Blaster keeps blowing topend

Hank751

Member
Oct 29, 2019
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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.
 
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.
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?
 
besides the leakdown test mentioned above .............

40 pilot
4th clip on needle

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 ?

head was milled .035 before last rebuild
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:
 
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:

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.
 
Well guys I did a full rebuild on the blaster and the crank ended up being shot. Looked to me like itd never had a rebuild.
Mods
-3mill vitos stroker crank
-bored .080 over with Namura pistons and ebay cylinder
- ebay cylinder head
-Vforce 4 reeds
-fmf fafatty pipe
JETTING
-32.5 Pilot
-3rd clip needle
-300 Main
PLUG- BR9ES
93 Octane mixed with klotz benol
Atf in tranny.
Have 3 tanks of gas ran through and it is breaking in really nice! Plug is a good solid brown
Has slight hesitation off bottom but I think with having the cheap cylinder with its porting it will have a bit of a hesitation.
Thanks for the help
 
head was milled .035 before last rebuild
I'm going to have to agree with Awk on this one. Head milling is one thing for cars and other four-stroke engines. Two-strokes have VERY tight tolerances, so that may have done your engine in. I wish I would have held onto my stock head for you. But do yourself a favor and buy a good quality used OEM head. These can be had for under $50. Don't have it milled and see if that yields similar results after setting your needle to the middle slot, measuring your ring-end clearance, a proper break-in, and getting a much larger pilot jet. If you're doing mostly road riding (not that you should with a two-stroke ATV), you should get a 310 or larger main jet.
 
If you at 80 over already on a cheap cylinder make sure your jetting is right .i think someone makes a 90 over.probaly should keep a eye out for a stock cylinder.at least your riding.good luck
 
I'm going to have to agree with Awk on this one. Head milling is one thing for cars and other four-stroke engines. Two-strokes have VERY tight tolerances, so that may have done your engine in. I wish I would have held onto my stock head for you. But do yourself a favor and buy a good quality used OEM head. These can be had for under $50. Don't have it milled and see if that yields similar results after setting your needle to the middle slot, measuring your ring-end clearance, a proper break-in, and getting a much larger pilot jet. If you're doing mostly road riding (not that you should with a two-stroke ATV), you should get a 310 or larger main jet.

Road riding has ZERO to do with anything. It comes down to proper jetting.