KMX 125 mixture + MPG issue

Curtisg890 · L Plate Warrior Joined: 13 Apr 2014 Karma :

I got my 1990 KMX 125 on monday and when riding for the first time it stuttered horribly just before 7K rpm but if i held the throttle half way, it would creep past it and be fine. I cleaned the carb out multiple times with compressed air and carb cleaner but made no difference. I found out it had no air filter so i thought that might have been the problem but putting one on only made the stuttering worse and wouldn't go past 7k at all.

Just out of curiosity i removed the top of the air box and rode it like that, it ran perfectly! so it was running too rich. But now i'm confused as to why it doesn't run properly with the cover on.

Another issue is that i'm only getting 60 miles out of £10 of petrol! i've done alot of research and i should get atleast 90-100. I've checked for leaks and adjusted the float valve but has made no difference.

Any help would be appreciated,

Thanks (:

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

Is the main jet standard?

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

Curtisg890 · L Plate Warrior Joined: 13 Apr 2014 Karma :

Yeah, it's all factory :/

gavcarter · Could Be A Chat Bot Joined: 28 Mar 2009 Karma :

do a compression test

Curtisg890 · L Plate Warrior Joined: 13 Apr 2014 Karma :

As it is at the moment with the top off the air box, it runs perfectly and accelerates fine, so i doubt it would be a compression issue.

gavcarter · Could Be A Chat Bot Joined: 28 Mar 2009 Karma :

not a major one but if its a bit down on power, could explain the fuel loss....

Curtisg890 · L Plate Warrior Joined: 13 Apr 2014 Karma :

It's far from down on power Razz

. It's more of a fueling issue i think

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

Might be worth checking the jets in detail in case someone has modified them (it is possible to buy jet drills to drill out jets to larger sizes.

Also check the float height, although if that was out enough to cause it to run seriously rich I would expect it to flood when parked.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

Curtisg890 · L Plate Warrior Joined: 13 Apr 2014 Karma :

Ah, yeah good point! i'll have a look.

Curtisg890 · L Plate Warrior Joined: 13 Apr 2014 Karma :

Right, just went to take the carb off and fuel started to pour out of the pipe between the carb and airbox, so i've adjusted the float valve again so it shuts off earlier but it might need a new one by the looks of it.

The Main jet looks unmodified, by the way