Motorheads Help Please

[Yamahopper]

I have a older XT 500 Yamaha motor cycle that needs something. The thing is super hard to start, I got to jump on the kick start for hours. Seams to run ok when it does start maybe lacking power. It is a four stroke single. I went threw the carb, replaced the intake rubber boot but it just won,t suck gas into motor. Seems to blow gas out carb over flow line. compresion seems good. Any ideas, vales or ruff cylinder maybe? 12000 miles on it.

[CHOPPERTHEDOG]

What kind of psi # do you have for compression? I am not sure what spec is but I am sure you could find it online somewhere or at the library.

Does gas come out the vent line all of the time? Possibly a bad needle @ seat or fualty/misadjusted float.

Did you clean the pilot jet/slow jet out when you went through the carb? They can get scaled/gummed up pretty bad and can be a real bear to clean thoroughly. This is a common runability problem with bikes.

[Yamahopper]

Motor has 120 to 125 psi compression,over flow drips once in a while sitting. Leaks more when kicking over motor. Has good spark. When it does run secondary air screw needs to be in almost all the way. Head gaskets show no sign of leaking from outside. Spark plug seems dry every time i check it.

[sledhead]

Compression way to low. Needs to be around the neighborhood of 150 to 170 psi. That could be just a tight valve. or could be a worn out motor. 12000 miles is quite a lot for a duo sport. Try a leak down test if you have the tools available. if it's more than 10 to 12 percent she needs refreshing. Also when you kick it put it just past top dead center. That way you get a run at it. The older xt 350's and 500's start much easier this way.

God luck

[Yamahopper]

Just got my Haynes manual in the mail today. Nothing in there for compresion psi, just 9 to 1 on the ratio. I will start looking at the valves and head and go from there. The bike is in great shape for it,s age, so i will through a little money at it. Carb job and upper end if needed. Thank,s for the help so far. Looks like another winter project begines soon.

[Yamahopper]

I pulled the head on the XT today, the valves will need to be worked over for sure. The cylinder still has the cross-hatch marks but there is a few ultra fine vertical marks. Any body know where i can have a expert look at these parts for repair work? Somewhere near the north metro.

[sledhead]

You could certainly bring them down to the post in south st.paul and I'll take a look at them for ya. If not go see Myron at Waldoch sports on Lake Drive. He'll point ya right.

[CHOPPERTHEDOG]

Do a search for Bill Bune. He does alot of the machine work for the dealers around town anyway, you may as well have him bore it and check the head. He is in Anoka I think?? I have had him bore a couple jugs for me and I was very happy with the outcome. Fast turn around time and price was as competetive as you will find.

[Moose-Hunter]

Ahhh yes... The old Yamaha thumper... FUN bikes!! I used to own TT 500. The "dirt only" version of the XT you have. If memory serves, I went though possibly the save problems as your having now. For my motor, it turned out to be a cam problem. Flattened lobes. Although the mileage was not known (no speedo) I'm sure, with mine being a 1976-77 model, it had seen quite a few HARD clicks of the wheel. We ended up doing the head, cylinder and a new piston. Ordered up a nice cam from White Brothers Racing, and finally a carb rebuild. Then it ran like a champ!! We called it the two kick wonder. First kick to get the motor "loose", and the second would always get fire.

With a few hunderd ice studs (and quite filleted hands ) the two kick wonder was a gas to ride on the ice. Plenty of power to keep up with "most" of the two strokes that were out at the time. Kinda cool to wheelie out of corners on a dinosaur!!

Good luck with your project!! It'll be a FUN bike when you're done. I just wish I could have been of more help.....

[spearchucker]

Go through the carb first. If you have gas leaking from the carb, it is need of cleaning or rebuilding and reseting the float level. This is where you need to start.

[oilguy]

check your camshaft timing

[Yamahopper]

Thanks to all who replied! I had to put the thumper project on hold for the holidays. I still can not believe the wife said she did NOT want a carb kit and piston rings for christmas. So after New Years i will have the valves done because they leaked for sure, Do a compleat carb job, touch up the jug and add rings, reset timing and hopefully have a fun time playing on this bike. Happy Holidays to ALL.