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Message started by J Mac on 07/14/08 at 09:13:44

Title: Humidity and bad hair day
Post by J Mac on 07/14/08 at 09:13:44

I've posted on this before and bugged Lancer today, but this issue is driving me crazy and making my bike unreliable. I did the half-spacer mod in the winter or spring, and it worked out well until the weather got more warm and humid in Houston (more meaning like a steam room 24x7). Now, if I start up cold when it's dark, for example, or encounter rain, the bike won't run worth anything or idle. It will stall requiring open throttle starts and constant revving while at a stop. Various changes like a main jet, air mixture screw, and Dyna Muffler install have not changed or eliminated the problem. I tried a stretched carb slide spring for a while (sticky slide?), and that helped but cut back too much on throttle response/top end. It's not necessarily rain related, but it seems to happen after sitting and starting in the morning or at night. The only thing that improves it is a long, stumbling on-the-road warm-up. Then, it usually runs like $$$ all day, unless rain is encountered. Pulling the choke normally makes it worse. Maybe that's part of my problem. The bike has 4000 miles. Plug problems are not intermittent right? I'm about ready to put that spacer back in (gasp, you can't do that!!!!). What about the half-spacer and this crazy carb icing? Thanks in advance for any opinions!

Title: Re: Humidity and bad hair day
Post by T Mack 1 on 07/14/08 at 09:26:54

What does the sparkplug look like. Is it nice and tan? Or white .... or black????

Title: Re: Humidity and bad hair day
Post by J Mac on 07/14/08 at 10:30:38

6C1575595B5309380 wrote:

What does the sparkplug look like. Is it nice and tan? Or white .... or black????

Excellent question. I will look at it tonight and ascertain "tanness". I didn't think a bike with that few miles could have a spark plug issue, but clearly I have an issue.

Title: Re: Humidity and bad hair day
Post by serowbot on 07/14/08 at 10:31:44

Humidity, makes your bike run richer. The added moisture in the air is reducing the amount of air in the air. So you run rich.
It seems like you are too rich in normal conditions, and the humidity puts you over the edge.
Try putting the spacer back in, or reduce the pilot jet one size.
Houston is near sea level or below, so you may not be lean with stock jetting. I am 2500ft up and ride up to 9000ft and run 150#/50# main/pilot with 2/3 spacer. K/n filter and dyna muff. And I get popping on humid days, so I'm a little rich.
I'm guessing maybe 150# or 147.5#/47.5# main/pilot and no spacer mod for you.

Title: Re: Humidity and bad hair day
Post by J Mac on 07/14/08 at 10:53:48

Thank you, sir. I have a 150 main right now. I had no issues last summer (all stock), but the issue did occur with my stock main jet (and spacer mod). I will look at the plug tonight and try putting that spacer back in.

4A5C4B564E5B564D390 wrote:

Title: Re: Humidity and bad hair day
Post by vtail on 07/14/08 at 12:17:59

This carb operates the slide by vacuum. Check your vacuum hose (no obstruction or fuel in hose), take top of carb off and clean the slide and bore of that black stuff (with carb cleaner). make sure slide moves freely. Do not change the spacer mod. remove fuel bowl and check float (for fuel inside float cuase float to sink) and check that floatvalve is not sticking (turn fuel on pri and move float by hand up (no fuel) and down (fuel flow)). make sure both jets are un-obstructed (clean). stretching the sping is not a good idea cause you will need a lot more vacuum to make that slide move. advice:get a new one. Also make sure that the O-ring on top of the carb inside the groove, and is not being pinched. ;)

Title: Re: Humidity and bad hair day
Post by J Mac on 07/14/08 at 13:39:42

Thanks. Every thing you have mentioned has been verified. The carb is very clean. The vacuum hose going to the petcock as been changed a couple times. Are you saying that if it was blocked there would be too much vacuum available to the slide, keeping the needle up? Remember that this problem often goes away with warmer or drier conditions.

Title: Re: Humidity and bad hair day
Post by Max_Morley on 07/14/08 at 14:06:41

How about next time it acts up, take your hand and carefully reach down and see if the carb is freezing cold, or better yet stop and see if it is frosted. I still believe that under the right conditions the carb can ice up, and prevent it from working correctly. In college I had a 54 Mercury sedan with what was called a "teapot" carburetor. It would regularly ice up in very humid temperatures, usually close to freezing, but clear up to the 40's. It would freeze the moisture out of the air on the outside of the carb and stick the throttle in place and shrink the venturi down to the point it ran rich enough to finally die, if I didn't stop and let it sit and thaw out. As they didn't used ducted air off the exhaust in the 54, I just lived with it. Had a 78 Dodge 350 crew cab that did the same thing, cost me a new Mitsubishi Galant in 86 when my wife said she wasn't driving that truck to school another year. Also had a 81 Chrysler K car that did it to me once or twice. Near freezing but snowing a very heavy wet snow and just the right airflow through the carb drops the temperature enough to freeze the moisture out of the air, not the fuel. Any pilots on the board who can give us the technical answer to carb icing, I know small plane pilots dread carb or wing icing as it has caused many an unplanned landing in a less than favorable spot. If you've flown in the winter, they de-ice commercial planes to prevent wing icing on take off preventing such event. Ruins the lift of the wing and the pilot has an " o nuts" moment. Max

