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Setting Hi press on 73 185 IO-520

Tom3holer

Tom3holer

MEMBER
Cape Cod
My mech and I have have set the low press unmetered press and mixture as it was off quite a bit.
Now we are trying to set the high press and can't seem to see/find the adjustment screw.
The engine is a 2009 FREM IO-520D and the we cannot find the screw.

Any thoughts?

Tom
 
Not the back of the pump for full throttle needle!!!

The full throttle pressure adjustment needle screw is on the left side of the pump below the inlet fitting ( the larger fitting on left side of pump). On your engine it will likely be accessed thru a small hole in the alternator mount/engine mount leg just below and just forward of the alternator pulley fan. Some are slot screws, yours is likely a 5/32" allen wrench.


Look in that hole with a flashlight and you will get the picture.

Your mechanic has probably hated all this advice from those Supercubdotorg guys, but this time we are saving his ass, if not his pride
 
and the hole in alternator leg Dave speaks of might not be in the right location :) you may need to modify it....

i welded up a LONG Allen wrench end to a thin screwdriver

(and we always set the Hi a few pounds higher than stated in manual... 3 pounds hi)

allen driver.jpg
 

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mike mcs repair said:
and the hole in alternator leg Dave speaks of might not be in the right location :) you may need to modify it....

i welded up a LONG Allen wrench end to a thin screwdriver

(and we always set the Hi a few pounds higher than stated in manual... 3 pounds hi)

View attachment 29360
Click to expand...

Mike's point re: setting the high pressure setting higher than recommended is important, and right on.....

MTV
 
Thank you all for the advice.
We wound up removing the alternator. Your right the access slot does not quite line up with the 5/32" allen screw so may mill it a bit.
Do you have to loosen the outer nut/collar to be able to turn the allen screw? We did not want to stress the screw till we milled the slot to be able to get a allen wrench in there square. Actually my mech has been very appreciable of all the advice I bring him from you guys.
Tom
 
Last edited:
Mike,

You are right, I looked all over the TCM and Cessna manuals for my year plane and their guidance was very weak and incorrect on this important area.
 
Tom3holer said:
Mike,

You are right, I looked all over the TCM and Cessna manuals for my year plane and their guidance was very weak and incorrect on this important area.
Click to expand...

you are just lucky there IS A MANUAL for yours!!!

you are here on the supercub site, and there isn't a manual for these...
 
you are jogging my memory... been decade ++ or so...

the other piece of the puzzle is,

once you have set(and rechecked BOTH the hi and low fuel pressure numbers) you want to adjust the mechanical mixture adjuster between the butterfly and mixture, till you get some black smoke exhaust at very LOW idle... if your cam lobes are in good shape, you will be able to go down to around 350 RPM on the ground idle and keep it running reliably.... not that you will want to idle this low ever, but it allows you to SLOW down the plane in the air on final, and land short....
 
Last edited:
mike mcs repair said:
you are jogging my memory... been decade ++ or so...

the other piece of the puzzle is,

once you have set(and rechecked BOTH the hi and low fuel pressure numbers) you want to adjust the mechanical mixture adjuster between the butterfly and mixture, till you get some black smoke exhaust at very LOW idle... if your cam lobes are in good shape, you will be able to go down to around 350 RPM on the ground idle and keep it running reliably.... not that you will want to idle this low ever, but it allows you to SLOW down the plane in the air on final, and land short....
Click to expand...

And idle up to a dock slow.

MTV
 
mike mcs repair said:
and the hole in alternator leg Dave speaks of might not be in the right location :) you may need to modify it....

i welded up a LONG Allen wrench end to a thin screwdriver

(and we always set the Hi a few pounds higher than stated in manual... 3 pounds hi)

View attachment 29360
Click to expand...

Mike, seems to me you should have your own mail order tool catalog! You are clever. Wish I had Grandpa's hand made tools from the 30's-70's. Maybe some day they will surface.

I third the extra fuel. Helped on jug change to prove it.
 
Mike,

Had not heard of that but sounds interesting.
The engine has 160hrs on a factory reman. It seemed to idle kinda lumpy for the lack of a better term. I decided to check the idle pressure and mixture first with a new 0-15 psi gauge. hooked it up and it was slightly beyond the high end pf the recommended range 9-11psi. The sage advice was to set it to the low end at 600rpm which I did. Had to readjust the mixture quite a bit to get the 50-75 rpm rise. When all that was done noticed the WOT FF which had been at the red line was now just slightly over 24gph. We will set it up tomorrow to around 26 gph per the calibrated installed JPI FF gauge.
 
Sorry. But I am a firm believer in a calibrated gauge for setting fuel flow per the manual. I do not use the fuel flow meter. I suggest your mechanic use a calibrated gauge. Really.

Yes, Mike, the Cessna book describes the idle peessure screw when they are writing about full throttle pressure adjustment

Tom, you do NOT need to loosen the collar to adjust the full throttle screw. And do NOT use a ball end allen wrench. Use a square ended allen wrench.

MTV, and stop a moving skiplane with a nice low idle! Maybe!
 
Don't know about the Cessna 185 manual but the Agwagon manual has a very detail description of everything.
 
The 69-76 U206 service manual describes the wrong screw for full throttle pressure adjustment also.
 
Happy New Year and an interesting one it is sure to be.

Thanks for all the help. I have not seen any mention of accessing it through the alt bracket published in any of the Cessna pubs but after a moment with a dremel tool to align the slot up correctly am able to adjust it with the cowling on now.
Thanks again for all the help and advice.
 
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