1982 xj650 rpm's slow to fall after rev. RESOLVED

I have a 1982 650Maxim that has a "new" set of just cleaned carbs. I have read alot of the searched posts that I can find from the site guru's but still have not found this issue addressed. I have sync the carb's and they all are the same with a good idle and nice acceleration but..... the rpm's are dropping slowly like a second or two from 6000 to 1000. It doesn't sound like much of an issue but their is no engine braking going on so it makes for a uncontrolled feeling while slowing down. This is a new symptom so I know it is an adjustment I am just not sure what one to head for.

Thanks for your help and the great site here.


Art

Clean clean clean then clean the carbs again. Flush with a ear cleaning bulb and seal the flange from the engine to the intake rubber on the carb. Don't be fooled the engine can pass the propane test with the leak in the gasket. I cranked the engine with a rubber gloved hand over the inlet and if it is not leaking it will hold a suction for a few seconds.

 

Re: 1982 xj650 rpm's slow to fall after rev.

hello aplumma

- I believe there are many cases on the site of revs not dropping and it usually points to one of two things (or both); synch and/or mixture.

Mixture includes an air leak, so check if you have a small air leak anywhere.

Have you run a colourtune yet? A slightly lean mixture will present the symptoms you are experiencing.

These points are where I would start to look and check.

 

Re: 1982 xj650 rpm's slow to fall after rev.

i had to turn my idle adjustment way down to keep it from doing the same thing, but now mine wont idle on its own, other than that i dont know whats causing it either.

 

Re: 1982 xj650 rpm's slow to fall after rev.

Yes, if you turn the idle down it will bring the revs down as doing that effectively closes the butterflies and eventually you'll have a no-idle situation and possibly a no-start one too.

Do check, firstly your valve clearances, then a bench synch to bring you to where the engine will actually run. Bear in mind that after a bench synch, when you hit the start button, the revs may be way too high. Just bring the revs down with the idle screw to a manageable point.

Then a on-bike synch to fine tune, alternating between mixture tuning (colourtune) and synch (as each one will affect the other). I usually do synch/colourtune/synch/colourtune, otherwise you'll be at it for evermore.

This is assuming of course that you have checked for any air leaks. If there is a hint of an air leak, you will be chasing your tail.

 

Re: 1982 xj650 rpm's slow to fall after rev.

Do your slides pass the clunk test?

 

Re: 1982 xj650 rpm's slow to fall after rev.

Sorry to jump on someone's thread---but what is the clunk test?

 

Re: 1982 xj650 rpm's slow to fall after rev.

The vacuum operated carb slides, should be so highly pollished that they spring closed with a clunk.

 

Re: 1982 xj650 rpm's slow to fall after rev.

Thanks for the input... The bike passed the propane test and has new rubber before and after the carbs with fresh stoppers on the taps as well. The slides were polished using 1200# and wd40 and all slide down with a nice clunk. Number 2 and 3 are slightly slower than 1 and 4. I have the pilot circuit set at 2.5 turns and I did not bench sync them but did sync with a manometer. While the valves clearances are not perfect with the old carbs it did not do this but #4 was not feeding fuel correctly thus the reason for the different carbs. I am not worried about fixing the old set it is a winter project for me. If the butterfly are correct and closing is it possible that I am feeding to much fuel thru ? circuit in the carb. I will pull them down again and bench sync them but after you bench sync them and hook them up too the manometer I am using the same screws and adjusting them to a different setting ? I haven't used the color tune yet because i don't have one but if it is the cure then I will get one.

Thanks for the ideas and keep them coming


Art

 

Re: 1982 xj650 rpm's slow to fall after rev. more info 6/19/

If two and three are slower than one and four, then that's likely your problem. There should be *NO* resistance at all when dropping them.