Prop Question
 

Guys - I have a 1988 Cig Bullet with 502 Mags. I picked the boat up late last season. Port engine has always run faster than the starboard and I assume that the slower engine is just getting tired. I have the drives now off in the garage and I notice that the prop on the slower engine is a 25P Mirage PLUS, while the faster engine has s 25P Mirage. I know the pitch is the same, but the props look slightly different in design. Could this be the problem? I would hate to buy new props to find that it is not even though they don't exactly match.

Thanks for your help, Don.

Re: Prop Question
 

How much RPM difference?

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There is about 400 RPM difference which is enough to have to run the throttles with one advanced about 1/2" in front of the other :(

Re: Prop Question
 

The same size prop shouln't have that much diff.
I would check the motor.
Check comp. first.
Then check timing, fuel, codes, ect.
Check leakdown if you have the tool.
I have worked on alot of these motors with clogged injectors, they will idle with no miss and pick up a miss under load.
If they are clogged try to take them to a local injector cleaning machine. You have to take them out to do this.

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Call your local Merc.dealer and ask or call Merc. Racing 1.920.921.5330 Don't start taking things apart until you get some answers about the props.They don't have different part numbers for nothing.You didn't mention anything about a miss so unless you're bored or need the practice be patient and ask questions.BOB

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In '88 where there EFI/MPI 502's? I thought they were carbed.

What is the difference in the props? I'd want to run them wiht identical props, if there is a difference in the Plus and standard.

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Sorry read right past that.
If it has bravo's you could switch the props around, run the drives in reverse and see if you have the same diff. If so then go back to orig. post - the efi part.

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The Mirage plus has more cup and blade area.

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Bingo, I think we just found your 400 RPM???? :evilb:

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Nobody - Good idea, swicthing the props and running the drives backward would tell right away.

SearayJim - the engines are 2000's 502 MAG MPI's - blew the 1988 454's a long while back. Of course, they were originally carb'd.

Thanks again for the help

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You really don't need to bother switching the props and testing that way. The Mirage and Mirage plus are diffrent propellors and you would see an Rpm diffrence between them. what you should do is contact your local Merc deale who should offer a loner prop program and play around until you find the right combo. But there deffenitly is a differnce bettween your props it was more than a diffrent name.

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Hillbilly - I think they are different also, thanks for the advice.

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You most likely did this already but put both throttles about 3/4 open and check to see if you Throttle body is open exactly the same on both. Could be a small cable adjustment would add to the prop difference

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There indeed is a difference between the Mirage and the Mirage Plus. The Mirage Plus has a larger blade surface area allowing for additional cup. Typically the RPM Difference is about 200 at WOT. So there is still 200 unaccounted for. Now if the propellers have ever been worked then this could make the difference as well.

Julie

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What kind of top speed are you seeing with that boat? I have looked at a couple with 500HPs and wonder what the top will be. Thanks

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Top speed is 67 MPH.

Don

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Don't always treat your tach readings as the gospel truth either.

The Stewart-Warner tachs in my friends 1989 Bullet have not told the truth in years.

The Mirage Plus is more efficient and will cause less RPM.

I would do a compression test just to establish that the internals are healthy.

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Which motor is your power steering pump on? I don't think that it would be 200 rpm, but it has to be something.

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I never considered the power steering pump - it does happen to be on the engine that seems to run slower (the side with the Mirage Plus, not the standard Mirage). I don't think the power steering pump should have much of an effect.

The Tachs were updated within the last 5 years, but they could be off.

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do the motors sound in sync? When you get them sync'd they will make a steady sound ,,,when off a litttle, a long wave and as you differ the engines more the "wave" will go faster. You'll hear it after playing around a little then you'll know for sure if your tachs are correct in relation to each other.

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CoolToys61 - also a good idea, I am pretty sure they sound in sync, but I will have to wait until the thaw to find out. :(