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Discussion Starter · #1 ·
I've just built a Fuel injected 660R with CP686 12.5comp/ratio, Skimmed head, Over size valves, CromeMolly Rod and lost more.

Without the sparkplug the motor turns stiff but at a reasonable speed. With the sparkplug in it is not possable to turn past compression stroke. Is this normal? The comp ratio on static is about 1200psi
That means very high and race fuel only.

would you advise to pullstart it?
 

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sounds like it needs a new one way i think lnot sure but i know those go


and or is your battery fully charged
 

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well seems like you need to check your decompression mechanism on the cam shaft, many people mistke this part when they talk about o much compression for the starter, thats why it is there, to let go of some of the motors compression when starting, sounds to me like your main prodsponder might be a little too tight, go back and loosen it up and see if that works
 

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warwgn said:
1200psi :eek: did you mean 120??
Ditto...

120 is a touch low even with the decomp kicking in (130-140 range), and 1200 simply isnt realistic.
 

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Discussion Starter · #7 ·
The motor cranked very slow over the compression stroke, so the reading will be low, on my gauge it reads something like 1200 but the measurement might be pounds per square foot.

I have no Decompression devices, the motor turned smoothly without the barrel; I have an uprated rod fitted. The started is very strong but I thing that the fit of the piston, Clearances, and hone grid is a bit course; I did set the ring gap.

I will pull start it this weekend. I also advanced the camshaft witch in fact increases the static compression ratio.
 

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Chrisjan said:
The motor cranked very slow over the compression stroke, so the reading will be low, on my gauge it reads something like 1200 but the measurement might be pounds per square foot.

I have no Decompression devices, the motor turned smoothly without the barrel; I have an uprated rod fitted. The started is very strong but I thing that the fit of the piston, Clearances, and hone grid is a bit course; I did set the ring gap.

I will pull start it this weekend. I also advanced the camshaft witch in fact increases the static compression ratio.
1200 lb/sqft would be 8psi. The only explanation would be if you're using metric units, 1200 kpa would be around 175 psi.

If you're without a decomp you should be looking for around 180 psi with a stock piston, so somewhere north of 200 psi for your piston depending on porting.

Don't advance the camshaft, if it isn't the current problem it's going to be the next. If you've done it one tooth it wont run as well, anything more and you might have to start looking at new valves with that high dome piston in there. If for whatever reason you think you'll make more power playing with timing, either use a programmable cdi or a degree key. Neither of which have been shown to make any significant increases in power output.
 

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buckethead672 said:
well seems like you need to check your decompression mechanism on the cam shaft, many people mistke this part when they talk about o much compression for the starter, thats why it is there, to let go of some of the motors compression when starting, sounds to me like your main prodsponder might be a little too tight, go back and loosen it up and see if that works
What is the main prodsponder?
 
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