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Old 07-13-2019, 03:15 AM
quattrotto quattrotto is offline
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Boat: 1991 Prostar 190
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1991 Prostar 190 351 surging between idle and 2000 rpm

Having my first issue with my new to me last year and 60 trouble free running hours ago 1991 Prostar 190 351. Have loved this boat since I got it at 860 hrs and have done lots of the usual maintenance that one wants to do on an old boat. Yesterday I developed an issue after setting out for the day....topped up with 13 gallons of ethanol-free 91 at a reputable Exxon on the way to the lake. Put boat in water, starts normal, runs normal. Several wide open runs and hole shots on glassy morning water and all is good. Temp and oil pressure guages read as usual. Boat sat for about an hour then went out with first skier of the day. Setting out from the dock, starts and idles normal but upon initial acceleration I noticed something not quite right immediately....stumbling/surging power between idle speed and 2000 rpm. Above 2000 rpm engine runs fine all the way to full speed, but immediately powering down to 2000 rpm or below, stumbling/surging happens again.

So, with a full day of watersports planned, tried to assess the issue on the water (the dock space was not available anymore)....fearing I got some bad gas, I had some Seafoam available and poured a couple of bottles in the tank (tank was full with 30 gallons). Also changed out the cap and rotor to new ones I had on board. After running for a 20 minute to a half hour no change. Pulled the boat out of the water and brought it home.

After some research on this site, it still seems to be fuel related, however the opposite of what others have experienced (boat starts and idles fine and runs great above 2000 rpm.) I visually tested the Accelerator Pump and seems to be squirting as prescribed. I only have one fuel filter, on the front passenger side of the motor, so I'm going to change that and see if maybe there was some water in it somehow. Looking for some other things to check out over the weekend on my own before getting some professional assistance.

Recent maintenance: New plugs, Cap, Rotor, fuel filter during winterization, new impeller at start of this season, cleaned the flame arrestor and carb when winterized last fall....and some other stuff I can't recall at the moment. Planning on keeping this for awhile so planning on replacing the fuel line, get some new plug wires, etc. If anyone has any ideas before I go pulling the carb off, please chime in....thanks!
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  #2  
Old 07-13-2019, 07:34 AM
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SuperSquid SuperSquid is offline
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Boat: 1976 Master Craft Stars & Stripes
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do this

I would check the carb needle and seat valve. Does the problem get worse after you run the boat for 20-30 minutes? Then the next day when the engine is cold the issue is gone until the engine warms back up? Good luck and keep us posted.
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Old 07-13-2019, 10:36 AM
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1redTA 1redTA is offline
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Boat: 1981 MasterCraft 351W slot
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test the vacuum secondary
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Old 07-13-2019, 01:52 PM
quattrotto quattrotto is offline
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Boat: 1991 Prostar 190
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Quote:
Originally Posted by SuperSquid View Post
I would check the carb needle and seat valve. Does the problem get worse after you run the boat for 20-30 minutes? Then the next day when the engine is cold the issue is gone until the engine warms back up? Good luck and keep us posted.
I have not been back on the water with it since I pulled it. It did not get any worse after running it the 20-30 minutes after the Seafoam treatment. I was afraid of doing some damage to the motor at that point so wanted to get it off the water to diagnose. Going to swap out the fuel filter and check the gas for contamination first, then go through the carb suggestions. Hope to maybe get it on the water tomorrow morning for a warm up test as you suggested.

Thanks for the help!
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Old 07-13-2019, 04:34 PM
quattrotto quattrotto is offline
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Join Date: Jul 2018
Boat: 1991 Prostar 190
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Posts: 40
Pulled the fuel filter and filter is clean and no water to speak of....replaced with new anyway.

Put the Vacuum Secondaries through their range of motion and although they opened, there seemed to be a bit of resistance through the range....wasn't smooth operation. Before I take it to the lake tomorrow am, going to run it in the driveway and test for vacuum leaks around the gaskets. Then take a look at the Vacuum Secondaries on the water, as what I've seen you need full load for them to work properly.

Question though, seems the secondaries only engage under heavy load....my issues arise with very little throttle from idle all the way to 2000 rpm. Then when I would think the secondaries would engage, it runs great. Maybe I'm missing something in how they operate?

