The elusive 224/3.7 MerCruiser banger

the stock jets were 49 I went to a pair of 45 jets. Like yours, mine was running way rich, at times it smoked I bought every size of jet pairs from 42 to 55. Note: Holley jets don't fit, you have to have ford jets.

Yes, I had a nice looking 2 bbl Rochchester. I began with it but it did not work well. I could not keep the engine running smoothly under 4000 rpm using it. After the initial startup and cam break-in I removed it. I had a several autolites from a previous engines and some worked excellently, thus It was a no brainer to change from a malfunctioning carb to a known good one that I was familiar with. (And my 289 Mustang routinely got 28 mpg with its Autolite, on the road.)

Autolites are simple so tuning them is easy and the smaller ones flow right for this engine. See my application chart above before buying one if you go that way.

If you have a good Rochester, you could just rejet it. Or you could buy a rebuilt one and return it promptly if it isn't right.

I have used Autolite and Mikuni carburetors for 48 years. I like both makes have accumulated parts to work with. I can't say that I really "like" Rochesters but some quadrajets have worked very well for me., Keihein and su carbs I dislike. Weber I like as all of the parts are available and they seem to work well.

 

I have a Suzuki Samurai that has received a few modifications, one of which is this cool motor.
Drivetrain consists of the 3.7, TH350, the front half of a NP231, and a Dana 300. Toyota Mini truck axles and 38.5 super swampers.
I'll try to provide more details later. I've been working on this for over 2 years, and hope to take it on it's maiden voyage this weekend. I just have to get this carb sorted out.

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Bad Zuk,

Your Suzuki is great.

Please let us know how it works out.

I love sleepers and have thought about building a jeep using a fiber glass body on a jeep frame and powering it with a 470 and a T-5.

It would be 2 wheel drive and very light and it would be a round town scrambler.

Anyway it would come after my Model A's and the Volvo 544.

Your light weight Samurai is perfect for one of these light weight engines.

Sometime someone will put one of these engines on a Motorcycle and make a great road cruiser.

I am anxious to hear how it works out for you and what modifications to the engine you made to the 470 to make it work in your installation.

Good luck, Dick

 

What are the thoughts on running E85 through the stock carb? The jetting may be close then. The compression is reasonable for it. Anyone know how bad the alcohol will react with the stock fuel system? This is an off road toy, not something that has to be street able.

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Zuk: please tell what was necessary to fit the TH350 to the engine.


By comparison, we mill 5/8" off the rear surface block to fit a standard chevy bellhousing and its Saginaw transmission. It is then a straightforward bolt up.

 

I struggled with this for awhile, being a backyard builder (literally, I have no garage or shop, just a small shed) I lacked access to fancy tools and equipment. A Flexplate off a 74 Maverick with a straight 6 fits nicely, and would work perfect by milling the block 5/8". You would still need a pilot adapter for the nose of the torque converter.
However in my case I didn't have the resources to mill the block, so I reused the stock flywheel off the mercruiser and drilled the appropriate pattern in it to bolt up the torque converter. The spacing was perfect, 1/8" between the two.
Then I just fabricated my own pilot bushing that indexed off the pilot in the flywheel. So far so good, but time will tell. For my purposes the added flywheel weight is a benefit, with all my gearing this thing is like a tractor. In 1st gear, low range in both transfer cases & 5.29's in the axles this thing is unstoppable. The brakes can't even hold it.


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think one of these would be simple to setup for marine app... would it bolt direct to stock intake.. and the flame-arrestor diameter?

I hear the 2b Mercarb is oversized for 224 and tend to run rich..

Thanks

 

Yes, it would be simple to setup, for any application.
The carb will not screw directly to the manifold without an adapter, but they only cost $12 as aftermarket auto parts.
The old flame arrestor will probably not fit, but you can use one for a 302 marine application, or you could adapt what you have to fit using the bottom of an air cleaner. I made my air cleaner (except for the element),and it was easy.

