How fast should I be able to get up too?

SirEnvy · Mar 23, 2011

I have a 1985 Johnson 150. On a 1990 Sportcraft 22'. My speedometer doesnt work, but thats all getting replaced this weekend actually, but my GPS tells me, on plane, that I am only going 33MPH. I recently had a new steering box put in, but I dont think that has anything to do with it. I also, change my plugs regularly, and just had my carbs clean. Everytime I put gas in, I put in the proper amount of Marine Sta-Bil. I like to take care of my things, but 33MPH seems low...maybe my GPS is wrong, dunno.

Dhadley · Mar 23, 2011

Re: How fast should I be able to get up too?

Those boats are known for having a pretty good hook, that's why they get up pretty good with a smaller motor but it makes them a little slow with a V6. However, it seems like you might be able to get a bit more speed without working on the hull. Let's start with the basics. What's you top rpm with an average load?

SirEnvy · Mar 23, 2011

Re: How fast should I be able to get up too?

shoot, I knew you would ask me that, im taking it out tomorrow, and I will get back to you on the RPM. All my instruments are original, which is why I am replacing them this weekend. Could it be a bad cylinder? What kind of signs would it make if I had a bad cylinder.

Whats typical for RPM?

Dhadley · Mar 23, 2011

Re: How fast should I be able to get up too?

In a perfect world you'd target 5800 but we may not get there in this case. Let's start by looking for at least 5500 with an average load.

Chris1956 · Mar 24, 2011

Re: How fast should I be able to get up too?

I have a 21 foot Dual Console with a '98 150HPV6 Johnny. I can get 40MPH going downhill with the wind, and my 19" pitch prop. if your boat is heavier or the motor is a bit worn, 33MPH might be the best you can do.

Wishiniwuzfishin · Mar 24, 2011

Re: How fast should I be able to get up too?

I had a 1988 19-1/2' bowrider with a 1988 150HP Evinrude some years back. Mine did 45mph (by speedometer/no gps back then) with me alone on a perfectly flat lake.....that was with standard factory (don't remember specs exactly) prop in like new shape and perfect condition and waxed hull.

I don't think your top speed necessarily indicates problems with the motor.

Lots of things could be slowing you down...Like dhadley said maybe your rpms aren't at the top range....load.......prop specs and condition...hull configuration and condition......maybe an engine tune-up.....

Is the motor mounted at the optimum height?

Then again maybe thats all you will ever get out of that boat/motor combo.

Could easily go to a SS prop spec'd at proper top rated rpm's if you really want more top speed

Silvertip · Mar 24, 2011

Re: How fast should I be able to get up too?

Throttle not opening the carbs fully? Engine getting tires?? Dirty hull?? Hull full of water soaked foam (weight issue)??
At this point buying a prop is the very last thing you need to consider -- especially since you have no idea what the engine rpm is with the one you have.

Wishiniwuzfishin · Mar 24, 2011

Re: How fast should I be able to get up too?

Didn't say he should run out and buy a prop.

SirEnvy · Mar 24, 2011

Re: How fast should I be able to get up too?

Okay, just got back from the water, its a bit windy outside, but I need to get to the bottom of this. According to my RPM instrument, I am hitting between 4800-4900 RPM.

SirEnvy · Mar 24, 2011

Re: How fast should I be able to get up too?

bump

Chris1956 · Mar 25, 2011

Re: How fast should I be able to get up too?

A prop with 2" less pitch, might (might) get you some additonal top speed, by raising the WOT RPM and allowing the engine to develop greater power. See if you can borrow a prop and try it. Your current WOT RPM is a bit low. 2 less pitch will get you to 5300 or so.

jonesg · Mar 26, 2011

Re: How fast should I be able to get up too?

SirEnvy said:
Okay, just got back from the water, its a bit windy outside, but I need to get to the bottom of this. According to my RPM instrument, I am hitting between 4800-4900 RPM.

Thats 1000rpm under, I would do a compression test next to get an idea of the internal condition.
How often do you decarb the cylinders?
MAke sure you don't have a stuck ring or two before playing with faster props or you may snap a ring and self destruct.

SirEnvy · Mar 26, 2011

Re: How fast should I be able to get up too?

jonesg said:
Thats 1000rpm under, I would do a compression test next to get an idea of the internal condition.
How often do you decarb the cylinders?
MAke sure you don't have a stuck ring or two before playing with faster props or you may snap a ring and self destruct.

This motor has been recently serviced, had a compression test, and also the carbs were just cleaned by a mechanic.

What do you mean by decarb the cylinders?

SirEnvy · Mar 27, 2011

Re: How fast should I be able to get up too?

Decarbing a motor sounds pretty easy, let me get this straight.

1. Take out the plugs
2. Spray decarb in the spark plug holes to reach cylinders
3. Rotate the fly wheel so the bearings and all internal parts get cleaned
4 Let it sit over night
5. Start it up and should notice smoke coming out meaning its cleaning

am I missing anything, or is that about it?

nymack66 · Mar 27, 2011

Re: How fast should I be able to get up too?

Please have your mechanic or you verify your Throttle Advance is moving forward at WOT it may be stuck or just sticking ...It can be removed dissembled and re-lube,,Just did mine today I was a little surprise at the crap around the spring ...Harden black grease to be exact ...Reason you ask what lead me to service mine? I could not get her down to 750 rpm in gear with the adjuster all the way in ..Idle is now right on..

SirEnvy · Apr 2, 2011

Re: How fast should I be able to get up too?

Okay, just checked my plugs, and saw that all of them were normal(somewhat dirty) and one was clean.....couple of my buddies who have been around boats for awhile told me that I may have a dirty carb...a quick story:

When I bought the boat, the fuel had to be dumped because the fuel had water, from sitting around too long. I had my carbs cleaned, but maybe I still had some debris still left over from the tank. Maybe I should clean my carbs again? What do you guys think? Or should I do a quick decarb without actually spraying my carbs...

blimp · Apr 2, 2011

Re: How fast should I be able to get up too?

a perfectly clean plug indicates either lack of firing or a water intrusion into the cylinder. confirm you have spark to that plug with a spark tester, and if so, you may be looking at a head gasket or exhaust cover gasket issue.

Dhadley · Apr 2, 2011

Re: How fast should I be able to get up too?

Was the clean plug on #1 cylinder?

SparkieBoat · Apr 2, 2011

Re: How fast should I be able to get up too?

if you are getting 33 MPH you are not far from expected top speed IMO. So I would not think it could be a bad coil/power pack. But you should redo compression test after decarb and do a spark test also with a spark gap tester. also what is you WOT timing?? You could also be having a slight fuel issue. But even on a high speed hull, a 150 on a 22' boat will probably not get much past 35-38. Did you ever try a smaller pitch prop?? what pitch is your current prop??? you said in your first post you just had carbs cleaned, it is possible they need to be redone or your fuel pump is getting weak,

SirEnvy · Apr 2, 2011

Re: How fast should I be able to get up too?

Not sure if cylinder labels are all the same, but if you are facing the motor, its the bottom right cylinder.......

My current prop is 14' x 19

How fast should I be able to get up too?

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