Title: Re: Humidity and bad hair day
Post by Todd Perry on 07/14/08 at 18:42:13

Quote:

Any pilots on the board who can give us the technical answer to carb icing, I know small plane pilots dread carb or wing icing as it has caused many an unplanned landing in a less than favorable spot. If you've flown in the winter, they de-ice commercial planes to prevent wing icing on take off preventing such event. Ruins the lift of the wing and the pilot has an " o nuts" moment.

Actually, carb and wing icing are two completely different things.

Well, except the ice part. :-?

Carb icing occurs due to water vapor in the air cooling while being sucked through the carb (Boyle's law) and solidifying as ice on the walls of the venturi or on the butterfly valve (or equivalent - in this case it would be a slide valve, I guess) - the key is that the ice gums up the works and causes a reduction of air to the engine (i.e. richer mixture) and thereby a reduction in power.

Note that carb ice (as was previously stated) is a function of temperature, but also of altitude and most importantly, humidity. I'm sorry to say that we lose people here in Florida every year due to that. ("It's 70, it can't be carb ice...") I think I read somewhere (Continental or Marvel manual - one of the two) that you can get carb ice as warm as 90 degrees F given the right humidity.

In wing icing, on the other hand, the concern is that formation of ice or rime on the surface of the wing disrupts the flow of air over the leading edge by turbulating the laminar boundary layer. This leads to a lower C_Lmax and resultant lower critical AOA or higher speed stall or both..... uh...... It makes the plane lift less, m'kay? WAYYY off topic.

Anyway, the way cars and airplanes solve carb ice is by use of a manual (typical in airplanes) or automatic (typical in cars - called a diverter valve) valve that typically sucks some inlet air past the hot exhaust headers to prewarm it or mixes in a little exhaust gas (how and what depends on your setup). Either way, there's less O₂ to work with (both because it's warmer=less dense, and because it may actually be exhaust) so it's actually a lot less efficent, but it's so much warmer that it eliminates the ice.

How do you keep this from happening in a M/C carb without such a system? Well, you could theoretically rig something like what an airplane has (a manual carb ice diverter) by running some of the inlet air....over the exhaust would be easiest, I think. and using a valve with a plunger...but practically, leaning it out seems a much better idea to me.

Title: Re: Humidity and bad hair day
Post by J Mac on 07/14/08 at 20:46:14

T-Mack, the plug looked nice and tan. Suspiciously, the plug wasn't very tight. I'm used to practically needing an air wrench to remove car plugs, and I think I could have turned this one out using the chrome socket extension only. Perhaps when the engine got good and hot, metal expanded enough to make a tight seal, etc. Regardless, since I don't like taking the tank off daily, I used my usual scientific method of changing 2 or more variables at once and put the stock spacer back in to see what I see. I know that's a mortal Savage sin, but I did it anyway. It seems to run almost as well, and I can take it back out in the winter when I'm bored. I really want to put the unreliability behind me, and the thing was guzzling gas like a pig anyway. I've still got the air mixture screw I can mess with. Thanks to all for your opinions. The carb icing discussion was cool, but I really don't think that was the issue for me. Well, who knows, I've been wrong a few times already. I'll see how the next muggy morning goes.

Title: Re: Humidity and bad hair day
Post by J Mac on 08/03/08 at 20:43:23

I'm finishing this thread out hoping it will help somebody else out. It turned out after all that diagnosis and messing around that the problem was the petcock. When I first got the bike, when it had 1700 miles, I had a problem with open-throttle stalls. Replacing the petcock vacuum line cured that. Little did I know that the petcock would act up again later in a different way. This time, it had been not opening properly at lower idle speeds until it was good and hot. Had I just thought to try PRI weeks ago when this dumb behavior started, I could have cured it. I was so sure that rich running was causing the problem that I refused to think of another cause :-[. It turns out I was running out of gas unless I operated the bike at high speed/open throttle conditions. My last 2-3 rides, I rode on PRI, and everything was fine. Yesterday I converted the petcock to manual operation, so I should be set for a while. I did a seat lift also. I think I'm happy for now. :-?