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Old 08-06-2018, 08:36 AM
caffn8r's Avatar
caffn8r caffn8r is offline
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Join Date: Apr 2018
Boat: '87 PS 190
Location: southeast
Posts: 38
Idle issue

I'm sure this has been asked before, but a fairly intensive search of the forum did not quite cover my issue. I have an 87 prostar with the 351 and a Holley carb. I bought the boat in fairly poor condition after it having sat for probably 15 years or so. After thoroughly going through it mechanically, I have put it in the water twice. Each time it has started and ran nearly perfectly, EXCEPT, after it has run for a few minutes the idle goes up a couple hundred rpm's and won't come back down. Here is a list of what I've done:
1. Rebuilt carb (thanks thatsmrmastercraft)
2. Replaced ALL fuel system components, i.e. lines, filters, pump, pickup
3. New Pertronix distributor and coil, new spark plugs and wires
4. Timing is set at 6 btdc @1000rpm
5. I adjusted the idle screw back to 800 rpm
6. Engine starts, runs, accelerates smoothly. Temp is steady and oil pressure is good.
7. I have checked for vacuum leaks, but not once it is up to temp and running at the lake.

So, once on the water and after it has run for a minute or two, the idle increases to 1200 rpm's and won't come back down. i was able to back the idle screw out and get it to 1000 rpm, but that was the best it would do. I tried wiggling the throttle handle around and manually pushing the throttle plate closed. nothing works. Any ideas or suggestions??? Please???
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Old 08-06-2018, 04:45 PM
Cumminscj Cumminscj is offline
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Join Date: Oct 2016
Boat: 86 Magnum Skier
Location: Southeast
Posts: 281
Disconnect the throttle cable and see if the problem persists. Sometimes the cables will hang them open and no amount of adjusting the carb will fix it.
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351, fast idle, holley carb, throttle

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