Why am I getting low WOT rpms???

[jg480]

http://www.donzi.net/ubb/confused.gif Can someone tell me why I am getting low WOT rpms. I have an 87' 18' Donzi with a 350 mag with about 300 hrs. I am using what I believe to be the original prop (23' mercrusier cleaver) and I get only 4000 Rpms at wot. I have just replaced the the gimbal bearing and u-joint bellows since there was a hole in the old bellows and water was leaking through the gimbal bearing. upon reassembling the drive I found that the engine was about an 1/8" out of alignment. Is it possible for the misalignment and the wet bearing to sap 600 rpms or could there be additional problems? This is my first Donzi which I have only been able to use twice since purchassing in october so I am not sure what to expect with a "stock" setup. Any input would be a great help Thanks.

[onesubdrvr]

Misallignmet can definately cause a loss in RPM's, it puts additional strain on the coupling. More additional information would be helpful, such as what type of out drive, is this the original motor?

Wayne

[jg480]

Wayne the motor is the original mercrusier 350 mag with a 4000-4600 rpm operating range stamped on the water pump housing and the drive is 1st generation Alpha 1

[MOP]

There are quite a few 18's on the board with 350 Mags, these guys should have fairly solid answers for you. My gut is a 23 cleaver may be a bit fat for your setup plus it steals bow lift which I have read helps the 18. With every thing fixed is when you saw 4000?

Phil

[jg480]

The low Rpm problem was prior to changing the gimbal and realigning the engine. Since there is ten inches of snow at the boat ramp I won't be able to tell If the problem is corrected. I was just curious if it is reasonable to assume if the alignment and worn bearing could steal 600 rpms.

[Rootsy]

has the ignition been tuned up? Ignition timing verified? are you sure the secondaries are opening on the carburetor? when was the fuel/water seperator replaced last... have you checked the fuel filter screen in the carb? is it getting enough fuel? how about too much, it's not belching black smoke or making a sooty transom is it?

a motor being an 1/8th inch high or low... man you'll have a tough time getting the drive on or off...

JR

[MOP]

I have a hunch it will run better now that it has had the new U joint, bearing and alignment, you eliminated some good sources of binding thats for sure. Get it wet the first warm day and let us know how you make out.

Phil

[jg480]

It was a pain to get the drive off. I had to kinda rock it back and forth using wooden shims to pry it out. I'll check the ignition and carb out, the previous owner said he had hard starting problems but I have not experienced that yet. Thanks

[Sam]

When spring rolls around give us a shout, there are several Donzi's in the area. Between us I'm sure we can figure it out. In the mean time check in with Randy Oak, he has a similar set up except he has a Bravo. I would think that at a minimum you shoud be at 4800 rpm. Check out the "gatherings and events" section, there is a winter gathering in Novi on Jan 8th. Hope to see you !


Sam

[Rootsy]

I ditto sam, I'm willing to lend you a free hand this spring if you still have issues... I'm not too far away...

Jamie

[jg480]

I really appreciate the offers for assistance this spring and look forward to meeting you MADCOW guys thanks alot. Jim.:beer:

[DonCig]

I know that this sounds like asking if the electrical cord is plugged in, but did you trim the outdrive up? If the drive is kept all the way down it can be hard to rev past 4,000 rpm.

Don

[jg480]

I trim up to the trailer limit switch. What type of props are the guys with stock 270hp 350 mags running?
I know that this sounds like asking if the electrical cord is plugged in, but did you trim the outdrive up? If the drive is kept all the way down it can be hard to rev past 4,000 rpm.

Don

[MOP]

Every boat is different, same boat, same power but still different and will not always use the same type or pitch prop. You need to get solid numbers on top RPM then a few sugestions should come from the guys.

Phil

[DickB]

I trim up to the trailer limit switch. What type of props are the guys with stock 270hp 350 mags running?
My 18 is a stock 350 MAG with a 23 Merc Mirage. Runs right at 5000 RPM.