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