Jump to content
Sign in to follow this  

I think my 250 is detonating

Recommended Posts

I don't even have an hour on a new wiseco piston... but when I get in 5th and wide open on the road .. I start hearing $hit. im thinking its detonation. I've read it sounds like gravel hitting the pipe, and that really is the best way to describe it. What should I do?

Share this post


Link to post
Share on other sites

This may or may not help....Try putting some Maxima Octane boost in your gas.I use 3 ounces per gallon,and you don't need to change your pre-mix ratio.I put it in my 05 YZ250 just to be safe.I know for a fact that it does work,but you may also have a timing issue.I have a 2-stroke 1975 MT250 Elsinore Enduro,and it got to the point where I was getting kinda scared to ride it,the piston would rattle(that's what it sounded like)so bad.Under a load or going up hills it sounded like it was going to break into pieces.I put a few ounces of the Octane boost into the tank and it immediately started better,had better throttle response,and got rid of 95% of the knocking.Try it.

 

  • Like 1

Share this post


Link to post
Share on other sites

Better gas/retard timing

its 93, I believe its stock jetting... up a size on pilot and main if anything... pro circuit pipe, r304, boyesen power reeds, 400ft 85F.. its a 2004 model.

I'm thinking it has to be detonation or piston slap? Also I thought its weird, my idle is a little high with a cold engine, it seems the idle lowers as it gets up to temp?

Share this post


Link to post
Share on other sites

Air leak=high idle? Maybe

I retarded my timing just as a safety net, also heard there was some midrange gains to be had. Couldnt jet my way out of a wet paper bag

Edited by BloodBMcG
  • Like 1

Share this post


Link to post
Share on other sites

How was your piston clearance? It might just rattle a little.

I had my local dealer measure the cylinder, they told me to use this size piston. I know they used to sell race gas, I plan on going to see if they still do when I get off work to see if it helps.

Share this post


Link to post
Share on other sites

As stated air leak, fuel, or timing could be the cause. Did you do a leak down after rebuild. I chased my tail on my last bike and it ended up having a leak between the cases. Also if you believe it may be piston slap it's only 2 bolts and 2 springs to remove your head pipe and take a gander at the piston skirt.

Share this post


Link to post
Share on other sites

As stated air leak, fuel, or timing could be the cause. Did you do a leak down after rebuild. I chased my tail on my last bike and it ended up having a leak between the cases. Also if you believe it may be piston slap it's only 2 bolts and 2 springs to remove your head pipe and take a gander at the piston skirt.

I'm going to try race gas tomorrow.... if it was piston slap what would show it if I looked thru the exhaust port?

Share this post


Link to post
Share on other sites

I'm going to try race gas tomorrow.... if it was piston slap what would show it if I looked thru the exhaust port?

You would see damage to the skirt. Even with low hours. Scuffing, polished spots, scratches. You would know if a certain spot was getting more wear than others. I used to run straight c12 and that air leak still cause failures. Leak down is a good idea always. I spent over a $1000 before I realized it was time to build a $20 gauge.
  • Like 1

Share this post


Link to post
Share on other sites

Most likely pinned wide open on the road, lots of heat and low octane gas.

I've always been of the opinion a high performance race machine should high performance gas.

Actually the Japanese have always set up bikes at lower compression because they know guys won't use good gas.

A pity they can't build a proper engine because they know users won't use them correctly.

Share this post


Link to post
Share on other sites

Most likely pinned wide open on the road, lots of heat and low octane gas.

I've always been of the opinion a high performance race machine should high performance gas.

Actually the Japanese have always set up bikes at lower compression because they know guys won't use good gas.

A pity they can't build a proper engine because they know users won't use them correctly.

I tried the race gas today.. it did seem the motor was quieter (wide open at high rpm in 5th) and didn't flatten out on the top end so I believe it was to low of octane for the way its set up....

I also was having a bog at low rpm when I went wide open in all gears besides 1st.. but I noticed the air screw was almost 2 turns out, I put it at 1 turn out before I tried the race gas... what is stock air screw setting on a 04 model?,

Share this post


Link to post
Share on other sites

I tried the race gas today.. it did seem the motor was quieter (wide open at high rpm in 5th) and didn't flatten out on the top end so I believe it was to low of octane for the way its set up....

I also was having a bog at low rpm when I went wide open in all gears besides 1st.. but I noticed the air screw was almost 2 turns out, I put it at 1 turn out before I tried the race gas... what is stock air screw setting on a 04 model?,

When you say low rpm, how low? Turning wide open on a 2t well below its power band will cause all kinds of weirdness.

Don't forget the main jet is likely set for off-road. Meaning lots and lots of part throttle or short bursts of wide open.

For long periods of wide open you'd need to richen your main to keep egt within the realm of the melting point of aluminum.lol

I suggest you don't do too much wide open long bursts on the road. For the benefit of your engine and other kinda obvious reasons. Saw a lot of blown New bikes when I worked at the mc shop caused by running on the road.

If you do and I say don't, richen your main at least two sizes.

I've always tuned air screws by ear. Turn it closed more and more wicking the throttle open quickly from idle until the throttle response starts to get worse. Open it until you get quick throttle response back. Once you find the sweet spot turn it closed a hair. Neutral is no load, riding with a load will require a slightly richer setting.

If you find you need to be below 1.25 or more than 1.75 or 2ish. Pilot is likely wrong.

Ymmv.

Edited by Supertuner_tb
  • Like 1

Share this post


Link to post
Share on other sites

I don't even have an hour on a new wiseco piston... but when I get in 5th and wide open on the road .. I start hearing $hit. im thinking its detonation. I've read it sounds like gravel hitting the pipe, and that really is the best way to describe it. What should I do?

 

Are you saying you did not hear this noise before the new piston? If so, I can't possibly be a fuel quality issue. Always ask what changed when the problem began.

Share this post


Link to post
Share on other sites

Are you saying you did not hear this noise before the new piston? If so, I can't possibly be a fuel quality issue. Always ask what changed when the problem began.

Uh it most definitely could be a fuel quality issue. If it's got a fresh top end, it's got more compression than it did before assuming the top end was installed correctly. If your running like 120 psi in a old top end your not going to notice much detonation, if it's up around 170 or whatever it has new (could be even higher if it's not an OEM piston) then you will notice a huge difference.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×
×
  • Create New...