1989 evinrude 150 fueling issue

[cdoliver]

This engine started life as a 155comm. I ran it for a year or so as is, ran fine. I decided to try to improve performance so I added:
boyeseen reeds, intake stuffers and the 772/773 heads from a GT150. I also have milled out the plenums between the carb inlets on the intake.
After this the motor runs ok, but it has a hesitation anytime you immediately go to full throttle. The hesitation lasts for maybe a half a second then it picks up and runs decent. under partial throttle It almost feels like it's surging (power coming and going), and if you tap the primer it definitely picks up. If you hold the primer it never really bogs under partial throttle.
The idle is perfect in and out of gear.

If you hold the primer just before you go to full throttle, NO HESITATION...

So I'm assuming this is a lean condition due to the part changes. I do know the mid jets are 31C and high speeds are 58.5C

My question is: how many sizes is a good guess to go up? and... Do I increase the mids, highs, or both?
Or
Am I even barking up the right tree?
Thanks for the help in advance.

 

[cdoliver]

Re: 1989 evinrude 150 fueling issue

100 view bump. still looking for a tip

 

[metriccrescentwrench]

Re: 1989 evinrude 150 fueling issue

Yeah, it's lean. You might want to post your question to screamandfly.com , there are plenty of hot-rodders and racers there who have experience with performance modifications. From what I've read it seems that you'll want to richen the mains a couple of sizes and from the sound of it you'll need to go a good bit richer on the mids.

The experts will tell you that the proper way to get a read on the mains is to put in fresh plugs, do a full throttle run then immediately shut down (easier said than done). To be on the safe side I'd get the mains richer before trying to run it any more, then work from there. But definitely introduce yourself on screamandfly, and get some advice from those guys.

 

[cdoliver]

Re: 1989 evinrude 150 fueling issue

ok I ordered some 61C jets. That's 2.5 sizes larger. will try them out to see if its better and report back.