Kawasaki Motorcycle Forums banner

1 - 5 of 5 Posts

·
Registered
Joined
·
2 Posts
Discussion Starter · #1 ·
I have noticed a pattern. I was having some issues with my 96 Vulcan Classic coughing and sputtering at the very early point of rolling on the throttle. Figured this to be gack in the main jet. It seems as the carb is switching from pilot jets to main jets, this coughing and sputtering happens. Once I dump a bit more fuel in there with more throttle, we're all good. It idles fine after it warms up properly. I use choke for a few minute for a cold start. I plan to schedule myself to pull out the carb to clean the jets up. So that will probably help.

Here's the curious part for me though.

I've noticed that on my way to work (6:30 am in Canada), this happens, but on my way home it doesn't - at all. ??? So there are only three differences that I can think of between these two rides.

  1. I'm pointing in the opposite direction. I'm not seriously thinking this has anything to do with it. :)
  2. The gas is lower in the tank on my way home. Doesn't seem important as the coughing has happened later in the evening as well when the tank is lower.
  3. The air temperature is cooler on the way to work. (As low as 1 Celsius (34 F) on the way in, and usually more like 15 Celsius (59 F) or warmer on the way home.

I think the most likely issue is the third, but I don't know why. Can any of you think of a reason why colder ambient air temperature could affect the bike? The bike will be sucking in colder, denser air on my way in to work.

Let me point out that the motor is completely warmed up when this happens as well. It's not specific to a warm motor or a cold motor. If it's happening, it happens at all speeds after any length of riding time including right after it's been started and before it's been ridden at all. The two factors seem to be around 1/4 throttle and cooler ambient air temp.

So what do you guys think, does the colder air matter? I know in cars, some systems have a valve that draws either from air close to the engine (warm air) or cooler air sourced from somewhere away from the engine. Do these bike have a similar thing? Do I have a bad valve or sensor or something?

Any input would be good. Even if my jet cleaning resovles the symptom, if the bike wants warm air and isn't switching over to be able to get it, I'm not sure that would be a good thing.

Couple of other quick details. I'm running the stock air box with a K&N filter in there (by my left knee). Right now it has cheap shotgun pipes of some kind on there. I have a set of Vance and Hines Straightshots with some quite baffels on the way to remedy this. Right now, the pipes I have are offering little to none (probably none) back pressure. I can't think how this would matter too much with the air temp thing, but you never know, I guess.

Any help would be great.
 

·
Registered
Joined
·
522 Posts
Almost certainly carb-icing m8, it's been a bane in the UK (first noticed, and trumpeted by the press with the GPZ900R in 1985 on), so much so most bikes have carb-heater circuits fitted, either re-routed coolant or electrical heaters.

The conditions you mention are perfect for it, cold-air (not freezing) with a reasonable humidity-level, the refrigeration effect of fuel-vapourisation in the venturi causes ice (from water vapour in the incoming air) to form over the pilot-outlets or progression-drillings causing the poor pick-up from closed/partial-throttle.

If when it first starts you pull over and stop the engine for a few minutes it should be cured, for a while at least.

Lads over here often add something like Silkolene Pro-FST to the fuel to help prevent it, i use ethyl-alcohol now and again 'cos i always remove the heater-circuits due to the bleedin' clutter it adds.
 

·
Registered
Joined
·
461 Posts
Almost certainly carb-icing m8, it's been a bane in the UK (first noticed, and trumpeted by the press with the GPZ900R in 1985 on), so much so most bikes have carb-heater circuits fitted, either re-routed coolant or electrical heaters.

The conditions you mention are perfect for it, cold-air (not freezing) with a reasonable humidity-level, the refrigeration effect of fuel-vapourisation in the venturi causes ice (from water vapour in the incoming air) to form over the pilot-outlets or progression-drillings causing the poor pick-up from closed/partial-throttle.

If when it first starts you pull over and stop the engine for a few minutes it should be cured, for a while at least.

Lads over here often add something like Silkolene Pro-FST to the fuel to help prevent it, i use ethyl-alcohol now and again 'cos i always remove the heater-circuits due to the bleedin' clutter it adds.

Awesome answer brotha'. I learned something today, Thanks!
 

·
Registered
Joined
·
2 Posts
Discussion Starter · #5 ·
Almost certainly carb-icing m8, it's been a bane in the UK (first noticed, and trumpeted by the press with the GPZ900R in 1985 on), so much so most bikes have carb-heater circuits fitted, either re-routed coolant or electrical heaters.

The conditions you mention are perfect for it, cold-air (not freezing) with a reasonable humidity-level, the refrigeration effect of fuel-vapourisation in the venturi causes ice (from water vapour in the incoming air) to form over the pilot-outlets or progression-drillings causing the poor pick-up from closed/partial-throttle.

If when it first starts you pull over and stop the engine for a few minutes it should be cured, for a while at least.

Lads over here often add something like Silkolene Pro-FST to the fuel to help prevent it, i use ethyl-alcohol now and again 'cos i always remove the heater-circuits due to the bleedin' clutter it adds.
This is great. It looks like one of the FARs totally remedied this - though I did read a few posts about people who say it was only temporary. Too bad.

So do you think if I were to rig up an air warmer somehow in the airbox (I have some ideas to experiment with) that I could counter this icing? By my symptoms alone it seems this should work. Like if I took air from between the cylinders and made a way for me to switch between the stock air draw from up under the tank and this one, maybe it would make the difference. Sound crazy? Crazy enough that it JUST MIGHT WORK?

Otherwise, I need to see if I can buy the heater system they were putting in with the FAR. I just don't seem to see where i can get one. Anyone know where they are for sale? Might be too old and rare?
 
1 - 5 of 5 Posts
Top