how much temperature range are the CV carbs good for ?

[tirebiter]

Just got back. She ran ok this morning at 26F outside. I was not taking my time and did not notice if the symptoms were there. In other words there was no steady speed cruising for long enough. Less then a minute or two of light throttle steady speed cruise, if that, early this morning.

On the way home just now, I took a look to see just how much rotation I'm operating with on the twist grip. It is 5 degrees or less as an estimate. The edge of the rubber throttle grip moves an eighth inch or less when I back off, from 60 MPH on level ground.

I was paying very close attention on the way home and noticed the symptom several other times. As if it was a slight missing from one cylinder or just a general almsot imperceptable loss of power. Turns out I feel the same thing at other times besides after the typical extended cruise at low RPMs. It happens every time I pass someone on the highway or if I am being passed. Just as I get the blast of wind that tends to slow me down a little.

I'm over thinking this as usual but it seems the air piston, slide, whatever you want to call it, receives a slightly different signal from the vacuum of the partially open throttle, every time the engine gets a heavier load such as a blast of wind pushing back on me from an adjacent car/truck on the highway. It may not be enough of a vacuum signal change to alter the position of the air piston. Maybe it's not enough of a vacuum change and a slightly higher enedle postion would help.

I notice the same effect/symptom when I'm climbing a bridge that spans a large river at highway speeds and the wind happens to blow at the same time. It seems to affect the engine somehow. Still it is only there when I am keeping the throttle steady and holding a steady speed. Maybe it is where the transition occurs between the idle circuit and the main circuit. Richening up the mixture screws did seem to fix things in the lower gears but it didn't seem to help at all to eliminate the symptom in 5th.

I'm still thinking about trying the smaller air jets to see if it makes a drastic change or if it even helps at all.

First half tank was before I turned the mixture screws out. 2nd half tank was after. 42 MPG. The best yet ! Obviously the richening did not ruin my MPG. I'll try to go slightly richer with the screws and see if that eliminates the symptom or makes any difference in 5th or not.

Joe Garfiled. I see your point and forgot these carbs had plugged/tamper-proof mixture screws. That would explain a carb that is supposed to run all year long in all temperatures. The plugs on mine had been removed before I got the bike. The ones I have are aimed upwards though. I use a long thin screwdriver to go straight down, next too and between the frame members to adjust, after dismounting the gas tank. I assume your photo is for illustration purpose or I have the wrong carbs entirely.

Another thought is that I might do well to install some type of warm air intake to keep the carbs from getting so cold. I know it makes a big difference regarding winter dirveability on some engines in cars and trucks. Maybe just a couple of flat shroud pieces one ach side from the head to the airbox. See if reataining some of the warmed air and keeping the carbs warmer will make any difference.

[mrbill5491]

tirebiter, how do you have the two breather hoses running off the carbs routed? They need to be in dead air space, like under the seat.

[tirebiter]

Good thought mrbill5491 ... I'm Hopeful, this remark makes the most sense to me.

I have the 2 vent lines going up over the air cleaner housing on each side then down behind it ending about half way down. Wasn't sure where they are supposed to go. The right side triangular frame cover is missing. Blew off one day I guess and did not notice. The end of the vent hose is exposed on that side. I'll try rerouting both of them up to the top of the battery.

I can see how the float bowl could be subject to negative or positve pressure if the vent hose gets wind blowing across it. That could certainly make a profound difference in fuel mixture.

tirebiter, how do you have the two breather hoses running off the carbs routed? They need to be in dead air space, like under the seat.

[Grimly]

I have never heard of a non-computer controlled carb that does not require a periodic idle mixture adjustment to compensate for seasonal air temperature fluctuations.

Other way around; I've never come across a carb that needs summer/winter jetting.
What used to be common was an air intake that pointed towards the front of the car in summer and to the exhaust manifold in winter, in an attempt to even out some the air intake temperatures and avoid carb icing. About 30 years ago, various makers started doing this automatically, with bimetallic sensors and mover, so the driver was unaware of any need to change anything.
It's remarkable that the bike installations never needed any special treatment of this sort.

[tirebiter]

I get your point Grimly. Seems like I'm barking up another wrong tree with my thinking that I need to allow specail pre-heated air to the carbs. My bit of two-wheel experience is that people just don't normally use motorcycles on the highway in these temperatures but again, seems like I'm wrong there, also.

I'm guessing the forum members who replied saying they ride in 20 Fahrenheit degree air with the same settings year 'round - no special mixture screw adjustment for cold weather/temperatures - are also travelling far enough at 60-75 MPH to chill everything, at least the same amount as I am. Wind chill is different at different speeds isn't it ?

Wingsconson's remark regarding the fuel mist condensing on the side wall of the carb bores seems plausible but apparently nobody on this forum has experienced any problem first hand.

I looked at the vent hose on the right side where the triangular frame cover/side cover is missing. The vent hose goes through a metal tab that looks stock and is held close to the back of the air cleaner housing. The vent hose ends down low behind the gearbox actually. About 10 inches off the ground.

It's cold AND wet out today so no testing until the surface of the streets are not dangerous for motorcycles. I do not do snow, ice or mixed rain/sleet on two street tires.

