First bike 81 xs650 bobber. Flat power at high rpm

Gavin Mackenzie

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Hey there everyone, new here, new to riding, working on bikes etc... looking for a little advice in the right direction.

Recently purchased my first road bike 81' xs650 bobber. Fun little bike so far! Issue I'm running into is, the the bike starts fine, idles fine, and rides fine, as long as I don't get on the throttle (like i want to). I don't have a tacometer or speedometer so I can't really relay any speeds or RPMs to you. But it feels like what's happening is when I try to get to the top of each gear too quickly, or even when I do it slowly, it reaches this flat point and sputters a little bit. Where as I would think I should be able to give it to her as hard as I want in each gear, no ?

Anyway what I can tell you is I changed the main jets from 140- 142.5 this morning, thinking it wasn't getting enough fuel, messed around with the mixture screws ALL day with no significant changes, other than it was very slightly better when I had the screws almost 4 turns out.

I've got these fishtail shaped exhausts, and metal screened AirPods with 142.5 main jets, pilot jets (I think that's what they are) are plugged with rubber plugs.

Also checked the needle height as i had read earlier there may be 3 settings for that clip, but I only saw one setting for the needle.

Any help at all is greatly appreciated and I will document any changes I make on here to hopefully benefit the next guy. Thanks!
 

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You'll need to get rid of the K&N filters. The CV's don't like 'em. Mixture screws are for idle mixture.... nothing to do with the range you're concerned with. You should probably read this carb guide and go from there.
Welcome to the forum!
 
Thanks everyone, unipods is what I'm hearing/ reading everywhere. Would you recommend the Canadian needle with the 3 settings instead of 1, even with unipods ?
 
Just try the Uni's with your new jets and see how she runs.
Double check the rubber slide diaphragms for any pin holes or cuts if it continues.....costs nothing to check.....
 
Right on will do. I had the whole carb apart today for a little inspection after not seeing much difference with new jets. The rubber diaphragm on one carb did look a little worn out, cracked, dry, I'll add those to the order. This site is amazing I can't believe how many people are already helping out. I really do appreciate all of this!
 
now another thread about the same thing with posts wasted.............Not wasting my time here
 
now another thread about the same thing with posts wasted.............Not wasting my time here
Damn man my bad, just made a profile here today, posted on a different thread before starting my own. Obviously learning quickly how things are run around here. Didn't mean to piss ya off!
 
Another suggestion. Edit your "signature" to include all the info on your bike (year, carbs, ignition etc.). That way every time you comment, all that info will be displayed for others to know what kinda bike we're dealing with here.
 
I see you have a HHB Hydrolic clutch set up...........What else of his products has been installed..........need to identify the ignition system and the charging system. If the charging system is factory ..............then it could be battery related......... If a PMA it could still be electrical..............Post all the changes to ignition/charging systems or what you know you have..........or if you don't know then have a look, take pics and ask.

Electrical systems can be confused as carb problems and vise versa..............
 
The only way to learn about setting up your carbs is to forget what the PO has told you, ( if he knew then why didn't he do it), and start from factory settings and go from there, using the recommendations from the carb guide, (and read the link to the carb page i posted in the other thread), relating to any bike modifications, (exhaust, carb air supply), learn to sync the carbs and don't just adjust pilot screws willy nilly. There are recommended settings but every bike is different and so is each cylinder, meaning the difference could be as much as a 1/4 of a turn on the screw from recommendations.
 
Ok, I'm going to do the test on the rubber slide diaphragms from that carb guide tomorrow to see if those little abrasions are affecting anything. I can to that conclusion too, just cuz the PO said he knew what he was doing, doesn't mean he did it correctly. The only other things he changed were the hydraulic front brake lever, front and rear wheels. I put a new battery in it this morning as well.

Other potentially useful/useless info...

-after new main jets (and thinking mixture screws would finish the issue)
I would ride through 1st and 2nd gear over and over again until I hit that flat spot, continually drawing out the mixture screws.

-eventually the new battery died but i got it jumped. Did it die from starting it and stopping so many times without an actual ride in between ? I was in a parking lot so I wasn't riding far in between each time I started it.

-when it did stop starting (with the button) I tried kicking it probably 40 times and pop start on a hill once with no luck. Kick start SHOULD start the bike even if the battery is dead correct ?

Hopefully that gives you guys some info. I'll post some more pics of the whole bike tomorrow to give a better idea of what's going on.

And looking at the bikes VIN I believe it's the XS-H special II as I just added to my signature on here.

Thanks everybody
 
Kick start SHOULD start the bike even if the battery is dead correct ?
In a word... no. Until you tell us otherwise, I'm gonna guess you've got the stock TCI ignition system. It get pretty "iffy" when batt. voltage drops below 10-11 volts. Charge your battery, start it and you should see about 14V charge at about 2500-3000 RPM. At this point I'd strongly suggest you make sure your charging system is in good working order before carb tuning. As skull already pointed out, carb and electrical issues can easily fool you into blaming the other....
 
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