HeadSmess
Well-Known Member
- Local time
- 2:51 PM
- Joined
- May 17, 2010
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- 3,048
as i do more and more to a ht, im amazed they can run as stock.
the first and simplest mod is to cut the piston skirt down.
note EVERYONE SHOULD MAKE THIS MOD BEFORE THINKING SILLY THOUGHTS ABOUT COMP RATIOS AND EXPENSIVE CARBS.
it was the ONLY thing that i did to my first engine. it screamed
if you peer into the intake, and rotate the engine, you will note the piston never completely uncovers the port. so this does two things. reduces the amount of air that can flow through the port, and how long for.
so. turn engine to TDC. scribe a line on the piston.
disassemble. file down to scribed line.
this has changed the induction timing from roughly 98 degrees (pathetic) to 120-130 depending on material removed.
better to use a half round file than just grinding it all off dont overdo it! and get new circlips for the conpin! real ones that need pliers!
i then had a bit of a chew at the port itself. mainly widened as i need it to be equivalent to 19-20 mm, without affecting the timing. flattened bottom of port a bit, hence the piston...
this brings my induction timing to 148 degrees.
um. then the exhaust. this needs a lot of metal removed!
wider is better for volume, but at 138 deg stock, the top of the port can be raised somewhat.
so here we are at 160 degrees exhaust duration, widened, the port is now basically parallel. much better
dont smack the file into the opposite cylinder wall!
last but not least was to clean up the casting flash in the transfers.
they will need opening up as well, plus a little more duration, as they have about 110 degrees max now. this requires my mill to get set up again as die grinders can slip and ruin otherwise perfect jobs... the angles and depths are sort of important
so just a clean for now.
anyways. how does it perform?
well, with a stock nt carb and a slightly restrictive tuned pipe... a scalded cat! and getting fatser daily so as soon as this mill gets set up its a cnc manifold for the mikuni and a new pipe as well as transfers...
i guess i better put a vid up one day...this thing spools up like a proper 2 stroke now instantly, not when its thought about it for a while and decided that yes, that is WOT...
the first and simplest mod is to cut the piston skirt down.
note EVERYONE SHOULD MAKE THIS MOD BEFORE THINKING SILLY THOUGHTS ABOUT COMP RATIOS AND EXPENSIVE CARBS.
it was the ONLY thing that i did to my first engine. it screamed
if you peer into the intake, and rotate the engine, you will note the piston never completely uncovers the port. so this does two things. reduces the amount of air that can flow through the port, and how long for.
so. turn engine to TDC. scribe a line on the piston.
disassemble. file down to scribed line.
this has changed the induction timing from roughly 98 degrees (pathetic) to 120-130 depending on material removed.
better to use a half round file than just grinding it all off dont overdo it! and get new circlips for the conpin! real ones that need pliers!
i then had a bit of a chew at the port itself. mainly widened as i need it to be equivalent to 19-20 mm, without affecting the timing. flattened bottom of port a bit, hence the piston...
this brings my induction timing to 148 degrees.
um. then the exhaust. this needs a lot of metal removed!
wider is better for volume, but at 138 deg stock, the top of the port can be raised somewhat.
so here we are at 160 degrees exhaust duration, widened, the port is now basically parallel. much better
dont smack the file into the opposite cylinder wall!
last but not least was to clean up the casting flash in the transfers.
they will need opening up as well, plus a little more duration, as they have about 110 degrees max now. this requires my mill to get set up again as die grinders can slip and ruin otherwise perfect jobs... the angles and depths are sort of important
so just a clean for now.
anyways. how does it perform?
well, with a stock nt carb and a slightly restrictive tuned pipe... a scalded cat! and getting fatser daily so as soon as this mill gets set up its a cnc manifold for the mikuni and a new pipe as well as transfers...
i guess i better put a vid up one day...this thing spools up like a proper 2 stroke now instantly, not when its thought about it for a while and decided that yes, that is WOT...
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