70 horse Johnson stalls below 1500 rpm

[tinhog69]

I recently bought a boat with a 70 horse Johnson. <br /><br />Problem<br /><br />It starts great but stalls when put in gear and the throttle is advanced.<br /><br />The motor runs ok in gear if just left at idle. <br /><br />Also the motor will idle and rev up ok when not in gear. <br /><br />It takes several tries to get the motor to get past 1500 rpm when in gear.<br /><br /> After it is warmed up it will accelerate ok past 1500 rpm. But after the engine is turned off after about 8 minutes the problem is back. The problem of getting past 1500 rmp is really noticable in reverse. It if gets above 1500 rpm it runs great. <br /><br />History<br /><br />Motor was not winterized last year<br />Has 15 degree prop<br />I am in Denver which is at 5000 ft above sea level<br /><br />Tried<br /><br />new gas in separate tank (not boat tank)<br />Sea foam carb cleaner to last tank of gas<br /><br />Took to boat shop and motor checked out<br />- compression good<br />-adjusted idle mixture<br />- idle set at 1100 to 1300<br /><br />They thought it was ok when it was returned to me. They did not notice problem in test tank.

 

[thosch]

Re: 70 horse Johnson stalls below 1500 rpm

I had much the same problems with a 90hp Johnson. Carb kits took care of it. Ran like new afterwards.

 

[Chuck B.]

Re: 70 horse Johnson stalls below 1500 rpm

tinhog, I have posted the same problem on a 75 hp. Johnson. Just about all the resoponses that I have recieved have led me to build the carbs. The kits are only around 11.00 ea. so other than time and about 40.00 you have nothing to lose. Just be sure to clean every orifice with carb cleaner and blow them out with compressed air, or at least that is how I build the carbs on the cars I work on, has never failed me yet Chuck B. P.S. I am no boat engine mechanic, But a heavy equipment, car, and truck mechanic for 14 yr.

 

[tinhog69]

Re: 70 horse Johnson stalls below 1500 rpm

Thanks for the reply. I am going to try rebuilding the carbs today. <br /><br />Did you guys try any carb cleaner before rebuilding? Did you have the same symptom of the engine running good after it warmed up?<br /><br />I will post my results after rebuilding carb.<br /><br />thanks,<br /><br />Paul

 

[thosch]

Re: 70 horse Johnson stalls below 1500 rpm

Don't use the carb cleaner. Rebuild the Carbs. It sounds like that will solve your problems.<br /><br />Regarding the better running after warmup, mine did run better after the engine got up to temperature, but still not good enough. I still had the hesitation at throttleup, just not as bad as when the engine was cold.

 

[tinhog69]

Re: 70 horse Johnson stalls below 1500 rpm

I purchased a manual yesterday. After inspecting the engine I found that the throttle linkage was not set up properly. The throttle arm was not set against the its idle stop. I adjusted that and the throttle cam and throttle cam follower to .010inches. I took it on the lake to see if this made any difference and to check the idle timing. The idle timing was set to -4 degrees and the spec was 4 (ATDC). I changed it to 4 and adjusted the idle mixture. It idled ok but would not accelerate at all. It bogged big time when trying to advance the throttle even out of gear. The idle was 900 rpm after all of the adjustments, the same as before. I changed the timing back to as it was. <br /><br />The thing that is concerning is the book mentions if the idle is too fast there could be a leak to check induction system for air leaks. How do I do that and is 900 rpm too fast for this motor in gear? And the timing is 8 degrees off and runs good above 1500 rpm? A posting from member 1231 (topic 94 Evenrude Frustration) it seem a very similiar problem (problem went away after 1500 rpms) as mine but his cure was taking the VRO off. Go figure. Going to rebuild carbs today.

 

[tinhog69]

Re: 70 horse Johnson stalls below 1500 rpm

Rebuilt carbs and did not find any goo or blocked passages. Tested carb rebuild. This did not solve the problem. Also was told the timing and idle speed ok for that year of motor. It was timed correctly, my mistake. <br /><br />Out of ideas.

 

[metalmantis]

Re: 70 horse Johnson stalls below 1500 rpm

Hello just thought I would add my 2cents since all are here for a reason and that is help or to offer help. You mentioned that rebuilding the carbs did not help, just wondering if you checked anything between the tank and the carbs ie: all the hoses, vent valve working properly, fuel filter pump etc. may be worth looking at! Good luck!

 

[tinhog69]

Re: 70 horse Johnson stalls below 1500 rpm

I have a onboard gas tank. Where is the vent valve if there is one and how to check it? The boat is only 2 years old and the hoses all look ok. I don't know about the fuel pump. Guess I can try to figure out how to check that later.