6-71 TI rpm

[shaun1010]

I recentky bought a 1988, 38 hatteras with the J&T 6-71 TI engines. The port side works just fine. The starboard however does not cross 1600 rpm. I have check all the fuel filters, blown out the fuel line from the tank with a compressor and cleaned the intercooler but nothing helps. The temp and pressure are normal. The engine smokes more than the port one when the boat is planing but disappears soon after that. Can anyone suggest a reason for this. i would be very thankful.

Shaun

[REBrueckner]

I assume engine runs smoothly, not excessive smoke? When you trialed the engines before purchase, was the engine running normally...or is this an "old" problem?

Do both engines have the same no load (in neutral) RPM?. Is the Morse throttle cable properly connected at the controls and the engine? Is the prop fouled with marine growth...or a rope.....likely that should be evident from vibration???

You can also check each exhaust outlet to the exhaust manifold with an infrared thermometer...a significantly colder one will indicate a cylinder not firing, but likely you should be able to feel some vibration, some missing as well...

[shaun1010]

Rob . Thank you.

I had my mechanic adjust the throttle directly from the engine while the boat was running and we still could not get more than 1600 rpm so i dont think the cable is the problem. There is also no vibration at all and the bottom of the boat has been cleaned less than a week ago. No excessive smoke either. The engine with the problem idles about 300 rpm less than the good engine.

The boat did not have this problem when I bought it but started about a month after. Someone told me that the problem may lie with the govenor box or the engine may need a top end adjustment. Any other ideas?

[Avenger]

Idles 300 RPM less? Like 350?!?! It would probably stall when you put it in gear. Are you sure the tach is good?

If it can reach rated no load in neutral it probably doesn't have a governor problem, so outside of such a mechanical problem it's likely to be a fuel problem. Try getting a clean container of diesel fuel and run your supply and returns right from the engine to the can, bypass as much of the fuel system as possible and see what happens. Also check for any air restrictions, like an emergency air shutdown partially closed (not sure if you have those or not).

[mobilemn1]

You said you just recently did some work to the bottom, the boat out of water, did it begin this before or after the bottom work. Check the throttle cable at the bracket that holds the sleeve solid. I had one with broken end and it would move, but once it got to a certain spot the sleeve would move but nothing else would. Just a thought. Not knowing, but are the engines turboed. I had an engine one time that drove us crazy, no smoke under load, as a last resort I swapped a good turbo to it just to see, and wahla. Turns out the bearing in the turbo were about to go out and she just wouldn't turn up.

[shaun1010]

Scrod - I think your suggestions about the fuel is a great idea. We have had our problems with the quality of fuel here in Trinidad. The engines also do have the emergency shutdown, I will have the mechanic examine this as well.

Mobilemn1- The engines are turboed but the mechanic says since there is no smoke it should not be a turbo problem. Not sure myself.

Thanks Guys.

[REBrueckner]

All the above suggestions are good ones; because its cheap/fast/easy I'd see if the troublesome engine turns up rated RPM in neutral...likely about 2500 RPM....if NOT, while the engine is still running, disconnect the Morse throttle control and activate the engine throttle control by hand....if RPM's are still low, then I'd consider fussing with the governor...or confirming the tach reading....I did not suggest that initially since those things are more reliable than the items I mentioned.

Will a bad turbo permit reaching rated RPM in neutral?? I do not know for sure...

What does "check the fuel filters" mean. You should change ALL....

I'd not start with a tune up, but others may disagree, because its unusual for an engine to suddenly go out of "adjustment"...but its possible you have a faulty component....but many will result in excessive smoke and vibration, like a bad/clogged injector or stuck valve...

Fuel is always a potential issue, but usually will affect both engines unless you filled most recently only one engine supply.

You did not lose raw water cooling before this loss of RPM right?? If you did, a burned and bubbled exhaust hose could be causing back pressure and limiting RPM....Am unsure how much smoke such a condition would cause....

What else did the mechanic check?

[shaun1010]

I tried throttling up at no load and got the 2500 rpm. Next week I have a DD specialist coming in to check the top end alignment and the governor. I'll let you guys know how it worked out.

[APTL1]

I tried throttling up at no load and got the 2500 rpm. Next week I have a DD specialist coming in to check the top end alignment and the governor. I'll let you guys know how it worked out.

I have the same problem, what was the end result to fix the problem with yours?

[captcrunch]

i am looking at the same boat, overall how do you like it?