Blaster keeps blowing topend

Discussion in 'Engine' started by Hank751, Oct 29, 2019.

  1. Hank751

    Hank751 New Member

    Joined:
    Oct 29, 2019
    Messages:
    3
    Likes Received:
    0
    Trophy Points:
    17
    Gender:
    Male
    Bought an 01 blaster went through 2 top ends in 2 weeks. Mixing 32:1 with klotz
    Jets-
    40 pilot
    4th clip on needle
    270 main
    Fmf pipe, head was milled .035 before last rebuild. Had not even a tank of gas ran through before it completely fried the piston. Putting a new bottom end in to make sure it's all good just wondering if these things will blow that easily or how can I avoid it if so.
    Ride a lot of roads have 14/40 gearing right now and going to a 14/38 after this rebuild.
     
  2. Noxtol

    Noxtol Member

    Joined:
    Aug 15, 2018
    Messages:
    53
    Likes Received:
    5
    Trophy Points:
    45
    Are you following proper break in procedure? And have you done a plug chop to test the jetting? By frying the piston do you mean carbon build up or like a hole burned in it?
     
  3. Pj Uptmor

    Pj Uptmor Member

    Joined:
    Mar 11, 2015
    Messages:
    138
    Likes Received:
    12
    Trophy Points:
    54
    Gender:
    Male
    Did you do a leak down test ?
    Where did you get your top end at? Hope not EBAY.
     
  4. Awk08

    Awk08 Administrator Staff Member Technician

    Joined:
    Jan 30, 2009
    Messages:
    24,273
    Likes Received:
    2,184
    Trophy Points:
    175
    Occupation:
    Electrician/Contractor
    Location:
    Pa.
    besides the leakdown test mentioned above .............

    Where did this jetting come from ?
    32.5 pilot and middle slot on the needle has worked for every blaster I've tuned with a stock carb.

    270 main with your mods is sure to blow when riding roads at full throttle for extended runs.
    these aren't street machines made for long periods of wide open throttle with borderline jetting !
    The FMF's I've tuned required 290-310 mains even for woods riding.

    were plug chops done ?
    https://www.blasterforum.com/threads/how-to-plug-chop.53237/

    what was the piston to cylinder clearances after these rebuilds ?
    what was compression ?

    this could very likely be your biggest problem, just a milled head without modifying the combustion chamber raises compression too much which can cause detonation with too low of octane fuel. was there a hole in the top of the piston ?
    detonation needs to be closely listened for, and plugs read after each plug chop to check for specks of aluminum on the plug.
    a properly modified head with an improved combustion chamber, and correct octane fuel to match the new compression # is highly suggested....... ( http://kenoconnorracing.com/ns/pricing )
    general rule of thumb, but not written in stone .....compression over 140psi could require 89+ octane fuel, 150-ish to 165ish psi requires 90 octane minimum, up to 180-ish could require a mix of race fuel and 90 octane, 180+ psi requires straight race fuel.
    not just mill X amount off the head and send it :eek:
     
  5. Hank751

    Hank751 New Member

    Joined:
    Oct 29, 2019
    Messages:
    3
    Likes Received:
    0
    Trophy Points:
    17
    Gender:
    Male
    I'll try that jetting set up and see if it works. Was running 93octane fuel. Probably am gonna go back to just a stock head.
     
  6. Hank751

    Hank751 New Member

    Joined:
    Oct 29, 2019
    Messages:
    3
    Likes Received:
    0
    Trophy Points:
    17
    Gender:
    Male
    No I didn't do a leak down. The pisto. I was running was a wise standard bore with a new cylinder. Cylinder was from ebay
     
  7. Awk08

    Awk08 Administrator Staff Member Technician

    Joined:
    Jan 30, 2009
    Messages:
    24,273
    Likes Received:
    2,184
    Trophy Points:
    175
    Occupation:
    Electrician/Contractor
    Location:
    Pa.

Share This Page