Old 4 hp (1971) 2 cycle won’t start.

[Holmboat]

Rebuilt carb, checked timing and coil/stator. All ok. About 90 lbs of compression. Pull to start and nothing. Pull plug, it is dry. How do you check the vacuum created in the crankcase and the operation of the reed valves. Any guidance appreciated.

 

[AceCombat]

Your compression is way to low! You should be up in the 130 to 140psi! Is it almost trying to start?

 

[Holmboat]

Nothing. Just a sore arm. Does not even try. The dry plug makes me wonder about the vacuum in the crankcase being low. Hesitant to open the engine up, but am thinking that’s coming very soon.

 

[Scott Danforth]

first, how long was it sitting? then why was it sitting to begin with

if it was sitting for more than a year or two, you need to go thru the fuel system.

do you have spark, if not, you may need to service the points

90 psi on a 4 hp motor is fine

 

[jimmbo]

Is fuel getting fuel through the carb? Spray some gas-oil mix into the carb, and try. You are using the choke? Is the Spark strong enough to jump a 7/16" gap? I doubt that engine would ever have 130 lb compression. Yours, at 90 should still fire, and run.

 

[jheron]

Unless that thing has been serviced since 71 the crank seals are very likely toast, or about to be.
Cheers,
Jon

 

[Holmboat]

Thanks for the feedback guys. I just saw online last night how to spin it without the cover on, that will help.
I installed new points. Today I used a meter to see what the points were doing and found continuity coming and going as I rotated the flywheel. Took the point plate out and cleaned all the mating surfaces and that went away. Going back out in a bit to see if there is spark. I have not shot fuel in through the carb, but with a dry plug after trying to start with and without choke, I suspect something in the carb. I took the carb down and soaked it in carb cleaner, blowing air through it afterwards. Did not have new gaskets,so plan to order some tonight. I will get it or learn a lot in the process. the journey continues.......

 

[racerone]

Seal at the top would be easy to check.-----Not sure there is a lower seal on those cranks ?

 

[Holmboat]

On to the spark. Rotating with a drill, new points with 0.020” gap, no spark. Disconnect the point wire from the coil and jump to ground on and off and have good spark. Reconnect, no spark. Points show open and close with ohm meter. Verified the wire is good. What could this be?

 

[Holmboat]

Looking through the manual, I see what looks like a ground from the throttle link. Mine does not have this. I will try this later today to see what effect it has. Should there be a ground from the throttle linkage?

 

[Holmboat]

Tried the ground, no difference. Ordered the only remaining thing I can think of, the insulator where the point wire is connect. Hoping that’s it.

 

[jheron]

My old 4HP has a kill switch button on the end of the tiller arm, not sure where it is connected.
Cheers,
Jon

 

[Holmboat]

After a 2-1/2 week wait for a new isolator, installed, the motor now has beautiful blue spark. No apparent cracks on the old one, but apparently is was. Now on to fuel. Rebuild kit one the way.