1975 250 Missing

[herman]

I have just finished a total rebuild and took the bike out yesterday to seat the rings, after about a hour i cranked it up and as the rpms got up from midd. to high it was back fireing and missing.Can any one give me some ideas.It has all new bearings and seals and on standard bore,starts up on second kick tons of commp.I have 110 octane with amsoil @ 40:1 ratio plug is nice and tan. Herm

[firstturn]

Herman,
  Just a note, the first thing I would check is all that you have all good grounds.  If you rode it for a while before it started this problem something could have loosened up.  Also I have seen this occur on powder coated frame where you start out with a marginal ground and it goes down from there.  Check all engine bolts and coil connections.
  Next check for any trash in the carburetor.  This is just initial things based on the limited information given.  I have only have limited time right now, but will see what the experts come up with.  Good luck.

Ron Carbaugh

[herman]

Ron, Had this bike painted all my grounds seem to be clean and good.This only happens from mid. rpms and high rpms. carb is clean in the bottom.can i have a problem with the motoplat?Its good hot spark and starts very good.Thanks Herm Ron this was my first ride on one of my pentons and i am very impressed the power is so smoth and plenty, the ride is very controlled ( i had put works shocks on two of the bikes)seams to be a excellent bike with a bug in it.

[rob w]

Because this was the first time the motor had ran for any length of time, you mentioned it was about after an hour, and those symptoms sound a little like some leakage from the top-end. I would check or retorque the cylinder head again. Congrats on getting your first Penton running!

[Dwight Rudder]

First I would like to note that unless you have bumped up the compression and timing that you don't need nor want 110 Octane fuel.
Too much octane and you will not get a complete or clean burn. 110 octane burns too slow. I would suggest no more than say 100 octane. But good quality 93 octane is probably plenty. But if you are sceptical you could blend the 110 with the 93 to get a more reasonable octane and fuel  quality.
Good luck.
Dwight

Dwight Rudder
7 time ISDT / E medalist
8 time National Enduro Class Champion.

[Steve Minor]

I believe Rob nailed this one....I ran into the same situation recently on my 400 and found the head bolts to be lose, allowing leakage. I retorqued and it solved the problem.

[tlanders]

For a new head and base gasket rebuild, standard procedure is to warm the engine up for 15 minutes, then let it cool COMPLETELY, then retorque the head. Then warm the engine up again for 15 minutes, then the same procedure. Keep doing this until the head doesn't need retorquing. It has always taken from 2 to 4 times for me.

Teddy

[herman]

I will check the toque on the head i hope thats it. thanks Herm

[herman]

Bob, Thanks you were right on the torque was way off from when i set it so torque it and warmed it up let it cool and retouqued it and i am so happy with this 250 that this week end iam going to indiana to pick up one more 1975 250.