7.4 MPI, MEFI 3 odd timing problem
10-15-2021 | 12:20 AM
#14
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Correct, the MEFi 3 tries to test the knock sensor on first throttle up after re-start. It advances the timing fully to make it knock. If it doesn't see it, it retards timing a bit. This can happen from using 93 octane instead of 87 gas. Mine was doing that running 89, so I went in a turned it off using MEFIBurn
10-15-2021 | 01:36 PM
#16
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From: Lake Charles, La
dt21
Ive got twin 502's Mefi3, but had same issue, very low timing. I will attach the timing chart. But if you look at orig specs that is what it is supposed to be for your motor. I guess for engine safety - old gas, over-prop'd , etc. Anyway i attached a timing chart and sure enough your advance is exactly where the specs say it should be.
Around 16.9 deg advance in the 2nd column from the right which is about where you'd be running near WOT mid/upper rpm.
I used mefiburn and advanced mine 4/5 deg more than chart said where the timing was low at mid/upper rpm and lower MAP. Basically the mid/upper right section of chart. It felt like a different motor, peppier. Gained 3mph also.
But i have always run premium, occasionally 89, and fresh gas.
Ive got twin 502's Mefi3, but had same issue, very low timing. I will attach the timing chart. But if you look at orig specs that is what it is supposed to be for your motor. I guess for engine safety - old gas, over-prop'd , etc. Anyway i attached a timing chart and sure enough your advance is exactly where the specs say it should be.
Around 16.9 deg advance in the 2nd column from the right which is about where you'd be running near WOT mid/upper rpm.
I used mefiburn and advanced mine 4/5 deg more than chart said where the timing was low at mid/upper rpm and lower MAP. Basically the mid/upper right section of chart. It felt like a different motor, peppier. Gained 3mph also.
But i have always run premium, occasionally 89, and fresh gas.
10-15-2021 | 08:28 PM
#18
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Joined: Apr 2009
Posts: 286
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From: Lake Charles, La
With the orig timing i could only turn 26 Bravo one 4 blades, 5200rpm. 76mph. Now with more timing i can turn 28's, but just barely. 5050 rpm, 79mph.
FYI my motors are stock except for air filters, roller rockers only because the orig where worn out, and Eddie Marine standard log type exhaust - but they flow well over stock, gained another 3 mph with them also.
FYI my motors are stock except for air filters, roller rockers only because the orig where worn out, and Eddie Marine standard log type exhaust - but they flow well over stock, gained another 3 mph with them also.
10-16-2021 | 05:39 PM
#19
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From: frankenmuth michigan
With the orig timing i could only turn 26 Bravo one 4 blades, 5200rpm. 76mph. Now with more timing i can turn 28's, but just barely. 5050 rpm, 79mph.
FYI my motors are stock except for air filters, roller rockers only because the orig where worn out, and Eddie Marine standard log type exhaust - but they flow well over stock, gained another 3 mph with them also.
FYI my motors are stock except for air filters, roller rockers only because the orig where worn out, and Eddie Marine standard log type exhaust - but they flow well over stock, gained another 3 mph with them also.