 

Zuk, I respect your accomplishment in spite of a difficult work environment. We can't mill the blocks ourselves as most machine shops mills are too small to cut this block. I had to request the resources of an aerospace shop to mill it.
I used the merc flywheel also, it is a ford flywheel.

 

Fuel distribution question for the two barrel manifold:

I read of egt temperatures being higher from cylinders fed by long intake runners. So I have mounted thermocouples in the exhaust gases from three cylinders. My preliminary measurements seem to bear out the statement that there is a difference. It may only be showing that the instrumentation has sizable errors in it.

A possible solution would be to turn the carburetor 90 degrees so that one ventruri fed the lean cylinders* and the other fed the rich cylinders*...and then rejet to get even exhaust temps. It may be necessary to insert a baffle under the carburetor to separate flow between the two venturi.

* this is not the case. There is only one lean cylinder.[ #1]

Plug readings from this engine show a difference in mixture, with cylinder #1 being the lean one. So I rejetted from 45 to 46 and the engine ran cooler but worse. I will try #47 jets as a test as soon as I check its ignition timing. I went back to 45 jets as the others left carbon in the engine.

 

Unless it is that it is due to my engine being higher at the front, I can not account for cylinder #1 being leaner than 2,3 &4 which are about equal to each other and richer.

Are these engines setup level in a boat? The carburetor is perpendicular to the stock manifold. Any change from this would change the angles the fuel/air mix would have to take and that should have an effect on mixture.
I expect that a little more fuel would run back to cylinder 4 simply due to gravity. The heated stock manifold should reduce this somewhat.

I have always favored a single downdraft carburetor, but right now, the reason for 4 carbs is clear in spite of the tuning complexity and the difficulty in getting them running in synch.

The synch & linkage problem could be solved by running a modified 4 bbl carb with a manifold made so that each ventruri would feed only one cylinder. The secondaries would have to be converted into primaries. Unlike the Quadrajet, the 4bbl Autolite had secondaries which seem much like the primaries.

 

The majority of the time they sat pretty level as most of them were I.O. setups but they were used as inboard occasionally which would have placed them at an angle. I don't know if they had different manifold or if they just tossed a tapered carb spacer in them.

 

Thanks. Mine is installed at a steeper angle for ground clearance as I did not feel that it would make the difference that it seems to be making. Since the jets are fore and aft the tilted carb has a tiny bit less fluid head over the front jet.

 

Reading my plugs this morning, they are all about right. Thus fuel distribution in the merc manifold is just fine.

 

Yesterday I took my Mercriuser powered Samurai out for its maiden voyage, and all I can say is WOW!
What an awesome motor for an off-road rig. It has an amazing amount of torque, and pulls hard from a low idle to wide open-put a smile on your face-squeal like a little girl-hang on tight-things are getting squirrely-ok I better lift but I don't want to!
I still need to fine tune my jetting, as
I'm still running rich, but wow that was fun.
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My experience too.. It pulls really well throughout its rpm range and revs well too.

You've an especially good application for it as you can't load it long enough and heavily enough for it to detonate, even with stock combustion chambers and stock compression ratio.

Have you weighed it? Mine weighs 1800 lbs with fuel.
You asked about jetting, I ran mine rich the first year, leaned it out a bit and it ran stronger. I published the jets I use, their size number is the jet size in thousandths of an inch, so you could still make a rough comparison that way. Lowering the float level will lean it too...I do that when a carb has me backed into a corner. It is easier to control it with jetting.

 

Guess I just joined the club...LOL.
81 Sea-Ray with the 170hp "big banger". Just followed me home.

 

I soldered and re drilled my jets so I could see if I could get close on jetting. I would have to look at my notes (written on the underside of the hood) to see where I ended up. Seeing as I'm still running rich I'll solder them back up and drill them smaller. Once I'm close I could purchase some jets the same size.
I do also want to lower the float slightly, more to help keep the off camber flooding to a minimum than general jetting adjustment. I was quite surprised how well the stock carb performed off camber, the flooding was minimal.

