Ok, upgraded from 52mm head to 54mm head ported and polished from Hetrick racing. Also have the 28mm carb kit with reeds and full exhaust from Hetrick. When I had the 52mm head it ran great!. Carb setting was pilot jet 50 and the main jet 125. Dont know what the clip was set to, but it ran great with ithe set up for the 52mm. NOW I have the new 54 kit and got it to fire up, but couldnt get her to idle. So I should have adjusted the idle screw, but just held the throttle for several minutes till she was warmed up. Then tried to goose the throttle and bogged. Then I checked plug and it was white.. lean. So I made error and put in 120 main, but that got it to run up to moderate speed, drove down the street about 200 feet then turned it around and it died in front of the drive way. It would not start from there. Ok pulled plug and still white and realized I needed to go bigger not smaller on main. So dropped in 135main and put it back together. Now it wont start at all even dropped original 125main and no luck. What Ive done up to now is: new 100octane race mixed 32;1 new fuel filter, cleaned out carb jetts and all. Pulled head to check for any damages, nothing I can see was wrong. Try to fire it up and the best I can get is a couple pops coming out of the exhaust. I do have spark so I know the safetly lanyard is working. Im starting to worry with 1st ride of season 2 weeks away. Thanks for your experienced help!

 

Ok, just got back from store and bought compression tester. Whoa! 30PSI? What the heck? stock ive learned is supposed to be over 100psi? Its a brand new head, piston and seals what whould have caused it to detonate like that! Im pissed!

 

I think you already know the answer to your question but... here ya go

first of the right jets are important a lean situation will kill even a well broke in motor! with a new one it should idle slobbering rich through at leat 3 heat cycles (idling) cooling in between the each for about 30 mintes then ride it slow checking plug regularly and it will last forever, skip a step sometimes you will be fine... some times you get 30psi and a frown instead of 130 psi and a huge grin

rich

 

you're luckey it's a 2 stroke and easly fixed, carburator jetting and ignition timing are 2 of the most important thing on keeping 2 strokes alive, low compression is caused by eaither a bad head gasket or burned piston and rings, and it sounds as if you might have burned the piston, remove the cylinder and look at the piston for any unusally marks or scuffing, if it still looks new then replace the base and head gasket making sure to torque head according to your factory manual, never reuse these two gaskets. remember it's better to start rich and work you way down on the jetting, i take it you didn't mess around with the timing yet?

 

I don't want you to take this the wrong way , but did you have the throttle WOT when you checked the compression? I did this mistake before when I thought my bike had compression issues.

 

Pulled the head and checked for scarring. Clean walls and narrowed it down to a burned piston rings. The piston slides very easily all the way to the top of the head with little resistance. Expensive lesson to pay for not starting on the rich side, But then again it ran rich with the 52mm kit installed so I thought it would be close. I realize that a port and polished head makes night and day differences and take the costly mistake as lesson learned. Quick question then, when I put in the new piston, am I suppposed to put at least some lubrication on the rings like engine rebuild lube cause kinda scared now if I go through another piston. Or just make sure to run rich. Also how will I know its running lean once I fire it up? Im sure I'll get it to start and once I finish adjusting idle. Previous attempt to give it gas it just wanted to stall, so is that a sign of lean or rich? Thanks guys!

 

before you just go ahead install a new piston, you need to get both the cylinder and new piston measured and check for proper clearance, their's never 2 pistons the same size. this should have checked before even if you purchased the cylinder and piston as a kit, this is very important that on a 2 stroke that the proper piston-cylinder clearance is maintained. as far as using lube when installing a new piston their's 2 rules of thought , the first says yes, it prevents piston scuffing, the second which i'm included says no, oil will glaze the cylinder walls preventing the rings to seat properly, also on a 2 stroke just as soon as the engine starts it will lube the cylinder anyways, i've always assembled my race engines dry. but of course it's your decision. any time you increase airflow you need to increase fuel flow

 

Billl2099 you nailed it!! After ordering and spending another piston $130 including overnight shipping from Hetrick. Got to start perfectly and although it ran a tad lean after a few very easy runs up and down the block, brought it in to check the plug. Checked plug and found it to be border line lean. Ok, just tried to start it again and guess what no compression again!!!! 30 PSI!! only after less than 10 minutes total on new piston. Pulled head again and checked for damage and found none. No scarrs no holes. Narrowed it down to bad piston rings cause what else can it be. these pistons come from Taiwan so what else can be expected?! I hope Hetrick racing has good customer service, cuase no probs with their other stuff. Gonna send them back their head and let them try it out themselves. Bill are you the same guy from WRH Racing?