why is my xj650 topping out at 97km/hr?

Hi. new to the site. I have a 1983 XJ650 Maxim that was chopped into a bobber. When I am in 5th gear the fastest I can go is 97km/hr or if I remember correctly 4000rpm? but I last rode it in September. It begins to feel like a wheel is out of balance but that isn't the issue. When I first bought it the bike had been sitting for a year or two with a cut ignition. It wouldn't start until we took the carb out and cleaned it to loosen up one of the plungers. Now it runs but tops out at that speed. I took the carbs apart thinking a rebuild kit and some ultra fine sandpaper would get her running smoothly. Now I am not so inspired and am eyeing a set of Murray's Carbs but that price tag is steep. Thoughts? Solutions? Patrick

 

No to sandpaper!
One or more of the slides are stuck closed?
Are the jets in correct location?
A good cleaning of all jets and passages
Check diaphragms
Float levels
Throttle shaft seals!!
Etc etc
Oh yes and valve clearance

 

Does carb issues make sense with the topping out of speed?

 

Fuel supply issue?

 

Chopped into a barber are you using pods instead of the airbox that would cause you to top out of the speed you're talking about as well as the carbs not being properly cleaned and functioning

 

Sorry but this sounds like a PO ( previous owner) strikes again . Toomaybikes is spot on if the carbs are not done right and valve clearance off the bike will NEVER run as it should . If you do the carbs the RIGHT way the FIRST time then you will have a good running bike , skip steps and you will be frustrated. The ONLY way to do carbs you don't know history on is full tear down and full soak and replace the butterfly seals ( this is where a full tear down is involved ) If you don't feel up to this member Hogfiddles can rebuild them for you , but they are not hard to rebuild . As to trying aftermarket carbs this is something that will STILL require tinkering with . I have rebuilt numerous carbs the Hitachi carbs are for the most part are easy to rebuild . The parts are all available from xj4ever ( click on the upper right corner of the home page ) . Good luck .

 

This I totally disagree with.
Yes, strip, clean thoroughly (no sandpaper) the carbs and all their tiny orifices, jets and needles. The throttle seals are only important at the idle end of the scale, and have nothing to do with your top speed issue. Sure, if you want to do the job once, and have a perfect running, ticking over bike, you may need to change them, but this is not a job to be undertaken lightly, with many trip up points allong the way.
I've turned three sets of green gungy carbs into perfectly acceptable working sets without even opening the throttle shafts - two mukunis and one hitachi. Ask yourself, or look up old posts - see how many people have failed with this job. Send them to an expert if that person isn't you, or just clean properly and rebuild.

 

the original airbox is still in play. will burn sandpaper even though the Aussie on Youtube said to use it. . they are already stripped down completely and ultrasonically cleaned. I am a novice when it comes to the ICE. I will look up Hogfiddles.

 

Somthey've been cleaned - did you squirt carb cleaner through all the orifices to check them?
Also, this:-

 

Have pulled everything apart, purchased a rebuild kit, waiting now on replacement seals for the ones that are dry and brittle.

 

A set of carbs out of synch can cause poor running at speed , even though it might idle , had a guy brought me a set of carbs , it felt like it was only running on three cylinders . Checked them over , found number two slide would only go up half way , it was gummed up , a little scotchbrite and it was better . I looked closer and found all the butterfly seals were packed full of RTV . I replaced all the seals end result bike ran great . All I can say unless you know the history of a bike and the carbs there is a good chance carbs will need internal cleaning, float height adjustment , synch , valve clearance checked and possibly adjusted . All can effect how well a bike runs . I realize not everyone has the capability or knowledge to do some of the things listed , but with a little time and patience many things even a novice can learn how to make it rungreat.

 

Sorry, not buying it. The principles of carburetion don't allow it - tiny leakage paths at the spindles, compared to wide open throttles, slides right up, masses of air and fuel coming through the carb bore? No way. In your example above you actually changed two things (seals and a gummed up slide), so the argument is moot.
Anyway, I won't dispute you have to have the valve clearances right, or at least not a mile out, the jets in their right places and clean, fuel level correct, I won't even argue that the original filter and airbox should be there (although my 650 runs fine without filters, or even with the dreaded Chinese pods which I binned).
The thing is though, rebuilding a rack of carbs is fraught with difficulty for the beginner - the attention to detail needed is just not grasped by the novice, and to take it on as a first job? What are the chances of success? Pretty low I would say.
To @ThePadraig - your rebuild kit - was it Chinese? If so bin any jets, float valves and needles. Get your stuff from @chacal , that way you know it's correct. Keep each carb seperate, use jis screwdriver, check all orifices are clean by squirting the liquid of your choice through them. Set fuel heights within spec, bench synch using the first progression hole. Don't overtighten screws, but make sure the butterfly screws aren't coming out...

