Choke drops off

[RiderX]

So it has gotten colder here lately and my '98 needs the choke for quite some time before wheeling her out of the garage. The problem is when I first start it the choke seems to engage for a few seconds and then drops off and the engine stalls. I have to re-start it and hold the throttle up slightly for 30-60 seconds and then the choke will begin to reengage. RPMs will pick up to about 3k and I start to ease off the choke ever so slightly to bring the revs down. If I take it off too much the engine will stall again. After about 3-5 minutes its safe to take off the choke and away I go on my merry way. Can anyone tell me is this a choke setting, a carb jet setting, or what? I recently readjusted the idle/air mixture screws to fix a cold weather stalling problem I was having. The two outer ones were 1/4 turn out and 3/4 turns out. The middle one was about 2 turns out. I set them all to 2 1/4 per discussion over on the "Carbs???" post. Any ideas?

[nightrunner]

The problem is that its very difficult to adjust those mixture screws without some feedback from something like an exhaust gas analyzer or CO analyzer and obviously those aren't cheap.  Without feedback you could have one cylinder way too rich and another way too lean.  One turn is a huge change.  The good news is that Triumph did put sampling ports on each header pipe so at least it can be done.   The other way is reading the spark plugs but its rough at best and very cumbersome on the steamer because the plugs are so hard to get to.   Plus its usually done for the mid and high RPM's.  It may work at idle.

The choke is only a butterfly valve that restricts air flow and makes for a richer mixture.  My experience is that motorcycle chokes have to to be adjusted a many tmes as the bike warms up and feathering the throttle is also required.   And lean jetting makes cold starts an almost continuous balancing act.   I can report that mine starts much easier since I rejetted.  You told us in another thread that the PO already drilled the caps off.  Did he rejet too?   Stock 98 steamer (Keihin) jetting is #38 pilot & #98 main.  Hmmm.  Cold weather means denser air so the mixture would get leaner as winter approaches if no adjustments are made.   I dunno.   I fought with jetting and finnicky coils for like a year so I know its no fun.  If I were you, I would first check what jets you have.  If stock, I would go to 40/102 (assuming stock exhaust).  And then find a shop with EGA or CO analyzer and ask them to set it for 1.5% CO.  [Note the factory manual specs 1% CO for U.S. version, and 2.5% for the U.K. version]  Its all in my jetting thread.

[RiderX]

Its all in my jetting thread.

Cool Scott, thanks very much. I am leaning towards the re-jetting procedure at this point. I bought the adjuster tool from Motion Pro (for 30 bucks) and had hoped that setting to your recommendations would take care of it. According to the previous owner the carbs had not been rejetted, he just had to adjust the mixture screws to get it to pass AZ smog. They guys down at the BMW/Triunph dealer said that they would set the mixture screws for about an hours labor, so I invested in the tool instead. I honestly am a little intimidated by the thought of pulling out the carbs and at least it is no longer stalling at idle like it was before if I let it warm up a bit. I'll keep you posted.

[nightrunner]

OK, well good luck with it.  You should also know that Factory Pro sells a jet kit for the 98 models for like $120.  I don't think they change the pilots though.   Someone on Advrider posted that he was planning on trying it.  I think it was in Beasts on one of the Tiger theads.