CR100 Jetting

[DWD-SF]

I just built a CR100 for my son.

2001 CR80 bored to CR100 with mild porting by Eric Gore. Gold series Fatty chamber with FMF siliencer.

Stock jetting 50PJ, 3rd clip, 2 turns out, 125MJ

ran bike, nice and crisp, a little hot maybe. think the water hose broke, then ran it out of fluid and blew the head gasket. piston had round pitt marks on top and pitted chamfer on the exhaust side of the piston edge.

replaced all hoses, clamps, piston, and ring. set jetting to 52PJ 4th clip, 2 turns out, and 130 main and run through 2 heat cycles.

bike runs good except it seems to hot again and a plug chop shows grey. Also the idle seems to run high (slighly erratic) when coming down to idle. takes a few seconds to come completely down to normal idle.

Do not want to overheat the bike again. Any suggestions on a jetting procedure? Thanks for any and all comments

Edit: elevation= 0 to 3000 feet...currently at 100 feet

Edit#2: Also using the pinned pilot circuit test above, do you use the same procedure except reverse the pilot sizes for a 2-stk air screw?

[ninjariderwannabe]

What mix are you running??

[DWD-SF]

What mix are you running??

mix is 40:1

[ninjariderwannabe]

mix is 40:1

hmmmmmm ?

[Wayward Son]

what fuel?

yes,the pilot circuit test is opposite for a air screw.

[DWD-SF]

what fuel?

yes,the pilot circuit test is opposite for a air screw.

The bike was setup for 91 pump gas....thanks

[Wayward Son]

what happens when you close the air screw a half turn?

[DWD-SF]

what happens when you close the air screw a half turn?

dropped the PJ to 50 (stock) , clip to 3rd (stock) and MJ to 128 (125 stock). seems to be running crisp and strong. jetting problem resolved (I think). I am impressed with the work Eric Gore did. lots of mid and upper end power. should be a great woods and track bike. However, the bike keeps losing coolant to the overflow. need to resolve this. could be head bolt torque, blown head gasket, head gasket upside down, warped head, or cracked cylinder? seems to be ejected by motor pressure. Any other thoughts? I will have to dig into a little bit deeper.

Kid is waiting in anticipation.?

[Wayward Son]

it pushes coolant while riding at a normal pace?

[williamsmotowerx]

You may have to re-surface the cylinder. It's a probem on these bikes if you try and get 100cc with just a bore... makes the webbing thin close to the cylinder and they can warp.

[DWD-SF]

it pushes coolant while riding at a normal pace?

Yes, it was pushing coolant while test riding. I believed it to be a blown head gasket. I replaced the head gasket. after one short test ride the coolant is now holding:applause: . Lets see if it will hold. unfortunately I can not test it to much this week because of an upcoming enduro. The bike is running crisp and strong...great power ban and power over stock. My only uncertainty was which way the head gasket was installed. The book says put the "up" mark up. But the aftermarket Cometic gasket did not have "up" mark and also did not have instructions. A search to Cometic website, TT, and KTMtalk also did not yield any information. So I installed with the embosses upward. Is this correct? or does it matter.

Aside from the coolant leak repair issue, the only other issue is that the idle does not return quickly after revving/riding. The rev hangs slightly above idle for about 4 to 5 seconds after coming to a stop then returns to normal idle. Any ideas?

William thanks for the info:thumbsup:

[Wayward Son]

embosment goes up.does matter.

if it leaks again,as williams suggested you need to get it flat.

hanging idle.try closing the air screw a 1/2 turn.

also,i turn the idle speed down so it only idles for a few seconds then dies.

[DWD-SF]

it pushes coolant while riding at a normal pace?

This is my 10 yr old sons first real motorcycle, he is coming off an XR100. He could really use the power and suspension. He is really stoked and ready to take this bike over full time.

Eddie your the "shit" and thanks for all your help ?

Oh and the leaking gasket had embossments down.

[DWD-SF]

This updates the project bike:

First, I had Eric re-cut a new head. He wanted to cut a used head but I insisted on a new head. The re-cut new head resolved the problem of blowing head gaskets and coolant leaks. I also added a fluidyne radiator and extended the hosing to increase cooling capacity... maybe not necessary but the bike cools very well. Final jetting is: Summer (85 deg.) 118 MJ, 48 SJ, needle 2nd clip and 2.5 turns on AS. Winter (45 deg) 122 MJ, 52 SJ, needle 2nd clip and 2.5 turns on AS.

Bike absolutely rips. Much improved over a stock 80 top end power and also has much improved low and mid range power. Handles very well in the woods. Much different bike. Son is no longer interested in 4 strokes.