Any other thoughts at this point? Thanks!
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  #6  
Old 07-13-2019, 06:17 PM
waterlogged882 waterlogged882 is offline
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Boat: 93 190
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Quote:
Originally Posted by quattrotto View Post
Question though, seems the secondaries only engage under heavy load....my issues arise with very little throttle from idle all the way to 2000 rpm. Then when I would think the secondaries would engage, it runs great. Maybe I'm missing something in how they operate?

Any other thoughts at this point? Thanks!
Normal operation for the secondaries. They don't open until a higher RPM. Nothing like running up the river and gouging on the throttle to hear the secondaries open and redline the tach....

My suggestion is a new carburetor. In particular if that is an OEM carb or by chance a Holley 4010 carb. You will fair very well with the marine Holley 4160 600 cfm.

I found one last September at Discount Inboard Marine for under $600 shipping and tax (for TN) included using their 10% discount code "USA."

Make sure you have a good coil and a good EI module. They both can deteriorate over the course of time and heat.

Check the proper operation and setting of the electric choke.

Monitor the engine temperature as well. If it is running a little hot, that is another point of consideration for an easy (and unexpected) fix. Poor exhaust hoses (internal collapse) will affect the performance as well, all unsuspecting until complete failure (internally).

.

.
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Last edited by waterlogged882; 07-13-2019 at 08:05 PM.
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  #7  
Old 07-13-2019, 06:27 PM
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thatsmrmastercraft thatsmrmastercraft is offline
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You have done everything right so far but mention your timing and ignition type. Points or electronic ignition? What is your timing set at?

I'm going to guess that you have points that are completely worn out. If so, replace them ans set with a dwell meter.

One note about a new carb.....it will come with the wrong accelerator pump nozzle, wrong accelerator pump cam, and wrong secondary diaphragm spring for your application.
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$125 LED TRAILER LIGHT PACKAGE - FREE SHIPPING
REBUILDING HOLLEY MARINE CARBS - $325 DELIVERED
REBUILT COMPLETE MARINE HOLLEY 4160 CARBS $549 DELIVERED
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  #8  
Old 07-13-2019, 06:33 PM
waterlogged882 waterlogged882 is offline
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Quote:
Originally Posted by thatsmrmastercraft View Post
You have done everything right so far but mention your timing and ignition type. Points or electronic ignition? What is your timing set at?

I'm going to guess that you have points that are completely worn out. If so, replace them ans set with a dwell meter.

One note about a new carb.....it will come with the wrong accelerator pump nozzle, wrong accelerator pump cam, and wrong secondary diaphragm spring for your application.
Fortunately, Discount Inboard sent the new one to me with all of the correct parts installed.

The odd parts are typically installed when bought from an auto supplier such as Summit Racing or Jegs, etc....or so that has been my experience...but you have a valid point regardless.

I think the 1991 model came with OEM electronic ignition. I could be wrong....

.
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Old 07-13-2019, 06:45 PM
waterlogged882 waterlogged882 is offline
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Boat: 93 190
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Quote:
Originally Posted by thatsmrmastercraft View Post
You have done everything right so far but mention your timing and ignition type. Points or electronic ignition? What is your timing set at?

I'm going to guess that you have points that are completely worn out. If so, replace them ans set with a dwell meter.

One note about a new carb.....it will come with the wrong accelerator pump nozzle, wrong accelerator pump cam, and wrong secondary diaphragm spring for your application.
Do you install the #28 nozzle, the 31, or 37, etc...? And the cam color??

.
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Old 07-13-2019, 07:18 PM
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thatsmrmastercraft thatsmrmastercraft is offline
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Quote:
Originally Posted by waterlogged882 View Post
Do you install the #28 nozzle, the 31, or 37, etc...? And the cam color??



.


Purple spring, white cam, #25 nozzle, 5.0 power valve, and #66 jets.

Forgot to mention power valve and jets are usually wrong. Most of these carbs are set too rich.


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CUSTOM WHEEL & TIRE PACKAGES


CUSTOM DECALS - EMAIL FOR MORE INFO

$125 LED TRAILER LIGHT PACKAGE - FREE SHIPPING
REBUILDING HOLLEY MARINE CARBS - $325 DELIVERED
REBUILT COMPLETE MARINE HOLLEY 4160 CARBS $549 DELIVERED
Email - [email protected]
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