i think i know whats wrong BUT....is it the carborator?
 

this is the first year in the last 3 since ive owned my boat im finally using it due to repair after repair after repair.....anyways i was on the lake this past weekend seeing how fast i could get her up to.., this winter i did a full tune up on the engine and replaced the thermostat and prop did all the service on the outdrive. the engine sounds great. no knocks. no pings. not overheating....anyways idk if this is normal or maybe the carb needs rebuilt...my mariah is the orginal 1990 and its believed to be about 3400lbs with the 5.7 v8. My top speed is only 30 mph @ 4500 rpms. it has no problem getting to that speed and no problem getting to plane. could it be the carb? i see no reason why a 22 ft boat with this engine like that should only go 30 mph when my buddys late 80's overweight sea ray with the 7.4 has no problem with getting to 45mph. any suggestions?

Re: i think i know whats wrong BUT....is it the carborator?
 

should also mention the fuel filter is new , flame arrester was cleaned and the gas not only was new but was 89 octane. there was maybe 3 gallons left from the previous season but on top of 25 gallons of new i dont see how this could be an issue.

Re: i think i know whats wrong BUT....is it the carborator?
 

Fuel , Carb , Timing , Filters Even.
I'd check fuel filter or filters , check the timing , check to make sure choke isn't sticking or staying closed , go run it.
If that does nothing , I'd run a compression test on all cylinders. If that checks out rebuild the carb. Try it again.
Something else that comes to mind is make sure the flappers in the exhaust Y aren't stuck shut.

Just some ideas for you to kick around! :)

Re: i think i know whats wrong BUT....is it the carborator?
 

not sure how to check the timing, never really done it before but i can do the other items. if the timing was off wouldnt the engine make a racket? just curious. the engine has 550 hrs on it and it did sit for a number of years b/f i bought it so all of these could a issue.

Re: i think i know whats wrong BUT....is it the carborator?
 

Just a few degrees of timing off can affect the performance of the motor drastically.
You can rent a timing light at any of the name auto parts discount stores(Autozone , O'Riellys , Etc.)
Do a web search for timing adjustment and you can probably see the process on Youtube. :)
Do the stuff that doesn't cost a lot first.

Re: i think i know whats wrong BUT....is it the carborator?
 

I'm more inclined to think its a timing issue. I believe the correct timing setting for a carbed 5.7 is 10o BTDC.

And if you have a Thunderbolt V ignition here is the correct timing procedure:

Setting Base Ignition Timing
1. Connect timing light to number 1 spark plug. Connect timing light power supply leads (if applicable)
to 12 volt source.
2. Connect a shop tachometer to engine.
3. Using a jumper wire, connect the ignition system timing lead “13” (PUR/WHT wire) to a good engine
ground (–). This locks the ignition module into the “Base Timing Mode”.
4. Start engine and run at normal idle speed. Allow engine to reach normal operating temperature.
5. Aim timing light at timing tab, located on the timing gear cover and crankshaft torsional damper.
6. Adjust timing using the conventional method. IMPORTANT: Be sure to disconnect the jumper
wire from the ignition system test terminal before attempting to resume normal operations. If the
jumper wire is left in place, the ignition module will operate in the “Base Timing Mode”. This
means that the additional timing advance features would not function.
7. Make sure that the distributor has been tightened. Remove the jumper wire from the timing terminal.
8. Stop engine and remove timing light.
9. Remove the jumper wire from the timing

Re: i think i know whats wrong BUT....is it the carborator?
 

What pitch prop is on it?

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Re: i think i know whats wrong BUT....is it the carborator?
 

that is quite a bit to check the timing ....ill have to see if there is a video on it. i am not a mechanic by trade i can however follow instructions and read quite well thou. ;). And as far as the prop....that is also i good question. i can answer the question about my prop pitch this way.....i have no idea! i know i said i got a new one, it was actually redone to brand new condition. i think its original, this could be something to look at too. Actually ever since ive owned the boat i was never able to get it above these speeds but i was hoping with the work ive done would have helped. i will research all of these items see what i can figure out.

Re: i think i know whats wrong BUT....is it the carborator?
 

Sounds like you have two more things to look into with both the timing & the prop. I'd do the prop first since its the easy one. ;)

Re: i think i know whats wrong BUT....is it the carborator?
 

ok now that i learned something new today lets start here......my prop is a p19. like i said i was @4500 rpms and reaching 30 mph on a alpha 1 outdrive. 5.7 v 8. i have a stainless steel prop i have never used that is a p23. never used it cause i mostly go on the river and was told that they are not forgiving if you hit something....when i conducted this experiment i was on the lake. ill have to throw the stainless on at the lake see what happens b/f i dive into the timing issue.