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Have 02 FLHTC. Below 30 deg F it starts running rough after ~15 miles. Have to use choke just to keep running. Happened to my 92 low rider also. Any ideas what causes this? I always use BP premium gas. Is this normal for an HD? I usually ride to work but this issue really limits winter days I can ride. Thanks for any ideas.
 

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Curmudgeon
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Have 02 FLHTC. Below 30 deg F it starts running rough after ~15 miles. Have to use choke just to keep running. Happened to my 92 low rider also. Any ideas what causes this? I always use BP premium gas. Is this normal for an HD? I usually ride to work but this issue really limits winter days I can ride. Thanks for any ideas.
Don't know if it's normal for a harley, but most eng. that are cold will need choke, sounds like eng. isn't comeing up to temp. Maybe you need to adjust carb to make it a little richer for cold weather. Wait and see if the other guys agree with me.
 

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May need to use your choke longer on the intial start up, so the engine will get good and warm. Leave it on for the first 5 or 10 miles or so. Then take it off (or ease it down say half way) and see. Otherwise it sounds like an adjustment problem.
 

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They dont run good cold. nor does any engine with out all the automatic chokes and sensor controls, preheated air, they have on stuff nowadays.
Your cage would run crappy too. Used to put some cardboard in front of the radiator and choke it a lot longer.
 

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Some thing's not right there.

Every Harley I ever had ran GREAT when it was really cold out, even better than usual. And those were carbureted bikes. Used to tell myself that was the reason it was worth the hassle of getting all dressed for the cold, for the improved performance.

IMHO, if the bike will run at all for 5 or 10 minutes, even at an idle, let alone under load, it has to be up to temp and it can't need any more choking. If you're not in Siberia or Antarctica, anyway.

When you say under 30F, what's the humidity?
Is it possible he's having carb icing, or water in the bowl, or fuel line, or air bleeds or somewhere that freezes, or gets frost clogged or something? Everybody's fuel has alcohol any more, so I can't see how it could need a fuel line deicer.

Is there a plunger on the bowl to dump the bottom contents?
Sorry if that's a dumb question, been a long time since I had a carb'd Harley.

Wonder if it might be the alcohol? The bikes that I had run well at those temps didn't have 10% alcohol, that would make the fuel more difficult to vaporize when it's cold. Don't see why it would get worse after a few minutes tho.

While it's really cold, I might back off of the premium, it doesn't sound like you have to worry about knock, try a tank of regular.
 

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Some thing's not right there.

Is it possible he's having carb icing, or water in the bowl, or fuel line, or air bleeds or somewhere that freezes, or something? Everybody's fuel has alcohol any more, so I can't see how it could need a fuel line deicer.
Well yea mine pretty run good too. now you got humidity and freezing air also I think he did say 30 Degrees. How long/miles is he operating? Enough to get warmed up? Maybe slide is freezing up.
 

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I always let it run while I get my gear on when it's cold out and it seems to help.
 

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The cold air is creating a leaner condition than warmer air would. I have had bikes that would "pop" on decel more so in the cold than in warmer temps due to the natural lean condition the cold air creates. Pull out a sparkplug or two and see what the color is. If it is white than you need to retune your motor. Carb = rejet and Fuel Injection= remap.
 

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I always let it run while I get my gear on when it's cold out and it seems to help.
If I go back in the house and leave mine running for that long, when I come back it looks like I've got dim red LEDs casting a red glow on the engine, but it's the back side of the exhaust pipes, behind the shields. Can't say I've seen it happen at 30 or below.
 

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Thanks for the replies. In this part of NC humidity is pretty low when below 30 deg F. However the bike is garaged and I have thought maybe there is some condensation forming at night. Fuel line icing matches the symptoms, it just runs so good for 25 minutes. Has anyone tried a gas additive to dry out water?
I have tried the choke maneuvers, in fact when it first started I thought I was over using it. I've had this bike since new and all service up to date. I've rode Honda's down to zero but the fuel lines and carbs are generally behind the cylinders. Glad to hear other H-D’s do well in cold.
 

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I put on my gear in the garage and it's 3 to 4 minutes. Never saw it glow! Maybe it's trying out for Rudolph?
 

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Oh mine run good But it will sputter in cold weather. If I had to ride for a goodly distance I might would get some kinda non flamable "ear muff" type of thing for the carb and air cleaner to retain more heat in that area just too see.
 

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It seems to me the use of the choke improving the motors performance even after warmed up pretty much confirms the lean condition.

If it were fuel line icing wouldnt your scenerio be reversed? Run bad for the first 25 min and then run better as the motors heat thawed the freeze?

Just trying to help out.
 

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If it were fuel line icing wouldn't your scenario be reversed? Run bad for the first 25 min and then run better as the motors heat thawed the freeze?
I wasn't really thinking fuel line freeze-up, seems that would stop the engine dead. And 10% alcohol in almost all gasoline today means we've all got fuel line anti-freeze all the time. What I was thinking, particularly if the temp was closer to freezing, and if it was also real humid, was that the added cooling effect of fuel evaporating could cause icing inside the air bleeds in the carburetor, or maybe the carb throat.

