Jump to content
Sign in to follow this  

questions about investigating "hard starting"

Recommended Posts

i'll spare the gory details, but my 08 200 has become somewhat hard to start. i'm starting down the road of figuring it out.

~110 hours. i need to acquire a compression tester (any suggestions? sears? harbor freight? kinda cheap bastid)

jetting has been great with the jd kit, it might have been just slightly lean today? it was cooler than i thought it'd be, and we rode at a lower elevation than i had planned.

when do people usually replace reed valves? do they have "anything" to do with hard starting?

i figured it's probably time for a top end.

any suggestions?

tia

edit: i've been reading about setting the x dimension etc. what differentiates which piston people go with? cast vs forged etc. when you order a piston you also order a bunch of different thickness base gaskets? sorry for the scatterbrain q's, been a long day!

Edited by clapped_r6

Share this post


Link to post
Share on other sites

What kind of riding do you do?

If you've got messed up reed's, the bike wouldn't wanna run and it would be lacking power. I usually burn through reeds pretty quick, every 20 hours or so and the corners are cracked enough for it to leak.

I mean, if its really hard to start, it could be many things, I wouldn't just say your compression was low until you measure it. So buy a cheap gauge and see what it says, anything less then 150psi and you should start thinking about a piston/rings. Anything less then about 100 and the bike usually won't run.

The OE piston is made by Vertex, so you can just buy one online. Once the motor has gone through its "first run" sized piston, you can usually buy one size larger. If you have a set of calipers you can measure your cylinder and determine the exact number, minus the necessary clearance. But I've found, if you pop the old piston out and look at the number, you will most likely be able to use the next size up, especially with 110 hours on the motor.

In terms of base gaskets, if you buy a gasket kit, they usually come with a variety of gaskets. I usually set my piston/head clearance a bit on the conservative side, 1.5mm squish roughly. You can measure squish, OR you can just make sure you piston in TDC, doesn't go above the inside skirt, as in, its flush or slightly below the skirt. I'd pull the head off first when disassembling and find out where it is now. Most likely its flush with the inside skirt, so just repeat that on the re-built.

Finally, with 110 hours on it, you might be looking at a new bottom end as well. When you pop the cylinder/piston off, pull up and push down on the rod. Also from the top of the rod, go left and right to see if there is any deflection play. If there is any play besides the rod going left/right on the bearing (which is normal) then you probably need to do the bottom end. You can send the whole bottom end to Andrew Cooksey, let him do it for ya. Or you can do it yourself, if you're willing to buy the tools. If you don't feel any play at all, if things seem OK, then make a note of when you did the piston and come back to it in 50 hours or so, just to check it again.

Hope that helps. :smirk:

Edited by tye1138

Share this post


Link to post
Share on other sites

Reeds that do not seat all the way can cause hard starting.

If you look through the reed cage and see light comming through, they should be replaced.

If they do not seal then air can escape back through the intake instead up up the transfer ports. at low RPM (like starting) this can mess up the charge and not fire.

Share this post


Link to post
Share on other sites

thanks for the replies. this is my first 2 stroke so i'm just wrapping my head around how to do everything!

i'll get a compression gauge to get a baseline, then i figure i'll take it apart to see what is going on.

what do you use to pull the top bearing? a specialized tool, or small socket?

Edited by clapped_r6

Share this post


Link to post
Share on other sites

a small socket will do but you need to hold the whole piston in your palm and carefull not to rock the crank side to side. or you might bend it?

id check wossner, wiseco then vertex if i were you. if forged then ALWAYS take the first size not the second. if cast then you can go larger like from B-C-D.

take a look at boyesen power reeds or its pro series reeds.

Share this post


Link to post
Share on other sites

thanks for the info

id check wossner, wiseco then vertex if i were you. if forged then ALWAYS take the first size not the second. if cast then you can go larger like from B-C-D.

can someone give me a quick 'splanation why you'd choose one piston over another? lost,

Share this post


Link to post
Share on other sites

thanks for the replies. this is my first 2 stroke so i'm just wrapping my head around how to do everything!

Two strokes are big air compressors. As the piston goes up, it sucks in air/fuel through the carb and as it goes back down again, that mixture is forced up above the piston for combustion. The reeds are the only thing blocking the air/fuel mixture from going right back out the hole they came in on. Once the piston starts going back up again, it compresses the mixture and fires a spark to ignite it. As the piston goes back down, the remainder of the charged fuel/air goes out the exhaust port and the whole cycle happens again. Once you can get your head around how a 2 stroke works, the whole big air compressor theory, then you can diagnose them much easier. Unlike a 4 stroke, which the rings only have to a good seal on the compression stroke, on a 2 stroke, the rings work double time, both up and down to generate that "compression" which sucks in the air/fuel. So if things arn't perfect, the bloody thing just won't start. Higher the RPM, the more compression will get generated, which is why sometimes you can get it to start, you generate just enough pressure and once it gets started, it will run.

i'll get a compression gauge to get a baseline, then i figure i'll take it apart to see what is going on.

Yeppers, but with that many hours on the clock and NO piston/ring replacement, it needs one guaranteed!

what do you use to pull the top bearing? a specialized tool, or small socket?

1/2" socket extender. Fits the hole perfectly and I use a little rubber mallet to gently tap it out. The nice thing about using a socket extender is, you can pull the pin out and push the extender all the way through to hold the piston in place if need be. Putting the pin back in is actually more difficult then removing it. Usually I set it in the piston first, get in far enough, right before it peeks out from the inside hole where it grabs the rod and then put it in place.

In terms of pistons, Vertex is the OEM manufacturer, so just buy one of those. They are sized (as I said above) so make sure you order the right one by first checking the size/number of the piston currently in the motor.

2 strokes are a blast to work on, lots of fun, very little can go wrong unlike a 4 stroke. So enjoy your time, ask more questions if needed and I find the parts look up to be very helpful in terms of remembering which part goes where! :smirk:

Edited by tye1138
  • Like 1

Share this post


Link to post
Share on other sites

If you're using a 38 pilot at low elevations and cold temps then that may be you problem. Pilot too lean or air screw open too far.

Share this post


Link to post
Share on other sites

thanks for all the info.

i took it apart today, made some measurements, and ordered some new parts.

thanks again!

edit: i looked at the "x-dimension" before taking the cylinder off, and i'm not 100% sure where you're supposed to measure from.

the piston came right exactly level with the lower "step" in the cylinder. does that make it "0" x-dimension? or is it measured from the

machined outer part of the cylinder?

my base gasket was .75 fwiw

Edited by clapped_r6

Share this post


Link to post
Share on other sites

turn piston UPD.

measure from skirt below to crown with 15mm

take your calipers and use it to measure from intake to exhaust side of the piston. not the sidewalls where the circlips are.

try to make the caliper`s mouth as level on the piston as possible.

you might even anticipate a size. say 66.34mm. thats an A size for 250cc 2t. try to get that measurement as much as you can.

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...