78 evinrude 25 hp with rebuilt carb...idle issues

pottord

Cadet
Joined
Nov 2, 2009
Messages
8
I just rebuilt the carb on my 78 25hp....everything is great except the idle. It will fast idle in neutral, but the minute you slow down the RPM to the shift setting or lower the popping begins and will kill the motor. (New power pack have been install just two months ago with good spark.) I adjusted the low speed needle valve but that doesn't make much of a change. It is almost all the way out to get it idle some what.

I put it in some paint thinner for a few hours because I could not get the main metering tube out of the carb base and remove the plastic vanturi. All passage ways were blown clear with my compressor. I wanted to put it in some good old carb cleaner, but no go with the plastic in place.

The duck season is here and I need some help or advice? I can't trust this to run the river if it will not run correctly.

Can you get a new replacement carb for this year and model?

Thank dp
 
Joined
May 4, 2009
Messages
18
Re: 78 evinrude 25 hp with rebuilt carb...idle issues

That usually means the air/fuel mixture is to lean, I had the same problem with an 18hp, I rebuilt it but the gasket that sealed the low needle screw wasn't very good so i had to put another one on and adjusted the screw out a bit and it fixed it.
 

pottord

Cadet
Joined
Nov 2, 2009
Messages
8
Re: 78 evinrude 25 hp with rebuilt carb...idle issues

My kit came with a new seal, I think it was red in color and replaced the outer seal is all I could find on the carb. I could not find a seal closer to the jet. I looked at removing the jet but I could not find a good way to do that. I would have loved to remove it and clean it out totally!
 

kbait

Commander
Joined
Nov 13, 2007
Messages
2,446
Re: 78 evinrude 25 hp with rebuilt carb...idle issues

Sounds like low speed circuit is clogged. The needle jet meters fuel flow from pickup in carb bowl when assembled, to the little holes in the carb throat near the throttle butterfly. Make sure those are clear, and should be good at low speed adjustment about 1 turn out..
 

Elbo

Petty Officer 2nd Class
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Sep 12, 2009
Messages
136
Re: 78 evinrude 25 hp with rebuilt carb...idle issues

There are two small packings that go in before the plastic grommet that fits the keyway,the notch in the needle hole,If you put the packing in before the needle went in,odds are the packings got pushed down into the needle jet oriface .Ckeck the hole in the carb where the needle goes in and see if its plugged.The packing stops the air from intrusion, the grommet keeps the needle from backing out.
 

tashasdaddy

Honorary Moderator Emeritus
Joined
Nov 11, 2005
Messages
51,019
Re: 78 evinrude 25 hp with rebuilt carb...idle issues

looking at the diagram, http://shop2.evinrude.com/ext/index.aspx?s1=bf6ad09c53cead335fcfd8a6471c0f7f , both jets high and low speed are fixed jets. it sounds as if you did not get the top jet clean or the orifices that the fuel comes out into the barrel, or the slow speed pickup tube. the pick up tube is the small tube inside the large tube, into the bowl.

orifices, fuel comes out, into the barrel.
carbdetaillowspeedventuri001.jpg
 

pottord

Cadet
Joined
Nov 2, 2009
Messages
8
Re: 78 evinrude 25 hp with rebuilt carb...idle issues

Looking at the pic of the throttle plate mine is upside down.... after looking at BRP pics of the carb the whole in the plate should be towards the bowl. In the pic sent the whole is near the top of the idle ports.

Any idea which is correct?
 

bhughes

Seaman
Joined
Apr 28, 2009
Messages
57
Re: 78 evinrude 25 hp with rebuilt carb...idle issues

Why don't you try actually cleaning it with carb cleaner first, then see if it works.
 

bktheking

Vice Admiral
Joined
Jul 29, 2008
Messages
5,057
Re: 78 evinrude 25 hp with rebuilt carb...idle issues

Take it into a small engine shop with an ultrasonic cleaner, pop the welch plugs out and get them to clean it for you, don't waste your time with thinners and buying carb cleaner.
 

pottord

Cadet
Joined
Nov 2, 2009
Messages
8
Re: 78 evinrude 25 hp with rebuilt carb...idle issues

All is well...I took out the low speed ajustment needle and removed the plastic packing piece (none was on it when disassembled, which I took for it was missing or removed by someone else.) Reassembled it put it back on and she runs great and will idle....duck hunting agian today will be the acid test of the carb overhaul.

Thanks for all the help and ideas!

Got to be some ducks some where that need killing!

dp
 
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