15 replies to this topic

[cooper956]

as some have you may have seen im new here iv made a couple of post up to now.

iv now riden my 96 250 jtr? and it would only run well on choke haveing cleaned the carb it now runs without choke but im unsure how to set the carb up all i can see is the idol screw and near in a small mix screw? how do i ajust the correct?
i also carnt get it to idol nicely its ether too high or to low and stops i can ride it and its fine when on the revs ect pulls very well but when u let off or are on low rev it bounces thats the only way i can discrbe it so if you going slow and low revs it sometimes lurchs hard to dicribe but im sure its not right as no other bike iv riden has done it. any help welcome i realy want to get it runing spot on
iv cleaned the carb air box and fuel tank and cleaned the plug

on my list of to do are
new folk seals
new plug
new airfilter
and oils (whats oil do thay use?)
anything else i should check?

Edited by cooper956, 23 July 2010 - 05:25 PM.

[Blocky]

Sounds like you should add crankshaft seals to your list

[joekarter]

It sounds like an air leak. A couple of quick ideas:

Check to make sure the sparkplug is tight and has a good gasket.

Check all the carb vents to make sure they're not clogged or pinched.

Take a squirt bottle and fill it up with water with a bit of soap. While the bike is running squirt it around the intake manifold, carb junction, case seam, and base gasket areas and see if you can detect any where that's leaking (you'll see it suck in the soap bubbles).

Plug the vent hose that comes from the crankcase and see if the issue goes away (clutch side crank seal).

Take a tube of silicone and REALLY seal up the ignition cover and see if it changes (ignition side crank seal).

Rebuild kit for the carb.

Joe

[JSE]

 cooper956, on Jul 23 2010, 06:57 AM, said:

as some have you may have seen im new here iv made a couple of post up to now.

iv now riden my 96 250 jtr? and it would only run well on choke haveing cleaned the carb it now runs without choke but im unsure how to set the carb up all i can see is the idol screw and near in a small mix screw? how do i ajust the correct?
i also carnt get it to idol nicely its ether too high or to low and stops i can ride it and its fine when on the revs ect pulls very well but when u let off or are on low rev it bounces thats the only way i can discrbe it so if you going slow and low revs it sometimes lurchs hard to dicribe but im sure its not right as no other bike iv riden has done it. any help welcome i realy want to get it runing spot on
iv cleaned the carb air box and fuel tank and cleaned the plug

I'd try adjusting the carb before doing anything else (always start with the simple and inexpensive things first).

Engine warm in neutral, quickly open and close the throttle, each time adjusting the mixture screw 1/4 turn (the screw to the left of the knurled screw in the middle of the carb body) in or out until you get the best RPM pickup or throttle response. You can start by going in or out with the mixture screw, the engine will tell you when you need to go the other way by bogging.

Then, with bike in gear and clutch lever held normally in (usually one finger to knuckles of hand), adjust the idle speed (the screw in center of carb body) to where you like it.

If the bike continues to lurch, I'd look for an air leak, usually the intake manifold gaskets area to start. The manifold is commonly overtightened and bows out the flexible manifold in between the bolt holes.

Jon

[cooper956]

hi thanks for the quick replys i had thought of crank seals. are thay a big job? h ave noticed the carb to engine rubber manifold is cracked it may be the leak any advice on where to look for these parts and how much thay are likely to cost we do have a local gas gas dealer i beleve in buxton are but there website dosent list many parts and prices

[joekarter]

Not sure on the price but someone close at this link should be able to help you:

http://www.gasgasuk....gas-dealers.php

[cooper956]

nest question what size should the folk seals be on a 96 jtr to save me takeing them out to look before ordering some still not found many parts online supose ill have to go to the shop or ring up but as im on a budget i was jaut wanting to look things up

[joekarter]

Instant parts manual......ain't the internet grand!

http://www.gasgasmot.../Resources.html

[JSE]

 joekarter, on Jul 23 2010, 01:06 PM, said:

Instant parts manual......ain't the internet grand!

http://www.gasgasmot.../Resources.html

That's a good resource.
The 96' takes the ST950220 seal which is an RSC 38-48-10 double lip type. I just pulled one out of my parts box
to check it against the manual.

Jon

[cooper956]

still havent got the parts i need but been on the bike tonight and my be a daft queston but what way is choke on? with the lever down it runs while cold okish but when wormm isent as good but when you stop it you have to lift the choke up if i leave the choke up it idols and ride quite a bit better am i just useing the choke the wrong way round or is this a sign of whats wrong? thanks in advance

[joekarter]

With the lever down the "choke" (actually in your case the enrichment circuit) is on. You use that when the bike is cold to richen the fuel/air mixture. With the lever up, that circuit is disabled and the fuel mixture become leaner. That would be the normal setting once the bike has warmed up.

This is a pretty good primer on typical motorcycle carbs:

http://www.motorcycl...om/carbs101.pdf



And here is an explanation on the various types methods used to make the fuel/air mixture richer for starting:

http://www.dansmc.com/starter.htm


Joe

[JSE]

 joekarter, on Jul 25 2010, 04:09 PM, said:

With the lever down the "choke" (actually in your case the enrichment circuit) is on. You use that when the bike is cold to richen the fuel/air mixture. With the lever up, that circuit is disabled and the fuel mixture become leaner. That would be the normal setting once the bike has warmed up.

This is a pretty good primer on typical motorcycle carbs:
http://www.motorcycl...om/carbs101.pdf
And here is an explanation on the various types methods used to make the fuel/air mixture richer for starting:
http://www.dansmc.com/starter.htm
Joe

Thanks, Joe, those are good basic sources.

You may be confusing the Mikuni with the Dellorto with the choke levers. Pressing down on the early Mikuni type lever turns the choke "on"
and pulling the black plastic lever straight up on the Dellorto turns the "choke" on, which I'm sure is what you meant.

Jon

[joekarter]

No sweat,

The truth is I wasn't sure exactly which he had. I've not worked on a Dellorto and didn't know if it had the "pull up to actuate" operation or the push the lever down "which actually pulls up the actuator" type of setup. He had mentioned a lever so I took a stab at the answer.

[cooper956]

just a thought and may be wildlt wrong but could it be the head gasget? looks like its got some sealnt round it on the mag side of the bike not sure why

[JSE]

 cooper956, on Aug 4 2010, 12:41 PM, said:

just a thought and may be wildlt wrong but could it be the head gasget? looks like its got some sealnt round it on the mag side of the bike not sure why

The JTR's don't use a head gasket but have inner and outer o-rings to seal the head to the cylinder.

You might want to check the jets just to be sure they are open, the pilot, for instance, is only about .35mm and is easily clogged or obstructed.

Jon