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Nice job Bill, lots of good information.

Thanks
 

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Supurb introduction for newbs. Now you just need to turn it into a pop-up feature on the board index screen :lol:
 

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Make this a sticky? Hell even make it show up on the front page!
 

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I didn't catch the 95 octane requirment in my manual, that's good stuff. The highest pump gas we can get is 94 from sunoco.
 

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gord said:
I didn't catch the 95 octane requirment in my manual, that's good stuff.
Me too! I have been filling up with 87
 

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I looked this up in my manual. It says to use a Pump Octane level of 86 or higher, or a Research Octane Level of 91 or higher for a CB360.
 

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... and isn't "today's" octane rating an average of the two? Research Octane + Motor Octane / 2?

That'd be (86 + 91) / 2 = 88.5

I'd still save the 10 cents per gallon, and go with 87! :lol:


**edit** - oops, I just Googled it - Pump Octane IS R+M/2, which would imply that you'd be good with today's 87. On the other hand, the CB360 came out in '74, when Honda surely would have known of the coming changes in fuels availability, and likely designed the engine around those availabilities. But not the older 350s, I'm thinking...
 

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mine CL350 ran like a top on the highest octane at the pump, and felt sluggish with 87. just my gut feel, but i will run the 5 dollars a more a year in gas for the good stuff.
 

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tbpmusic said:
JeyLux said:
mine CL350 ran like a top on the highest octane at the pump, and felt sluggish with 87. just my gut feel, but i will run the 5 dollars a more a year in gas for the good stuff.
Like I said, the proof is in the pudding - you can't argue with results......

My butt-dyno has proven to be pretty accurate in the past.
 

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Hi, a question about comp. testing a cold engine, I understand that this will result in about 5 psi less than a warm engine but would the same apply to an engine that hasn't run in yrs. or should I expect less? Thanks
 

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Bill......you'll be happy to know that I'm busy studying everything I can get my hands on so, your thread here should serve me well.

Tanks a ton !!!
 

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Compression should be taken cold BUT--a motor that hasn't run in a while will have unlubed cylinders and the rings may be a bit off there best. So run it up to temp and cool it down, then the test is done at wide open throttle, remove the plugs from all the cylinders durring testing. A 9 to 1 motor runs on regular. Carbon build up and/or engine work can make your motor more than 9:1. Running low test gas when you need high test gas mean self-distruction of the motor, as soon as you hit the peak tourque RPM's plus open throttle the gas will explode not burn (detonation) "ping ping rattel rattel snap crackel pop" keep it up then-- burnt valves, or pistons, or head. Even if you get it taken care of before distruction the detonations pit the piston crowns and the head. Too early timming and or too lean a fuel mix leads to detonation. The three things compression, timming, and mix are collective, a little of each works like too much alltogether. Worse case is an air cooled motorcycle motor, detonation wastes these motors fastest of all. Don't run low test gas if you need high test it's not an option.
 

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Discussion Starter #13
CB200 said:
Compression should be taken cold BUT--
A compression test should be performed with a warm engine. Please let us know if you've got a source that states differently. I've never heard of any manufacturer recommending a compression test cold.
 

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Sensei
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OK...First off, Compression readings should be taken at operating temperature (HOT)... Fuel off, plugs out, Throttle wide open...... A 10% difference in readings between cylinders indicates rebuild time.....I only allow a 7% max difference on my bikes, which usually translates to about 10 PSI.....

A statement like "a 9/1 engine runs on regular" is NOT necessarily true... A DOHC 450 has 9/1 ratio and requires premium fuel, preferably leaded, as do MANY older bikes......

I would say that "sweeping generalities are usually inaccurate" but that would be one.....
 

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If the publisher of your compression numbers states "cold cranking compression" that would be cold ,if it states warm or hot then warm or hot. The basic rule of cold cranking is something that has come about since the time these motors have been made too. My numbers for CB Twins is for cold.
Compression ratio and an absolute number is as well a motor specific number. Our old twins have numbers like 160 for 9:1 but a slow speed lugging V8 will be a different number for 9:1 So one really sould read the directions for the motor in question's published data as to PSI, test temp, and other conditions. There can also be one set of numbers put out by one source saying 160 cold, another for the same motor saying 170 warm ect.
But I do stand on a cyclinder being "wet" oil coated--and the rings free before taking a reading. And by wet I don't mean put a spoonfull of oil in the spark plug hole-that's a different test.
Head ,piston and swirl determine how much compression a motor can take before the need for high test gas, but 9.2 is about upper end for the best and 8.7 or less on poor. Lead is for your valve/valve seat lubrication it's other job as an octane boster has been passed by from other additves and I hope it's lubrication qualities too--anyone know if some motors still need lead?
 

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I checked my manual when I got to the shop today--it said to run the motor untill everything was compleatly warmed up--what I was taught was called a hot compression test--warm were I come from is warm to the touch. Anyway thanks because I've been cold testing and this will help me with my numbers on this motor. I'm so use to cold cranking compression that I forgot these motors are 35 years old--today somebody gets burned doing a hot compression test and litigates over it.
 

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Good info here. This is exactly what I was looking for to get an idea of the condition my engine is in. I guess I should start w/ oil and a compression check. :)
 

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Great stuff. I am going to print this off and go through it one step at a time, despite the fact I've done some of these things already.
 

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Just wanted to thank you for the write-up, followed it and found out my points timing was way off. Turns out I was only setting the gap when I replaced points and didn't check the timing.

Bike's running like a top now! Other than my non-functional voltage regulator...
 

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are there any cb/cl450 shop manuals available on here? the clymer's just not doing it for me.
thanks!
 
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