 34's on it and the jets are #62 and #150, I can't get the thing past 60000 and it starts sputtering just over 5000. I read it the other threads that 70/140 is the best Combination, for running the pods, but I'm concerned, would switching to the larger main burn more fuel? I'm sure dropping the secondary might help. Right now the thing drinks gas like a 67 Ford pickup with a big block.

Wired George is the expert on jetting.

One thing I know, if the jets are wrong it will hose your mileage just because you have to crank the throttle open more and tach it up higher to get it to go.

Clean the slow jets as best you can, find some #70 main jets and #140 secondary main jets (normal Keihin mains). The #150s are quite a bit too large and the mid-range is weak with the #62s.

I found the main problem with the acceleration, the vacuum gauges were telling me what was wrong and I wasn't listening.
The mechanical advance was froze up and would not move. Once I freed it up, cleaned it and got it working smooth, the bike went right to running out like it should.
I do think you are right, #70 main jets might help the midrange. Pulling a hill, it's a little week between 3500 & 4000 but still 500% better than it was.
I would also hope switching to #140 Secondarys (instead of the 150's that are in it) would help the fuel mileage. I don't really know what kind of mileage the bike is suppose to get, but on a run of a little over 100 miles today it got 30.1 mpg. Is that close or should it be better? part of the run was on state road at about 50 mph, and part of it was interstate at 65-70 mph.

I get about 95 miles to a 10$ tank-ful doing mainly 65-70 mph.

I have exhaust, pods and Jetting, and have learned that is somewhat par for the course for a bike as old as mine.

Different bike, different carbs.

wrcarter wrote:

I found the main problem with the acceleration, the vacuum gauges were telling me what was wrong and I wasn't listening.
The mechanical advance was froze up and would not move. Once I freed it up, cleaned it and got it working smooth, the bike went right to running out like it should.
I do think you are right, #70 main jets might help the midrange. Pulling a hill, it's a little week between 3500 & 4000 but still 500% better than it was.
I would also hope switching to #140 Secondarys (instead of the 150's that are in it) would help the fuel mileage. I don't really know what kind of mileage the bike is suppose to get, but on a run of a little over 100 miles today it got 30.1 mpg. Is that close or should it be better? part of the run was on state road at about 50 mph, and part of it was interstate at 65-70 mph.

I'd think it should do better than that, but my 750 is a twin not a four. I get 40mpg (all stop and go) and got about 50 - 55 mpg on the freeway back when I still rode on the freeway.

Do you have a windshield? Wind drag has a HUGE effect on mileage on the freeway. The upright windshields are like air brakes. The streamlined fairings can actually increase mileage.

I don't have a windshield yet. I did another run today and filled it up after 69 miles, the mileage was up to 32.8, I'll check it for a few more runs and see how it comes out. speaking of accessories, does anybody know where I can find a passenger back rest bar and luggage rack to fit this bike, or should I just give up and build one.