Yanmar 3GM30FC not getting full RPM's

[vsfoster]

Hello all, I recently purchased a 1983 Newport 30 Mark III, While out a couple weekends ago I was out motoring and could only get ~ 2000 RPM and on occasion the RPMS would drop. I think I may have some water in the line but what concerns me is the engine manual says I should get ~ 3600 RPM.

Any thoughts?
Thank you.

 

[kappykaplan]

When was the bottom cleaned? Same question for prop shaft and prop.

 

[vsfoster]

Actually I need to get a bottom job. I am planning on getting the pressure wash and paint in 3 weeks.

 

[Benny17441]

Basics first, is the tachometer working well and accurate? Have you noticed a loss of power and/or speed? If the engine and boat are running well, check the tachometer contacts. Is the engine smoking at wide open throttle? A fouled prop can cause loss of RPM together with smoking. The other common causes are 1) clogged fuel filters and strainers, 2) fouled exhaust mixing elbow 3) clogged air intake tube 4) clogged fuel tank vent.

 

[Ralph Johnstone]

Before you do the basics, do the basic basics first .

Does the engine reach 3600 RPM in neutral ?

 

[vsfoster]

Before you do the basics, do the basic basics first .

Does the engine reach 3600 RPM in neutral ?

Negative.

 

[Davidasailor26]

Negative.

That eliminates bottom or prop fouling, or transmission issues. Most common causes still on the table are tachometer (check with a cheap optical tach), exhaust elbow (any smoke in the exhaust?), or fuel delivery.

 

[dmax]

Add the throttle cable to the list of things to check.

 

[Ralph Johnstone]

Negative.

How negative ?

Most common causes still on the table are tachometer (check with a cheap optical tach), exhaust elbow (any smoke in the exhaust?), or fuel delivery.

Meh, can't get too excited about either the exhaust elbow or fuel delivery as the problem. It only takes a microscopic drop of additional fuel to drive an engine to 3600 RPM with no load. If it can idle, it can probably go to 3600 RPM in neutral even with mixing elbow or fuel delivery problems.

My vote is either a defective tach not registering, or slightly ahead of that might be the throttle cable. Got to check the tach before you can check the throttle cable.

Next step (after the tach) is to disconnect the throttle cable and move the governor adjust with your finger to see if you make 3600 RPM in neutral.

Let us know and we'll go from there.

 

[vsfoster]

Basics first, is the tachometer working well and accurate? Have you noticed a loss of power and/or speed? If the engine and boat are running well, check the tachometer contacts. Is the engine smoking at wide open throttle? A fouled prop can cause loss of RPM together with smoking. The other common causes are 1) clogged fuel filters and strainers, 2) fouled exhaust mixing elbow 3) clogged air intake tube 4) clogged fuel tank vent.

I am not sure about the TACH but the engine does not sound as if it is running above 2000. The engine does smoke at full throttle and i suspect that one of the other issues is occuring.
thank you.

 

[vsfoster]

How negative ?


Meh, can't get too excited about either the exhaust elbow or fuel delivery as the problem. It only takes a microscopic drop of additional fuel to drive an engine to 3600 RPM with no load. If it can idle, it can probably go to 3600 RPM in neutral even with mixing elbow or fuel delivery problems.

My vote is either a defective tach not registering, or slightly ahead of that might be the throttle cable. Got to check the tach before you can check the throttle cable.

Next step (after the tach) is to disconnect the throttle cable and move the governor adjust with your finger to see if you make 3600 RPM in neutral.

Let us know and we'll go from there.

I will disconnect the cable and see what happens when I adjust the governor manually.
The salesman said that the owner took it out often, but when i talked to my new neighbor in the marina, he said it had been sitting for two years. I suspect that i will need to clean all of the fuel line and components.

 

[kloudie1]

Note about the small amount of fuel to get to 3600 unloaded. That is true, but on a diesel, the governor may be keeping it from going there. (probably not the problem on this)
The shop manual on this site kinda talks about that stuff. Go to "Owner Resources" then "General Downloads" then scroll down to the Yanmar manuals. I agree with the other posters about prop and bottom and fuel tank vent and intake .