Evinrude Carburetors And Boyesen Reeds

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Hooty

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I'm installing late model(3-5/8" bore)235hp carburetors and Boyesen reeds in my early model (3-12" bore)235hp Evinrude. I think Boyesen recommends increasing primary orfices 2 sizes. With the larger cid carbs, sholud it be necessary to change orfices?<br /><br />Thx. & c/6<br /><br />Hooty
 
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Jim@KSC

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Re: Evinrude Carburetors And Boyesen Reeds

Hooty -<br /><br />Their recommendation is to run it richer so you don't backfire. Apparently it eats them up on just a few pops.<br /><br />The larger bore maintains the same (or close to the same) gas/air mixture. It just gives more of both.<br /><br />The jets are cheap compared to pulling it down again with a new set of reeds.<br /><br />(and thanks for the link to tinytach)
 
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Hooty

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Re: Evinrude Carburetors And Boyesen Reeds

Roger the jets being cheap. I guess I better figger on puting the larger jets in. I'm looking for the reeds Mon. or Tue. so I'll see how much bigger they really say go to.<br />Thanks Jim, I appreciate it. Hope ya'll had a Happy Thanksgiving.<br /><br />c/6<br /><br />Hooty
 
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Dhadley

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Re: Evinrude Carburetors And Boyesen Reeds

If the idle jets are air jets going bigger will make it leaner.<br /><br />Just a thought.
 
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Forktail

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Re: Evinrude Carburetors And Boyesen Reeds

Good point Dhadley, the backfire would probably come from the idle jets or pilots, not the mains. He'll be increasing the volume and velocity of air and fuel mixture throughout the throttle range, so I'd increase the mains too.<br /><br />Here's what Boyesen says....<br /><br />IMPORTANT-CARBURETED ENGINES ONLY: STEP 10 MUST BE FOLLOWED OR THE WARRANTY IS VOIDED. USE THE PROCEDURE SPECIFIED FOR YOUR TYPE OF ENGINE. <br /><br />10. BACKFIRING (a lean condition in the idle circuit, sometimes described as a lean pop, coughing, or sneezing), will cause REED DAMAGE. This MUST be prevented by one of the following methods: <br /><br />A. Carburetors with IDLE AIR JETS controlling idle: EVINRUDE and JOHNSON engines - downsize idle air jets 5 sizes (5 thousandths of an inch). MERCURY and MARINER engines - downsize idle air jets 2 sizes (4 thousandths of an inch). <br /><br />B. Carburetors with LOW-SPEED FUEL JETS controlling idle: Increase 2 sizes (2 thousandths of an inch). <br /><br />C. Carburetors with IDLE MIXTURE SCREWS: <br /> <br />Richen by turning counterclockwise 112 to 1 turn out more than stock setting. <br /><br />D. On some worn or modified engines, no adjustment will be necessary.<br /><br />Hope this helps. :D
 
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Hooty

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Re: Evinrude Carburetors And Boyesen Reeds

Thanks for all the input. I'm attaching a foto of one of the carbs. The main (high speed)jet is stamped "62C" but it measures closer to .065". The idle jet is stamped "29". My first question is should I go up in size of either one of them? And nr.2, are the arrows pointing to idle air jets?<br />I guess what I'm really asking is what size should I change which jets too, and last, what functions do the pull-over jets and pull-over air bleeds perform? I appologize for the long question, but I'm trying to figger ouy what all the circuits in these things.<br /><br />Thx. in advance and c/6<br /><br />Hooty
site1025_t.jpg
 
H

Hooty

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Re: Evinrude Carburetors And Boyesen Reeds

Here's a better foto (I hope)<br /><br />c/6<br /><br />Hooty
site1026_t.jpg
 
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Hooty

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Re: Evinrude Carburetors And Boyesen Reeds

Ooops!<br /><br />
site1026.jpg
 
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Jim@KSC

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Re: Evinrude Carburetors And Boyesen Reeds

Hooty - the first picture came out good; the rest didn't (for me).<br /><br />I also found that my high speed jets (56D) were enlarged by 0.003". I replaced both, but that makes it a bit leaner. Has anybody else found this? :confused: <br /><br />I don't think backfiring is an issue at RPMs above idle, unless something else is wrong. I had some earlier problems with gas lines leaking and it stumbled at idle after coming off high speed. It felt like I hit something, but it was definitely a backfire. After solving, I put in Boyesens, but have yet to really run it.<br /><br />Idle went up from 800 to 1000 RPM :) and I went through all the adjustments.
 
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Forktail

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Re: Evinrude Carburetors And Boyesen Reeds

Your picture isn't too clear here. I'm guessing those carbs have idle air jets instead of idle fuel jets, hard to tell. I woudn't go up on them until you're sure, otherwise you've got a lean condition happening. The mains should be fuel jets, so going up on them won't hurt.<br /><br />Best thing to do Hooty is give Boyesen a call. They'll know exactly what you should do. :D
 
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Jim@KSC

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Re: Evinrude Carburetors And Boyesen Reeds

Hooty -<br /><br />What engine did the carbs come from?
 
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Dhadley

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Re: Evinrude Carburetors And Boyesen Reeds

The 1 3/8 carbs were used mainly on the XP/GT crossflows. Its not unusual to find the actual size of the opening in the jet is slightly different than the number (rating). The pull over circuit adds additional fuel at higher rpm's. The 62c's should be fine up to about 6500 rpm on a stock motor. If you are running the cut heads and/or have changed the port timing the final jetting and ignition timing will be determined by testing. <br /><br />Those carbs will flow a lot of fuel but will be slower accelerating than the smaller ones. I still would not go bigger on the idle jets as a lean condition is the one thing that will kill the Boyesens almost instantly.<br /><br />Good luck!
 
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Hooty

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Re: Evinrude Carburetors And Boyesen Reeds

I don't know where the ftot went. It was there yesterday. O-k, here it is again.<br /><br />Thx. & c/6<br /><br />Hooty<br /><br />
site1027.jpg
 
H

Hooty

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Re: Evinrude Carburetors And Boyesen Reeds

Now that I've got the foto back, are the arrows pointing to the "Idle Air Jets"?<br /><br />Thanks,<br /><br />c/6<br /><br />Hooty
 
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Hooty

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Re: Evinrude Carburetors And Boyesen Reeds

Now that I've got the foto back, are the arrows pointing to the "Idle Air Jets"?<br /><br />Thanks,<br /><br />c/6<br /><br />Hooty
 
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Jim@KSC

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Re: Evinrude Carburetors And Boyesen Reeds

Hooty -<br /><br />Blow some air or liquid through the holes and see where it goes. If it just bypasses the throttle valve and goes to the air intake, they must be "Idle Air Jets". In that case Boyesen says to reduce the orifice.<br /><br />If it goes into the float bowl, it delivers gas and they are "Low-Speed Fuel Jets", which they say to increase the jet size.<br /><br />The other way would be to find out what engine takes them and go through the manual.<br /><br />Good luck!
 
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Hooty

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Re: Evinrude Carburetors And Boyesen Reeds

Hey Jim,<br />I've traced the circuit out and they do go behind the throttle plates. That's why I figured they were idle air jets but I wasn't sure. You've confirmed that they are and I appreciate it.<br /><br />Thx. & c/6<br /><br />Hooty
 
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Dhadley

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Re: Evinrude Carburetors And Boyesen Reeds

Any jet that is exposed meters air. Covered jets meter fuel. Go smaller (less air) to go richer.<br /><br />Good luck!
 
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