Very poor running problem

[Mrchairman]

hi guys, been having a strange intermittent running fault where she is lumpy beyond belief at low revs and has a huge flat spot when reving at 5k'ish but push past that and she comes alive.


Went out last night and by the time I got back she started to get better (15miles) not perfect but better. She did have an aftermarket can on but I took that off and went back to standard. When I say intermittent when I took it to the workshop I use they could find very little wrong with it.


It's strange as when the weather is warm she is worse and when cooler it's better


I must also add I am not the best with a spanner. But willing to give anything a go. If anyone can help or knows somebody local to Oxford who could help out I would be very grateful.


Thanks for any advice in advance.

[Falcon 269]

Sounds like she's running too rich perhaps at part-throttle.  The following is worth a look:

http://www.yamahafz1oa.com/forum/showthread.php?t=103599&highlight=found+carb+failure+mode

Essentially, if the O-rings in question are leaking slightly you'll have too much fuel in the float bowl.  The fact that she runs better when the weather is cooler points to a rich fuel condition in the affected rev range.

[hotmetal]

Given our relative levels of mechanical nous I would expect Mike to be right, but I also wonder if your air intake could have some blockage? I only say this as I had a similar thing a few years ago and it turned out to be an Autocom lead/connector that I stashed under the seat getting into the air intake bit under the front of the seat/back of the tank. Probably not but takes 1 min to check.

[Mrchairman]

Gave it to the mechanics this morning with this information.


They said they would investigate and let me know. It is a proper misfire type problem. They are thinking someone may have taken a sh!t in the carb or spark or lack of spark problem.


We will see what they come back with. But gutted as I was going out Sunday to Weston super mud for a blast 


Thanks for the info guys

[Falcon 269]

Other possibilities that the mechs should hopefully look at are a fault plug breaking down at various times and a poor connection between plug cap and the plug lead. 

Changing end cans shouldn't have been the cause but do you know if the carbs have been rejetted at some point? 

[solorider]

Mine had a similar fault and the coils had corrosion where the leads went in, and on one the pin had broke off. I modified my bike by going to 4 individual stick coils, I have had no issues since.