I have replaced the ignition system and the carb....the engine is hard to start...and does not seem to have full power...the only way to start it it to put starting fluid in the carb...doesn't seem like the flywheel key is out of wack...but i guess that is kind of hard to determine....almost seems like the engine is out of time...or the valves are not working properly...has a kind of hissing sound..when you try to start it....does anyone have any sugestions...this engine has a tube that goes underneath the head to the other side of the head...from the carb...it is model 143.996704....railroader10..

 

Could be low compression either rings or valves. The best test for this is a leak down test but requires some specialized equipment. To check the rings you might try putting about a teaspoon of engine oil in the spark plug hole, then with the plug still removed turn the engine over 1 or 2 turns by hand, replace the spark plug and try to start.
This manual may provide more info
http://www.cpdonline.com/692509.pdf

 

it could be a dirty carb so its not getting enough fuel. If the spark plug is white youll know its running lean.

 

Does it try to kick back when you start it? Does it smoke?

 

Turned out crankshaft was bent due to hitting something....had another 6.75 back up motor...put new carb and ignition on that...runs perfectly now...thanks for all the information provided by the people who answered this......railroader 10.....