Reeds

[Eric Eberlin]

I own an old 1966 80 horse Evinrude that I am haveing problems getting 2 of the 4 cyl. to work. I have fire and gas to all 4, 110 lbs of compression in the two good cyl., 100 in another and 85 in the last. Two questions, Can the reeds be affecting compresion and how tight are they to be against the stop? I can easily see a small gap. Can I turn them over?

 

[marinemech]

Re: Reeds

reeds only work on crankcase side of compression <br />throw away the gauge it is useless on a two stroke<br />rotate flywheel with a wrench and you will feel if you have low compression if you do look at head gasket

 

[walleyehed]

Re: Reeds

At rest, the reeds may be slightly "gapped" from the plate suface, but vacume closes them somewhat when running.<br />The eng should still "run" at the compression values listed.<br />This set-up is also prone to ignition issues...have you looked at the cap and rotor closely???<br />EDIT: On a 1966 engine, I'd be looking at more than a head gasket for a low compression 2-stroke...this isn't a Briggs-N-Stratton here.<br />The numbers aren't as important as having the values all "near" the same...hard to tell with a wrench in-hand.

 

[JB]

Re: Reeds

Hi, Eric.<br /><br />Your compression on the low cylinder is a bit out of spec but that shouldn't prevent it from running. Reeds have nothing to do with cylinder compression, they valve scavenging pressure.<br /><br />After you get it running decarb it (see FAQ) and check it again, using the same guage. Compression guages are required for reliable compression testing on any engine.<br /><br />If you have spark on all 4, squirt some fuel mix into the carbs of the failing cylinders as you try to start her up. Chances are that you have a bad carb (side by side cylinders dead).<br /><br />If the other two cylinders try to fire remove, clean and overhaul the gummed up carb.<br /><br />Get and use a Service Manual when you do this or you will probably cause more trouble than you fix.<br /><br />Good luck.

 

[walleyehed]

Re: Reeds

Well said, JB....<br />That would be the best place to start Eric.<br />Keep us posted!

 

[nordy]

Re: Reeds

Hello Eric,<br /><br />You wrote:<br />Two questions, Can the reeds be affecting compresion and how tight are they to be against the stop? I can easily see a small gap.<br /><br />Of couse reeds can affect compression.<br /><br />If there is a gap the reeds may not close enough when the piston comes down, not pressing the air in the crankcase into the combustion chamber but part of it back into the carb.<br />You have the same effect on compression when the carb's butterfly is not opened when doing the compression test.<br />Filling up the combustion chamber with air increases the compression value up to 25 psi.<br /><br />The power may be deteriorated severly through leaking reeds.<br /><br />Greetings from Germany<br /><br />Nordy

 

[G DANE]

Re: Reeds

I'1 just jump in here. <br /><br />I once lost a whole reed leaf and chipped another on my 35HP evinrude. Compression was not affected. At crancking rmp. The motor will either get air from intake or exhaust ports and start to build up compression at first when both are cloused by piston. That my experience. I couldnt figure out why it wasnt running on the one cylinder, it has only one carb, spark was fine and both had exactly same compression. Luckily JB helped me out there, Thanks again JB !!

 

[lark2004]

Re: Reeds

with referance to the last question you had, "can I turn them over?" I whjould advise against it. The metal in the reeds has (for want of a better word) set into flexing on that side. If you turn them over you run a very real risk of snaping one off (possibly the cause of your failure G Dane?). I'm sure that someone will dissagree with me on this, but it does happen. The small gap that you can see is fine, when the piston comes down on the power stroke, it compresses the crankcase and forces the reeds shut, until it starts to create vacumme on the comression stroke when it will open up again for the next fuel/air charge to be drawn in.

 

[nordy]

Re: Reeds

Hello lark2004<br /><br />You wrote:<br />The small gap that you can see is fine, when the piston comes down on the power stroke, it compresses the crankcase and forces the reeds shut<br /><br />Think of idle or low load situations when the pressure from the pumping piston may be too low to shut the reeds.<br />Can't find the gap fine at all then.<br /><br />Nordy

 

[G DANE]

Re: Reeds

Lark 2004 - yes turning reed leaves to make them clouse more tight was the reason I lost a couple of leaves. Metal gets "tired" when they have to bend both ways. I'v seen two motors with a couple of slightly open reeds at rest, both ran without problems. If there is no severe visible spit back at iddle there is no reed problem. If motor isnt running, but both plugs get wet with gas when crancking, slightly open reeds are not the problem, otherwise it would backfire. Overturquing the little reed center screw will damage reed aluminium frame and make reeds show gap. It can be corrected by sanding plate against fine sandpaper laid on a glassplate. I tried this and it did work. Remember to lock those screws with locktite, and only use fine grit paper.

 

[lark2004]

Re: Reeds

Ok Eric, just to help clear some of this up, How big is the gap you can see in reeds?