Yamaha Blaster Piston Slap

[meepz]

Hello,

This is my first time owning an ATV personally. Growing up I had a dirtbike and a 350 Rancher atv, but my father did most of the maintenance on them. I've never had a 2-stroke ATV before and noticed some noise coming from the engine and would love if anyone had an idea if it is piston slap or if it just the normal sound of a blaster.

It is a 2001 Yamaha Blaster with all stock except foam air filter and oil block off kit. My knowledge of anything mechanic is pretty basic but I have pretty good at picking things up. If the problem is isolated, I'm sure I will be able to fix it.

I've included a video:
Video here

Here is a better video

The ATV started up weird today too. The high revving at the end then it shut off. I checked the choke and it was out all of the way so I don't know why it did that.

 

[harley1-5]

sounds like it needs a rebuild if you keep running it with slap you will break a pisyon skirt.As for the reving it could be an air leak leak test it

 

[meepz]

Just did some searching and I will be getting a kit. What are signs to look for when determining the bore. And if I need to bore the cylinder, how much does that go for?

 

[Blaaster]

Has the carby been jetted for the foam filter and pre mix, check the main jet, it should be in the region of #260.

Blaster motors are notoriously noisy, if you have concerns that the piston is slapping do the following.

Leak test, then pull of the top end and have piston and bore measured.

I they measure out of specs replace them.

Before I pulled down , I would be inclined to remove the header pipe and look up the exhaust port for signs of piston damage.

 

[harley1-5]

blaster is right

 

[meepz]

I don't believe the carb has been jetted. I recently purchased the ATV about a week ago so my information is limited.

Foam Filter:
Should I replace the size of the jets for the foam filter? I will open it up today and see if I can get a brand/model of the filter

Leak Down Test:
I just ordered a tester so when that comes in I can check for air leaks.
When I look for piston damage, am I looking for obvious damage such as a gouge in the metal or if the rings look like they are damaged, or something more discrete like a scratch on the piston?

 

[Blaaster]

The damage will be apparent, scored piston, rings jammed in the ring grooves, piston burnt or melted above the top ring.

Start it no more until it has been leak tested.

List all your mods and we will talk jetting later.

 

[meepz]

Ok great, I really appreciate the help.

I won't run it until I get that test done and I will try to ask the previous owner for any other mods.

 

[Blaaster]

I can list the mods that require jetting changes.

Pipe, air filter, air box lid, pre mix at 32:1, any changes to intake ducting, all require different jets.

 

[meepz]

Wow never though of all of that. Makes sense though.

So I just ran it real quick to make sure I was hearing it right. At idle I can't hear any knocking but when I get it revving high for a few seconds is when I hear a knocking. It isn't consistent one after another, it's more of every 5-10 seconds I'd say. Some were even further in between.

It definitely made a distinct knocking sound though.

 

[Blaaster]

Start it no more until it has been leak tested.

.

I won't run it until I get that test done .

So I just ran it real quick to make sure I was hearing it right. .

Sure hope that the piston suffered no more damage that you have to replace it.

 

[meepz]

Yeah, I re-read your first post about Yamaha Blasters being noise machines and wanted to double check my suspicions. Now that it's confirmed I'm not going to start it until I fix the problem.

 

[MrTwoJay]

Could be one of many things, check the ballance shaft/weight if you have to open it, mine was knocking from there, and I suspect it is what caused the gearbox to crankcase seal to break.

 

[ProjectBlasturd]

Yeah, I re-read your first post about Yamaha Blasters being noise machines and wanted to double check my suspicions. Now that it's confirmed I'm not going to start it until I fix the problem.

So I'm aware this is an old post but did you ever figure out what your issue Was? My motor makes the same noise. Somewhat loud ticking noise like that at idle and I can hear it more as I walk away from the bike. Odd though because I don' hear it too much after it' all warmed up and been running for a few.

 

[Putmeonblast-r]

So I'm aware this is an old post but did you ever figure out what your issue Was? My motor makes the same noise. Somewhat loud ticking noise like that at idle and I can hear it more as I walk away from the bike. Odd though because I don' hear it too much after it' all warmed up and been running for a few.

If no one replied to your post I will I always go thru old posts just for brain stimulation lol.. the reason u here it more when u first start it up is because it’s cold as it warms up the chamber expands thts y it is imparetive tht u warm up a 2 stroke if your certain it doesn’t sound rite do as blaster ^ says and do a leak down test check for piston slap... for me every time I think I hear something off YouTube is my go to I look up videos of blasters w same type mods as mine and give a listen as well as vids of blasters tht have issues to me sound is key it tells me everything I need to know of how my bike is running and listening to other blasters on YouTube is a BIG help...