Unable achieve RPM range on 200 Johnson

[darkgreenhead]

My 1992 Johnson 200 HP has a recommended RPM range of 5000 – 6000 rpms however I can’t seem to get above 4900 and would appreciate suggestions as to what to look for to correct the problem. I have tried the following props and received the following results with an average load. The propellers condition were all very good to excellent with the exception of the 14.5 x 19 Aluminum which was fair.<br /><br />14.5 x 19 Aluminum 4950 <br />14.5 x 19 Stainless 4800<br />15 x 17 Stainless 4900<br />15 x 16 Stainless 4850<br /><br />The motor is mounted about an inch above the transom (not sure how many mounting holes that would be). The engines compression on all six cylinders is in the 125 – 130 range. I don’t believe I have a problem with prop selection as the changes in size, pitch, and material made don’t seem result in any significant change. I am thinking I need to look at the engine itself for problems and would appreciate any and all advice on the matter.

 

[ob]

Re: Unable achieve RPM range on 200 Johnson

What lenghth,style,and weight boat are we talking about here??Did the motor ever perform higher RPMs with present set up?How high is the motors anti-ventilation plate in relation to the bottom of boats transom?If we know the answer to these questions we can look into other possible causes to your low RPM situation.(ie carburetion,spark etc.. )

 

[darkgreenhead]

Re: Unable achieve RPM range on 200 Johnson

21' Boston Whaler Walkaround (23' LOA), weight of the boat (including engine, fuel, two passangers, gear, etc) would be about 3800 lbs. I should make note the boat is 20% under the maximum rated horsepower. Since I have owned the boat it never has run above 5000 (5000 was hit during sea trials and again at spring launch). I don't know the distance from anti-ventilation plate to the bottom of the transom off hand but will post it next week.

 

[ob]

Re: Unable achieve RPM range on 200 Johnson

Another quick item you can look at is to insure the throttle linkage is allowing your carb flaps to open fully horizontal when controls are at WOT.You can check this with engine not running by removing the silencer cover and observing position of flaps.Make sure and have someone turn the prop clockwise while shifting controls.That engine should easily turn a 17" pitch prop to 5500 on that boat.

 

[Solittle]

Re: Unable achieve RPM range on 200 Johnson

What do the plugs look like? I suspect that you are runnin on five - not six.

 

[darkgreenhead]

Re: Unable achieve RPM range on 200 Johnson

ob, It would be my estimation that the distance from the cavitation plate to the bottom of the transom would be somthing in the range of two to four inches. I will verify on my next visit to the Marina. Thanks<br /><br />SoLittle, The last time I checked the plugs all were in similar condition and appeared to be clean with just a little oil on them. The engine sounds good and strong throughout it's range but I wouldn't know how a motor running on 5/6 cylidners would sound. I hope to be able to check for spark and fuel over the weekend. Thanks

 

[ob]

Re: Unable achieve RPM range on 200 Johnson

2" to 4" above or below?

 

[darkgreenhead]

Re: Unable achieve RPM range on 200 Johnson

ob, 2 - 4 " above

 

[ob]

Re: Unable achieve RPM range on 200 Johnson

More than likely the engine height is not your problem then. It would be nice if we could get some gains in RPMs by reducing prop pitch which would rule out possible restriction in one or more of your carbs,fuel delivery to carbs, or need of enlarging fixed high speed orifices.<br /><br />Still need to have a look at whether the carb flaps are opening fully with controls at WOT.

 

[Dhadley]

Re: Unable achieve RPM range on 200 Johnson

What brand tach? Is it set on position 6?

 

[darkgreenhead]

Re: Unable achieve RPM range on 200 Johnson

ob, i had hoped the reduction in pitch on the props would have had an effect but it hasn't in the least, in fact going from a 15 x 17 to a 15 x 16 resulted in less rpms, go figure something is surely wrong. <br /><br />Dhadley, the tach is an OMC but i don't know what position it's set to. I'll take a peak at it and let you know. Thanks

 

[Dhadley]

Re: Unable achieve RPM range on 200 Johnson

Good choice on brand. Let us know the setting.<br /><br />Good luck!

 

[darkgreenhead]

Re: Unable achieve RPM range on 200 Johnson

ob, I checked the carb flaps were vertical at WOT. <br /><br />Dhadley, The tach was set to position 6.<br /><br />I also did a compression test on a warm engine at WOT and found that the compression ranged from a low of 78 to a high of 90, not the numbers i had originally been told by the boat dealer. I later checked with a certified OMC dealer and then Bombardier and both stated the compression result I obtained was perfectly good for a 92' v6 looper.<br />I also cleaned the carb (simply used CRC brand carb cleaner), replaced the inline fuel filter, and put in six new champion plugs and saw no increase in the number of rpms. I haven't checked for spark yet.

 

[clanton]

Re: Unable achieve RPM range on 200 Johnson

78 aint great, do a decarb and redo test with diferent guage.

 

[darkgreenhead]

Re: Unable achieve RPM range on 200 Johnson

Clanton, I agree 78 isn't great but the differential is less than 15% (well just under!). If I can locate another gauge I'll take another set of readings but i did use a high end gauge for the test. thanks

 

[Capn Mike]

Re: Unable achieve RPM range on 200 Johnson

I have the same engine on a 23' Striper, which fully loaded weighs 4000+. I've been fussing with props too: I use a Michigan alum 15 X 15.5, which is readily available, and seems to work OK (5500 max). The next size down is their 15 X 13, which is just too fast.<br />Before you spend any more time or money, have a technician check your power pack/electronics. You need to make sure all 6 cylinders are actually working....you can't tell from the sound. The reason I suspicion it may not be the prop is there should be more of an rpm difference when you change pitch.