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Discussion Starter · #1 · (Edited)
Guys, my 1983 CR250R hotsaw build is coming near to completion ready for testing starting out with stock cylinder porting.
I bought a brand new 2003 CR250R FMF gold series fatty pipe for $170US & free shipping. Felt it would be a great pipe to hack up in testing to eventually build a custom hand built cone pipe after I get porting etc to tune.
My dilemma is the 2003 CR250R is a case reed versus my 1983 cylinder reed. I will have my porting around what the 2003 is at approximately 190°/130°.
But a adjustable length header and stinger may be needed for the differences in crankcase and cylinder reed assemblies. So the case reed distance should be shorter to the outlet flange then the cylinder reed cage? If that's the case I should lengthen the header for my cylinder reed cage?
 

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"But a adjustable length header and stinger may be needed for the differences in crankcase and cylinder reed assemblies. So the case reed distance should be shorter to the outlet flange then the cylinder reed cage? If that's the case I should lengthen the header for my cylinder reed cage?"

I would not.... this is a slippery slope. Theory is fine, real world is a lot different. If it was my saw; I would start equal lengths, on the long side for each, and adjust on a bench Dyno under a real-world load. The only real way to answer your question correctly.

Carlos
 

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Discussion Starter · #4 ·
Thanks for the reply Carlos,
The FMF pipe is just temporary while I test and run in the engine. I'm working on a blue print drawn up of a slip style joint for the header .
I think 2 inch adjustment would be plenty to dial it in as I go along with testing and then cylinder and head modifications later on


During run in of the piston rings and bearings the saw will always be under load making many short rpm controlled cut runs through a 16 to 20 inch diameter log.
The only way to get used to the saw, testing for efficiency and ergonomics and durability.
I'll be busy as I'm building two hotsaws side by side at the same time.
Finishing touch will be a custom hand built pipes.
Already got the YZ125 pipe welded up ready for mounting.
64546
 

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Discussion Starter · #5 · (Edited)
Hello @acecarlos,
I'm bumping this thread now 13 months later.
My hotsaw projects are still in full swing and I took on another project a 1984 Honda CR500 engine.
I'm still in the assembly stages and will be testing in the few weeks to come.
Cylinders and cases for the YZ125 and CR250R are ready for painting and I got my ignitions and carbs ready to install.
Art Gomez of Jetworks Performance out of Santa Ana, California built me his Black Jack 38 and 40mm Mikuni SBN racing carbs blueprinted for the 125 and 250 builds. These jetski carbs are holeshot winners and flow like crazy by removing the bombsight out of the venturi. Art is famous for these carbs in the hotsaw community.
This one year only aircooled CR500 I have has very high factory porting in the neighborhood of 190°/130°.
It's also the only year with the large oval exhaust port and I already figured out how to add a pair of auxiliary exhaust ports.
I got a NOS short rod crank with a Crank Works billet rod.
This saw will be the last to be run with testing, still lots of work to remove the transmission housing and the majority of cooling fins.
I will stay in touch as progression is on going.
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Discussion Starter · #6 ·
So I gave the CR500 a haircut with trimming the cooling fins and transmission housing saving over 5 lbs and adding some compactness.
New Selettra ignition makes spark at 300 rpm so this 514cc beast will have more reliable starting with the help of 2 Harley Davidson decompression valves.
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How much HP do you think it gains by getting rid of the transmission? Always been curious about how much HP it takes to turn a bike transmission.
 

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Discussion Starter · #9 ·
When I built my YZ125 hotsaw 38 years ago I gained 2,000 rpm more then what it was in the bike.
Some of the extra rpm will have come from the pipe running with no silencer and carb running with no filter.
 
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