Magnum 18 Magnum 15 Twin Difference

Mechanic · #1 03-18-2015, 09:44 PM

I would find it hard to believe the only difference between a M18S 15 horsepower magnum and a 18 horsepower magnum is the stickers on the air cleaner.

The 15 must be de-rated somehow. Since all of the engine specs are the same, it must be the carburetor. I noticed the carb is mounted horizontally like on a K series engine. Does anyone know what carb number is on the 15 magnum and what carb number is spec on the 18 magnum?

I would appreciate hearing from anyone who has had experience with both the 15 and 18.

jimbob200521 · #2 03-18-2015, 10:18 PM

Good news is they are the same exact engine short the carb. Snag a carb from a KT-17 or M18 and you just upgraded a few ponies

ccannon222 · #3 03-19-2015, 10:30 AM

It's been a while since I looked at the Carb on the M15, but if I remember correctly it had the same size bore as the M18. It was also adjustable unlike the one on my M18. Both were Walbro #52. I will check next time I'm in the storage area.

If the bore is the same, and the jets are adjustable and are adjusted property, wouldn't that carb produce the same or more power than the non-adjustable one on the M18?

Any engine/carb experts out there care to explain?

Chris

J-Mech · #4 03-19-2015, 12:19 PM

Quote:

Originally Posted by ccannon222

It's been a while since I looked at the Carb on the M15, but if I remember correctly it had the same size bore as the M18. It was also adjustable unlike the one on my M18. Both were Walbro #52. I will check next time I'm in the storage area.

Not all M18's had a fixed jet carb on them.

Quote:

Originally Posted by ccannon222

If the bore is the same, and the jets are adjustable and are adjusted property, wouldn't that carb produce the same or more power than the non-adjustable one on the M18?

Any engine/carb experts out there care to explain?

Chris

Jetting is different. Not all that difficult. Smaller jet= less HP produced.

Mike McKown · #5 03-19-2015, 12:43 PM

I raised this same issue last year.

I have one M 15 engine in a tractor that I believe is unmolested. It's a 1535 model. I can't remember what the air cleaner says but the spec tag on the engine is the same one as on my M 18's and I believe the tag says it's 18 hp.

If the spec # is the same, can you assume all the components on the engine as built by Kohler are identical?

J-Mech · #6 03-19-2015, 01:02 PM

Quote:

Originally Posted by Mike McKown

If the spec # is the same, can you assume all the components on the engine as built by Kohler are identical?

If the spec #'s are the same, I would have to say that you do not have a true M15. Motor may have been replaced with a Mag 18. If you look up a 1541 (Mag15) and an 1861(Mag18) and look at the carburetors in the parts book, they carry a slightly different part number. My assumption is they have different jets. The jet is not listed in the parts book for the motor, you have to have a carb book for that. Which I do...... but haven't taken the time to sort it out. Plus, I would need numbers off the two carbs to be able to look it all up. Since it's been discussed at length here, I should have a Mag15 here at the shop soon to compare. I can post findings, but I'm certain that the jets are the only difference.

ccannon222 · #7 03-19-2015, 04:55 PM

Quote:

Originally Posted by J-Mech

Not all M18's had a fixed jet carb on them.

Jetting is different. Not all that difficult. Smaller jet= less HP produced.

J-Mech,
I believe you are correct, however I am trying understand this better as my knowledge of carbs is limited.

A smaller jet will pull less fuel. However, if the jet is adjustable, wouldn't screwing the jet out = more fuel?

Example, Two carbs, same carb body, one with large jet, one with small jet. Both adjustable.
When you adjust the carbs to get the fuel mixture correct, wouldn't the carb with the small jet require the jet to be screwed out farther than the one with the large jet to reach the same air to fuel ratio?

I'm sure I'm missing something, just trying to figure it out.

Thanks

Chris

ol'George · #8 03-19-2015, 08:07 PM

I have to go along here with you.
Unless the flow characteristics are modified, one has to maintain the proper jet mixture or it will not preform correctly.
I've done some carb jetting over the years and you can only go so far rich/lean
before you exceed the carb flow characteristics, and usability suffers.
Now if the lesser H.p. engine has a smaller carb bore/venturi then it can have smaller jets, and perform correctly
jets can be fixed or adjustable.

Mechanic · #9 03-19-2015, 08:46 PM

The carb that is on the engine has both low and high speed jet adjustments on it.

This engine will be rebuilt and made to breathe a bit better. I am going to need to make the carb perform up to the engines expectations.

I have only had the tractor for a few days and it has not been in the shop yet. Paid $350 for it without a deck.

I cannot totally read the model number. There is a faint M, no 1, a faint 8 and a faint S.

Spec. 24647
Serial 2011508446

I am new to this model engine. Are aftermarket rebuild kits available for it?

J-Mech · #10 03-19-2015, 08:57 PM

ccannon222,
Imagine this: You have two garden hoses. One is 1/2" and the other is 3/4". You put the same adjustable sprayer on each hose and open both up all the way. You are going to get more water out of the 3/4" hose right? Even though they both have the same "adjustable" end on them, the larger hose just flows more water. Carb works the same way.

Now, for argumentative purposes, you have to also limit the air to keep the motor from going lean from lack of fuel. (This goes right along with what George was saying, I was just trying to keep it simple.) So I also suspect the Mag15 to have some sort of limiter for the throttle plate. Or a throttle plate limiter alone, and the same jetting, just exactly like the CH18's do. That's the only difference between the CH18 and a CH20 (throttle plate limiter). Mag15 may even have a slightly smaller venturri size. I know the carbs are different part numbers, but not 100% sure on the exact difference. I just know how you can limit HP with two exact same motors just by changing fuel systems. I stated earlier that my assumption was a jetting difference. After all my research this afternoon I believe it has some sort of WOT limiter difference rather than a smaller jet. Just makes more sense that way and it would have been easy to install to limit HP. Just too much work to have a jetting difference on a spec'd out M18 to run it down to 15HP (see below).

I just did some more searching, and I want to add that Kohler does not recognize the Mag15 engine. Mike, your spec number is most assuredly correct, and I apologize for the doubt. According to my CC spec book, the engine in the 1541 was listed as a Mag 18 and carries the spec #'s associated with it. However, the tractor only boasts 15hp. I would say that the de-tune was a CCC thing, and had nothing to do with Kohler. So that is why there is no real info on this engine.