350 mag efi, high idle 1300rpm and low top speed

[Cdn20valve]

1997 donzi 255
350 mag efi
Bravo 1

I just bought the boat used. The place i bought it from replaced the engine and outdrive as the were not winterized properly and cracked.

How do i adjust the idle?

Top speed is 31mph at 4000 rpm. Is this normal for this kind of boat? It seems low... Bottom end is freshly painted.

Anything I can check?

Thanks

 

[thumpar]

Something is not right. I would think you have a 1.5 ratio drive and with those numbers it would come out to be a 14 pitch prop which I don't even know is made for them. I would make the place you bought it from figure it out. Maybe a bad sensor or who knows.

 

[biggjimm]

I'm not sure of how to set your idle on that particular set-up but the pro's will be along soon.

Make sure your throttle linkage & cable are opening the throttle all the way. I had a bent linkage & a bad cable on a carb'd 7.4 & it wouldn't open the throttle plate all the way & had the same symptoms as you. Except for the high idle that is.

 

[alldodge]

1997 donzi 255
350 mag efi
Bravo 1

I just bought the boat used. The place i bought it from replaced the engine and outdrive as the were not winterized properly and cracked.

How do i adjust the idle?

Top speed is 31mph at 4000 rpm. Is this normal for this kind of boat? It seems low... Bottom end is freshly painted.

Anything I can check?

Thanks

Howdy

The idle is controlled by the ECM and is not adjustable, but 1300 is way to high. I wonder if someone left the engine in base timing mode. Look for the DLC connector and see if it has a jumper wire on it or another connector on it. If there is no connector or jumper, disconnect the throttle cable and see if it idles down

 

[Cdn20valve]

I found the dlc harness. It has a plug on it. But the plug is a "blank".

 

[alldodge]

I found the dlc harness. It has a plug on it. But the plug is a "blank".

That's what it should be, someone didn't leave it in base timing, that's good.
Now disconnect the throttle cable at the throttle body (item 11) and see if you can get it to idle down.

 

[Cdn20valve]

I found the dlc connector. It had a blank plug on it.

 

[Cdn20valve]

So after digging around, i found out its a tbi efi. The guy inbought it from said it was a mag. But its only got 2 injectors at the tb.

Im going to check the throttle linkage on thursday in the water. Also, am i able to set base timing by using a timing light and a paperclip in the dlc plug? If the timing is off it could cause these issues, no?

 

[alldodge]

With your TBI systems and a TB-V ignition putting your engine in base timing is done a bit different. Need to connect a jumper wire to the Purple/White wire (No 13) to a good ground. While in base timing mode also adjust idle to 600 rpm, do this sitting in the water

 

[Cdn20valve]

Update: the shop had the boat for nearly a month. They repaired everything and some. There was a fuel leak in the front bilge (leaking fuel sender) which they repaired(had to cut fibreglass to remove contaminated foam). They also repaired the idle..it's now 800rpm, which is not ideal but works. At least I can put around the marina and not drive into things. They said it was timing related...
Top speed is still kinda low but improved slightly 36mph at 4000 rpm.
The prop is a 4 blade 14.5x18. Should I experiment with a diff prop?

 

[alldodge]

The prop is a 4 blade 14.5x18. Should I experiment with a diff prop

Yes need to get it up to around 4800, so 3 blade 17 is where I would start.

 

[Cdn20valve]

Same diameter? Thanks

 

[alldodge]

Same diameter? Thanks

For the most part yes, might not be able to find the exact diameter, but being close should help.

The issue your into is, for every 1 inch of pitch drop your rpm goes up 200 rpm (with 3 blade prop). Now your dealing with needing an increase of 800 rpm. If you were running 3 blade props I would say you need to go to a 13 pitch prop, but no one makes a 13. You do have a 4 blade so the decrease is more, but then again the 4 blade is also limited.

You just might wind up with needing another drive ratio, hope not