Runs good cold, not great warm

My XJ 700N runs great when just barely warm, clean through rev range to about 4K. Not much top end after that.

When warm though good revs only between 2.5-4Kand outside this slight splutter. when i increase throttle the bikes clears itself. also when warm the idle seems to hunt and comes down off acceleration much slower.

I have had lower end carb rebuild, clean throughout including enrichment circuit, floats checked with both measurement from gasket surface and with clear tube method (3-4ml), bench sync, carbtune on bike with yics, colortune, valve clearances checked and shims replaced as needed.

I do have a rich condition on 2 no matter what do, could this be the cause?

any ideas greatly appreciated. im not sure where to go from here.

cheers

 

I was gunna say it sounds like you're running rich

 

this is a reach but I remember reading about a guy who's head gasket was bad and it would suk air into one of his chambers causing the idle to hunt..along with other problems, you may want to spray some carb cleaner around the boots to make sure they are tight, it sounds like you have had a good amnout of work done to the carbs but may need to revisit them but before that how are the plugs? and plug wires? .

S!

 

if your sure its rich on just one cylinder and not a valve seal leak then

possibility #1 your carbs are out of sync
Possibility #2 Fuel Mix
Possibility #3 Air Leak(s) between carbs and engine
possibility #4 Upper Fuel Circut
I'll Stress the air leak possibility for now based off the information you have given. also is this an Idle plug phop or a WOT plug chop?

 

What about your slides & diaphrams, see clunk test.

 

Wiz's thought was my first one after reading your symptoms. Have you checked your throttle shaft seals? When mine were leaking, I had a idle condition that jumped around too.

Have you tried the unlit propane torch trick to look for any leaks? I used starter fluid, but I read where someone did not recommend it since you are spraying a volatile liquid on a warm engine.

 

I'm with Wiz on this one.

 

thanks guys for your replies.

i did the clunk test and all drop solidly as per other forums and checked diaphrams for splits. I did check for leaks but with WD40 at both air box and manifold sides. No change in idle.

I didnt check the throttle shaft seals though.

The plugs a dry carbon at idle, havent done a WOT plug chop. The plugs were new as of about one week ago. now since playing i think they are covered in carbon.

I do have a 750 set of jets in the bike with a K&N air filter. Would this be the problem? i was hoping that as long as all jets are for the 750 it would be fine. dont know.

i think i will need to takes carbs off again.