120 mercruiser wot only 2800rpms

[david r. lubinski]

Could use some advice was what to check next. Heres what I have 120 l/0 in 20 foot bayliner. Cannot obtain rpm higer than 2800revs when underway. Heres what I have done, new gas in tank. Checked fuel delievery system, all new fuel hoses, checked fuel tank pickup it is ok, new fuel/water seperator,new fuel pump with new pump filter, new strain screen at carb. New plugs gap.032 new points gap.022.checked advance weigths they are free and clean, new rotor and cap new wires, verified correct firing order, timming set at 8 degrees btdc at idle 850revs.,36btdc degrees at 4300revs in neutral at dock, new remanufactured carb, compression is 125psi. in each cylinder with cold engine, install new 15x17r prop. new gimble bearing, new u-joints Test are done with only one person aboard boat bascially bare Engine runs excellent at dock but test runs can only obtain 2800revs Outdrive is pre alpha, no unusual noise from outdrive. Hull is clean no marine growth. Sure would like to solve this problem
Engne is 4cyl. G.M. 153cu.in. engine.

 

[searay3]

Re: 120 mercruiser wot only 2800rpms

One more thing to buy, replace the coil. When all else looks ok, it could be breaking down under load. No real way to test it, but it's fairly cheap. Worked for me. Hit a rock, and the coil no longer worked in the upper rpm ranges.

 

[Don S]

Re: 120 mercruiser wot only 2800rpms

How long have you owned the boat? Has it ever reached full rpm's that you know of? Are you trimming the drive correctly? Has the drive been replaced and is it the proper gear ratio?
Also, 850 rpm at idle is too fast. Should be around 700. Will it idle that slow?

 

[david r. lubinski]

Re: 120 mercruiser wot only 2800rpms

searay3 you are correct coils do tend to break down under loads just slipped my mind wihile I was working on boat.Will install new coil when I get off rotation in 3 weeks.
Don S. I bought this boat this winter. I am third owner of boat have all paper work includling repairs starting from when first owner bought boat in portland. Even logs kept by both owners. Outdrive was rebuilt in 2003 in Anchorage. I have tried all angles of tilt allowd by tilt cylinder even used trim tabs to increase revs. No I do not know if boat has ever reached full rpm`s. Outdrive gear ratio is 1.98:1. Idle was a little high but it does idle down to has low as 600rpm`s. When off rotation I will get to Seward and change out coil and see if It improves if not will winterize and take up next spring.

 

[david r. lubinski]

Re: 120 mercruiser wot only 2800rpms

Sorry hit reply button to quick. Thank you to both of you for your help.

 

[Don S]

Re: 120 mercruiser wot only 2800rpms

Since it's never run at the proper speed, and the drive was rebuilt. I would say to verify the gear ratio. It sure wouldn't be the first with the wrong gears put in it.
Here is how to check it real quick.
Put the shifter in gear, pull the coil wire and turn the engine 2 complete revolutions (by hand). The prop should turn 1 complete revolution.