Topic: Compression test numbers, yours vs Honda book value.

[Maraakate]

You know this is entirely bologna, right? Not using a $40 Amazon/Harbor Freight/eBay tester will give you meaningful results.  If it's still low with a half-decent gauge then you should run a leakdown test.

This whole length of hose thing is silly and harmful advice.  The only time it might make a difference is with a 49cc Moped.  And guess what?  It doesn't really.  I know, because I've personally tested my own mopeds with a half-decent gauge, an OTC one that I know is accurate to my old man's 90s snap-on gauge.  One of them read 115psi and that bike was weak off the line.  Had it bored oversize and now it has 150psi and runs great.

Having a gauge that has a schraeder valve in the hose and a pressure release on the gauge will give you a meaningful result.

Throwing math equations in an attempt to make an excuse for low compression due to mis-adjusted valve clearances, valve recession, or tired cylinders is just that... an excuse.

Please stop perpetuating this harmful information.  The basic point is this: if you have low compression and a competent gauge run a leakdown test.  The teaspoon of oil trick is also bologna.  Who dictates its a teaspoon?  How about an eyedropper?  Tablespoon?  I mean come on.  Get the right tools and do the proper diagnostics.

[Maraakate]

And in case you don't believe me and think these numbers are unobtainable... except only from a Kowa brand tester from 1969 take a look at my CM400A at ~35K miles dead cold, WOT, no teaspoon of oil and I have 170psi:

[HondaMan]

And in case you don't believe me and think these numbers are unobtainable... except only from a Kowa brand tester from 1969 take a look at my CM400A at ~35K miles dead cold, WOT, no teaspoon of oil and I have 170psi:

I'd suggest you also have a well-carboned chamber, and piston.

Some examples, from experience:
The 750 in stock trim can produce 115 gage PSI with a brand-new piston-and-ring set in a freshly bored cylinder (the CB450 twin can make this number 145 PSI.) After 150 miles this will typically come to around 125 PSI, and after another 1000 miles of slow city riding (well-carboned, think "Chicago traffic") it can read up to 155 PSI. Then after hitting the hiway for 1000 miles of interstate riding, it will come back to around 120 PSI (160 PSI for a CB450) and stay there if toured. These numbers were/are obtained using a compression gage I have had since 1970, which has a 1.5" long, 3/16" ID pipe after the (tire type) checkvalve, and have had much experience with in the years of working on bikes. It usually read 5-10 PSI lower than the Honda manuals' numbers on any given Honda/Suzy/Kawi engine (I didn't work much on Yamahas).

[Maraakate]

And in case you don't believe me and think these numbers are unobtainable... except only from a Kowa brand tester from 1969 take a look at my CM400A at ~35K miles dead cold, WOT, no teaspoon of oil and I have 170psi:

I'd suggest you also have a well-carboned chamber, and piston.

No, I don't.

[Maraakate]

You do realize 115psi is practically un-runnable on any of these vintage bikes?  They will be incredibly difficult to start, not idle well (and no your spring trim "trick" is not the answer), and be with really reduced power.

Break-in is mostly a myth, plenty of videos and real world experience from actual career techs who can prove otherwise.

You really overthink this and make excuses for it.  The fact is not using aftermarket junk, including gaskets and rings, and not lapping the valves but having the seats cut correctly will bring this stuff to spec first compression test.

But, it's your forum.  In before you say you're not an admin or moderator.  Your word is the gospel here.  And it's harmful to young people who do not understand these bikes.  However, you are set in your ways and so are others here.  These bikes are not temperamental when correctly tuned with the correct parts and rebuilt properly.

You know you can't measure a cylinder to piston clearance with a feeler gauge?  If you can it's so grossly worn.

I'm completely floored by your statement of 115psi at fresh rebuild.  In before you tell me the thousands of engines you rebuilt and hose lengths you experimented with and so on.  It's bull#$%*.