I had the following setting 1985 PX150 E engine with case matched Pollini 177 cylinder, Malossi Reed valve,Dell Orto carb. 60mm stroke crankshaft, HP4 flyweel, Mallossi 8% main gear, T4 Fourth gear. It had a lot of power but it run too rich. Done may carb. adjuctment with out good result.
while you are changing the barrell have a look at the reed condition…malossi tend to use fast.
And if you still find your engine run flat at high rpm then you know you have to do something with the port.
I tried many combination with polini 177 hp4 and reed, what I liked was head gasket 1,5mm, I got more torque, very nice feeling, but flat at high rev, it doesn’t overev, it is because of the altered time port using longstroke. And more difficult to set the carb.
Only after working the exhaust port I got global satisfactory results. Widening left right, and 1mm higher (up to 2,5mm higher if you want more power but your low will pay a price) … but you know at the end we have to do our experiences.
One of my engines has a very similar set - up.
Are you using a longstroke crankshaft with base or head 1.5mm gasket?
If you use a longstroke with mild ported cylinder as Pinasco, you have more power, but if you use it with a Polini is not that simple matter. A Polini 177 is already sport ported. If you use a 60mm crank you will alter the porting and for example with a head gasket insted of gaining power you will loose power at high rpm.
The engine will have very good torque but it will have problem passing 7000rpm. It is like it is constantly running reach and can’t rev beyond a certain point.
At the end a Polini 177 with 57mm will make more power and rev higher.
There are two cures:
1- Use a 57mm crankshaft (a standard will work perfect with reed and will have better balanced that specials)
2- Alter the porting of your cylinder for using with 6omm crankshaft.
In the second option you will have more power but be carefull with relyability
In the long run if I had just one engine and still have the standard crank I will use the Polini 177 with a 57mm stroke.
If you have more question …
I find that the cylinder was broken in the base. So I will install newone and will see.
I would like to add something since what I said in my first reply could be too radical.
You didn’t mention which carb you have, but with this kind of tuning is of the greatest importance for your engine to breath. Sometimes a wrong filter or a filter that is not real clean will not only loose power but also setting your carburation impossible.
So take your filter out and go for a ride so you can consider how much of the problem could be responsability of the air intake.
Then, if you really want your engine to be powerful take your cylinder out and send to a professional to port it. Maybe the piston too.
When you use 60mm is expecially important to report the exhaust cylinder port.
And then let me now…just for curiosity.
…in your set up timing will be 17.