Sputtering when warming up

[Klunkshift]

I have sputtering when starting cold that is very annoying. For the first few seconds of operation the bike "coughs" and sends unburned gas through the exhaust - you can smell the rich mix and gas.

It has been happening since new and it seems to get worse in hot weather. After it warms up, no problems.

Is there a way of fine tuning the automatic choke, which is possibly controlled by the ECU and a bunch of temperature sensors throughout the bike?

 

[Queensland Ken]

RadioHowie did a good write up re "The automatic choke" ie: Further details on Fast Idle system

 

[RossKean]

Is yours a California spec bike? Even if not bought in California, it may be a Cali bike (mine is and it was purchased in Connecticut). The problem comes from the vapor recovery charcoal canister. Gasoline vapors from the tank are routed into the charcoal canister. When you start it up, you are drawing air through the gasoline saturated charcoal resulting in an extremely rich mixture and rough running for a few minutes. You might wish to bypass the vapor recovery system but MAKE SURE there is no way for unfiltered air to make it directly into the engine - ask dcarver about that! The problem is MUCH worse in hot weather.

If you aren't sure what version you have, look for an extra drain hose through the bottom of the cowling just under the radiator. This comes from the canister. If you know what you are looking for, you can see the canister behind the front panel below the rad.

If you have confirmed that your bike is NOT a California bike, then you can ignore all of the above and look elsewhere for the problem.

Good Luck

 

[Klunkshift]

RadioHowie did a good write up re "The automatic choke" ie: Further details on Fast Idle system

You nailed it Queensland Ken, Thanks. This must be the culprit.

I will mess with the fast idle adjust screw during my next throttle body synch and I am positive this will cure the coughing symptoms when cold

Also thanks to RadioHowie for the detailed discussion on the fast idle system.

This forum rocks as always.

 

[RossKean]

I don't know if anything other than bypassing the system will really help. There's just too much fuel getting in from a source that isn't under the control of the ECU. In hot weather, its probably a good idea to park in the shade and plan on letting the bike idle for a few minutes before trying to drive. Normal response should return within a few minutes as the fuel evaporates from the canister.

 

[Fred W]

RadioHowie did a good write up re "The automatic choke" ie: Further details on Fast Idle system

You nailed it Queensland Ken, Thanks. This must be the culprit.

I will mess with the fast idle adjust screw during my next throttle body synch and I am positive this will cure the coughing symptoms when cold

Also thanks to RadioHowie for the detailed discussion on the fast idle system.

This forum rocks as always.

Not so sure... The fast idle mechanism is just an (additional) air circuit. It raises the idle speed when cold starting but has no control over the fuel mixture. That is all handled by the ECU and temp sensors. So, if your cold idle speed is adequate, adjusting that screw may not cure your sputtering.

OTOH, all 2nd gens seem to have too low of a "fast idle" speed, as compared to 1st gens. It seems that Yamaha may have dropped the fast idle speeds on the 2nd bikes to accommodate the AEs. If the idle speed was too high the AE could begin releasing the auto-clutch (once put in gear) spontaneously. So raising the fast idle may be a good idea on any nonAE 2nd gen anyway.

Let us know how that adjustment goes (it is pretty hard to get at)

 

[RossKean]

RadioHowie did a good write up re "The automatic choke" ie: Further details on Fast Idle system

You nailed it Queensland Ken, Thanks. This must be the culprit.

I will mess with the fast idle adjust screw during my next throttle body synch and I am positive this will cure the coughing symptoms when cold

Also thanks to RadioHowie for the detailed discussion on the fast idle system.

This forum rocks as always.

I assume you have verified that this is not a California spec. bike?

Another possibility - is the vent in the tank cover working properly? Under hot conditions the fuel system could be pressurizing and affecting fuel delivery. If blocked, it could be a double-edged sword. In addition to pressurizing while hot, you could run the risk of collapsing the tank as fuel is depleted. A quick check is to open the cover before starting. If there is a "Woosh", you may have a venting problem. Do this with care; fuel fountains have been known to occur although this has been more often a Gen I issue because of more direct heating of the tank.

 

[Klunkshift]

RadioHowie did a good write up re "The automatic choke" ie: Further details on Fast Idle system

You nailed it Queensland Ken, Thanks. This must be the culprit.

I will mess with the fast idle adjust screw during my next throttle body synch and I am positive this will cure the coughing symptoms when cold

Also thanks to RadioHowie for the detailed discussion on the fast idle system.

This forum rocks as always.

I assume you have verified that this is not a California spec. bike?

This is not a California bike for sure.

Fred's comments add another dimension to the problem - with pesky sensors and ECU interaction playing a role. Probably harder to troubleshoot and fix.

Thanks