426f starting


2 replies to this topic
  • ahschwenk

Posted July 01, 2009 - 08:58 PM

#1

I know the first thing that is going to be said is search and i did. The problem is it will not start with the kicker, it has a few times but not often. I live on a nice paved hill and if i push it up it will pop start in 5th. The motor is freshly rebuilt piston, rings, rod, cylinder. The timing is dead on i checked it twice. We went through the carb and cleaned it very good. It has white brothers exhaust and what i think is jetting to match. I know the procedure for starting and have used a handfull of plugs. I tried starting it in first on the stand to act as the blue wire mod but no luck. One of the things i did not look into yet was valve adjustment would that make fore very hard starting? Any input would help. thanks

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  • ajeb

Posted July 01, 2009 - 09:19 PM

#2

You have stated the bike will basically only start in 5th gear.
This indicates to me the engine is lacking in compression, it is very likely your valve clearances are to small or non existant.
Overly tight valve clearances will create a reduction in cylinder pressure due to the valves being held open
either too long or open for the entire duration of the cycle.

As the engine speed increases, so too does the compression. (not the compression ratio).
The higher engine speed allows an increase in cylinder pressure enabling the engine to start.

Checking and/or adjusting the valve clearances would be my first port of call.

  • grayracer513

Posted July 02, 2009 - 07:39 AM

#3

You have stated the bike will basically only start in 5th gear.
This indicates to me the engine is lacking in compression, it is very likely your valve clearances are to small or non existant.
Overly tight valve clearances will create a reduction in cylinder pressure due to the valves being held open
either too long or open for the entire duration of the cycle.

As the engine speed increases, so too does the compression. (not the compression ratio).
The higher engine speed allows an increase in cylinder pressure enabling the engine to start.

Flawed logic: Engine speed is lower in 5th than in the lower gears at any given chassis speed.

He also did not indicate that it would start only in 5th, just that it will start in 5th. If he had said that it would point to very high compression, necessitating the use of a high gear to overcome it.

If the engine has compression, spark, and is in time, the carb is more likely the culprit. 90% of all troubles with starting the 400/426 lie in having improperly set up the idle circuit, or simply not using the correct technique. Look up the posts on setting up the pilot screw in Common Threads, get it running, and dial the fuel screw in. Then, watch the two videos at the bottom of the Common Threads page again, just to be sure you have it right, and go from there.





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