xtz 660 problem....

[bobbyrandall]

hello all....my friend and I both have identical xtz 660´s from the same year...his will get to almost 100 mph but mine will not go over 70mph...have checked and both sprockets,chains and exhausts are the same...any ideas..
he will not let me swap the carb before anyone suggests this......!

[futronix]

well bobby, thats a bit of a weird one... firstly your trusty old xtz should be able to get you a long way over 70mph. not that you need to be told that.

i would probably start with a compression test of your engine, that would be the first idea, then check carby differences, ie jetting, internal mods,check the spark output to the plug...and perhaps the plug itself.... if all this is the same as your friends i would be surprised...

and perhaps check to see if you are running similar rear tyres, if you have a lower profile tyre this may effect its top speed...

very broad reply i know but.... difficult to say, but im betting your motor is a little down on compression compared with your friend bike, do they use the same amount of oil on long rides ?...phil.

[smokinrider]

you say they are identical.
are they the same year, are they both standard? are they both the same mileage? before you start pulling bits off lets establish the facts.
has he fiddled with his, you with yours? if so what. i presume you have done a service, set the valve clearences, new plug, cleaned the carbs and air filter, checked your brakes arnt binding.
if not then thats your starting point, youll need to have the carbs off anyway at some point to compare jets so when its off cleaning it, take note of jet nembers and sizes, to save time later. post them on here and no doubt someone will notice if they are seriously wrong.
your bike should be doing well over 70 so something is out somewhere. but often its a simple thing like blocked jet, fouled plug? dirty air filter.
if the motor runs and doesnt rattle and smoke then the chances are that there isnt anything major wrong with that.

[Bill Ryder]

Also check the exhaust to see if it has become plugged. Sometimes they rust up. If it has a diaphram type carb check that the diaphram is identical to your friends. It is quite easy to swap that one part. If He is your bud he would help you out wouldn't he?

[bobbyrandall]

its not the exhaust..i have swapped the exhaust from his bike to mine...at standstill you can rev the bike to the redline easy....when on the road the revs go to the redline but the bike is doing 70 mph or less at that output...i have opened the carb and the diaphram in the second body is sound....am going to fit different carb soon from another bike and check...also should it run temporarily with no air filter as it does not want to run with the filter out...?

[Bill Ryder]

Did you say that your bike will redline the tach in high gear? Count the number of teeth on your front and rear sprockets and compare it to your friends. If the motor is redlined then to increase your road speed you have to change the gearing. Unless you have a faulty tach or speedo.

[AnteK]

Originally Posted by bobbyrandall

hello all....my friend and I both have identical xtz 660´s from the same year...his will get to almost 100 mph but mine will not go over 70mph...have checked and both sprockets,chains and exhausts are the same...any ideas..
he will not let me swap the carb before anyone suggests this......!

First of all, check second carb membrane...

[onepotbaz]

Originally Posted by bobbyrandall

its not the exhaust..i have swapped the exhaust from his bike to mine...at standstill you can rev the bike to the redline easy....when on the road the revs go to the redline but the bike is doing 70 mph or less at that output...i have opened the carb and the diaphram in the second body is sound....am going to fit different carb soon from another bike and check...also should it run temporarily with no air filter as it does not want to run with the filter out...?

clutch .?.

[Livotlout]

Hi Bobby,

I have a MZ Baghira with the same XTZ660 engine, and my guess it is fuel starvation - you did say it would not run without air filter!

Things to check are , is good delivery from tank petcock?, is filter to petcock clear?, delivery line to carb in good condition and not kinked, connection tube between primary carb float bowl and lower end of Seconday carb - is this clear?, and lastly is the very small fuel filter, that sits on top of inlet valve (you will have to remove it - one screw) to the float bowl on the primary carb, clear?

Best wishes

Alec

[bobbyrandall]

the adjustment between first and second carb body...someone in its life has fiddled with the screws..the throttle was opening ok but not opening the second body butterfly correctly.......aaaargh!!!
RUNS FINE NOW.....!