Ok, there's a mystery pipe on my Dellorto DHLA "H" carb's (circled in green) and it's caused my No. 1 spark plug to burn out, this obviously isn't good

So that do you think it's for? and can I just blank it off and replace to plugs, I may boroscope the engine to check for damage but would love to use it this weekend.

ATB Dan.

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At a rough guess i'd say a Vaccume take off for either Servo Brakes or Vaccume advance maybe.

If its been sucking fresh air in there then that would make the mixture lean and thus burn the plug and probably a valve.

not very difinitive but an answer all the same at this time of night!

Ya, what he said.
Its a vacuum nipple that only draws vacuum from one cylinder. Meaning that it will only suck in a bunch of air and lean out one cylinder.

Plug it off, replace the spark plug and fire it up.
If it runs on all 4 holes you are fine. You may have to adjust the carbs and then just drive it. If #1 is not firing, or it backfires out the intake or exhaust you have a burnt valve and the head has to come off.
Good Luck.

Yup Dan as the 2 above replies, its running lean on that cylinder, block it off.

Fozzie

Cheers folks, I'll get a new set of plugs, looks like a journey into work this evening.

ATB Dan.