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View Full Version : Loss of Power above 1500 rpm


JBB
08-19-2009, 06:54 PM
Let me explain what's going on and then I have a few questions. I have an '88 prostar with a 351 Indmar. Cranks and idles fine. Throttle to around 1500 rpm and starts bogging, more throttle and it starts slowing down (i can't even plane). Rebuilt carb, changed fuel filter, and checked fuel pump (6psi) and it's still the same. Ordered tune-up kit, plugs, wires, and will check timing (needs to be done anyway). Going to bypass on-board fuel tank and main fuel line to rule those out.

1. Is there anything else I can try if the above does not fix it?
2. I know that the secondaries aren't opening but i read somewhere on here that they don't open until around 3000 rpm. Is this correct?
3. I have access to an auto holley 4160 to further rule out carb. If so, I'm assuming the vacuum secondary is different and will actually have to be tied into the manifold somehow. Anybody tried this?


Thanks for any help. It may be worth noting that this occurred after it sat up for a good while.

TMCNo1
08-19-2009, 07:03 PM
Let me explain what's going on and then I have a few questions. I have an '88 prostar with a 351 Indmar. Cranks and idles fine. Throttle to around 1500 rpm and starts bogging, more throttle and it starts slowing down (i can't even plane). Rebuilt carb, changed fuel filter, and checked fuel pump (6psi) and it's still the same. Ordered tune-up kit, plugs, wires, and will check timing (needs to be done anyway). Going to bypass on-board fuel tank and main fuel line to rule those out.

1. Is there anything else I can try if the above does not fix it?
2. I know that the secondaries aren't opening but i read somewhere on here that they don't open until around 3000 rpm. Is this correct?
3. I have access to an auto holley 4160 to further rule out carb. If so, I'm assuming the vacuum secondary is different and will actually have to be tied into the manifold somehow. Anybody tried this?


Thanks for any help. It may be worth noting that this occurred after it sat up for a good while.


Don't install a street carb on a boat, plain and simple!

rholmes
08-19-2009, 07:07 PM
Did you check the filter at the fuel pump, located starboard side front of the motor?

AFX-30
08-19-2009, 07:08 PM
I had a problem losing power before above 1500 RPM's and it turned out to be a bad exhaust lk.

JBB
08-19-2009, 08:33 PM
Yes, tha'ts the filter i was refering to.

Where was the exhaust leak?

katmat
08-20-2009, 08:16 AM
I had a 88 prostar w/ the 351 ford engine. I had a similar problem after a tune up. The problem was that the spring tension on the points I bought was not strong enough (standard ignition). The points would "float" above 1800 rpm. I replaced the points with a good brand & the problem was solved!
Matt Murphy

okrazerback
08-20-2009, 01:57 PM
I have a 1998 prostar 190 with the vortec 5.7 lt. and when I give it gas it cuts out. Its real bad in the corners or when Im cutting in hard on my board. I replaced the roter and wires and plugs and hoses. I also checked the pressure on the fuel line and it was fine. Its been doing this for years and I cant figure it out. Is there somethings with these motors I need to check out that I am missing?

AFX-30
08-20-2009, 04:08 PM
The exhaust leak was coming off the silentmaster connections and exhaustmanifold seals. It was fine at idle but as soon as you put it under anykind of load it would start to stall out.

JBB
08-24-2009, 07:42 PM
I think i may have found the culprit. I inspected the exhaust from the back of the boat and found a small piece of the baffle toward the end of the exhaust. pulled that out, shined a light in and saw a bigger piece inside of the muffler that had broke and was essentially blocking any passage. I assume this would cause my systems. I'm going to run straight pipes for now to avoid the costs. Are there any effects this may cause to the engine that i should be concerned with?

Jesus_Freak
08-26-2009, 12:37 PM
I think i may have found the culprit. I inspected the exhaust from the back of the boat and found a small piece of the baffle toward the end of the exhaust. pulled that out, shined a light in and saw a bigger piece inside of the muffler that had broke and was essentially blocking any passage. I assume this would cause my systems. I'm going to run straight pipes for now to avoid the costs. Are there any effects this may cause to the engine that i should be concerned with?

MYMC has talked about this a few times. You might find it buried deep in http://www.mastercraft.com/teamtalk/showthread.php?t=21980.