Hello All,

I brought my 4rt in for a routine valve adjustment to a shop I'd never used before. The mechanic is definitely competent, but totally unfamiliar with 4rt's. I left the manual for him to check out the specs, etc. When I picked up the bike, he said the exhaust valves were slightly tight, and he adjusted them accordingly. Tonight I got a chance to ride the bike. It starts easily and idles well, but when I whack the throttle open it just coughs and there is nothing. Is there potentially something he overlooked or a common error that he might have made? Thanks in advance for your help.

Regards,

Wardo

Hello All,

I brought my 4rt in for a routine valve adjustment to a shop I'd never used before. The mechanic is definitely competent, but totally unfamiliar with 4rt's. I left the manual for him to check out the specs, etc. When I picked up the bike, he said the exhaust valves were slightly tight, and he adjusted them accordingly. Tonight I got a chance to ride the bike. It starts easily and idles well, but when I whack the throttle open it just coughs and there is nothing. Is there potentially something he overlooked or a common error that he might have made? Thanks in advance for your help.

Regards,

Wardo

I guess anything is possible however I would suggest mostly likely is a fouled plug. If they guy gave it a bit of an handfull before it was warmed up, mine typically behaves as you have described when the plug dies.

Try a new one first before you investigate further.

After the run in period of my bike I checked the clearances, The exhaust valves were tight also.

Backed off to manual spec and had the exact same problem.

Changed plug and it was better but not spot on, done the valves again and slightly tightened, 0.001" and not had a problem since. Its a bit of a strange one, i've asked about but everyone seems to have spot on clearances with the bike running perfect??

I'd check them again, take a note of the reading and tighten them in small increments taking special care not to go past what they originally were positioned before backing them off. Test after each nip up. You shouldn't have to tighten them too much before you'll notice a difference!

Today I had a chance to look the bike over. I cleaned the air filter, although it was pretty clean and replaced the plug. The bike ran fine afterwards. I am pretty sure it was the plug. I had just changed it 5 hours of run time previously. I think either the mechanic or I gave it too much gas before it was warmed up and carbon fouled the plug. I might also try going lighter on the airfilter oil. I do find it interesting that the 4rt is more sensitive to spark plugs than any 4 stroke I've owned, and even my '06 YZ 250. Thanks for the ideas.

Regards,

Wardo