How much more RPM gain with pitch

[3chap0]

My son has a 2002 Merc. 60hp bigfoot, I dont know the pitch that is on his prop now, but he is only getting 3500rpms on it now. Would a different prop get him up to 5500? We thought he had a bad coil, and replaced all the coils, Had carb kits put in, changed fuel filter, sea foam, stay build, new spark plugs. After replacing coils and everything, went 30 seconds at 5500rpms in gear then back down to 3500rpms, he can rev it up when in neutral to 5500. After going up to 5500 for 30 seconds in gear, makes me believe that it is not the prop. Has anyone else had a problem similar to this?

 

[Scott Danforth]

Re: How much more RPM gain with pitch

what is the quality of your fuel.
when was the last time the carbs were cleaned and synced?
is this the first time that the engine is not going to WOT, or has it always been like that?

what is the motor on? is your motor at the correct height? there is no load on the engine in neutral. it will rev to the top even with a few spark plugs pulled while in neutral.
the fact that you state it goes to WOT for about 30 seconds then comes back down, it doesnt sound like a prop issue, however a fuel system issue

before you go any further, read this first: http://forums.iboats.com/showthread.php?t=287818

other suggested reading:
http://forums.iboats.com/showthread.php?t=283363
http://forums.iboats.com/showthread.php?t=188767
http://forums.iboats.com/showthread.php?t=295070

 

[Georgesalmon]

Re: How much more RPM gain with pitch

Probably right the prop is not the problem if you got 5500 for a bit. Don't see that you rebuilt the fuel pump? Might take a look at that. And, 5500 in neutral doesn't mean anything.

 

[3chap0]

Re: How much more RPM gain with pitch

Probably right the prop is not the problem if you got 5500 for a bit. Don't see that you rebuilt the fuel pump? Might take a look at that. And, 5500 in neutral doesn't mean anything.

Sorry for the dumb question, after thing about it. No load so it doesnt mean a thing when revved in neutral . Going to check the fire, with a sparkplug checker again when we get back out to the lake. When he first got the 24' pontoon boat it ran good. If we have good spark from these new coils, then we will probably some how check the fuel pump. Sorry about the prop question...

 

[Scott Danforth]

Re: How much more RPM gain with pitch

if the motor is too deep, it will not spin up to WOT. if this just started happening, are the toon' tubes filling with water? is the motor on an adjustable transom, and has its position been changed?

 

[emoney]

Re: How much more RPM gain with pitch

You can easily check the fuel pump diaphram before you take it out next. There's one flat-head screw holding the fuel pump cover on, take that off and you'll see the diaphram. If it's torn or cracked/flaky, then you need to replace it. Did anyone run a compression test ever?

 

[82rude]

Re: How much more RPM gain with pitch

if you can reach it ,put your hand behind the tac and giggle the wires maybe a connection is loose .it happed to me and drove me batty for awhile as it diddnt do it all the time.

 

[3chap0]

Re: How much more RPM gain with pitch

Dont think the toons are filling with water, and the motor has not been repositioned. Going to check spark, then diaphragm in fuel pump. I dont have a compression checker, but will find someone that does. I talk to a mechanic while ago, told him the problem. He was leaning toward the switchbox or trigger. I didnt think these went out that often. Especially for one cylinder. thanks for the replies and for anymore...

 

[steelespike]

Re: How much more RPM gain with pitch

If your doing it yourself you need a factory repair manual and you need to follow the ignition trouble shooting of each component.
If it goes to 3500 like you flipped a switch I would suspect an ignition component.Maybe as simple as a plug wire loose,damaged or corroded.