 

You never do.

While you are correct that throttle shaft seals won't cause the trouble that the OP is having, replacing them while the carbs are torn down for service is a good idea. Preventative maintainance on a 30+ year old machine saves trouble later on. If you're just flipping a bike you can get away with skipping some things, but if you're keeping it to ride for several years it's a false economy to overlook the little things, especially when even a visual inspection shows that a part needs to be replaced.

The OP is going to be happy that he doesn't have to tear the carbs down again when he ends up with a racing idle because of vacuum leaks at the throttle shaft seals. And before you say that it can't happen, it has been observed and confirmed to happen, and corrected by just replacing the throttle shaft seals with new.

 

While you are waiting for replacement seals, make sure to have a read through of the entire RickoMatic post on cleaning the carbs. https://www.xjbikes.com/forums/threads/clean-your-own-carbs-the-whole-9-yards-by-rick-massey.2908/ I found it very useful. Especially the part mentioned above by Minimutly. The Haines manual incorrectly identifies the pilot and main air jets. I fell into that trap it was running way too rich after the rebuild. After correcting them it ran like a sewing machine. If you have questions this forum is the best place to ask them. Everyone I've interacted with here has been great! In fact I think I owe a couple of people here beers.

Jeff

 

My friends, XJ bikes and carbs are the perfect learning ground for the beginner from start to finish. Though I know all of us value our machines and think highly of them, we also know they are almost 40 years old, were a mass production vehicle, and in many cases will not increase in value over the long haul. ThePadraig's bike has already been chopped and who knows what done to it. Great learning experience to completely disassemble and reassemble a complicated carb like ours. Hopefully, the individual will pay close attention during disassembly, learn and research replacement parts, carefully reassemble, and tune. Trial and error. Great bike to learn new skills without breaking the bank, and fun reward to ride once the repair has been successfully accomplished. Carbs will likely have to come off and on numerous times before getting it right; all part of the learning curve. If it never runs right, well, likely didn't break the bank on the XJ and hopefully have a lot of take away knowledge about the mechanicals of a carbureted motorcycle. I'm not a big fan of amateur mechanics f'ing up motorcycles, chopping up the XJ's, or ruining running machines. But, we all learn somewhere; for some as part of a career path in a mechanical occupation, for others garage hobby. Some of us had mentors, others learned through various failed projects and trial and error.

 

Well said @Scott I. And the 650 Maxim definitely is a perfect first bike to tinker with - there are lots of examples out there in every condition from crusty parts bike to pristine, and parts are mostly readily available. So even if you completely mess it up, you can recover pretty easily.

In fact, my "trial and error" bike is my beloved XJ650J. I still recall the first time I checked valve clearances - seemed terrifying at the time. Now it's just like routine maintenance.

I would never want to discourage somebody from doing their own stuff. But if they feel they know their limits and choose to outsource some work, that's cool too. I have sent a rack to @hogfiddles - I don't regret that decision at all. They came back perfect. No way I could have done that. Plus it freed me up to do other projects.

My general advice:
- Learn all you can, especially from this site.
- Be patient (I struggle with this)
- Have fun. Yes, things can be frustrating sometimes, but you'll get it
- Mistakes are OK as long as you learn something

 

Some newby comes on here and asks a question - and the answer is allways "church of clean" well maybe that's what the carbs need, but the problem, and the correct sollution is being ignored, so no one learns anything.
Carry on self flaggelating, I'll bring the birch branches, or your tree of choice and watch.
And stop doing what you allways tell me I shouldn't - put your words into my meanings - leaky throttle seals will never (should I use shouty caps for effect?) ever cause a top end issue - I guarantee it.

 

Get the flags and bunting out, I'm correct!!,
Aand, the second bit - "just replacing the throttle shaft seals with new" - what so this person who observed this did not then set up the vacuum synch correctly? So it was not just a replacement seals job.
I tell you what, my seca has a clean but grubby set of Hitachis that need going through properly (I only cleaned them).. so when the time comes, I will strip and remove all the shaft seals, put them on the bike and set the vac synch. If it doesn't idle and run near enough as intended I will be very suprised, but I promise I will upload a video of it - whatever the outcome - fair enough?

 

could be main and pilot fuel jets are reversed. even if just on 1 carb
could be he has pods
need the poster to let us know a few things.
dirty emulsion tubes possible

when i see bobber I do think he may have pods.
it will end up being a collection of things
slides not moving fully or freely
maybe he needs to sync carbs

 

holes in diaphrams too