RPM question 1972 Trojan

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BMac
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RPM question 1972 Trojan

Post by BMac »

I purchased a 1972 30' Searaider last year and we just finished our vacation up in Georgian Bay. Lots of fun and mostly sunny days. During the trip the most I could get out of the Twin 318's was about 3100 RPM's. In smooth water the top end was about 25 mph and in rough water about 18 mph at top end. Both engines were rebuilt about 450 hours ago and have given me no problems other the the RPM concern.
The owners manual states the engines max recomended rpm should be 4000.

Anyone have any previous problems like this ?
rossjo
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what RPMS

Post by rossjo »

What RPMS in neutral? Full revs?
Captain Ross, 2009 Trojan Boater of the Year
"Viva Mahia" F32 Cummins 6BTA diesels,
"Mack Attack" Chaparral 244 Fish, SeaPro 180, McKee 14, Montauk-17
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JuiceClark
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RPM mystery

Post by JuiceClark »

Other than the obvious things like barnacles on the props or oversized props, I have one unlikely thing. One time I took a piece of junk Sea Ray I had out and could only get about 3000 rpm. I kept checking the engines because I knew the bottom was clean.
It turned out the trim tabs had clogged up and were frozen in the down position dragging my ass across the sea. The SeaRay design was so crummy, I couldn't even tell it was plowing a bit. You'll be able to feel it plowing in a Trojan.

Good luck,
Tony in Fort Myers, FL
ronski
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low rpm"s

Post by ronski »

I had a problem like that They replaced the filters tuned the engines replaced the carbs and finally they replaced the distributers and my power was back up to specks
BMac
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RPM'S

Post by BMac »

The RPM's in neutral are ~ 750. I put on a snorkel and there is no buildup around the props. I will check the trim tabs next weekend (did not think of that) . The mechanic is suggesting carb rebuilding, not being a mechanic I just thought it odd both engines at full throttle are still the same. I thought if it was a mechanical problem the engines might perform differently.

Thanks for the suggestions.
Bill
rossjo
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neutral

Post by rossjo »

Can you get fll revs (4000+) in neutral? This is a quick 1st testt - then you know if your problem is very basic (alternator?) or a load issue.
Captain Ross, 2009 Trojan Boater of the Year
"Viva Mahia" F32 Cummins 6BTA diesels,
"Mack Attack" Chaparral 244 Fish, SeaPro 180, McKee 14, Montauk-17
Image
ronski
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Location: chicago

Post by ronski »

My engines did have different top rpm's port ran to 2900 at the begining and the starboard ran at 3100. They were close. The most improvement came from carbs,and distrubuters
rossjo
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Neutral revs

Post by rossjo »

You only got 2900 ad 3100 RPM in neutral @ full throttle?

If so - you've got ignition or fuel delivery issues!
Captain Ross, 2009 Trojan Boater of the Year
"Viva Mahia" F32 Cummins 6BTA diesels,
"Mack Attack" Chaparral 244 Fish, SeaPro 180, McKee 14, Montauk-17
Image
ronski
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Location: chicago

Post by ronski »

NO!NO!

This was with the engines engaged. I was running the boat on a calm river.
rossjo
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so

Post by rossjo »

what RPMS do you get in NEUTRAL?
Captain Ross, 2009 Trojan Boater of the Year
"Viva Mahia" F32 Cummins 6BTA diesels,
"Mack Attack" Chaparral 244 Fish, SeaPro 180, McKee 14, Montauk-17
Image
ronski
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Location: chicago

Post by ronski »

neutral 800 at idel to a clean 4400 redline
BMac
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RPM's

Post by BMac »

Engines went to 4700 in Neutral and the trim tabs were operating properly.
Bmac
rossjo
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Whos on 1st?

Post by rossjo »

Ronski and BMAC - we have 2 threads going here - I think Bmac started this - so I'll conitnue with him ...

If both turn 4700 RPMS in neutral - you sound like you're getting fuel and spark (possibly weak). What kind of voltage do you get onthe primary side of the coil? You need 12-14 volts (10-11 won't work) to pull a load.

OIl pressures strong at this RPM (20PSI+). 30+PSI @ idle when cold?

Smoke (white, black)?

You need to measure your cynilnder pressures - they should all be within 5 PSI of each other. Any cylinder down 5PSI lower than others indicates a problem.

Do you have good plugs and wires?

When were the carbs rebuilt (what type are they)?
Captain Ross, 2009 Trojan Boater of the Year
"Viva Mahia" F32 Cummins 6BTA diesels,
"Mack Attack" Chaparral 244 Fish, SeaPro 180, McKee 14, Montauk-17
Image
BMac
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Joined: Tue Oct 11, 2005 7:50 pm

Post by BMac »

The engines and carbs were rebuilt ~ 450 hours ago. The oil pressure is good. As far as voltage, carbs, wires and the pressure in the cylinders go I will have to ask the marina to check that for me.
The exhaust was white on startup.

Thanks
Bill
rossjo
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exhaust

Post by rossjo »

Is the exhaust clean or black (or different from side-to-side) under full load?

Plug wires don;t last long in the marine environment - I'd replace if they are over 5 years old just to be safe anyway. May not fix, but its cheap insurance. I also prefer the Champion SS plugs - they won't rust in place.

Compression check is imperative - if you've got a lot of hours, you may need a valve job ...
Captain Ross, 2009 Trojan Boater of the Year
"Viva Mahia" F32 Cummins 6BTA diesels,
"Mack Attack" Chaparral 244 Fish, SeaPro 180, McKee 14, Montauk-17
Image
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