So I have a blaster motor that was giving me some problems. It would ping at high RPM when you let off the throttle. Figuring it was a lean condition I proceeded to change the main jets, pilot and jet needles to the ridiculous and the problem was still there. I had the jetting perfect at one time. I made it ping intentionally just to do a plug chop. The plug looked perfect but when I turned the ignition off it still kept running with the ignition off. The motor was really hot. After researching pre ignition causes I stumbled across squish. I checked the squish and it is .070, is this to big and can this be my pre-ignition problem? I bought this motor used and rebuilt it with pro-X piston .060 over. The thing runs great otherwise.
squish band issue
- Thread starter darins
- Start date
.070" sounds like a stock head. Did the check grow significantly as it went towards the center of the cylinder?
if its stock then this is not your problem. what carb are you running? what modifications do you have to the motor?
I bought the motor second hand from a local salvage cycle. I rebuilt the bottom end with hot rod con rod and rebuilt the top end with fresh bore and new piston. the local shop did all the metal work and crank. I spared no expense in doing this, so I am a little disappointed with the results. Has a new genuine pwk28 carb.
well check compression if you have a compression tester. also what fuel are you running? you should be using premium 93 octane. has the timming been advanced on the motor? what other mods and what jet size are you running?
typically pinging would occur durring wot conditions as this is when the most stress is put on an engine however i have also had an issue with off throttle pinging at one point. it is kinda typical of a 2 stroke to make a pinging sound off throttle but im guessing you can tell the difference. where did you get that carb do you know what jets and what needle are in it? have you by chance done a leakdown of the motor? hopefully the shop did at least and a retourq of head and jug bolts after a good warm up and cool down. the best way to cool down an engine is more fuel. if everything else checks out find a richer needle or try moving it up a notch or two.
With your engine setup, you don't have a ping.
It's probably piston slap.... Pop the cylinder off and measure the piston to cylinder clearance.
It's probably piston slap.... Pop the cylinder off and measure the piston to cylinder clearance.
The piston is new, cylinder fresh bore with .003 clearance so perfect there. If it was piston slap would it over heat and continue to run when the ignition was turned off? I made it ping intentionally just to do a plug chop. The plug looked perfect but when I turned the ignition off it still kept running with the ignition off and was really hot.
this is exactly what my engine does, but i sent my head off for it to run on a lower octane it was at 184 pounds running sunocco 93, the new head is at 153 pounds but i have yet to see if it fixed the problem.
Well after a 5 min conversation with Ken at http://kenoconnorracing.com He convinced me my problem was a air leak somewhere, didn't take long to convince me as he is the man in the know. I set off to check the leak down and voila. It starts at 10 psi and drops to 4 psi in about 10 seconds and holds steady at 4 psi. I found it was leaking into the gearbox. Just to verify I equalized the gearbox and crankcase pressure up to 10 and it held steady and when I let the gearbox pressure go the crankcase pressure dropped with it. So it looks like I need to split the cases and do some investigating and ship them off to Ken for a lapping just to be sure. Thanks Ken you are a valuable asset to this forum.
Could this cause the ping at high rpm when I chop the throttle to 1/4 throttle?
Could this cause the ping at high rpm when I chop the throttle to 1/4 throttle?
Ahhh, you know I forgot the right side seal is in there. I will check it first. It was a new seal but I will check anyway. Thanks I:I
Sorry for the thread jack but mines leak free and does this not all the time but it's happens to me once so far and I just did another leakdown test to confirm this
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