Installed puch head, now cant get it to run well...

B

borntofli

Member
Put a 70 hi hi head on and now I can get it started but have to really work the throttle to keep it running......

I used 2 head gaskets, would too low compression make it run this way??

It doesnt start harder than before so maybe i need only 1 gasket.....

I changed jets, 70 to 66 and it runs a little better, (can keep it running poorly by working the throttle alot...)

What did I do wrong...???
 
Check spark plug gap and make sure plug isn't fouled. I had the same problem, swapped to a new plug an it ran great. Worth a shot
 
Found the problem.... The piston hits the plug...... Should I add a base gasket to raise the cyl up?? At tdc the piston edge rises over the top of the cyl top.....

How much clearance is there supposed to be from the plug electrode and the top of the piston???
 
ermm...how long of a plug are you using? that shouldn't be happening. sometimes the puch's squish band hits the piston but ive never heard of a plug hitting. An extra base gasket sounds like a good start
 
Why not just add another brass washer/seal to the plug if that's what's hitting? Then you're not changing port timing or conpression.
 
make sure you have at least 1mm clearance between squish band and piston. Use solder at both sides of the piston to tell. If less than 1mm then add head gasket. If more then add spark plug washer.
 
Squish band is basically the space between the piston and head when he piston is at top dead center. Anyone feel free to correct that if im off
My bike loved the b7hs, I don't have any experience with the bps series though as far as differences.
 
Use a bit of play doh to check assembled clearance. It works much better than solder for measureing the head clearance and is much less likely to damage anything.
The 1 mm measurement sounds about right for safety.
 
maniac57 said:
Keep in mind base gaskets change the port timing as well as compression.
Click to expand...

Maniac is right, adding an extra jug gasket will not only decrease the compression slightly(probably no more than 5%) but it also moves the ports up a degree or two. While lowered compression might sound bad, it'll help it to start a little easier, improving low end torque. Top end might suffer a hit, maybe a mile off the top speed. However, it also exposes the ports a fraction sooner as well as unshroud the intake port a bit more too, allowing more intake gasses to flow, which makes up for the reduced compression. There is more air & fuel to burn, making for more bang & more power. This is the 2 stroke equivalent of advancing the camshaft in a 4 stroke engine, often used to increase low & mid range power.

Before you raise the spark plug(with a plug gasket) or carve a relief crater in the piston dome, try an extra jug gasket, might prove worthwhile.

Something else you might try; Bend the ground electrode back and file the tip of the the spark electrode down a little bit, then bend the ground electrode back, gaping it accordingly, that might buy you the necessary clearance you need.
 
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