90 Johnson Re-Jet Carb After Boring .30 Over?

[RBuch1974]

I have my 82' 90hp Johnson at the machine shop. They are going to bore two cylinders 0.30 over. I am not sure which two cylinders yet (If it matters).

Do I need to put larger jets in the carbs? If so, all (3) sets? How do I figure out what (or does someone know) what size jets to install.

 

[jimmbo]

Re: 90 Johnson Re-Jet Carb After Boring .30 Over?

No need to rejet. It will be fine as is

 

[RBuch1974]

Re: 90 Johnson Re-Jet Carb After Boring .30 Over?

Thank you.

 

[emdsapmgr]

Re: 90 Johnson Re-Jet Carb After Boring .30 Over?

The factory makes up to .030 over pistons, but does not require or suggest rejetting. I'd begin to get concerned if it was bored more that .030 over.

 

[Bob_VT]

Re: 90 Johnson Re-Jet Carb After Boring .30 Over?

I have encountered many outboards that have a single piston replaced with a slightly larger bore. On a 2 stoke it will not matter since all cylinders are independent

Just treat the assembly like an operation in a hospital......... be ULTRA clean and meticulous because that is something you should only need to do once.

 

[RBuch1974]

Re: 90 Johnson Re-Jet Carb After Boring .30 Over?

I have encountered many outboards that have a single piston replaced with a slightly larger bore. On a 2 stoke it will not matter since all cylinders are independent

Just treat the assembly like an operation in a hospital......... be ULTRA clean and meticulous because that is something you should only need to do once.

Understood. I have rebuilt several car motors over the years and it usually takes longer degreasing/cleaning, painting, retapping, and deburring than reassembling. I am trying to "play stupid" (so to speak) because I have found marine applications can be much different than my experience would tell me. For example, bore one or two cylinders 0.30 over? Well "double you-tee-eff" to that...lol Thanks for the info

 

[RBuch1974]

Re: 90 Johnson Re-Jet Carb After Boring .30 Over?

The factory makes up to .030 over pistons, but does not require or suggest rejetting. I'd begin to get concerned if it was bored more that .030 over.

Gotcha. Only going 0.30 to remove pitting from surface rust in one and a small ring scar in the other. Considering just having them do all four though since I'm buying all new pistols anyhow. It's only like $35/cylinder to bore. Thanks for the reply.

 

[emdsapmgr]

Re: 90 Johnson Re-Jet Carb After Boring .30 Over?

The factory has made .020 over pistons for these 99 cubic inch crossflows, but don't advertise them on their online parts lists. Check out the parts and accessory book at a Bombardier dealership.