'Pinging' at high revs

[phats]

Hi all,

So this was my first outing on the KTM, first time its probably been rode in 25+ years. Everything held up just fine, only thing i did notice, was a 'pinging' noise at top revs, like a detonation sound, is this common on KTM's? Or may it be an issue with Jetting or ignition? (1979 KTM GS250)

[454MRW]

I would take some full throttle plug readings to make sure that the main jet is big enough and it is not running a little lean on the top end and also verify that the timing is set to the 1979 spec. of 2.2mm Before Top Dead Center with a reliable dial indicator. In 1980 they backed it down just a little to 2.0-2.1mm, and it might not hurt to use that spec. What octane is the fuel you are using? Mike

Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1980 KTM 175-400'S
1975 Can Am 175 TNT & 77 250 Black Widow
1979 Husqvarna OR390
1976-78 RM & 77-79 PE Suzuki's
1974 CR250M 07 CR125R 79 CR250R

[phats]

Im running a 270 main jet, might try one size up. I couldnt find the exact jetting for the carb anywhere but it doesnt seem miles away. (still using 54 bing) I set the timing at 2.0mm BTDC. I use 99 RON fuel.

Cheers

[454MRW]

I think the newer "2" series jets are more precise than the older "1" series jets, but I am not certain that is the only difference.
According to the April 79 engine repair instructions manual, both the GS250, which used carb # 54/36/1220 & the MC250, which used carb # 54/38/107 had the same jetting:
185 Main-282 Needle Jet-45 Idle Jet- needle position 2-pilot air screw open 1 turn-throttle valve 230.
A technical service bulliten dated 4/26/79 lists the 38mm Bing jetting for the 250cc as:
175 Main jet-4K2 Needle-needle position middle- 45-50 Idle Jet-vaporizer No.(2)-and Air Screw 1/2-1 1/2 Turns.
I hope this helps. Mike

Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1980 KTM 175-400'S
1975 Can Am 175 TNT & 77 250 Black Widow
1979 Husqvarna OR390
1976-78 RM & 77-79 PE Suzuki's
1974 CR250M 07 CR125R 79 CR250R

[Gary Smith]

On my 82 250 the quish must be set using different thickness base gaskits or it will ping. Gary

[Rain Man]

Phats, I'm not sure what 99 Ron fuel is and if its available here in the States. All I know is we put vegetables in our pump gas (Ethanol).
   
Any detonation at all is eitehr because of hi compression ratios or timing.  Maybe trying  a lower grade/octane of petro might help?
2c

Raymond
 Down East Pentons