1993 phazer with dg pipe. Top end ping/spark knock??? How to fix?

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Phazerst

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Nov 21, 2014
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13
Location
Upper michigan
Ok here is the story. Years ago we put pipes on phazers, rejeted them and away we go. Now it seems like today's fuel is messing with me. I have a 1993 phazer that is Bone stock with low miles and it's resealed and runs perfect accept for the top end. Which I am getting the common mid range to top end spark knock sound after it warms up. I live at low elevation, 147.5 mains, changed primary nozzle and tube, 100 pilots and checked the timing. Dg pipe is all that is done. Still working on clutching and I am short rpms by 200 but I can fix that. Biggest thing is I can't get rid if my top end pinging. When you pull the plugs they look good. This sounds weird but maybe I need increase my rpms next to change the load on my pipe? As mentioned I changed the tubes and primaries to richin the midrange but I haven't did the old psi trick where you drill out an air passage under the welch plug. Anyone out there with any ideas to help me clean up the top end when it gets warm?
 
well,,87 octane is a mile away from 93 octane. I doubt you would have the same results with 87 and 93, theres a big stretch in between those fuels. If it pings on 93 it would have self destructed on 87 octane.
If your not going to use 93 octane then you need to jet up on the mains and I would also go to 110 pilots. Todays gas is no where near as good of quality so your gonna first have to decide what fuel your going to use. If its cheap 87 or run premium and then jet the carbs to suit the fuel. 87 is junk not good for a 2 stroke motor at all in my opinion, as there is no detonation sensor like whats on your car to prevent the damage from occurring,it simply ruins the engine.

With the lower quality fuel youll need more of it(bigger jetting) to keep away detonation. More octane burns slower and reduces or sustains detonation because it burns slower and cooler. If you dont have octane then you need the jetting made richer to compensate and use the fuel to cool the piston crown.

The basic answer is either up the fuel octane level or jet the carbs up to prevent detonation from low octane fuel.

200rpm on your clutching isnt going to be the differance of pinging or not, theres a straight advance curve in a phazer you still have the same ign timing at 7000-7500rpm.
 
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