Universal M-25XP or M-25 speed control screw or highspeed fuel mixture

Sep 16, 2020
10
Catalina 30 MKII San Francisco
So I got a bit ham fisted when removing my raw water pump this past weekend on my new to me Catalina 30. In the process, I removed the speed control adjusting bolt, number 1 in the parts diagram, red circled item just above the raw water pump in the second picture.

From my understanding this affects the fuel mixture under load at or near wide open throttle. There appears to be no specs or procedures for setting and/or adjusting the Speed Control Adjusting Bolt in either the owners or service manual for the Universal M25XP.
If anyone has any suggestions for the initial setting of the screw when reinstalled, or even wouldn't mind measuring their own, ie screw length protruding out from the locknut with the tamper cap removed.... It would be greatly appreciated.

It has been suggested to me, to adjust it out until black smoke is present in the exhaust at full throttle under load, and then adjust back it in a 1/4 or 1/2 turn from there until smoke disappears or is intermittent at best. Basically finding the rich end off the fuel mixture spectrum and backing away from it.

While I am new to the world diesel engines, I am very experienced building/rebuilding, and tuning motorcycle engines. So this makes sense as it's generally safer, albeit dirtier, on the rich end of the spectrum when it comes to air/fuel mixtures.

Any help or suggestions welcome. Thanks in advance for your input!


M25XP Speed Control Plate Group.png


M25XP or D950  engine front fuel adjustment.jpg
 
Feb 26, 2004
22,010
Catalina 34 224 Maple Bay, BC, Canada
Sorry, I don't have the answer and I've had our boat and M25 engine for 24 years.

But you got another BIG problem: you have the old style alternator bracket!!!!!!! [If that is YOUR engine.]

Alternator mount/bracket upgrade Important safety upgrade for M25 (not XP) owners by Stu Jackson

If you don't replace it, you WILL have a catastrophic failure of the bracket which will slam the alternator into the irreplaceable gear case housing.

You should read these, too:

CRITICAL UPGRADES includes a lot of engine information: Critical Upgrades CRITICAL UPGRADES - DO THESE OR ELSE!!!


Engines 101 - The BIGGEST & BEST collection of M25 Series Universal Engine Information on the Internet, plus some M35, too :) This includes a link to the Critical Upgrades topic which has more engine information please read it too.

Diesel Engine - c34.org
 
Feb 26, 2004
22,010
Catalina 34 224 Maple Bay, BC, Canada
If anyone has any suggestions for the initial setting of the screw when reinstalled,
I recommend calling either SeaPower in Oakland (a Universal dealer and good guys) or a Kubota tractor dealer maybe out past Pleasanton (I've gotten spares from them when I lived in SF).
Here is the tractor engine parts diagram for your M25:
Kubota Parts Manuals
No marinized parts, use with CAUTION - not all parts fit the "cousin" Universal model engine
Kubota D850-OEM engine block (M-25 cousin) Parts Manual - Searchable PDF
Kubota D850 engine block (M-25 cousin) Parts Manual from B6200 tractor manual- Searchable PDF
 
Feb 26, 2004
22,010
Catalina 34 224 Maple Bay, BC, Canada
You should also get to know these guys:



Catalina 30 Groups Link

Subscribe at the web forum:
Catalina30 groups.io Group
*All things Catalina 30 and 309! Sponsored by the International Catalina 30 Assn IC30A. FAQs, Q&A, comments, and experiences especially fixes and modifications invited. Share with over 2200 other owners. Website catalina30.com* *Please join the International Catalina 30 Association.
or by sending an email to:
Catalina30+subscribe@groups.io

This comes from this sbo thread by weekendrken:

1992 Catalina 30

Also: www.catalina30.com
 
Feb 26, 2004
22,010
Catalina 34 224 Maple Bay, BC, Canada
Here's another bracket discussion:


It is from 2014, 7 years ago. We have been preaching about this issue since at least 1991, which is 30 years ago. "We" includes our C34 group, the C36 skippers, many Ericson owners, Maine Sail (who used to own a C36) and others with M25 engines.
 
Sep 16, 2020
10
Catalina 30 MKII San Francisco
Thanks for all the links and suggestions. Lots of reading to do, and few groups to join. The pic is not my engine, but confirming which bracket is installed and or updating to the new design is on the short list. 1st item is just getting the new raw water pump installed and moved into my own marina. Then scheduling a haul out and tackling a long list of maintenance, repairs, and upgrades.