Runs crappy cold, then zooms when warm

I've seen other posts about this problem, but yesterday was the worst for me. Choke on, hit the button, bike starts right up and idles fine. Get under way and she bogs. Have to massage the choke enrichener to keep thing going but the bike runs terrible. After about 5 minutes though, when all warmed up, she runs great. Hmmm.

Asked a buddy what he thought. And his answer? carb icing. That's right, icing, even in the heat of summer. Well, this is new to me. So, some browsing on the web and new knowledge about carbs. The humidity has been awful and the air is full of moisture. That air gets drawn into the carbs and the water get vaporized along with the gas. But the pressure differential at the venturi and heat loss cause the water vapor to freeze, the slide stick, and you compensate by running full choke until the carbs are warmed up by the heat of the engine, and viola, the thing now runs fine.

Carb warmers, bs, thoughts and comments please!

Joe

 

My Vote goes to BS.

Humidity or not the sliders will not freeze in place. Not on any day you plan on riding anyway. :wink: It really doesn't matter as the sliders are doing nothing at the idle stage.

Bikes do need to be "tuned" for different ambient temperatures but the main requirement for this is related to altitude. Eg Air density at higher altitudes.

Yea, I know, XJ's don't have wings, but they do fly :wink:

Your problem is related to carb tuning/cleaning.

If you have to run the choke for too long then the bike is being supplemented with rich air which is what your bike is missing for normal running.

You need to look at syncing the carbs after a good clean paying special attention to the pilot jets and galleries. After that set the mixture with a colourtune if you have on otherwise start with two turns out.

Check plugs for lean/richness and let us know what you find.

Cheers
HG

 

totally BS is my vote. This sounds more like a mixture problem, and possible cracked carb boots, or throttle shaft seals, as sometimes when the bike is tuned warm, and it has worn seals or cracked boots, they leak will alleviate its self once the bike has warmed up some allowing the rubber to expand and fill the cracks. so when its cold the air flow, in this situation, changes as the bike warms. So since it is out of tune when it is cold this can screw things up.

also a good cleaning can never hurt.

Good luck!

 

Boy, I goofed this post up, shows twice...oh well.

Anyway, the carbs are clean and I've pulled the plugs, no problems found. The boots do show their age but there's no sign of leakage. Yup, been running Seafoam though her last two seasons.

It is true about the icing, though but maybe not in my case. I'm going to try a little dry gas in the fuel.

Yeah, I thought I'd richen the mixture a little also. A colortune gadget would be nice to have but I'm short on cash, as usual.

 

What temps have you been seeing? What humidity?

Some reading on carb icing: http://faq.ninja250.org/wiki/What_is_carburetor_ice%3F

Essentially it happens when it is < 10C and high humidity...

I don't think this applies to you as you say the bike runs properly after it is warmed up.

What I would suggest doing instead is checking your plugs (my first suggestion always).

Likely you are running too fat for a cold engine and will notice dark spark plugs. You should start the bike - do your morning routine starting - hit the kill switch and take a look. No point in checking when the bike is running properly as that is what the spark plugs will reflect...

This is an interesting one... good luck.

 

Definitely sounds lean at idle if its 'zooming' (lean surge). If everything else seems ok, you may want to check out your throttle shaft seals - mine leaked like seives - nasty zoom at idle when hot. Are you running the stock exhaust? Pipes and hi-flow cans are notorious for messing up carb jetting.
As for icing, its possible but highly unlikely given the position of the carbs and intake. Its never happened to me, even at temps as low as 5C with high humidity.
Good luck.

 

What really drives icing is that when you spray gas it trys to evaporate - when it evaporates it takes in energy in the form of heat. This cools the surrounding area. If the air is cold and there is moisture, the moisture falls out of the air (like a flurry on a really cold day) and creates carb ice.

Ever spilt gas on your hands and felt how cold it gets? Same thing.

The position of the carbs has a minimal effect as a carb heater... but worth noting.

Again I do not think this is carb icing. Carb icing will occur on the maxim if you ride late enough into the season, particularily in coastal areas with high humidity. Freezing fog is nasty.

 

First off, I am a pilot and carb icing occurs at "reduced" throttle settings or mainly when powering back for landing. It doesn't occur at startup or advanced throttle settings.

A bike that runs bad cold and better warm is indicative of a lean condition. She seems to need more fuel than she is getting to run well cold. This would indcate clogging in the choke circuit, fuel filter, starter circuit or fuel height is too low. At least as far as the fuel goes.
An air or vacuum leak could also be the problem. So check for cracks around the intake boots. Same for airbox boots but also check the clamps for looseness. Make sure choke cable is engaging the choke.
Most likely it is in the carbs. A heavy seafoam treatment would be good. Half a can to one gallon of fuel, run it until the seafoam smokes up the exhaust and let it sit overnight. Next morning fill the tank with fuel to dilute the seaoam concentrate and ride it. If it is still running bad after about 50 miles then pull and clean the carbs.

