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11-17-2019, 10:09 PM #1
2.4 Laser a little down on power (since upgrades) - timing method?
Hey S&F'ers, hope you all had a great summer. Summer is just kicking in here so I figured I'd have another crack at getting this old motor back to full power instead of just putting up with it being a bit flat for another year...
It's been running "fine" since a new Brucato ACU, reeds, stuffers, and head skim (34cc) a year or so ago, just a bit down on power right thru the range (probably lost 10mph or so, versus the best it ever felt). Starts awesome, idles smooth and clean. I was expecting it to go better, if anything.
I haven't touched the ACU fuel trim, Tony said to maybe take out 2% because of the altitude here but I'd prob rather stay slightly rich (old ECU seemed pig rich its whole life but still made good power).
I got a JSRE tdc gauge to index the flywheel but didn't find the process to be accurate enough at TDC. 2-3 degrees float with the piston at the top as the gauge sat still - didn't seem accurate enough to me, so I wound a bolt in each plug hole, wound the motor over to hit it, marked, then wound the motor backwards to hit it and marked. The centre point between the 2 marks has to be perfect TDC I figured. I then set the most advanced cylinder to 25degrees.
Yesterday I ran the boat with 1 extra turn out of the max timing screw, and it felt awesome. Like the power was back up to previous levels, or very close to it.
Is my TDC index method flawed do you think?
Engine compression and leakdown all tested fine back when I was chasing the original fault btw, she's a healthy old motor far as I've been able to test
Cheers
GeneLast edited by gmacrae; 11-18-2019 at 02:53 PM.
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11-18-2019, 12:51 AM #26000 RPM
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Oossible with shaved heads you would have to math out the difference on the bolt depths to be at tdc not before or after.
You should be be able to do the same with the other tool. The center between gauge topping out and just as it drops should tdc.
Yea the piston sits at the top a while as the rod peaks out cams over and collects the slack and starts moving down. If you roll it back after it drops on the gauge it will tighten up the marks.
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11-18-2019, 03:11 AM #3
The bolt I'm talking about was just down in the spark plug hole to stop the piston about 10mm from the top, then back the other way, so the shaved heads shouldnt make a difference? I did the indexing with the shaved heads anyway... and have since destroyed the dial gauge dammit (dropped a toolbox on it)
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11-18-2019, 08:46 AM #4
You done it right with the bolt. Your thinking on finding true TDC is the proper way. You could have used the gauge also just used the same amount of thousandths of piston travel BTDC and ATDC then split the difference the same way you did with the bolt
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11-18-2019, 08:51 AM #5
25* BTDC is .150 of piston travel downward of TDC. You just want make sure you know true TDC to make sure your pointer is adjusted correctly before you go marking your flywheel
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11-18-2019, 11:07 AM #66000 RPM
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Ok i thought you had made a stop. Some are out there that you screw in to .xxx”(not given for safety sake) or something which is stock xx* btdc. I personally don’t like them but they have a use.
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11-18-2019, 12:58 PM #7
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11-18-2019, 02:42 PM #8
Last edited by gmacrae; 11-18-2019 at 02:54 PM.
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