1981 Johnson seahorse 75 jetting

[Finznfeathers]

I was wondering if you guys could help me with jetting on this motor? I got this boat from a friend in Iowa and I live in Idaho. I'm not sure of his altittude but I'm sure it's not 6000 foot lol.

Like I said I'm at 6000 foot and I'm pretty sure it's loading up. Right now it has a 59 and 57 in it. I'm assuming these are air jets and not fuel jets? I've never dealt with this kind of carb before.

It's on a 19' bass boat. Weighing 1000 pounds without gear around 1600 with gear and people. It's also got a 13 1/4x17 prop which might be too much.

It idles good and starts good and runs good at the top end when it gets there. It has a mid throttle bog that is annoying. If I work the throttle slow I can work through the bog and then it will take off. With our fishing gear myself and my boy I can get 32mph on the GPS. All cylinders are firing and have 120 psi in each.

Any advice would be great!

Thanks

 

[Rustywrench]

Need to exact model number of your motor, please.

 

[jimmbo]

A midrange bog usually is a good indication of dirty carb circuits, a misadjusted or saturated float in the carb, poor sync between carbs and timing. As for the jetting, you might be hard pressed to find any Altitude Jets for those engines. OMC Race division(no longer around) may have had other jets for race tuning. Your only option may just be choosing a prop that lets the engine run as close to 5800 as possible.

 

[Finznfeathers]

Motor model # J75TRLCIM

Carb # 326951

I can give serial if needed also.

Thanks
Kris

 

[Finznfeathers]

Ttt

 

[Rustywrench]

Jets are listed under your model number as 67 idle fuel jet, 59 intermediate fuel jet, & 59D high speed jet. The idle jet is the one at an angle closest to the mounting flange. Intermediate is in the front of the cab top. High speed in the bowl. Look again to see if that 57 is a 67. Fuel jets are covered by plugs. Air jets are out in the open. No racing jets that I know of. Jets are jets. Not sure what to advise on altitude. Usually effects HS more than idle or intermediate. On bass boat applications always need more fuel in mid range. As suggested a good carb cleaning is where I would start. Make sure all passages are clean. Especially small emulsion tube up center of high speed nozzle.

 

[F_R]

Make sure the timer base isn't sticking. If it lags due to stickiness, the carburetors will open before timing reaches full advance, causing serious bogging, even stalling.

 

[Finznfeathers]

Thanks for the info!

Are these jets unique to these carbs or by chance is there a manufacturer that uses the same thread pitch and diameter as these?

My timer is moving freely.

Thanks
Kris

 

[Finznfeathers]

Ttt

 

[Rustywrench]

The smal jets are 8 X 32 thread count & the HS is 1/4" X 20 thread count, but I don't know of anyone who makes them?

 

[Finznfeathers]

I guess maybe I'll have to fire up the lathe and make some.

 

[Finznfeathers]

I've got my carbs sitting in a can of chem-dip right now. Waiting for rebuild kits and a new fuel pump. I'm praying it runs like it's supposed to after this!!