Hmm now what (A Rebore!)



  • @Calum It had a few small nicks, but was a whole load better looking than the other. Got it from where I bought the bike, it was the best 3mb he had, got loads of the more restrictive ones though.

    Sadly no snaps NINJA, I think maybe it's a slightly older head as it had 3mb and Yamaha embossed on the top of it which the other does not



  • @Pablo13 COOL so long as it works fine, then your good_to_go!!!!!!!!!! 😁



  • @Pablo13 If the other one did not have 3MB stamped on the head then it wasn't a 3MB head. Yamaha used the 3MB all the way till they discontinued the engine. I had a few non-stamped heads and run run on my dt.

    The majority of power is made or lost in the head, so it is important to get it right, but I am surpised you noticed it. I would have felt you would have needed a dyno...make sure the bike is setup right. I fear something else may be amiss and might be a little expensive



  • @NINJA yeah I got a bad exhaust so it's not making that much power really. It's got a whole lot of torque and I get very good gas mileage.



  • It's still basically the same 🙄

    Gotta be something else....not much left really, CDI, crankcase seals or clutching at straws for an extremely worn carb?

    I've never inspected the reeds and the exhaust is a bit of an unknown, so could both be causing possible issues and shouldn't be overlooked.

    Got a second hand CDI winging its way to me to rule that out. I'll do that and go from there....



  • @Pablo13 I would start simple, have you checked the plug or did you fit a new one? Perform a plug chop to see what the condition of the plug is, which will give you some clues as to what is happening. 😉



  • @NINJA I've been doing plug chops but nothing untoward has been spotted, here is the most recent, was a new plug when the new piston went in

    alt text

    And here is the old head with no casting on top, yet the heads dome defo isnt the restrictive head

    alt text

    And the new fitted
    alt text

    I cant see anything wrong with the plug, but feel free to chime in 😉



  • I never said restrictive, just that it isn't a 3MB. It's odd that's for sure. I've had a few in the past, and the belgarda models are stamped P.

    I think they must not be Yamaha heads or something. There must be a difference. And difference in Squish could be unnoticeable to the eye.



  • @Calum So there are other heads apart from them two, cool I didn't now 😉

    At least the whole top end can be ruled out now, plus ive got a spare head to play with, so not all bad. Just need to get to the bottom of this issue once and for all.

    At this rate I'll have a nice stash of spares 😂



  • @Pablo13 Got 4FU heads as well, squish is noticeably different on them.

    And the SP heads, which are O-Ring???


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