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Did you check the powervalve? If they fail due to backfire overpressure in the carb throat the engine runs terribly rich.
I checked my jets with a set of numbered bits and found there were several jet sizes between some bit sizes. But it is better than a guess to get you started. Float level should be exactly right when jetting. [Eliminating that variable makes jetting simpler.]
Jets are cheap enough, I pay $5 a pair..and keep my set in pill continers, the kind with a compartment for each day of the week. 14 jet sizes will take care of anything you will encounter. Even 7 should do it nicely.

 

I probably wrote that I use an oxygen sensor and a voltmeter to check my carb jetting. I have since found out that a normal oxygen sensor sends out alternating high and low Dc voltages which must be averaged. It is not difficult, an operational amplifier (NTE778A) is used to sum the two voltages and a resistor network divides that voltage by two to come up with the proper voltage reading. It is not expensive or difficult to do. total cost $5 plus a little box to house it and the two 9 volt batteries that power it. I set up a headlight relay to disconnect its batteries when the engine is not running.

 

It will only send out alternating voltages around stoich, if the mixture is actually bouncing back and forth through stoich, as that's what most EFI computers will be trying to do with O2 sensor feedback at cruise/light load.



All that you can really tell with a narrow band is that it's on one side or the other. Widebands have gotten to be very affordable, and you can likely find someone local that has one that would help you out if you don't want to buy one.

 

Hi again from Sweden, I havent been working so much on the engine because my wife has been really sick for a long time. Like always I have a question. Is the headgasket 27-13709 at mercruiserparts.com the right one to use?

 

I have a mercruiser 3.0 setting in a boat out back. we were thinking about putting on a stand and using in the auto shop!!!

 

Reading thru this i see comments about carbs and getting them tuned to this engine. I build race carbs for 4 cyl circle track cars, they can't use this engine but the properties are similar.
One big problem you need to fix in the holley is the 'power valve circuit restrictor' (PVCR), they all are sized for the V8 engine. I drill and tap for 6-32 brass allenscrew that is drilled to a .028 hole. There are other builders that sell brass tubes that you just drop into the pvcr - essenger can probably supply them to you.
Anyway, you restrict that circuit and it'll make jetting/tuning a whole lot easier.
Remember with a 4cyl you have only 2 pulses per revolution and that makes carb circuit sizing more critical than the same size cubic inch V8 motor.

 

I forgot about the PVCR. Is it the frequency or strength of the pulses that make the 4 cylinder more finicky?

 

Does anyone know anyone that is looking for a 224 mercruiser engine? I have one for sale...it is set up for boating right now....runs good...came out of a 1986 Fourwinns boat...boat floor and transom was rotten...looking to sale engine

 

I have an engine exactly like that one...do you know anyone that is searching for this one?

 

The engine was NOT the problem. The engineers & the bean counters were the problem. Apparently, the then new ZR-1 was due for demonstration and the Lotus / GM powertrain venture had numerous issues. So, the engineers decided to quickly employ the Mercrury Marine powerplant for its versitality as a temporary fix. It did work well enough for GM to abandon the Lotus option in favor of the Mercury Marine. The ongoing feud between the engineers and the accountants kept the ZR1 and other projects like the Fiero & Reatta from using state of the art components in favor of low quality cost cutting pieces as the Cadillac Cimeron also proved.

 

I'm a little confused, where did this come from?

 

Restricting the vacuum hole to the power valve sounds great. I will do it.
I posted my use of an averaging circuit but I have not yet been able to test it as my engine was reluctant to start and made loud explosions in its exhaust so I've been going through it and found that a new set of spark plugs restored its spark.

Considering its ignition, I'm wondering if the straight centrifugal advance marine distributor is the best choice for a Mecruiser powered car because the load on a car engine is not the same as for a boat engine. In other words, wouldn't it make sense to use a Chevy 2 automotive distributor with its vacuum pullback to modify the advance curve at part throttle to save some fuel?

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