Throttle-jockeys worldwide know your pain.

There must be a 2-stroke thing in the air. I dragged my trials bike out from under a 2" layer of dust and serviced the shock linkage. Found a broken spacer in there and had to replace it. Didn't get a chance to ride it yet.

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Resident Tightwad

Screw you, Photobucket.

Ha. Nice.

I have plenty of reminders to ride a 2-stroke here in Philly since it's basically lawless right now. I see dirt bikes on the street almost every day.

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95 SLE... a keeper. 241k miles. Low and Slow.
97 BMW 528i
98 Infiniti vq35'd i30: 13.3@104mph, 30MPG Hwy (RIP)
02 Jag X-type
03 BMW M5
05 Chevy Cobalt LS
07 Infiniti G35s 6MT (Sold)
07 Ducati Monster S2R 800 with DS1000 swap
83 Yamaha IT175K
72 Yamaha DS7: '74 RD250 swap, JL chambers

Info on dropping a 92-99: Here.

Hi all! I've been looking at your cool cars for a long time and am inspired. But I still can't make up my mind to buy my first car. I just can't decide between a powerful muscle car or a fast sports car. Just when I think I've made my choice, doubts start to plague me and I go back to the beginning. I don't know how to solve this dilemma. Perhaps some of you have faced the same problem? It would be great to hear your thoughts and recommendations. Thank you!

I went back and forth on how I wanted to get this thing back on the road. I melted pistons twice as a 350 (pre cylinder head temp sensors) but the 250 top end let me beat the crap out of it for the most part without every getting too hot. When I finally blew it up in May, I was really pushing it. Having machine work done to the 250 top end would cost the same as 350 but the 350 would have a higher time commitment with dialing in the jetting..Time I should probably spend elsewhere.. but well.. yeah, I went for it.











My 250 top end was happy with 35 pilots, 190 mains and a common RD carb mod that makes the 169-P0 needle jet, 2.0 air jet and 5DP7 needle (5th Clip) the most common RD250/350/400 combo.
The last time the 350 top end was together it had 37.5 pilots and 210 mains. I started there, tried 4 and 5 clip settings and messed with the air screw. Watching the cylinder head temps, it seemed to get hot quick and not want to cool off with no load. The left side was also noticeably hotter. I went to 220 mains with less needle, (2nd clip) and swapped the cross over hose since one side seemed loose. This seemed to even out the temps and cool it down with stop and go traffic. I'm not going to really wind this thing out with it breaking in but getting on the pipe a little bit and sustained 50ish mph runs seemed to make temps creep. I ordered 230 mains and 40 pilots. I think the pilot circuit is ok since temps come down at idle but I may mess with the 40s depending on how things go.

I also noticed not all of the YZ125 reeds are sitting completely flush with the cage even if I reposition them. I ordered Boyesen reeds to replace them.

I admittedly built this bike fast without properly documenting everything like I do with my other vehicles. I had a lengthy build thread on 2strokeworld but that site crashed and it's all lost. I'm now digging though emails piecing wtf I did over the wast 7 years to this thing.

Here's what I have:
RD250 bottom end and 6 speed gearing
Crank rebuilt and balanced by Team Scream (TS)
Milled Cyls for RD400 head gaskets (better comp/quench)
TS updated porting
65mm bores
TS boost bottle (volume tested by TS)
6.2mm Reed spacers (TS made, keeps 1.8:1 primary CR, larger drops CR)
Yz125 reeds
Foam uni's
Static Powerdynamo set @ 1.8
Oil pump set with mark matching pin
Jim Lomas Street/Race pipes

Carbs/Jetting:
Dave F Carb mod on RD400 carbs
2.0 air jet (drilled 5/64ths)(drilling reroutes air from capped ports)
Capped air ports on bottom
169-P0 needle jet
5DP7 needle

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95 SLE... a keeper. 241k miles. Low and Slow.
97 BMW 528i
98 Infiniti vq35'd i30: 13.3@104mph, 30MPG Hwy (RIP)
02 Jag X-type
03 BMW M5
05 Chevy Cobalt LS
07 Infiniti G35s 6MT (Sold)
07 Ducati Monster S2R 800 with DS1000 swap
83 Yamaha IT175K
72 Yamaha DS7: '74 RD250 swap, JL chambers

Info on dropping a 92-99: Here.

Jetting can be tricky on 2-strokes, especially small-bores, and they seem to be sensitive to humidity and altitude changes. 65mm bores, is that 250 or 350?

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Resident Tightwad

Screw you, Photobucket.

That's the 350 bore size. I'm 1mm over, 4th overbore with 1-2 overbores left if the wear isn't catastrophic.

To me it's wild how much the 250 top end let me beat on it without issue. The only things I can think that helped were a worn bore with some heat loss due to slightly less compression, less displacement - less boom, less static CR since the 350 stuff is milled. I've read the transfer ports on the 350 are more restrictive than the 250s to fit the cylinder. So the jetting isn't going to be as easy as a ratio. The chambers were also designed for the 350/400 and the off the pipe efficiency of the 250 is way worse.

I got the jets and the reeds but probably won't have another few hours to mess around until next Friday. I'm doing my best not to waste any free time with two young kids.

_________________

95 SLE... a keeper. 241k miles. Low and Slow.
97 BMW 528i
98 Infiniti vq35'd i30: 13.3@104mph, 30MPG Hwy (RIP)
02 Jag X-type
03 BMW M5
05 Chevy Cobalt LS
07 Infiniti G35s 6MT (Sold)
07 Ducati Monster S2R 800 with DS1000 swap
83 Yamaha IT175K
72 Yamaha DS7: '74 RD250 swap, JL chambers

Info on dropping a 92-99: Here.