Full choke not working, but half choke does

[CatatonicBug]

I'm working on a friend's bike, and doing all the normal annual maint things. I have noticed that when I pull the choke out all the way, it'll start fine, but never really rev's up higher than about 1500. I push the choke in to 1/2, and it slowly climbs to 2200 as it warms up. Once I push it in all the way, it idles great.

What might be causing the full choke to not function right? Where in the carbs should I focus my attention?

[TopCatGr58]

Hey Bug,

Since this post isn't in the "OTHER" bike forum, I'm going to assume that you're talking about a fellow XS1100???

How are the carbs jetted? Perhaps it's jetted a bit rich, or the floats are set a little too high, so that on FULL CHOKE/ENrichment, it may be TOO RICH, and that limits it's ability to rev too high due to being closer to flooding, whereas the mid choke is a better mixture range with enough air to allow the engine to run and therefore can rev as it warms up!?!? JAT!?

T.C.

[CatatonicBug]

Yeah, it's an SF. I just pulled a pilot jet, and it has 42.5 stamped on it, and all the mains are 137.5. That's stock, as is everything else on this bike. The air filter is a nice K&N, but that shouldn't make it richer, right?

[DGXSER]

Have you gone through the synch and tuning the mixture? Checked the valve clearnaces? All of this can add up. How much is to much all depends on what it is prepared to take.

[CatatonicBug]

Did the sync and colortune last year, and that didn't make the problem go away. I've got it all torn apart now, so I'll be re-doing that again tomorrow. Maybe that'll help.

I just hope I can get it all sorted out. He's got service receipts from Merriam Cycles on this bike, and it only has 11K miles on it. It's absolutely beautiful, and he's trying to sell it too.

[mack]

c clips

Heh bug: If you have it all apart, check the c clip settings on the needles. My SF runs best with the clip in the center position. Shot in the dark but it could account for running rich at idle/warm up.

[fredintoon]

Yeah, it's an SF. I just pulled a pilot jet, and it has 42.5 stamped on it, and all the mains are 137.5. That's stock, as is everything else on this bike. The air filter is a nice K&N, but that shouldn't make it richer, right?

Hi 'Bug,
those 137.5 main jet carbs should have cross-drillings from the main jets to feed the pilot jets and either rubber bungs or sealing screws in the pilot jet access holes.
If the bungs/screws are missing you'll see a real rich mid-range for sure.

[CatatonicBug]

Well, the carbs are now back together and re-sync'd and colortuned. The needles were in the center position and the passage/screws for the pilot jets were all there like they should be. I get a feeling the "too rich" idea is the culprit, but it runs just great with the choke pushed all the way in (colortuned to verify). Could it just be that the weather is not cold enough to need the full choke, and half choke is all this bike needs in warmer weather? Is that something that ever happens? I just feel really strange buttoning it all back up and calling it done when this one issue is not solved.

[petejw]

hi bug,
if ur happy the pilots are correct, the float
level is set to stock and the bike is running fine,
then i wouldnt worry to much about it, especially if the
weather is starting to warm up where u are, my bike
has never run past 1500 on choke.

[ManagerMike]

My 78 does pretty much the same thing, I pull the enricher full, start the engine, then drop it to the half detent position and let it warm up while I fasten the helmet and pull on the gloves. Don't recall leaving it at full position for extended periods at any ambient temp, so I can't say for sure if it won't climb up the tach or not at full enrich.

[DGXSER]

My bike used to act just like this, until I reshimmed the valves and then colortuned and synched. Now it climbs up to 3k on full choke!

[CatatonicBug]

My bike used to act just like this, until I reshimmed the valves and then colortuned and synched. Now it climbs up to 3k on full choke!

It's funny. My bike did the opposite when I installed the Dynojet kit. It used to rev over 5K with the choke, but now it stops at about 2200. It's strange how things that seem unrelated can affect other systems so much.

[Crusty Snippets]

[QUOTE=CatatonicBug;319836] Could it just be that the weather is not cold enough to need the full choke, and half choke is all this bike needs in warmer weather? Is that something that ever happens?

My first thought was it is not warm enough.

Unkle Crusty

[CatatonicBug]

My first thought was it is not warm enough.

Well, as the temps increase, the openings in the carbs will enlarge and fuel will thin and flow quicker, making the fuel mixture more rich. The "Choke" is actually an enrichener, adding more fuel to the mixture. So, if the carbs are feeding enough fuel with half choke to allow the engine to run well at room temp., full choke will make the mixture too rich and the engine will bog down. I know that when I'm riding in 30º weather, I need full choke on my bike much longer than I do when its 80º out for that reason.

[Crusty Snippets]

Choke

Well, as the temps increase, the openings in the carbs will enlarge and fuel will thin and flow quicker, making the fuel mixture more rich. The "Choke" is actually an enrichener, adding more fuel to the mixture. So, if the carbs are feeding enough fuel with half choke to allow the engine to run well at room temp., full choke will make the mixture too rich and the engine will bog down. I know that when I'm riding in 30º weather, I need full choke on my bike much longer than I do when its 80º out for that reason.

Yes that is what I was thinking.
Even when it is fourties F Yami will often need only hald choke.
These days I am firing up on full but gowing to half very quickly.
Yami may be running a tad rich but my milage is comparable to others.
I will jank a plug and look some day.

Unkle Crusty, with no idea what jets are in there.