1988 Johnson 70 HP 3 Cyl Issue & Fuel Consumption

[jholley]

I recently purchased a boat with a 70 HP Johnson VRO 3 Cyl.<br /><br />I was wondering what my fuel consumption at High RPM's was?<br /><br />Also, the engine stalls a low speeds, at idle and while shifting from Forward to Reverse. Anyone have a clue on what this issue might be?<br /><br />I just ordered the Service Manual. <br /><br />Also, someone told me that you can retrofit an Automatic Fuel Injector to this motor. Where can I find information on doing this? Can it be done by myself or do I need a pro?<br /><br />Thanks in advance for your help.

 

[JB]

Re: 1988 Johnson 70 HP 3 Cyl Issue & Fuel Consumption

Hi, JHolley.<br /><br />Werlcome to iboats. <br /><br />Fuel consumption depends on the load it is pushing.<br /><br />As soon as you get your manual, do the linkage and synchronization (link 'n' synch) adjustments.<br /><br />Never heard of fuel injection retrofit. I think I would have if there was one.<br /><br />Good luck.

 

[jholley]

Re: 1988 Johnson 70 HP 3 Cyl Issue & Fuel Consumption

JB Thanks.<br /><br />It is pushing a 1,400 lb 19 ft. center console. I am just trying to get a ballpark of fuel consumption. <br /><br />I don't have fuel gauges on internal tanks. Is it around 3-5 GPH? 5-10 GPH? More?<br /><br />Thanks.

 

[angus63]

Re: 1988 Johnson 70 HP 3 Cyl Issue & Fuel Consumption

about 7 gph at WOT. Maybe a little more for that size boat (70 hp seams a bit timid for a 19').

 

[DJ]

Re: 1988 Johnson 70 HP 3 Cyl Issue & Fuel Consumption

A 70 pushing a 1400 pound boat is not going to give spritely performance.<br /><br />Make sure this engine is propped to turn at least 5500 RPM at wide open throttle or, it will destroy itself in short order.

 

[jholley]

Re: 1988 Johnson 70 HP 3 Cyl Issue & Fuel Consumption

Thanks everyone. Yes, the boat is underpowered, but the engine has been on the boat and it has been used actively for the last 6 years.<br /><br />DJ, what do you mean "propped to turn at least 5500 RPM?" <br /><br />Thanks.

 

[DJ]

Re: 1988 Johnson 70 HP 3 Cyl Issue & Fuel Consumption

The engine should be able to turn at least 5500 RPM at wide open throttle. If it does not reach that RPM, you are in effect lugging the engine. This is no different than driving up hill in high gear, with a load.<br /><br />If you are not reaching 5500, you need to go to a lower pitch prop. As an example, if you are running a 17" pitch now and getting 5000 rpm, than something like a 15" pitch might be in order.<br /><br />Each inch in pitch is usually equal to about 200 RPM's, up or down.<br /><br />Getting a properly pitched prop may make the performance acceptable.

 

[Lowranger]

Re: 1988 Johnson 70 HP 3 Cyl Issue & Fuel Consumption

jholley, I have an '89 Johnson 70 pushing a 22' C-Dory Cabin Cruiser(fairly flat hull)that weighs around 3500# loaded. I run a 14x13 un-cupped Michigan 3 blade and turn 5800 r.p.m. @ about 24.5 m.p.h.. Acceleration is quite brisk. I've had this package for 15 years and I still can't believe how well it works. Pete