Technical trivia, but probably unlikely, if you had a good quantity of water contamination in the carb bowl, it would cause alcohol to attach to it and come out of gasoline/alcohol suspension, and that could eventually mean a good quantity of alcohol/water mix under the gasoline, but it couldn't freeze, I wouldn't think, I'd think it was half alcohol or more. That's why I asked about a bottom of the bowl vent.

Ed's prediction of lean mixture because of the added cold air density, besides the lost water vapor content would exaggerate the effect so it does make sense technically, but I'd be rather surprised if it could be so lean as to run badly, unless it was already really lean on warm days.

I'd be reluctant to try fuel line anti-freeze, if your fuel is already 10% alcohol, you might damage rubber or plastic components.

Do you have a purely stock air cleaner backplate? Any way to direct warm air off the fins toward the back of the air intake? Thin aluminum sheeting, used to make a skirt around the back of the air intake might help, the metal version of duck tape could attach it to the stock air cleaner sides and might not look TOO very crappy, and would be easily removed when the weather warms up.

Still seems like rigging for Siberia, in NC I'd bet there's another answer.
 

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I put on my gear in the garage and it's 3 to 4 minutes. Never saw it glow! Maybe it's trying out for Rudolph?
Ya there is an openig, Palin shot him remember?
 

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Is it possible he's having carb icing, or water in the bowl, or fuel line, or air bleeds or somewhere that freezes, or gets frost clogged or something?
I've heard of this. Low temp and higher humidity causing icing due to the venturi effect in the carb.
 

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I've heard of this. Low temp and higher humidity causing icing due to the venturi effect in the carb.
This actually sounds like a real possibility to me. The venturi effect in the carb throat coupled with the added cooling effect made by the atomizing fuel, makes freazing air even colder. It wouldn't take much humidity at all to start forming frost...if there's no warm air getting to the carb, frost starts to build up, and after 20 - 30 minutes of riding...you have a bit of a problem. Try and see if you can direct warm air around the cylinders to the carb. Maybe i'm just blowing hot air...but it might work.
 

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Thanks for the replies. In this part of NC humidity is pretty low when below 30 deg F......
Here in New Hampshire me and another guy I know with 2004's have the same issue. At colder temps, idle is erratic, pops, misfires etc. The colder it is, the worse it is. Normally, carbs don't ice at temps much below freezing, unless you are riding through clouds at high elevations (airplanes). I have had a number of H-D's including a 2000 big twin. I have had carb icing, but only at slightly above freezing temps and high humidity, and the reaction was a LOT more severe than this. Will not idle at all. Must rev the throttle. Generally, does not go away unless either the environmental conditions change, or you stop the bike and let the carb warm up from the engine heat. Generally it works great at wider open throttle settings though.

My 2004, as far as I can remember, did not have this problem until after they stopped using MTBE in the fuel and started using 10% alcohol. I have tried different jets, but that did not solve the problem. There is no intake leaks, etc etc.

There is also, when the bike is having a problem, an issue at wide open throttle. A little bit less power. And if the throttle is closed slightly, it actually accelerates. This is a test for lean running, showing the bike is running lean (or the timing is off). SO.... I have a couple of theories.

1) The Barometric Pressure Sensor is faulty at low temps. Since my friends bike was bought at the same time, could be. But what about everyone else?

2) The moisture for carb icing is coming from the engine breather. I routed the tubes outside the carb, same problem.

3) The moisture is coming from the alcohol itself. As the alcohol evaporates it releases the water it has absorbed which freezes. This is a possibility, as it does act SORT OF like carb icing, but is much more variable. To solve this, I would need to get gas with no alcohol. Avgas, racing fuel, something like that. I don't know why I did not consider this before. There are places this is available.

4) There have been minor changes to the carb from earlier models, maybe they are such that they are stiff in the cold. Unlikely, although I suppose the alcohol could be hurting the rubber in the diaphragm. It looks and seems to function well though.

I have over 600,000 miles on Harleys, and am just about ready to dump this, my last one. Not just because of this issue, but a combination of things. It seems H-D just doesn't care about people who ride any distance. Fire Willie G and maybe I will consider going back. Of course, I said this before I bought this current bike too. And before the one before that. And......

Bob L
 

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When I start my Sportster after sitting for a few days - in the 20-30 degree weather I try to start it with no choke. If it does not start I pull the choke all the way out. Give it gas - like when your riding - then it always starts. After a few seconds like that - I slowly back the choke down. An old Harley tech told me - the less you have to choke a Harley engine the better. Also - try adding fuel stabilizer to it - Harley stores sell it cheap - they are small packets - $1.50 each - but that would help with the lines freezing up as well.
 

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I had the same problem, but it was after I changed the intake and exhaust (running real lean). I fixed the problem by re-jetting the carb.

 
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