Carburetors or operator?

A week ago I pulled the carbs off the XJ to put in new float needles and seats. While I had them off I re-cleaned the pilot circuits because one of the mixture screws had 0 effect.

After I got them done I twiddled the pilot screws until I had the 'ol sewing machine idle at 1000 RPM. Was great for about a week.

Monday ride to work was fine. Monday evening it didn't want to run. Idling rough, bogged down and lost power when I tried to quickly enter traffic. After I got it moving and ran it through some revs it was fine. Idled like a swiss watch when I got home.

Tuesday ride to work just great. After work, similar problem. Straightned out after some revs. Went to a restaurant where the bikers go on Tuesday. Idled great when I got there. After dinner I fired it up and everything was great.

This morning leaving for work had the idle and missing trouble again. Great on the freeway and idled smooth as silk when I got to work. Same story all over on the ride home, noticeable surging first mile.

Adding more choke seems to make it run worse.

I'm pondering the situation wondering what's going on. My first suspicion was that I'm rich on one or more carbs at idle and that is causing a problem at the high temperatures we've been having in the afternoon. But then, it idles great when the engine is good and hot. HMMMMMM.....

As I think about it though, last night after dinner everyone was standing around the bikes talking. Instead of starting the bike (on choke) while gearing up I put on the gear first, then started and rode off.

So now I'm wondering if maybe my normal starting routine is wrong for this very hot weather and I'm fouling plugs with the choke on while I suit up.

Any opinions?

 

I'm thinking you have a Combo going on.

A whisker too Rich that a heated-up engine helps cover-up because it hot and contributes to allowing that Rich Mixture to fire.

Although, I'm surprised that it doesn't show-up by the engine hunting for a higher idle revs now and then.

One Diaphragm Piston not making it back down to close-off some Main Jet Bleed intermittently. Just hung-up enough to sneak a little bit of extra gas ahead of the other boys.

Then, when you crank-it ... all is well.

 

I would first suspect condensation in the tank. My Seca constantly had this problem. Opening the choke was a notable clue. When the choke is pulled the carbs suck fuel from the bottom of the float bowl where the idle and main jets pull from the top. So since fuel floats on top of water I would suspect the condensation which can also get by your inline fuel filter. You do have an inline fuel filter .....don't you Carl? You better.....your one of the gurus here! ;-)

 

Definitely no seeking at all at idle. Rock solid, at least when hot.

One thing that is different since I worked on the carbs though. No running the RPMs sky high with the choke. Once it gets to about 2500 more choke (enrichment I mean!) slows it back down.

 

Yes BlueMaxim I have an in-line fuel filter. I think this one goes to Rick - a bit rich at idle.

Didn't ride to work today (needed the AC in the cage thank you very much!).

Started the XJ when I got home (near 90 deg) no choke. Fired right up, had to finesse the throttle but after about 1 minute it idled fine. Re-adjusted the idle mixture. After it cooled down needed a bit of choke to start.

Gotta get my hands on a colortune.