So I have searched around and can't find any info on this particular symptom.

I have a '96 sportster 1200. All stock mechanically. Here's the best I can describe my scenario:

• Startup requires full choke when bike is cold, even in very warm weather
• Bike wants full choke until oil temp in can reaches >150-degrees (usually about 15 minutes of riding), OR I get this:
  • Tends to die at idle until good and hot.
  • Fine on acceleration/deceleration, but
  • "coughs" out air filter & balks/hesitates when trying to maintain steady throttle or accelerating SLIGHTLY.
• However, if I leave it on full choke, it idles/runs VERY fast (as in I can start from a dead stop, shift & ride it without touching the throttle, up through all gears, achieving moderate acceleration/speed). With full choke, I can literally go from a dead stop to top gear with no throttle, just loping along.
• Once it's good and hot I can take the choke off and it runs fine. Oil temp only hits about 200 even after long riding / hot day.
• My first thought was "running lean"... Checked for air-leaks and nothing there. Had a local shop look it over and they said the jetting is just fine, didn't recommend a change (also didn't have a solution). Stock pipes. Stock filter. Plugs look 'normal'.
• Bike doesn't seem to be running 'hot' like I'd expect with over-lean: No smoke, not "using" oil, oil is not 'ageing' over-fast, oil is not getting over-hot.

So kinda at a loss where to go next with this. The bike runs "good" if I keep it on choke until I get it really heated up... But those first 15 mins or so are a PITA with it revving up whenever I clutch in: feels like it wants to throw me off the back unless I'm real delicate with the clutch until I can ease off the choke.


Any input/advice is welcome.

 

Still sounds like it is running lean. Is the float level correct?

 

I suspect something simple but has to go through methodically. How many miles on the bike? Regardless of whether you can trust assessment made, here's what I'd check:

- Accelerator diaphragm
- Main diagphragm
- Check main/idle jet size
- Pull out and clean the enricher - even that can get gunked up or otherwise not seal.
- Spray out the jets - make sure no holes plugged. Use a magnifier if needed.
- Check smooth operation of float and slide.
- Replace carb boot
- Consider replacing manifold seals (you'll get a good test by spraying some propane around there.
- Check hoses - the hose to the VOES could develop a leak and then you have a lean condition and strange advance gremlins.

No recommendation on a poor running condition = not a shop I would consider valid for assessment.

 

Thanks for the good advice on things to check. Will do.

Agree about the "Dunno" from the place I took it (first time there). It's not a shop I'll be going back to...

 

Worth checking, and will do so.

However (and I should have said this), I did swap in an entirely new carb from a known-good-running bike and have the same issues. So I'm pretty sure nothing specific to the carb itself is the problem.

 

Doesn't seem likely you could have the exact same symptoms from two different carbs, but...... you're the witness so....
Excessive carbon build up on the intake side of things can wreak havoc on an attempt to tune a carb. You will never (never) get it right. The carbon acts to lean things out by absorbing gas at the early part of start up and running. That forces you to use the enrichener to keep it running. Then, once it's warmed up, it releases that fuel so you run rich for a little while. Then when it's hot, it leans out again by absorbing gas you need to run properly. You get mixed signals.
If you honestly have the same problems with two different carbs (and one was supposedly working fine) then I'd consider taking a good look at the condition of the carbon build up in the intake and the heads.
After being absolutely positive it isn't a carb issue.
But I'm betting there are some carb issues as well.

 

Yeah, I know, how could it NOT be a carb issue, that's the paradox. I literally swapped the carbs a couple times. Other bike ran fine with either carb, this bike did the 'hiccup' thing with either carb.

I'll be checking over all the carb stuff regardless - you never know. But certainly looking at the carbon build up is worth a shot too. Thanks for the tip on that.

 

I suggested the carbon issue because that was one of the things on my '93 that kept me from getting the tuning right.

 

I have a 97, replace the intake manifold gaskets......had same problem, this fixed it.

 

TStephen - I think you had a big factor there. Took a look and while not 'crusted' or anything, it seemed awfully carboned up for an 11K miles bike. Blasted it with a can of SeaFoam spray-in cleaner and then ran a tank laced with regular Sea Foam through. Carbon much reduced and problem seems to be 90% better. Gonna go through that cycle again next weekend.

I'd already ordered the intake seals set based on DustyDog's advice, so gonna go ahead and put those on 'cuz "why not".