Mercruiser 470 bogs down at 2200RPM

[carver2557]

Hi,

looking for a little help if possible. i have a 1989 Carver with twin 470. Had it in this winter to get the out drives rebuit and Helm controls replaced with all the cables from the contols. took it out on the water and the port motor would bog down at 2200 RPM. the gas had been drained while at the shop, cabs rebuilt and compression was tested. Resulkts of this are as follows, Cyl #1-148psi, #2-170psi, #3-150psi and #4-150psi. Aside from the #2 cyl bieng a little high this does not seem bad to me. a leak down has not been at this time. could there be a bad fuel pump on this motor? Could the high compression in the #2 cyl be an indicatror of a bigger proplem?Any insight?

Thanks

 

[Don S]

Re: Mercruiser 470 bogs down at 2200RPM

Did you have this problem before all that work was done?

List of possible causes of low WOT (Wide Open Throttle) rpm.

In no particular order

Engine Won't Reach Operating RPM. Check

1. Fuel condition. Type and Octane possibly old fuel
2. Propeller pitch or diameter, damaged blades
3. Restricted fuel pickup tube or anti siphon valve Fuel System Test
4. Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
5. Marine growth on hull and outdrive
6. Wrong gear ratio in outdrive
7. Restricted carburetor air intake (clogged flame arrestor)
8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
9. Poor cylinder compression Compression Test
10. Carburetor defective, or wrong type.
11. Fuel pump pressure and vacuum
12. Boat overloaded, improperly loaded, or improperly trimmed.
13. Engine Overheating
14. Engine timing and ignition system operation
15. Remote control cables and linkage for proper travel to open throttle plates fully.

 

[55evinrude]

Re: Mercruiser 470 bogs down at 2200RPM

I would do that compression test one more time again just to be sure that those numbers are correct. its just strange that #2 is 20psi more than the rest. other than that everything Don S said i would look at/ try

 

[tylermcclintock]

Re: Mercruiser 470 bogs down at 2200RPM

Could be fuel or electrical. Change fuel/water seperator. Check fuel flow. Check all your grounds. I had a similar problem with my 406 stroker and it was caused by a wire that came off alternator and was grounding itself and sending electrical system haywire. It would get to about 2000 RPM and sputter and cough.

 

[Bifflefan]

Re: Mercruiser 470 bogs down at 2200RPM

Hi,

cabs rebuilt

Thanks

The carbs is the question here.
I think that one on the motor in question is not working properly. Have the guy that rebuilt it look at it again. There is probably something in the float bowl or he forgot a jet or something. If I had to guess Id say that one of the air bypass' was plugged with some gook when they were dipped that did get blown out.
Dont get to caught up with the compression numbers, they will give you gray hair for no reason. Your are fine.

 

[a1nowell]

Re: Mercruiser 470 bogs down at 2200RPM

Besides the carbs that bifflefan mentioned, I would start with #15 on Don's list. One or two twist of the barrel screw can make all the difference in the world. $.02

 

[carver2557]

Re: Mercruiser 470 bogs down at 2200RPM

so here is what i have found out so far. Took the boat back to the mechanic and they replaced a cuople of screws that went through the three sections of the carb that hold it all together. this stop the carb from leaking. after getting it back from them i installed the pertronix ingnition on both engines. check the timing and boy was that something to see how off this was. set the timing where it needs to be. Changed the fuel filters, what a pain this was. Got it in the water and the boat ran at 4k RPM and well. thinking of going from the 19 pitch prop to a 17 pitch just to get a few more RPMs. After getting back home and taking a look at everything i noticed that the oil in the Port engine is a little mikly, getting water from somewhere. Most likey the cam seals rom what i have read on these engines. Another thing is the exhaust Bellows are seperated and cracked so need to replace. what is the best way to do this? do i have to remove the drives or can this be done with the drives on? One last thing that i noticed when on the water that the boat took on a little water not a lot but would like to find where it is coming from. looks like it was coming from under the starbroad engine area. Is it possible that the starbroad transome seal is bad? i cant thing of anywhere else the water is coming from. like i said its not a lot i was on the lake for over three hours and the bilge kick on four times or about 15 seconds.

Thanks for the advice that got me to this point,

 

[ctriverhouse]

Re: Mercruiser 470 bogs down at 2200RPM

"check the timing and boy was that something to see how off this was. set the timing where it needs to be.

I was looking at a 1988 Carver w/twin 3.7 180HP motors The sticker on the motor calls for 8 degrees BTDC. I understand Merc
changed it to 4 degrees BTDC due to poor gas. Pistons one and four were burning up. Was wondering what you used for timing number
and what the sticker read on the 89.

 

[Bondo]

Re: Mercruiser 470 bogs down at 2200RPM

so here is what i have found out so far. Took the boat back to the mechanic and they replaced a cuople of screws that went through the three sections of the carb that hold it all together. this stop the carb from leaking. after getting it back from them i installed the pertronix ingnition on both engines. check the timing and boy was that something to see how off this was. set the timing where it needs to be. Changed the fuel filters, what a pain this was. Got it in the water and the boat ran at 4k RPM and well. thinking of going from the 19 pitch prop to a 17 pitch just to get a few more RPMs. After getting back home and taking a look at everything i noticed that the oil in the Port engine is a little mikly, getting water from somewhere. Most likey the cam seals rom what i have read on these engines. Another thing is the exhaust Bellows are seperated and cracked so need to replace. what is the best way to do this? do i have to remove the drives or can this be done with the drives on? One last thing that i noticed when on the water that the boat took on a little water not a lot but would like to find where it is coming from. looks like it was coming from under the starbroad engine area. Is it possible that the starbroad transome seal is bad? i cant thing of anywhere else the water is coming from. like i said its not a lot i was on the lake for over three hours and the bilge kick on four times or about 15 seconds.

Thanks for the advice that got me to this point,

Ayuh,... If the exhaust bellows is Bad,.... So are the rest of the rubber parts in the transom...

Ya gotta pull the drive to replace 'em.... I'd do the lower shift cables at the same time, while it's apart...

 

[carver2557]

Re: Mercruiser 470 bogs down at 2200RPM

"check the timing and boy was that something to see how off this was. set the timing where it needs to be.

I was looking at a 1988 Carver w/twin 3.7 180HP motors The sticker on the motor calls for 8 degrees BTDC. I understand Merc
changed it to 4 degrees BTDC due to poor gas. Pistons one and four were burning up. Was wondering what you used for timing number
and what the sticker read on the 89.

On my "89" Carver the sticker shows 4 dergress BTDC. i would set at this degree. Just to let you know my Port engine was set 2 degrees ATDC and the Starboard engine was set at around 11 degrees BTDC, not even sure how this boat started in the first place. The shop that did the out drive rebuild and engine service will never see this boat agian , bunch of Hacks.