 

Ok - that makes sense.

Working backwards for a moment. The choke is an air restrictor? The restriction puts more preasure on the system, causing more fuel to flow into the mixture - enrichener.

If the bike is lean, extra choke would enrichen the mixture.

A cold bike runs lean until up to tempature - choke is added to richen the mixture by restricting the air and sucking more gas as a result of the higher preasure.

Cold air being more dense than warm air being part of it...

That makes more sense now... thanks.

From my experiences with carb icing - typically been the last 10 minutes of a ride where I've had to slow down for traffic. Might that be caused by the fact that at smaller throttle openings less air is going over the prone to icing? at 6c the air is above freezing and would melt the ice as it formed. Less airflow after a long wider throttle setting would allow ice to form, while at the same time the system has been cooled by the previously wider throttle opening?

 

the other tangential comment. With a stalled flooded bike one does the opposite - applying WOT (leaning the mixture out)

 

Actually the choke circuit on the XJ is an enrichener. It allows more fuel in. It doesn't restrict air flow as on autos. Method is different but the principal is the same. Rich mixture for a cold engine. The cold intake keeps the fuel from vaporizing well. So a rich mixture well atomized is used.

For aircraft most throttle icing occurs from 50 to 70 deg. F. This is because the warm air can hold more moisture. Some Piper aircraft have a temp gauge by the throttle carb heat controls for guidance in applying carb heat. Again only during landing or reduced throttle settings. The ice is formed on the butterfly plate. When the throttle is open the butterfly is parallel to the air/fuel flow keeping everything warmed and ice doesn't form. Close the throttle and the plate is now perpendicular and ice forms on the backside of the butterfly plate. The air/fuel mixture burbles around the plate and the fuel cools it enough for ice to form. One thing to remember is that aircraft engines have the air intake mounted on the front of the cowling. So humid moisture laden air is always being supplied just by the plane moving through air. Miss the approach, throttle up and the ice now heads for the intake where it really ruins your day. It's like adding water to the fuel. NOT GOOD!

 

that was a good read...

thanks.

 

Thanks for all the input, pretty interesting topic that I thought would get some discussion going. Back to my experience...temps have been between 45F and 50F early morning. The humidity has been HIGH! >90%. I will spray some carb cleaner around the boots this weekend and see if a leak exists. My choke system works fine near as I can tell. Maybe is was just some crap in the gas? Just seems kinda funny.

 

I found a chart on carb icing and uploaded it into my BlueMaxim photo album. Too large to fit it here and I don't have software to edit it.

 

Yup, I've seen those charts...takes me back to chemistry class...ow!

Triple points, phase changes, temp, pressure, holy moley! It does make me wonder if icing had occured.

 

What surprised me was the chance of icing at cruise settings. I know the butterfly is not exactly parallel to the air flow but I thought it would be enough to keep ice from forming. Of course things are different in England than her is the hot and humid south. We only use carb heat on landing.

 

Carb icing on a motorcycle ??? Absolutely - REDICULOUS. Run the bike for more than a minute and you can't touch a spot on that engine that isn't either HOT or WARM.

High revolution breakdown is generally one of two things:

a) Ignition related ... namely: Coils or the pick-up's -- corrosion in connections, loose connections, bag grounds etc.

b) Carbs: Fouled emulsion tubes, clogged Main Jets, fuel bowl siphon tube well metering ports solidly blocked or wrong Main Jets.

Carb icing ??? No Way -- No How -- Impossible ... EVEN if you live in some area above 20,000 feet !!!

 

got my bike to purr temporarily tonight! my question however deals with extreme cold conditions... currently the temperature was -1 F & windchill minus 25 F. I warmed the bike up all day cause I wanted to hear it run so after I got it fired for 10mins or so without any choke and idling near 1500 rpms, a problem arose in keeping it going. I needed to keep engaging the choke as well as throttle. by leaving it alone in the garage (with no wall insulation and temperature probably around 10F, out of the very cold wind), it would simply die rather than "zooms" and would then have a hard time starting again. I would imagine the extreme cold has an affect but am not certain if it affects the idle mixture differently from the warmer months?

I was just happy to hear it run, which is an indicator that fuel is flowing. I've attached new mufflers to the exhaust system and fixed the vacuumed petcock before putting tank back on this fall. with the little free time that I have back home *on x-mas break right now* from school, I want to keep this good looking bike running as well. any thoughts?? thanks in advance!

 

Sounds a tad lean, what do your plugs look like ?