1977 Johnson 85 hp Acceleration Question

G

GLPmike

Petty Officer 2nd Class
Joined
Dec 17, 2009
Messages
166
Hello,

We just took our "newer" motor out for a run yesterday. Had a little difficulty getting it to idle without stalling, but once we did we got the following results.

Compression topped out at 105 across all four cyl. and we topped out at 32 mph with two adults in a 16" tri-hull.

We have a problem with acceleration from a standing start. The motor is sluggish and does not sound smooth until the boat planes and then it just hums along.

We found a good crusing speed to be 23-25 mph (gps) @ 4k rpm.

The carbs. were rebuilt by the prior owner. Could it be a fuel related problem.

Thanks
 
E

ezeke

Supreme Mariner
Joined
Sep 19, 2003
Messages
12,532
Re: 1977 Johnson 85 hp Acceleration Question

There is no midrange orifice in those carburetors, so the transition is a bit rough. The best you can do is to be absolutely sure that the throttle plates are synchronized perfectly so that they move together.

The 4 idle jets are behind the plugs on the sides of the carburetor bodies and lead to 4 openings each on the floor of the carburetor throats, just beyond the throttle plates. You may want to assure yourself that all 16 of those openings are clear.
 
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