Not an absolute newbie . . . returning in need of assistance

[ziggylamont]

Eight yrs ago my Fazer was written off and I replaced it with a thundercat. Until recently I have had no issues with the Thundercat and have only had to use the old Hayes Manual infrequently.


Over the last twelve months the Thundercat has been stalling while idling. Maybe someone can assist pls.  

There are no power issues at all and the engine only cuts out while the bike is idling at lights. I have previously increased the idle but this does not address the problem. I have to increase the idle so much to prevent the engine from stalling that I'm at the point where the throttle takes too long to shut, and this has lead to dangerous emergency braking (throttle shutting too late when heavy braking - before being able to apply the clutch).I've ruled out fuel and air issues as the bike runs as good as it even has (v.smooth). Getting up to speed and holding speed is never an issue. It runs perfectly but just can't maintain an idle. Any useful suggestions would be more than welcome. Sorry for only returning to this forum for advice! 

[andy352299]

try this site seem like a decent bunch
http://www.yamaha-thundercats.org/
also I am breaking a thundercat at the moment

[Captain Haddock]

Sounds like a possible air leak, not enough to show at bigger throttle openings but enough to mess up idle, possibly split inlet rubbers, spray some solvent around carbs and rubbers while idling and see if the engine picks up or splutters, if it reacts you have an air leak.
Could also be crud in the air bleed system, carb strip and blow out job.
Have you checked compressions at all, could give some clues, I've known a burnt/sticking valve to not show under power but run crap at idle.

[JoeRock]

Rectifier/regulator on its way out. Had that exact set of symptoms on a Hornet 600 (although they are known for that issue) - try a replacement known good unit and see if that solves it

[ziggylamont]

Thanks CP JR. CP struck a cord. I've only ever changed the oil twice in seven years and had a full service 12 months ago. I missed having the compression check. Emissions come from two places along the downpipes and silencer before the "standard" exit too! Very possibly an "air" issue. I'm happy to hold the throttle open slightly at the traffic lights and will look a bit more into compression issue. I'll probably just sell it now as I must be due a change! Thanks fellas. 
 

[YamFazMan]

Hi
On the early Euro Fazers a faulty T.P.S. (Throttle position Sensor) gave the same symptom's
 
ATB YFM   

[Punkstig]

I had similar idle problems with my last T,cat, but also when I raised the idle the engine revs would 'hang' at about 3000 when releasing the throttle, very slowly dropping.
solution for me was adjusting the pilot screw setting.
Haynes says they should be 1 and 3/8ths turned out, which when I checked they were,  but after lots of searching on tinterweb I found out to try 2.5 turns out from fully in- fixed it

[Punkstig]

+ rebalancing the cards after adjusting the pilot screws!