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Compression Tests/KACR and KACR-less

7K views 6 replies 4 participants last post by  Damocles 
#1 ·
Based upon the number of reports of KACR failure (it's uncommon, but I attract disaster) and folks saying that they removed their KACR and had no problems, I removed mine.

I have had problems with occasional kickback while starting. Also, if the piston stops on the verge of a compression stroke (don't it always?) I will have to bump the starter to get things going, as there's not enough ooomph for the starter motor to push it through. The battery is new, in good shape, and charged. It always starts on the second bump. This is when cold. Hot is no problem.

Sometime this week I'll be pulling the tank off to install a different banjo bolt at the head. When I do that I'll be putting an exhaust cam with a KACR back on it.

Tom
Tom,
Can you do a before and after 'COLD Compression Test'?

I'd really like to know the limits of the 'starter limiter gear'. If I remember correctly, my buddy Keith C's. bike, was about 154 PSI. Too Much, for the limiter gear!
 
This post has been deleted
#4 ·
Better LATE Than NEVER!

Tom S.,
I would like to sincerely THANK YOU!
For taking the time and effort to Go Backwards, and do what Mike Coe (MC Mod) and Eagle Mike should have done, Right UP FRONT!

I could not even get Mike Coe to understand that he WAS affecting the Cold Start Compression, via the KACR. Sent 2 PM's on the 'other forum', way back, when this was Hot News. (Well, he was a Honda Racer. Not a Race Mechanic. As I remember.)

Hopefully, Eagle Mike clarified the issue, to Mike Coe! But, 'Why Not to the rest of the public?'
Full disclosure / documentation, early would have been 'Best' for all of us riders.

I tried to tell all / show all with my oil flow project.

OH, By the way, we have hi-jacked this thread!
Apologies to 'Music Man'. Have you been able to get any pics of the RH Exhaust Camshaft Bearing?
 
#5 · (Edited)
You're welcome, Paul.

I needed to end the 'no-KACR' experiment anyway, so it wasn't much extra work.

The new banjo feeding the cams went in.

I'm going to split this thread-jack off into it's own thread.

Tom
 
#6 ·
Tom, your kicking back experience, was that to Gen2 or Gen1?

If Gen1, I'm wondering if you could check to see whether unplugging and replugging the single yellow wire leading to the ignition module changes timing by 3 or so degrees? If that circuit isn't working during cranking, it might cause the symptoms you report.

I think it's Yellow/Red on Gen2 but don't think it can simply be unplugged as goes to Junction #12 in the harness. Perhaps I'll be feeling ambitious some time when time allows to disconnect a Gen2.
 
#7 · (Edited)
Since the MC mod closes the exhaust valves earlier in the cycle, closure of the KACR's exhaust valve lift earlier (and consequent higher cranking combustion chamber pressure with KACR) is no surprise. Thanks for validating an assumption, Tom!

With no increase in non-KACR cranking combustion chamber pressure measured with the MC mod in place, we must look elsewhere for the elusive explanation of how the MC mod produces additional power.

Invoking volumetric efficiency (associated with the pressure in the cylinder at BDC vs. atmospheric), valve overlap generally favors scavenging at higher rpm, consequently increasing combustion efficiency and delivering higher power. The MC mod, reducing valve overlap, somehow operates oppositely. The mystery continues! :)
 
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