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Old 11-23-2014, 04:57 PM   #1
LXnastynotch93 OP
Joined: Jul 2014
Location: USA East Coast
Oddometer: 22
625 SMC head on '01 LC4 Motor

I had a cracked tab on my head, bad rocker arm bearings, and wear on some critical parts of my valvetrain, and decided to purchase a full head/valvetrain assembly from an '04 625 SMC.

I have everything from the cylinder head to the valve covers, and everything in between. I also bought a full Pro-Circuit stainless exhaust, including header for the bike so it breathes better. My bike has the air-box snorkel removed as well. The motor will be coming out of the bike to do the head swap.

I'm looking for help in figuring out exactly what I need for parts to make this thing run correctly. It would be excellent if someone could tell me:

-The correct head gasket thickness.
-The correct jetting for my BST-40 (I'll be contacting motolab as well)
-If I need to use the 2004 CDI box, or if my 2001 CDI will be okay.
-Any other odds and ends

Thanks for your help.
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Old Today, 01:12 PM   #2
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Joined: Feb 2006
Oddometer: 2,315
Originally Posted by LXnastynotch93 View Post
-The correct head gasket thickness.
The head gasket should be selected to hit your squish clearance target. You will need to do a trial assembly with some rosin-core solder stuck to the front, back, left and right of the piston with some grease. Rotate the crank through, then measure the compressed thickness of the solder. .040" should be safe (I've run as little as .037" with no contact). Metal head and base gaskets make this repeatable.
-The correct jetting for my BST-40 (I'll be contacting motolab as well)
How many miles are there on the carburetor?
-If I need to use the 2004 CDI box, or if my 2001 CDI will be okay.
The early curve is overadvanced in order to get the response to be snappy at smaller openings. The later one will be much safer. In order to take advantage of the 3D map, you may want to install a later carburetor with TPS.


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