xj600 help.

[brianmm]

Hi all,I have a 91 yamaha xj600,Bought it about a month ago and the problem is a strange one,it acts like its restricted,top speed of about 75mph,itsquick enough getting there but then it just stops accelerating,its had new plugs,air filter,oil.checked the inlet rubbers and carbs for restrictors,nothing,fourth gear t will rise to almost dead on 7 thousand revs and thats it,no sign of engine wear,starts first time no oil burning gives 50 mpg and is smooth up until the point where it plays silly buggers,any suggestions?doesnt seem to be drawing ar from anywhere it shouldnt,any help is greatly appreciated.Thanks all.

[serlant]

My XJ600 does just under 100mph restricted but will still rev through to 10500rpm, so doubt its restricted to 33BHP, does the throttle open fully? could be a bodge restriction.

[Frost]

So it won't go above 75 in any gear? As it it stops at exactly 75 in 4th, 5th and 6th?

If so then there may be some electronic speed restriction in place, some wire may be disconnected putting the bike into some kind of a safe mode. This is unlikely. Non standard gearing may possibly cause this.

Or does it go slightly faster in 4th than 6th? This is more likely and will indicate a lack of engine power making acceleration difficult. The bike will also be slower up hill. Quite possibly it's only running on 3 cylinders. Start it from cold, weight 30 seconds and spit on each pipe, no sizzle means that cylinder isn't running.

Almost certainly your problem is due to air, fuel or spark (thats usually the case with anything) so eliminate one at a time. Spark is usually the easiest to check. Cleaning or replacing the air filter and making sure everything has a good seal is effort but inexpensive. Fueling issues are potentially expensive as they are difficult to test and prove without a dyno. Generally cleaning the carbs (manually, not some wonder spray) and putting everything back to what the manual states will solve and problems cause by armature efforts at 'tuning'. Checking that the choke isn't sticking on would probably be the first place to start.

Just to confirm, this is one of the old model ones?


https://t3.gstatic.com/images?q=tbn:C8X_cnfHyelLmM:https://texascycleusa.com/_images/Yamaha-XJ600-1984.jpg&t=1
I loved mine

[brianmm]

Hi Dfo,It does go slightly faster and it starts hunting if you know what i mean,as though it wants to go harder but is being held back,These are very good pointers m8 thanks,I will try them out this weekend.never owned a four cyl before so this is new to me,if t was only running on three would it not be rough?They only made this model for a year between 91 and 92 so it has some pre diversion stuff as well,it was just on the changeover.cheers.

[evoboy]

I have one these in the garage.

Itd pull 125mph indicated without much trouble, just stick it in 6th from bout 40 and wind on, love that motor!

The plugs are nice and easy to get to, dont even need to take the tank off.

Itd probably be worth giving it a service if its not been done recently.

A carb clean, plug change, oil and filter and an airfilter.

Ours is on 53k and it still runs spot on. (Tis' for sale if anyones interested!)
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Suzuki GT250 x7------- Fazer 600------CB250RS------Aprilia Rally 70----- Bandit 600

APT Motorcycles

[Frost]

Mine was a J reg and would easily get above 120. The older ones have more powerful revvy egines. Handling is very 80's though

[Pete.]

[brianmm]

Sorry about that pete,it does it in every gear,revs up to just under 7 thousand and then starts as though its lurching somehow,hard to describe,you know how a warped disc feels when braking?catches then releases well if you can imagine the engine doing the same thing sort of like hunting wants to go but holds back,sorry m8 my description is bollocks,almost like kangaroo petrol lol.

[Tiff]

Mine did that too, a good carb clean and balance sorted it out. Try doing it with the choke out ,see if it makes any difference..
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1996 Kawasaki GPZ1100s,1996 VFR750,1980 BMW R80,1982 Kwak Z250B,1992 ZZR1100C,1996 BMW K1100LT,1994 Kwak ZZR600E,1993 BMW R1100RS,1992 ZZR 600D,1988 BMW K100LT,1998 Aprilia Pegaso 650,1994 Suzuki RF900,1991 Yamaha XJ600, 1988 Honda Dominator,1992 Kwak KMX125,1987 Yamaha RD50MX,1984 Honda MBX50.1984 Honda Superdream 125

[iooi]

[brianmm]

The clutch is good,a blocked fuel filter is something i never thought of,possibly collapsing on itself.I`m not sure if it has one either but ill find out,Its a nice day to dig out the tools and watch the bikes go by lol.cheers.

[gearboxkart]

My H-reg xj600 flies upto well over 100, it was running a bit rough a few months ago, removed carbs cleaned all the jets out blew it all out with air line and also take carb tops off and check the diaphrams, and that totally transformed the motor, its 1 of 2 things carbs or a breakdown of the HT leads/plugs at high revs, does it rev past 7k when not under load as in on the stand will it rev past 7k and hold steady and smooth ! i know it sounds awfull revving the billies off the motor on a stand but its only for a few secs.

[brianmm]

Yes it will red line without a problem when its on its stand,nice and smooth,I found that rather strange.sounds horrendous as you say though

[iooi]