Low power/RPM's

trb · Sep 16, 2002

I own a 1994 30hp Johnson that when purchased (used) pushed my boat about 22 mph. Next trip, it would only do about 14mph with comparable loads. Has ran this way ever since. Starts very easily and idles great, but the rpm's are not there anymore. Engine does not miss or anything. Replaced fuel pump (leaking slightly), spark plugs, cleaned carb, checked lower unit, and made sure throttle was opening up fully. Have burned several tanks of gas, so bad fuel is not an issue. I don't know where to look next. Any help would be appreciated.

rickdb1boat · Sep 16, 2002

Re: Low power/RPM's

Check Compression first before you go any further. That may tell the story! Let us know what the reading are!

trb · Sep 16, 2002

Re: Low power/RPM's

I don't own a compression tester. Is there a way to due that without one?

rickdb1boat · Sep 16, 2002

Re: Low power/RPM's

No, but you can purchase one for about $25.00 at an auto parts store. Well worth it to have one if you own an outboard. You will be able to check the condition of your Engine in the future and Moniter it's condition, too. The only other option is to take it to the repair shop and have them do it. But that will probably cost you more than the tester!

rickdb1boat · Sep 16, 2002

Re: Low power/RPM's

If you are tight with your auto Mechanic, he can do it too! Just a thought!

trb · Sep 16, 2002

Re: Low power/RPM's

Thanks for the reply. I know the pressures on the two cylinders need to be close, but what would be a good pressure reading? (Buying one as soon as I leave work)

rickdb1boat · Sep 16, 2002

Re: Low power/RPM's

At least 100 PSI and within 10-15 percent of each other. Most important is the difference between the two! If one is say, 125 PSI and the other is 80 PSI, there is a problem. If one is 125 PSI and the other is 120 PSI, no big deal! Let us know!

trb · Sep 17, 2002

Re: Low power/RPM's

Hey, I checked them out and both cylinders are just over 120#. Also checked the filter in the tank and it looks good. Any other ideas?

rickdb1boat · Sep 17, 2002

Re: Low power/RPM's

Have you checked the Prop! Maybe you have a partially spun hub!

ad4par1 · Sep 17, 2002

Re: Low power/RPM's

Hiya TRB. I had a similar problem with my '71 Johnny 50HP. Problem solved today! When you cleaned the carb, did you check the needle valve/seat? When these go bad, you will get the symptoms you describe (the needle gets stuck in the seat). Older needles have a rubber tip that wears down until it wedges into the seat. OMC replacement parts have a full steel needle to prevent this. The carb kit for my engine was $15. Probably about the same for yours. Let us know how it goes.

trb · Sep 17, 2002

Re: Low power/RPM's

The rpm's are definitely lower than before and the prop seems solid. The other odd thing is that one trip it worked great and the next trip it had less power. Could the needle thing haved occured due to a long trailering?

rickdb1boat · Sep 17, 2002

Re: Low power/RPM's

Yes, it could have when you trailered it. Worth checking it out! Also, make sure you are getting good spark! Should jump from the wire to the block about 7/16"! I can't think of anything else right now. Hopefully, someone else will!

ad4par1 · Sep 17, 2002

Re: Low power/RPM's

The needle thing can happen at anytime. The carb gremlins like to wait until you REALLY need things to work right. I'm just guessing, but if I was forced to put a bet down, it would be on the needle valve. Just to satisfy your (and mine) curiosity, pull the carb and have a look. Besides, the carb kit is somewhat cheap and it can't hurt to put in new needle valve/seat/float/gaskets, etc (all inlcuded in kit). Keep us updated! (Have a look at my recent post: http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=17;t=019837 )

Low power/RPM's

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