Merc 25ss in 250cc Mod ?

[Heliarc]

Reading through the 2011 Modified Outboard Technical Manual left me with more questions than it answered It's not an easy read IMO. One particular question is this. Under "22 CU. IN. OMC & MERCURY MOTORS IN 250 cc MOD" it says, "It is the intention of the MORC to provide the means to run the 22 cu. in. OMC and Mercury motors as stock production powerheads on a racing lower unit". Do the legal 250cc Mod engines include the complete-as-manufactured racing 22 cu in Merc 25ss in it's stock form? I ask this because when I think of "stock production powerheads", I think of fishing/pleasure powerheads, not made-for-racing powerheads. Any clarification would be greatly appreciated. Thank you very much.

[G Stillwill]

The 25SS Merc in its stock form as it was raced back in the day is a leagle 250CC Mod motor. No Mods or pipes are allowed on it.

[Heliarc]

Thank you, George.

[ZUL8TR]

25ss

I suppose "as it was raced back in the 1day" (1970's era for the first 25ss that came out in 1973 I believe) would also mean with all the repairs as allowed like welding extra support for the recoil (that was the first part to go)and welding in the tower that did crack at the upper exhaust relief. Also prone to cracking was the flywheel flex plate at the inner bolt circle. This required regular inspection by removing the inner bolts on the flywheel to expose the flex plate at the bolt circle. I went thru those repairs when I raced 25ssh

Also it was legal and recommended by APBA in the inspection manual to replace the 25ss 0.010" reeds with the 0.012" reeds and to use the extended reed stops ftom the Merc 200 of that era. I believe this came about due to reeds flaging excessively due to their 0.010 thickness and the short reed stop on the 25ss. When I replaced my reeds to the 0.012 and the stop I also had to replace the reed cage due to reed tip digging of the 0.010 reeds. I noticed no performance reduction with the thicker reeds but greater reliability with no tip digging plus reduced chance of sucking a reed at 7000 rpm.

[STEVE FRENCH]

Not sure if this helps but.........https://hydroracer.net/forums/showthread.php?t=16102

[Heliarc]

Thanks very much for the input, guys.

[Heliarc]

I really wish that the Mod Tech Manual would be re-written. Some of it is vague, some redundant, and some is simply conflicting. It should be clear and should not require interpretation. Below is a good example of conflicting tech rules.

Under "250 cc & 350 cc MODIFIED CLASSES" it says:

c) All KA model Tillotson carburetors having a 1" venturi and 1-1/8" throat are permitted for use on any 250 cc or 350 cc Modified class engine.
------------------

Later on in the tech manual under:

"22 CU. IN. OMC & MERCURY MOTORS IN 250 cc MOD SPEC CHART" it lists the KA16A and the KC16a carburetors as the only permitted carbs for the Mercury.

So, which is it? The 22 CU IN Mercury in its stock form is "any 250 cc or 350 cc Modified class engine", isn't it? The key words here are 'any' and 'class'. It is a legal 250cc Mod engine.

Going by the first listed tech rule above, it should be legal to run a KA7A on the stock 22 CU IN Mercury and the Merc 25ss. Is it?

I would appreciate some input and clarification. Thanks in advance.

[flatsmoke]

The 25SS Merc in its stock form as it was raced back in the day is a leagle 250CC Mod motor. No Mods or pipes are allowed on it.

Is a stock converted 20-H with fiber reeds approved to run in the Mod 250CC class too?

[G Stillwill]

I think you have to use the stock Merc reeds in a 20H but would have to look up the last speck sheet for one which is 1987.

[G Stillwill]

Barry the key is 250cc=15cu in and 350= 20 cu in and can only us a KA carb the stock carb for the 25SS was a KC carb thus that is why it list those for the 25SS

[Heliarc]

Is a stock converted 20-H with fiber reeds approved to run in the Mod 250CC class too?

The answer is no. Fiber reeds were never legal in Stock Outboard 20H racing. And for the purpose of running the 20H in 250cc Mod, the Mod division uses the 1987 Stock Outboard specs. Sorry.

[Heliarc]

Barry the key is 250cc=15cu in and 350= 20 cu in and can only us a KA carb the stock carb for the 25SS was a KC carb thus that is why it list those for the 25SS

Really? Under the same "250 cc & 350 cc MODIFIED CLASSES" it not only talks about 15 & 20 cI engines, it also talks about the 20H in 250 and the 22 CI OMC and Merc in 250. It specifically includes those engines as 250 engines. It also includes the 25XS in 350. So, it's not as simple as 15=250 and 20=350.

It specifically includes the 20H (in stock form) as a 250 engine, which can run all those KA carbs. It also includes the 22 CI OMC and Mercs (in stock form) as 250 engines. But they can't run the KAs mentioned?

So, when it says, "All KA model Tillotson carburetors having a 1" venturi and 1-1/8" throat are permitted for use on any 250 cc or 350 cc Modified class engine", that means only 15 & 20 CI engines?. It does not say that it only applies to engines of 250CC & 350CC displacement. It says ANY 250 cc or 350 cc Modified CLASS engine. In other words - any engine approved to run in those respective classes. That's the way it reads. I am going by what it literally says, not by what perhaps it is supposed to mean. If it is supposed to mean something other than what it says, it should be changed to read what is supposed to mean. If that statement about the Tillotson KA carbs is supposed to be ONLY about 250 and 350 cc displacement engines, it should say so. And it doesn't.

Additionally, in my opinion the 250cc should be completely separate in the tech manual, not mixed together with other class references. It's not helpful. Throwing all that stuff together just makes it worse to try and wade through.

Also, there is no actual reference to the Merc 25ss at all for 250cc. Evidently it is assumed to be part of the 22 CI Merc stuff because of being 22 CI? It is specifically referenced in other class, however, but not for 250cc. If it's going to be specifically referenced in other classes, why not reference the Merc 25ss in 250cc for the sake of clarity? It should be specifically referenced, not assumed, especially when the tech manual refers to the 22 CI Mercs as "stock production powerheads on a racing lower unit". The Merc 25ss powerhead is not a stock production powerhead. It is a racing powerhead. There are differences between the two.

[G Stillwill]

The reason why the 22 cu in Merc and OMC plus the stock converted 20-H was added to the class was to increase the numbers to the class. The tec manuel keaves alot to be desired in being able to read it plus all the gray area's.

[Dave M]

Suggestion

Exploit the heck out of that gray area. That will get them to clean it up. Well not really, 850 is still kinda messed up.

I'd say a lot needs cleaned up in the spec sheets, and tech manuals, etc. It is very confusing to some. And it can lead to cheating in a class without even knowing it.

Best thing to do is contact the Mod Inspector and ask specific questions like you are here. Might work, might not. What I do see is a hurdle for new folks to get into the sport. A lot needs changed to make it easier to understand.

[flatsmoke]

I just read the rules and the converted 20-H is legal in Mod 250CC with a potted in filler block and carbon fiber reeds.

Thanks guys.