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 Post subject: Vintage carb tuning
PostPosted: Sat Apr 29, 2017 4:26 am 
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Joined: Tue Jan 17, 2012 3:19 am
Posts: 7699
Location: Hope, B.C Canada
He is a little something I had in my collection of files. It took me a while to find it again on the net.
I don't know if anyone is interested but there are some interesting points or argument in it for us. Everyone has a different opinion.
This is from Klemm vintage.
http://www.klemmvintage.com/mikuni-tuning.htm
The points to read in my opinion are:
1) Important Jetting Protocols -- About plug reading
2) Important Jetting Protocols -- Use race gas for tuning
3) Jetting for 21st Century Fuels
4) About Running 91-Octane Fuel

My Wisdom:
Every man for himself
I'm behind you all the way sir
Advance to the rear


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 Post subject: Re: Vintage carb tuning
PostPosted: Sat Apr 29, 2017 5:04 am 
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Joined: Tue Jan 17, 2012 3:19 am
Posts: 7699
Location: Hope, B.C Canada
Some more good reading from links above: http://www.klemmvintage.com/deto2.htm
(Yes I know they are talking about air cooled 1970's but it's still a good read)


Dispelling some Myths
“Piston Seizures are always a sign of lean jetting” …..Wrong. After working with a deto-sensor for a period of time, it becomes abundantly clear that 90%+ of all piston seizures (on air-tight freshly built engines) are not a result of lean jetting ….. but rather a result of the piston super-heating that comes from detonation. “Sometimes” richer jetting can reduce or stave off that detonation …. But not always. We encountered countless situations during our testing when our sensor showed dangerous detonation, but even significant increases in jetting had little effect on staving off the lethal percentages of detonation. The deto sensor helped us to “see” the other tuning issues that were the actual source of our detonation (ignition, compression, etc). Once we solved the true source of the detonation, we could run our Ideal (not over-rich) jetting with no deto at all. It’s also worth noting that if an Engine is built with a big enough measure of deto-resistance, it can easily survive being run a bit too lean. Testing with a digital tachometer reveals that this slightly lean setting will offer visible lower peak rpm numbers long before it is lean enough to deliver a seized piston.



“Detonation Always produces Audible Pinging” ….Wrong. There are “some” 2stroke race engines that do emit an audible “pinging” noise when they go into runaway detonation …. But that is the exception, not the rule. On top of that, virtually no 2stroke race motor (( Internal Combustion Engine ? )) makes an audible pinging of any kind, when experiencing the slightly elevated percentage of deto strikes that routinely deliver a seized piston.



“Lean Jetting on the brink of piston Seizure gives the best horsepower”…Wrong. This is not true, and it never has been. If you do high gear, peak-load testing with an on-board digital tachometer, you will quickly learn that the jetting that yields the highest “steady” peak rpm hot-numbers is well away from being too lean. In fact, if you do your jetting testing with a load of 110 octane fuel (to get a big margin of deto-safety), you can safely lean out the main jet until you see a very visible loss in peak rpm. The high octane fuel has so much deto resistance that you will see this visible loss in peak rpm long before you are at risk to experience any deto that results in a seized piston.

The best way to reduce Detonation to Manageable Limits:
Octane - It bears noting that most vintage air cooled two strokes were sold during a time when premium pump gas was from 98 to 101 octane …. And that fuel had no oxygenate additives nor blended in ethanol. Today’s 91-93 octane premium pump fuels do not offer near the deto resistance of yester-years pump fuels, but “most” air cooled two strokes can still be modified to run reliably on today’s pump gas.


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 Post subject: Re: Vintage carb tuning
PostPosted: Sun Apr 30, 2017 9:44 pm 
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Joined: Mon Dec 15, 2003 2:40 pm
Posts: 22512
Location: Chicago
I love reading Harry's tech stuff I have been through the town where the shop is Ft. Mohave, AZ many times I REALLY need to stop in some time see if they are willing to talk or are all business.


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 Post subject: Re: Vintage carb tuning
PostPosted: Mon May 29, 2017 1:06 pm 
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Joined: Tue Jan 17, 2012 3:19 am
Posts: 7699
Location: Hope, B.C Canada
Just wana bring this one back to life in case any of the new guys haven't seen it or read it.


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