WOT RPM Low. MAG350 MPI B3

G

gcarmich

Seaman
Joined
Jan 8, 2009
Messages
55
My Mag 350 MPI only hit 3870 RPM with throttle lever all the way down. Clean hull. New valves, heads, injectors.

Could it be a linkage issue since I had to reassemble the linkage?
 
Scott06

Scott06

Admiral
Joined
Apr 20, 2014
Messages
7,036
gcarmich said:
My Mag 350 MPI only hit 3870 RPM with throttle lever all the way down. Clean hull. New valves, heads, injectors.

Could it be a linkage issue since I had to reassemble the linkage?
Click to expand...
Couple of things I would look at -

first yes of course it could be the linkage make sure it is opening all the way

Verify firing order and the the indexing of the distributor. There is a procedure that Mercuiser has for this if you google it or find it in the manual.

Compression test could be something simple like rocker arm being too tight

@alldodge would probably have some things to verify as well.
 
Scott Danforth

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
50,944
it could be a throttle linkage issue
it could be a fuel system issue
it could be a wrong prop issue
it could be an ignition issue

what troubleshooting has been done?

compression test?
fuel pressure?
does your motor have the crab cap?
are the injectors from Mercruiser or ebay or amazon?
 
G

gcarmich

Seaman
Joined
Jan 8, 2009
Messages
55
Scott Danforth said:
it could be a throttle linkage issue
it could be a fuel system issue
it could be a wrong prop issue
it could be an ignition issue

what troubleshooting has been done?

compression test?
fuel pressure?
does your motor have the crab cap?
are the injectors from Mercruiser or ebay or amazon?
Click to expand...
Haven't compression tested since new heads/valves. Can do soon.

Props are original.

Is fuel pressure available through VesselView and/or RINDA?

Has crab cap.

Injectors are OEM. Just recently serviced and tested good.

I'll reconfirm firing order.

And check linkage and ensure full open all the way forward.

Thank you.
 
Scott06

Scott06

Admiral
Joined
Apr 20, 2014
Messages
7,036
this thread has the indexing of dist

Mercruiser 5.0 MPI distributor issue

Short version: Installed new distributor (Merc 5.0 MPI with crab style cap -- shaft separated from pressed fitting on top). Boat ran great, but chugged at idle. Friend came and looked at it and believed it was off by a tooth, so moved it by a tooth. Boat now idles great, but misfires above 2000...
forums.iboats.com forums.iboats.com
 
Scott Danforth

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
50,944
you test fuel pressure with a mechanical pressure gauge at the schroeder valve

verify the crab cap is in good order. get a new one if the old one is more than a year old

test compression with a known good gauge. should be between 140 and 150 psi on all cylinders
 
G

gcarmich

Seaman
Joined
Jan 8, 2009
Messages
55
Scott Danforth said:
you test fuel pressure with a mechanical pressure gauge at the schroeder valve

verify the crab cap is in good order. get a new one if the old one is more than a year old

test compression with a known good gauge. should be between 140 and 150 psi on all cylinders
Click to expand...
Does the fuel pressure change with RPM?

My crab cap is 2yrs old.
 
alldodge

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
43,063
Scott Danforth said:
Not enough to notice. it should be about 45-50 psi
Click to expand...
Scott, it's a Merc so most likely 43 psi, Volvo Penta is 50-60

gcarmich said:
Does the fuel pressure change with RPM?
Click to expand...
FP can change a few psi, like 40 at idle and 43 or so at WOT

gcarmich said:
Props are original.
Click to expand...
What are originals and what rpm was being able to turn prior to motor work?

gcarmich said:
Is fuel pressure available through VesselView and/or RINDA?
Click to expand...
Depends on your motor serial number, most likely NO
Rinda should be able to provide injector pulse width

What is motor serial number?
 
You must log in or register to reply here.
Top