Suzuki GN 125 wont idle or run when warm, without choke

[DannyTannkCol...]

i've recently been having problems with my GN 125 '06', it wont start or run when the choke is off, even after riding it for 30+ miles, every morning and evening i have to bump start it to get it to run as it wont start on the electric start when cold, in either choke position. once it has warmed up after 10+ miles i can turn it on via the electric start but again only if the choke is on full if choke is in off position or anywhere in-between it refuses to start even on bump, also if i try turning the choke off when riding it slows down and wont get above 30mph, also when running with full choke it struggles to get 40mph on flats where as before the problem i was able to get 50+mph on uphills.

please any ideas will help i have tried cleaning out the jets in the carb and there all good, the float is not getting stuck.

[Fizzer Thou]

It does sound more like insufficient valve clearances causing loss of compression once the engine is hot.Then any clearance is taken up by expansion and this holds the valve open slightly.

Lack of compression = lack of power.
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[DannyTannkCol...]

thanks for the quick reply i will check it but i doubt its that because of the circumstances that the problem occurred it was sudden i parked it up at a friends house then the next day not 8 hours later it was like this and no-one had touched the bike and from what i know about compression it doesn't just go like that its more gradual? but i may be wrong there, so i will double check the valve clearance to the spec in the manual

thanks if you have any more ideas that would be great

[Fizzer Thou]

I have heard of inlet manifold gaskets shrinking with hot/cold/hot situations.With the engine running spray some WD40 or Easy-start around the inlet rubber.If the revs pick up then there is an air leak.This will cause the engine to run very weak after you have managed to start the engine and to lose power from a weak mixture.

In the past I have cured this sort of situation with a smear of Blue Hylomar in the case of an 'O' ring that has shrunk.In others I have had to replace the rubber manifold.Normally about £15 in the case of a Yamaha R1 that I worked on last year,where I had to replace all four.
____________________
Just talk bikes.What else is there?

Always have a 'Plan B'

[DannyTannkCol...]

I have been talking to my dad about it and I have forgot to say that the plug seems to be black.

[Fizzer Thou]

Aha - the plot thickens.

Change the plug cap for a new NGK one.
____________________
Just talk bikes.What else is there?

Always have a 'Plan B'