As soon as it's safe to ride again, I'll try rerouting that one vent hose up under the seat. See if it makes any difference when I get hit by a sudden blast of wind from passing vehicles.

[chuck hahn]

If the tube from the breather cover is running to the airbox as it should be, its getting some preheated air via its normal function of recycling bypass gasses for reburning. If you have pods this isnt gonna happen.

[Grimly]

There is no such thing as wind chill on an inanimate object.

http://en.wikipedia.org/wiki/Wind_chill

[tirebiter]

You got me again Grimly. "Windchill" is not the correct description. True the carbs/engine do not "feel" any colder than the ambient air temperature regardless how fast the bike is travelling. Also true that the heat from combustion is being removed from the carbs/engine more quickly the faster I go. The carbs get cooled down closer to ambient temperature at highway speeds than at lower speeds.

Had a chance to try some changes with the carb vent hose. Getting passed and passing cars at 65 MPH did not seem to make any difference. I had not changed the vent hose routing yet but it was about 45 degrees out yesterday. Did not make any changes to the vent hose.

I'm leaning back torwards thinking it's a temperature thing and therefore, mixture related. Will look at the needle height in the air piston/slide and/or try an air jet change and report back.

I'm planning to ride "Little Suzy" all Winter whenever there are dry days and dry roads to ride on.

[GSX1000E]

All of these GS models were set lean from the factory and can be improved by upping the main jets one size. Especially at/near Sea level.
As you are now running in colder/denser air the problem is intensified. Z1 Enterprises is located close to you so why not just buy a set of 117.5 or 120 jets? Start with the 117.5's.

I run my bikes in all temperatures from 26F-105F degrees and they work just fine. I also know how to jet them for use above 4,000'

[Grimly]

It's possibly still mixture related, but the upsetting of the breather pipes might be the cause, and I might run my own carb bowl breather pipe to a better location, now that's been brought up.
I've found when futzing around with the jetting on the SU, that when it's nearly right it always runs a little better on cold damp days, just like the cars the SUs were fitted to, back in the day, and that was with the factory setup. The trick is to get it just right for 99.99% of the time without having to mess with it any more.
More often than not, when there's a stumble or slight misfire it's because I'm still on the lean side, but the SU is easy to adjust and there's the damper oil option on that too, which you don't have.

[Steve]

I looked at the vent hose on the right side where the triangular frame cover/side cover is missing. The vent hose goes through a metal tab that looks stock and is held close to the back of the air cleaner housing. The vent hose ends down low behind the gearbox actually. About 10 inches off the ground.

Both of your vent hoses should be in that metal tab, and they should end before reaching the bottom of the airbox.

Going almost to the ground is way too low, getting into turbulent air.

.

[tirebiter]

Steve,
I'll see if the left side vent hose will reach. There is only one tab on my air cleaner housing. It's on the right side.

Meanwhile I dug deeper and go ahead Steve, you can say it again, "you told me to go through the carbs entirely back at the beginning". I took out the jet needles and the nylon spacer was underneath the circlip on all 4. It's in the stock location now, above the circlip and a short test drive shows me she seems to like it. I did not touch the mixture screws. I'll know more after several more miles. Certainly does not seem to have done any harm. If anything it's better but like I have mentioned, it's very subtle. Not easy to replicate the symptom, at will.

I defintely felt a lot like Homer Simpson having a big "DOH" moment. All I could think was "all that careful jetting I've done already" DOH !!!

While I had the jet needle out I did some measuring to chart the profile. I have not seen anything like this for these carbs so what else could I do ? Grimly knows what I'm talking about. Apparently the jet needle is a 0.0118" diameter needle. (Bought micrometer before metrifcation became rampant). Not sure what the needle jet diameter is.

The following photos explain the measurements in some detail :








As you can see, I marked the jet needle at approximately 1/8" increments. The jet needle looks fine with no appreciable wear along the biased side that touches the needle jet. There is some polishing on one side of the jet needle which I believe happens within a very few miles of use and and as I understand things, it does not affect the air/fuel ratio.

If anyone is interested, I'll post the jet needle profile chart for a 5D50 needle.

[tirebiter]

So now both vent hoses go through the tab on the right side on the back of the airbox as (I guess) it's called on this forum. The one from the 3/4 carbs is a little long so I pulled it up through enough to match the vent hose from the 1/2 carbs. It is not kinked. I checked. Now the end is about 3" higher than it was and both float bowl vent hoses end at the same place about 1 1/2 inches above the bottom of the airbox or about 12 1/2" above the ground.

Test drive at 43 F this afternoon ... no difference. The symptom is still there. Tried pulling out the choke a little and the symptom disappearred 100% ! That did not happen previously, before I put the nylon spacers above the circlip on the jet needles. THERE'S HOPE !

I redadjusted all all the mixture screws 1/2 turn out from best idle when I got back. Amounted to slightly more out than they were. Lost track of exactly where they are at this point. Idle not quite as good now, not as stable, tends to slowly fall off within 15 - 30 seconds as if the plugs are beginning to foul but ...

Will be taking another long enough drive tomorrow night, weather/precipitation permitting. Should tell me a lot.