I have a 2000 Searay Sundancer 340 with 7.4 MPI V-drives. It won't go above 4000 RPM. At 4000 RPM, it is going about 21 knots. The bottom is clean and I just had a full service with compression check on the engines. I can't figure out what is wrong with it. Any suggestions?
340DA 21 knots @ WOT???
- Thread starter mmmendoz
- Start date
Alex D
Active Member
mmmendoz said:
Something is seriously wrong with something. first the engines should turn more like 4200 to 4400 rpm and at 4000 rpm your SOG should be close to 30 kts in that boat. Take a handheld GPS to check your speed
Converse48
Well-Known Member
Not that this is much help: That ain't right!
My brother has a 320 with 5.7s in it, and she cruises easily at 27-28 knots.
My brother has a 320 with 5.7s in it, and she cruises easily at 27-28 knots.
brimanst
Member
Any chance you ran aground, or hit something with your prop? Trust me a slight variation from normal can be big difference.
capz
New Member
There are so many reasons to lose WOT. Start with the easy checks. Inspect the props for damage and the hull for growth. Check for crimped fuel lines. Pop the cover off the flame arrestor and clean if necessary. Visually inspect your plugs. Look for carbon deposits on the tips. If you can get your hands on a timing light, you can check each cylinder to see if spark is rock steady, intermittent or no spark at all. If you can borrow some basic diagnostic tools (fuel pressure gauge, compression tester, multimeter), I'm sure folks here could walk you through some tests.
capz
New Member
BTW what was included with "full service with compression check". Did the problem arise right after you got the boat back?
Is the boat new to you and has never been able to turn more than 4000 RPM? If so, then you may also want to check the props that are on the boat as well. Sea Ray has a prop chart that you can download that will give you the correct size and pitch props for your boat. http://www.searay.com/prop_charts.asp?agree=1&year=2000 It could be you have the wrong props on the boat.
If this is a new problem which just developed, give us a little history behind it.
If this is a new problem which just developed, give us a little history behind it.
Bounty
New Member
- Apr 12, 2007
- 82
- Boat Info
- Sundancer 340 mfg. 2000
Zodiac dinghy w/15HP Yamaha outboard
Village Marine Watermaker
Esterbeke
- Engines
- 454 Mercruiser V Drives
Alex D said:
I agree. I have precisely the same boat and engines and it cruises at or around 27 knots at 3800-4000 RPMs. Be sure that you are using a GPS to measure speed, on a calm sea.
sdrevik
New Member
Definitely check the ignition wires and plugs- I had one cylinder that wasn't even firing and had loss in RPMs and speed (and a nice fuel smell in the exhaust, that would be a confirming symptom).
