" Three may keep a secret if two of them are dead" Ben Franklin
" ------- well Doctor what have we got a Republic or Monarchy? A Republic he replies if you can keep it"
Benjamin Franklin, 1787 Constitutional Convention, as recorded by signer James McHenry's in his diary at the Library of Congress
Location: SW Orlando, Fl
I have a Yamato-80 racing engine. All eight of its reed petals are raised about 1/16" of an inch off the blocks. A long while back, I e-mailed Rick Montoya about this and he said that it was normal for this engine. He was right!
Not only does the engine start in one pull under load, but the darned thing actually idles as good if not better than any fishing motor I have ever owned except for my 1958 Johnson 7.5hp.....The performance is super as well (65mph, no problem). I attribute this to raised reeds. It can easily pull in gulps of air at full power because of this and its got it!
I do not know the Yamaha torque spec for the reed stop bolt but for the older Mercs most models are 35 to 40 inch-lb (not ft-lb).
" Three may keep a secret if two of them are dead" Ben Franklin
" ------- well Doctor what have we got a Republic or Monarchy? A Republic he replies if you can keep it"
Benjamin Franklin, 1787 Constitutional Convention, as recorded by signer James McHenry's in his diary at the Library of Congress
Location: SW Orlando, Fl
The rougher grit will also hold oil and help to cushion the reed landing on the cage which is quite forceful high rpm. For my SS race Merc I use 180 wet on a flat glass plate (Merc has an aluminum cage). I sand it in 2 directions at 90 degrees from each other to make a hatch grid (per Jerry Wienandt, but he uses a coarser grit for his Merc race engine builds)
" Three may keep a secret if two of them are dead" Ben Franklin
" ------- well Doctor what have we got a Republic or Monarchy? A Republic he replies if you can keep it"
Benjamin Franklin, 1787 Constitutional Convention, as recorded by signer James McHenry's in his diary at the Library of Congress
Location: SW Orlando, Fl
Hey Grayson hows it goin. Bobby here from Louisiana. I have alot of trial and error with the Yammi 30 3-cylinder. Is this motor stock?? I had a 1998 25 3-cylinder it ran bad. I removed power head and the powerhead gasket was leaking. I went ahead and installed a shortened 30 tuner ( cut off at water intake ), Tohatsu 40 carbs with ( .122 ) highspeed jets. I tried CCMS reeds I actually lost rpm over stock. Boyesen was a little better. This motor ran the best with a set of stock 40/50 reed cages. I hope this helps.Please let me know if I can help. You can e-mail me @ bobby.crochet@lyondellbasell.com...
Hey Bobby, I think I have had a similar experience, I feel after trying ccm sport and the cfm race they maybe are too stiff for the little 30. Maybe if I had more compression than stock it would be better, but I went back to standard reeds and gained Rpm.
Going to try a set of doukas reeds next that are thinner than all of them, but still slightly stiffer than stock. Will keep them until I get my new shaved head with reshaped dome for more compression. I have tohatsu 40 carbs, 50 reed blocks too.
about "high compression heads", between two and four cycle engines......
I see a lot of people emphasizing on making the cylinder [combustion chamber(s)] tighter.... Well, on a two cycle engine, this will make it so that a more high performance fuel can be used and with less advanced timing. But other than that, it is really about accommodating high rpm action. It will not help make the engine have a stronger intake like as so with four cycle engines. With four cycle engines (like muscle-car engines), having a tight chamber does more than accommodate fast burning fuels with higher psi. It also causes a stronger intake vacuum at the pull of the piston so that bigger cams and carburators can be used as well as other flow enhancements.
Having a high compression cylinder in a two cycle engine has a very minute advantage compared to a four cycle engine because only compression and power take place there. With a four cycle engine, you would get intake, compression, power, and evacuation all in just the cylinder.....not a separate area like the crankcase.
Basically, my point is that if you tighten up the crankcase on your two cycle engine, then that will increase the intake and induction strength. A tighter cylinder volume will increase compression so a higher octane fuel can be used with a change in timing, for the higher rpm that will result as higher HP is made.
True, but if the exhaust is properly designed, a LOWER crankcase vacuum (meaning a larger volume) will produce more power--especially if one is using a properly designed expansion chamber. Weird, but the reason why is this: There's more air/ fuel mixture in there for the exhaust pulse to suck in. More volume means more power.
In the case of poor exhaust suction, however, then a higher crankcase vacuum (smaller volume) makes more power since it helps expel the exhaust gases.
Jeff
PS: A well designed expansion chamber will pull air in by the reeds when the exhaust ports are wide open! The designers of dirt bike engines found that out in the late 70s when piston port engines were down on power compared to reed valve engines. The idea that reeds, being far more restrictive than an open port, would produce less power was blow away when their improved air flow late in the stroke was finally understood. Since then, no dirt bike engines have been piston ports.
"We live at the bottom of an ocean of air." - General Marvage Slatington
There are currently 1 users browsing this thread. (0 members and 1 guests)
Bookmarks