break-in on new Powerhead

ibemoose55

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Sep 25, 2003
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I just got a new powerhead on my 1990 90hp Johnson, it was bored over 30, making it a 120hp. I disconected the VRO so now im running a 50:1 mix. Mixing gas and oil my self. Is this right? Also, is there a break-in period for this? Looking for help before I blow my $2400 investment. Thanks
 

walleyehed

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Re: break-in on new Powerhead

Boring .030 over only increases displacement, not really horse power. you might be putting out 1 or 2 more horses. I hope nobody told you it would make it a 120hp....... :rolleyes:
 

ibemoose55

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Re: break-in on new Powerhead

I did'nt know that it was only displacment, is that because the carbs have to be up to speed for that to be a 120hp? Also, how long do I have to run 25:1 and how long it the break in period? 10hrs?
 

walleyehed

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Re: break-in on new Powerhead

8-10hrs at 25:1. First time out, get on plane as quickly as possible, but bring RPM back to 3500-4000 as soon as you plane. Vary the RPM between 3000 and 5000, every 3-4 minutes for the first hour. the second hour is basically the same, but you can go to WOT for a few seconds, and then pull back. Just don't hold the R's in one spot for more than a few minutes. The third hour you can stair-step for longer periods. 3500RPM for 3-4 minutes, then 3700-4000 for a few min then WOT, making sure you don't go past 5500RPM-WOT, for about a minute and then back off to 4000.<br />The remainder of the third hour, you can come to a stop, then pour the coals to it to WOT then pull back to between 4000-5000. The fourth hour on, you can pretty much do as you wish but don't hold WOT for more than 1 or 2 minutes at a time. Before the 5th hour, I like to shut down lift the cowl, and look things over for leaks and what-not.<br /> Depending on your tank size, 6-8hrs is OK for 25:1. After that, you can start going 50:1, but easy on WOT until you pass the 10hr mark. :)
 

walleyehed

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Re: break-in on new Powerhead

BTW, carbs, exhaust porting, timing, and a few other items are the difference in HP. :)
 

ibemoose55

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Re: break-in on new Powerhead

Thanks Waleye, that helps me out before I head out there. :)
 

ezeke

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Sep 19, 2003
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Re: break-in on new Powerhead

Don't forget to recheck the torque on those head bolts during your break-in.
 

ibemoose55

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Re: break-in on new Powerhead

Will the Mechanic that did the word want to do this? If so after what time durring the break in period will I do that? :eek:
 

walleyehed

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Re: break-in on new Powerhead

After the 10hr period, take it in and have them re-torque the heads, and look it over. :)
 
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