Rough running in the powerband, knocking/pinking ? (ETZ251)

[keleto]

Between about 4800 and 5400 revs my engine seems to be knocking/pinking, or perhaps it is exhaust crackle ? It smooths out afterwards and more throttle seems to help which seems to kind of suggest a touch of lean mixture, but I already have quite rich settings and cannot really go much richer without plug fouling.

I have retarded the ignition to 2.0mm BTDC and started using premium (high octane) fuel which had made it a LOT better, but it is still noticeable. My carb needle is in the 4th position (ie one step richer than stoichiometric) and I have used a 140 main jet instead of 130. My plug colour is just on the rich side of perfect as one would expect with this arrangement. I have a morris minor air filter which is believed to be a little easier breathing than the stock one, and an aftermarket exhaust silencer (not a racing exhaust, just a generic china replacement). My squish measurement is good (1.1mm) and I am using a B7HS plug.

Any suggestions ?

[DAVID THOMPSON]

try a plug of a different brand same heat

and about a week after you get a 2 smoker running perfect expect a hole in the piston top

[keleto]

Yeah, easy to get them to run, but hard to get them to run really well. I have changed to a slightly colder plug for the moment as one was available, when the weather is nice I will try it out. Regarding a different plug brand, what brand would you recommend ?

[DAVID THOMPSON]

I use Bosch a lot
in the day when i had 2 smokers i used lodge and klg but i think they are not made any more at least i can not find them

my old Yamaha ym1 305 cc use the same Bosch plug as my later R50s BMW 4 stroke and was not bad about fouling them

[AIRMANBEAR]

Between about 4800 and 5400 revs my engine seems to be knocking/pinking, or perhaps it is exhaust crackle ? It smooths out afterwards and more throttle seems to help which seems to kind of suggest a touch of lean mixture, but I already have quite rich settings and cannot really go much richer without plug fouling.

I have retarded the ignition to 2.0mm BTDC and started using premium (high octane) fuel which had made it a LOT better, but it is still noticeable. My carb needle is in the 4th position (ie one step richer than stoichiometric) and I have used a 140 main jet instead of 130. My plug colour is just on the rich side of perfect as one would expect with this arrangement. I have a morris minor air filter which is believed to be a little easier breathing than the stock one, and an aftermarket exhaust silencer (not a racing exhaust, just a generic china replacement). My squish measurement is good (1.1mm) and I am using a B7HS plug.

Any suggestions ?

YOU HAVE TRIED WHAT I HAVE TRIED AS WELL. TO NO AVILA...THE GERMANS HAVE TOLD ME TO INCREASE THE CHOKE A BIT TO STOP THE PINGING (USA TERM).. BUT I DONT LIKE DOING THAT ….. I HAD SIMILAR PROBLEMS WITH MY 350 JAWA AND A U.S,A. 2 STROKE RACE MECHANIC TOLD ME TO DRILL A 1/8 HOLE IN THE PISTON JUST BELOW THE LOWER RING NEAR THE EXHAUST PORT ….. THIS COOLS THE WALL NEAR THE EXHAUST PORT WITH THE FUEL/ OIL MIX WHICH OVERHEATS AND CAUSES PINKING AND SEIZURE ..
EVER SINCE I DID IT NO MORE PROBLEMS,,,,,,,,,,,,,,,,...………… ED in N.Y.

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[Blurredman]

I imagine on a Rotary or Reed valve induction engine, it would be okay to have the hole there.. ?

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