Carb Tuning - Off Idle Studder

[TeamFrog]

Please HELP!!! My buddy and I spent all day trying to tune his '95 XR600R and have hit a wall. The bike is running great at idle and from mid-range on up. I mean this thing is running perfect and pulls real strong. The problem is that when the throttle is at zero (fully closed) and then you whack the throttle open, the bike coughs and dies or hesitates until you let off a little and then takes off like a shot. If the throttle is slightly open and then you whack it, off it goes. The problem is only when going from fully closed to fully open.

What's worse is that the bike has the ability to be put in a partial choke setting. On partial choke, the off idle studder seems to go away, but of course, the rest of the circuits run like crap. What gives?

Here are some specifics:

'95 XR 600R
Stock Main 152 - Currently running a 162 (Changed due to the addition of a 4" Supertrapp Silencer running 6 restrictor plates).
Stock needle clip position is 3 - Currently set at 4 as a test but was no better than at 3.
Pilot Screw is currently 2 turns out-don't know what stock setting is.
Everything else is stock.

The bike is being ridden is Michigan, roughly 500 to 1000 feet elevation, 75 to 90 degrees, 50 to 100 percent humidity.

Please HELP!!! Is there any way to cure the off idle studder?

Thanks in advance for you replies!

Jeff

 

[ellandoh]

does it do this while riding and in neutral??
while idling does it do the same when gunned to 1/2 throttle??
does it happen at all outdoor temps??

my first things i would do are free which is be sure air filter is clean, clean carb, set float height. play with it some more to get the feel of exactly whats up.

you could skip all this and try one size larger main jet that will most likely cure it, as the same thing happens to my cousins quad and i told him it was lean.........tada :cool:

 

[TeamFrog]

The bike will studder or hesitate regardless of being ridden or in neutral. If you roll of the the throttle (in either state), the bikes RPM's come up smoothly. If you pin the throotle too quickly from a closed position, it coughs so badly that if you don't let off the throttle, it will die. :bang:

We cleaned the carb pretty good but did not set the float level. However, my buddy told me that he never had this problem with the stock set-up (stock exhaust and jets). The kicker is the partial chock setting which makes the bike run better off idle. I'm thinking he needs a bigger pilot (idle to 1/3) as the bike runs awesome once it gets past the cough.

The only modification he did after installing the supertrapp was to go from a 152 to a 162 main jet. He did not touch the pilot. We've been tinkering with the air screw and idle speed but none of that seems to help.

Jeff

 

[ellandoh]

so it stutters off idle whether you jam it to 1/3 , 1/2 . or wot??


jetting is completely independent of rpm's if it is at idle and quickly turned wot you have bypassed all circuits and are dealing with the main, i would do the plug chop for the main however i start with the pilot. a pilot jet is always contributing to the amt of fuel delivered from idle to wot. try to lean the air screw at idle til you get a high rev as if youre running out of gas . you should be between 1-2.5 turns if not you will need to start with a corrected pilot. if you cant get a high idle with the air screw you are way rich and need a size leaner pilot then look for the high idle as you may need more adjusting.

 

[ellandoh]

The bike will studder or hesitate regardless of being ridden or in neutral. If you roll of the the throttle (in either state), the bikes RPM's come up smoothly. If you pin the throotle too quickly from a closed position, it coughs so badly that if you don't let off the throttle, it will die. :bang:

We cleaned the carb pretty good but did not set the float level. However, my buddy told me that he never had this problem with the stock set-up (stock exhaust and jets). The kicker is the partial chock setting which makes the bike run better off idle. I'm thinking he needs a bigger pilot (idle to 1/3) as the bike runs awesome once it gets past the cough.

The only modification he did after installing the supertrapp was to go from a 152 to a 162 main jet. He did not touch the pilot. We've been tinkering with the air screw and idle speed but none of that seems to help.

Jeff

is that 5 sizes larger?? put the 152 back in see what happens

you can roll on the throttle slowly because you have rpms to help suck up all that gas by the time you get to the main
ride around at full throttle for a while and your plug is probably wet :nod:

 

[TeamFrog]

so it stutters off idle whether you jam it to 1/3 , 1/2 . or wot??QUOTE]

Yeah, pretty much. Any sudden whack at throttle and it studders.

 

[TeamFrog]

is that 5 sizes larger?? put the 152 back in see what happens

I'll give this a try. Thanks Ellandoh!

Jeff