Boring .80 over. What else do I need to mod?

[Blinddesign]

I have a 98 blaster and i just blew out the piston last weekend. Took apart the top end and the piston has a crack and there are grooves all over the piston as well. I got ahold of Arnold's Motor and they will bored for $45 after i get my piston ordered. With boring out to .80, what other changes will or should i make to the engine or carb. I do plan on going to a full FMF Fatty and Silencer... Do i need to change the carb out and what about the spark plug? Will the spark plug still be the same size used? Thanx for any help, im new to this forum

 

[Larry's Shee]

Welcome!! Why are you going .080 ??

 

[sicivicdude]

First off, welcome!

Second, lets not put the cart before the horse. What's the current bore size of the top end now? ~.070" or 67.75mm? If not, hold on ordering that new piston for a minute there boss!

Boring an engine is solely for the purpose of cleaning up previous damage caused by a siezure event or FOD. Boring a top end adds neglible amounts of power and is taking away valuable engine lives for later. .080" or 68.00mm only leaves one more possible engine bore but won't even add 1 hp to your quad.

You should have the cylinder measured for bore, taper, and out of round and only bore enough to correct those problems back to factory spec (USUALLY the next overbore but sometimes 2 or 3)

If you are trying to get more power, you can to do a few basic upgrades to liven that engine right up. The first is a different pipe, FMF fatty and silencer is a decent upgrade. The potential power output with that pipe is MUCH better than stock but not quite as good as others...

Next remove the airbox lid if the riding you do is compatible. The stock "snorkel" off the front of the airbox is an extreme restriction on the incoming air.

Finally, rejet the carburetor to accomodate the change in incoming and outgoing air flow. You can either purchase new, genuine mikuni main jets from your dealer for about $3 a piece (you might need 3-4 to fine tune) or you can order a vito's JK200 jet kit "for airbox lid off". It comes with 5 main jets, a pilot jet (which most people don't use) and a thinner needle. For most applications the stock needle and pilot jets are fine but they're included in the kits. Stay away from the "staged" jet kits and dynojet jet kits. The "staged" jet kits are a joke and DO NOT mean your engine will be properly tuned! and the dynojet jet numbers do not correlate with mikuni jet numbers ( or any jet numbers for that matter!) so your numbering system will be different than everyone else.

Generally speaking, with a stock top end, FMF pipe, and airbox lid off, you will need about a 300 main jet and needle on the middle clip position. The only way to confirm this for sure is to do a plug chop!

Go up to the top of this section and click on the sticky links, sepcifically the "everything you need to know about your blaster" link and read read read read read read!

 

[Blinddesign]

I havent had the piston measure to see how much damage it has. Ill have to calibrate it to see and yea, I may not need to go to a .80. Maybe just a .30 to .05 will work just fine. My main concern was if i had to change out the carb since ill be adding a bigger piston. Other adjustments before blowing top end. Was removed TORS and added the screw kit into the side of Carb. Before removal of topend, i did a compression test and that came to only 25psi. Since i bought this toy 5 years ago, it seems that i have always been working on it. Big thing is cleaning plugs and changing after every ride. Oil was blocked off before i bought it and have been mixing 32.1. So, basically 7oz to 2gal. It was a craigslist buy for next to nothing. So really i cant complain. Also, its a 98 and it always seemed to out perform my 06.

 

[blasterdemon7]

Agreed .Boring larger then what you need is a waste of cylinder life. No extra power to be had by doing it.Sicivic knows what he's talking about.

 

[sicivicdude]

I havent had the piston measure to see how much damage it has. Ill have to calibrate it to see and yea, I may not need to go to a .80. Maybe just a .30 to .05 will work just fine. My main concern was if i had to change out the carb since ill be adding a bigger piston. Other adjustments before blowing top end. Was removed TORS and added the screw kit into the side of Carb. Before removal of topend, i did a compression test and that came to only 25psi. Since i bought this toy 5 years ago, it seems that i have always been working on it. Big thing is cleaning plugs and changing after every ride. Oil was blocked off before i bought it and have been mixing 32.1. So, basically 7oz to 2gal. It was a craigslist buy for next to nothing. So really i cant complain. Also, its a 98 and it always seemed to out perform my 06.

Plugs after EVERY ride? I've been riding my blaster on the same plug for almost a year.... and it's just dark colored, not fouled out by any means...

Do not bore that top end any further than you absolutely have to, you're only wasting engine life.

The stock carburetor is a little small for high performance applications but it works quite well on a "mild" blaster (pipe, airbox lid removed, new air filter, jetted properly). Boring the engine will not have anything to do with engine air demands except perhaps increase compression back to the point you will need to recheck the jetting again.

I suspect either the PO installed like a 350 main jet (WAY too much fuel) and that's what's fouling out plugs OR you have a leaking clutch side seal/broken case and you are slowly consuming transmission fluid. Not at a rate which would alarm you (huge billows of white smoke and a completely empty transmission after a 10 minute ride) but the air it was also leaking was allowing a lean condition which could be the "outperform the 06" (lean conditions run "hotter" but also don't last as long!) AND low compression of the top end (oil film break down due to "hotter" running results in piston to sleeve contact).

The way to diagnose is to pull the carburetor apart and check what mainjet is installed and then leakdown test the engine to diagnose a potential leak.

 

[Blinddesign]

Thanks for every piece of info from you all. I have been reading on this site for a couple years and finally just registered.. Glad to be here!