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Old 07-17-2016, 09:45 PM
TSTUBB TSTUBB is offline
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Boat: Mastercraft Prostar 1987 351 Indmar
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Rebuilt Carb

1987 Prostar 351 Indmar. Just rebuilt the carb and installed new shift cables. Boat runs good now and idles. Ran so ****ty before, it wouldn't even idle, so anyways runs good and does 4600 rpm about and 38 mph WOT. Seems a little low to me, also seems a little flat an less torquey now. What are stock settings for the low speed screws on both sides of carb? And anything else I should check??
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Old 07-17-2016, 09:53 PM
waterlogged882 waterlogged882 is offline
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Quote:
Originally Posted by TSTUBB View Post
1987 Prostar 351 Indmar. Just rebuilt the carb and installed new shift cables. Boat runs good now and idles. Ran so ****ty before, it wouldn't even idle, so anyways runs good and does 4600 rpm about and 38 mph WOT. Seems a little low to me, also seems a little flat an less torquey now. What are stock settings for the low speed screws on both sides of carb? And anything else I should check??
From a fully closed position, open 1-1/2 turns out (to confirm - counterclockwise).

Check the wear on the cam of the accelerator pump. If your boat is a 1:1 transmission, you should be pushing 45 MPH or so.

Make sure you do not have a vacuum leak at the base of the carb on either side of the spacer.

Just pulling straws from what you have said. Several other possibilities coming off of a rebuild.
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Old 07-17-2016, 10:15 PM
TSTUBB TSTUBB is offline
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I just went out and checked them, they were 2 turns out and 2 1/4 out so I adjusted accordingly to 1 1/2 on both sides. I checked my carb and have full travel with my new cable.
I have a power slot transmission.
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Old 07-17-2016, 10:49 PM
waterlogged882 waterlogged882 is offline
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Originally Posted by TSTUBB View Post
I just went out and checked them, they were 2 turns out and 2 1/4 out so I adjusted accordingly to 1 1/2 on both sides. I checked my carb and have full travel with my new cable.
I have a power slot transmission.
Not that bad off actually. I was just stating the default setting. Patience with the carb.

Make sure your electric choke is working properly. Other internal things could be a little off.
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Old 07-18-2016, 12:24 AM
TSTUBB TSTUBB is offline
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Granted I removed carb, disassembled and installed new gaskets, needle and seats, diaphragm w/ ball bearing, and cleaned. So only I can think of its running a lot richer now that it's getting the fuel it needs to run. Requiring it to be dialed in. I also should mention when I tested it today for the first time it did back fire throu the carb once on a hard take off. I'll check the choke but shouldn't have changed...

It's just lacking that really torquey feeling. What kind of RPMS should I be looking at for WOT? What ratio is my transmission?
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Old 07-18-2016, 07:28 AM
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paco_06 paco_06 is offline
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Your transmission is 1.52:1 ratio. Mid to upper 4000's on your rpm. So you're there. Really sounds more like a dinged prop than anything... Should be getting 43-44mph on stock 14x18 three blade cast prop. Lose 1-2 mph with four blade. My last boat had a powerslot, last prop I had on it was a 14x16 three blade(lower pitched and slower) it would make it to 40mph at around 4800 rpm, but I never ran it wot, it would have went way over 5k.
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Old 07-18-2016, 08:48 AM
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thatsmrmastercraft thatsmrmastercraft is offline
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With the backfire through the carb, you may have damaged the power valve which would leave you running too rich. There is a Holley power valve protection update (P/N 125-500) that I install on all the carbs I build, and it provides a pressure release so a backfire won't rupture the power valve diaphragm.

You might want to take a look at your timing, as well as points if you still have them. You should also check your plug wires if you had them off as crossing two wires is a source for backfiring.

What did you use to clean the body of the carb when you did your rebuild? If you didn't get the passages in the main body of the carb cleaned out, that could account for the sluggish feeling.
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Old 07-18-2016, 01:46 PM
TSTUBB TSTUBB is offline
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When it backfired it was probbly half way throu my test on water. Only did it once and that was on a hard take off and boat kept on going.

I mean the slug feeling isn't horrible, it just seems little flat, if that makes sense. I soaked the carb in mineral spirits and then used carb cleaner and a blow gun.

Cap and wires was done just before I bought it. My prop has a small ding or two in it. Not huge.

Keep in mind I ran it a few weekends before rebuilding the carb.
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Old 07-18-2016, 02:50 PM
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paco_06 paco_06 is offline
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Quote:
Originally Posted by TSTUBB View Post
When it backfired it was probbly half way throu my test on water. Only did it once and that was on a hard take off and boat kept on going.

I mean the slug feeling isn't horrible, it just seems little flat, if that makes sense. I soaked the carb in mineral spirits and then used carb cleaner and a blow gun.

Cap and wires was done just before I bought it. My prop has a small ding or two in it. Not huge.

Keep in mind I ran it a few weekends before rebuilding the carb.
My point behind the prop is that regardless of how the engine is running, a well tuned stock prop turning 4500 rpm, (actually 3000 due to powerslot), will propel that boat to low 40's. Either that, or your tach is wrong, or something is up with the tranny.
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Old 07-18-2016, 03:49 PM
TSTUBB TSTUBB is offline
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Boat: Mastercraft Prostar 1987 351 Indmar
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That boat ran fine before I rebuilt it and I was pushing 43-44mph. That's why I think it's carb related. I checked speed with my phone. That's why I was asking if there's any adjustments other than the low speed screws on the primary side? Because it's not a huge difference in performance more of a slight difference.
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