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I have an 80 Yamaha xjj650 sat for a couple of years, so I rebuilt carbs, replaced exhaust and intake boots replaced plugs cleaned and relined gas tank, replaced pet stick and fuel lines . adjusted jets to 3-1/2 turns set floats to suggested level 17.5, lubed gas cable replaced oil and filters . Bike starts with low rpms, once it warms up its about 1,000 rpms, when I accelerate the throttle it hesitates with a slow start before taking off I am 2 blocked at this point if any suggestions please let me know before I taking it to a shop thanks.

nikexj650 wrote: ↑Wed Jul 14, 2021 6:55 am I have an 80 Yamaha xjj650 sat for a couple of years, so I rebuilt carbs, replaced exhaust and intake boots replaced plugs cleaned and relined gas tank, replaced pet carrot and fuel lines . adjusted jets to 3-1/2 turns set floats to suggested level 17.5, lubed gas cable replaced oil and filters . Bike starts with low rpms, once it warms up its about 1,000 rpms, when I accelerate the throttle it hesitates with a slow start before taking off I am 2 blocked at this point if any suggestions please let me know before I taking it to a shop thanks.

I had the 1982 XJ650R and it was sluggish off the start stock as well. I found a fix by replacing the stock carb jets and needles with K&N Stage 3 versions... increased power quite a bit but at the expense of fuel economy.

Does your XJ only hesitate off idle or any other part of the powerband?

Mike

I'd make sure the accelerator pump is working properly, or maybe you need to size it up to reduce the bog.

yes the hesitation is there on take off, slightly during thrust for more speed . I don't believe the 80 xj650g has an accelerator pump, the Manuel doesn't show one I have never seen any thing that would make me think there is one. Parts book data doesn't show one either, I will look into the jets I installed to see if I can figure something out. Thanks for the feed back, I welcome any suggestions and will keep an open mind, again thanks.

Stock jet sizes? Why 3.5 turns out on the A/F screws? Seems excessive, like pilots too small. How does it behave on choke?

Seems like the choke has to be on all the way verses before it needed less choke, as far as 3.5 turns that was the original setting I tried 3 turns but that 1/2 turn made a small difference. The part I'm not to sure about is that the carb kit I received, the fuel mixing screw wouldn't thread in the hole couldn't send it back I had already installed everything else . I cleaned the mixture screws and reinstalled them I don't know if that's causing the bogging . I did pull a plug and noticed that its running rich because the plug had black soot on it. What do you think something to do with the turns not being right or not proper mixing screw for the kit, I didn't think the screws would matter since it acts like a regulator depending on the position of the screw . I may try resynchronizing the carbs to insure I did it right, by the way the jets were suppose to be stock . Please let me know your taught on this thanks.

You can reuse the A/F screws and their springs and washers, but you should install new o-rings. Try 2-1/2 turns out. Make sure the needles are in the right position, and don't have a stack of washers under them. Also double check your float heights. You should need a bit of choke when cold. No need for choke ever points to a rich mixture.

Did you use jets out of the carb kit?