25r69 low rpm sneeze, low top end

[Catfish2939]

I have a old johnson 25 hp on a 14ft boat. Anytime I try to idle the engine it starts sneezing through the exhaust. Motor will run as long a I keep the rpm's up. Also motor doesn't have very much top end. Will not plane out the boat. Motor starts good and isn't cold natured.<br />I really like the old girl and would like to keep her, If I knew she could be repaired. I know nothing about outboards and would have to put her in the shop. What test could I run to see if the motor is worth saving and spending money on.

 

[Bass Runner]

Re: 25r69 low rpm sneeze, low top end

I don't think there is anything wrong with it, pull the cover, on the front of the carb. you will see two adjustment screws, back both of them out 1/4 turn, then put it in the water and fire it up if it runs rough and really slow at idle turn the low speed screw in just a little at a time giving the motor time to adjust untill you get your idle then go out and run it wide open and do the same with the high speed screw untill the motor runs wide open, the all you have to do is put the top back on and pop a top. enjoy. ps you are running 50:1 mix fuel arn't you

 

[Chinewalker]

Re: 25r69 low rpm sneeze, low top end

The '69 should have a fixed jet for the high speed, but the low speed needle valve can be adjusted as per Bass Runner's advice. The sneezing you note is typical of the motor running slightly lean on the fuel/air mix. <br /><br />Another possible cause is a worn upper main seal. I've had several of the older 25s develop a worn seal and suck air through the seal - effectively creating a lean condition. If the upper portion of your motor is particularly messy with oil residue, you may have a problem with the upper seal. <br /><br />Also, check all of the bleeder hoses for leaks and cracking. These can also contribute to rough running.<br /><br />As for lacking top end power - you may wish to run a compression check. If compression is good and even (100psi or more each hole), then you may want to check that the ignition is giving good spark in each cylinder. Your motor will "sound" perfectly normal running on one cylinder in neutral, but will not have any top end speed in gear.<br /><br />- Scott

 

[oregonducker]

Re: 25r69 low rpm sneeze, low top end

Catfish,<br />Get a can of Seafoam at your local Napa auto parts or wherever you can find it. My 1972 25 horse didn't like to go fast until I gave it a dose of that. Now it will stand up and dance when I ask it to. That may not be the answer to your problems but it's cheap and it's good for your motor if it hasn't been done recently. Do a search on this forum and in the General Outboard forum for Seafoam and you'll find tons of info on it.

 

[Catfish2939]

Re: 25r69 low rpm sneeze, low top end

Yes, I am using 50:1 ratio. I will try to find someone with a compression checker. Also will do the Seafoam thing. One other thing, My motor seems to long for my boat. The cavitation plate sets approx 6 inches below the bottom of the boat. Will that affect the ability of my motor to plane the boat?

 

[G DANE]

Re: 25r69 low rpm sneeze, low top end

You have the wrong motor for the boat. That will affect performance and mileage a lot.<br /><br />If your are happy with boat as well as motor, there are at least 2 ways out.<br /><br />Mounting motor on a Jackplate that lifts it the 5 - 6" needed will get the right hight.<br /><br />With a motor of this limited weight it is possible to cut a piece of marineplywood, 20 or 25" high and as wide as the notch in your boats transom, and bolt it to the back of boat. Paint it reel good or even better cover it with mat and resin. Sides can be cut with slant in exa. 60 deg angle to make it look nicer. Bolt it thru motors mounting holes and a bolt at each side. Be sure it offers proper support for motor. Check that it adds the needed hight, making motors antiventilation plate sit even with, or just above bottumline of boat.<br /><br />You will be surprised how much the correct hight means for handling, faster planing and speed.

 

[Catfish2939]

Re: 25r69 low rpm sneeze, low top end

Adjusted the low speed jet like you said and the sneeze went away. Now it idles like a kitten..wow what a difference a little turn makes. Now I am going to raise the motor and see what happens.<br /><br />Wish me luck...<br /><br />Might also get some of that seafoam and run it through the engine. Ohh yes,,I did check the spark and it has good spark on both cylinders.<br /><br />Thanks Guys