low top speed on 05 340 sportsman with 8.1"s

[d. stevanus]

maiden vogage today and getting up on plane starboard engine seemed to be behind by a few hundred rpm.. at WOT port side was revving 4700 and starboard at 4450... im told normal is between 4400-4600 for the 8.1"s.. problem is i was only getting 30mph and research shows this boat should run 38-42mph at WOT... i purchased this boat in the fall from CT and it only has 65 hrs.. some previous maintenance reports showed excessive barnacles on props and shafts from not being used.. this was all cleaned at time of my survey being done.. could the low speed thing be a prop issue????? looking for some thots....

thanks in advance

 

[mainstream]

Could be the running gear when I got my boat as a left over it had 42 hrs on it. I had the same issue it was my plugs were fouled probably from the demo hrs and not being run. And the thing was it would only miss fire under load I had my mech in the engine room with his scan tool attached when he found the problem. Just my .02 good luck.

 

[party of 5]

at WOT I run at about 4660 rpm and 38 to 39 mph. at about 3700 to 3800 i'm running 30 mph I think. I would have to check. I would check the props. If you run one motor at a time at WOT with the other one in neutral. just for a short time to see what the difference is in rpm. you can pm if you want I have some other ideas. good luck. steve

 

[Jimmy Buoy]

Barnacles and growth on the props... in Lake Erie... in May... The boat probably couldn't have even been in the water long enough this year to accumulate any significant growth. The water is still less than 65 degrees making less than ideal growing conditions for algae. No barnacles in fresh water either, just zebra muscles and even they are not that aggressive.

I'd be looking at plugs/wires then props as being the issue.

 

[capecodcruiser]

DO NOT run the engine in neutral at WOT! To many reasons to go into here, just don't do it.

at WOT I run at about 4660 rpm and 38 to 39 mph. at about 3700 to 3800 i'm running 30 mph I think. I would have to check. I would check the props. If you run one motor at a time at WOT with the other one in neutral. just for a short time to see what the difference is in rpm. you can pm if you want I have some other ideas. good luck. steve

 

[src]

DO NOT run the engine in neutral at WOT! To many reasons to go into here, just don't do it.

I think you misread that. My surveyor did this: With one engine in neutral, take the other to WOT. Record top RPMs and back off. With second engine in neutral, take the first to WOT, record RPMs and back off. He was checking to see that the fully loaded WOT on both engines was within about 100-150 RPMs.

 

[d. stevanus]

barnacles and growth when it was in stratford CT last year.. not lake erie....lol... mechanics are going to check props and engines today... thanks for everyones input...

Barnacles and growth on the props... in Lake Erie... in May... The boat probably couldn't have even been in the water long enough this year to accumulate any significant growth. The water is still less than 65 degrees making less than ideal growing conditions for algae. No barnacles in fresh water either, just zebra muscles and even they are not that aggressive.

I'd be looking at plugs/wires then props as being the issue.

 

[capecodcruiser]

I apologize, I did read it wrong, too early in the morning! But still a little unsettling that you would run one motor(in gear, under load) to WOT throttle with the other in neutral. Just strikes me as an odd thing to do, but what do I know!

 

[src]

My understanding of the procedure is that it prevents a strong engine from "carrying" a weak one, giving a false reading of its true capabilities. And he only ran it like that just long enough for the RPMs to stabilize. No more than 15-20 seconds as I recall.

 

[party of 5]

DO NOT run the engine in neutral at WOT! To many reasons to go into here, just don't do it.[/Q

put one in gear and run at wot . one side at a time . thank you for correcting me. this will show each motor under a load by itself