Slow speed needle - what's the correct shape?

Swell · Aug 22, 2010

Does anyone know the correct shape of the slow speed needle? This is on a 1968 6hp Johnson CD-25c. The needle is nice and cleanly tapered but with a squared off end as opposed to a point - though it is squared off just before the point would be. I'm trying to correct an idling problem so have removed the freeze plug to find all 4 jets totally clear. So just wondered if the end of the needle might have sheared?

Many thanks,

Roger

jgriner · Aug 22, 2010

Re: Slow speed needle - what's the correct shape?

do all slow speed needles look the same way in the other carbs?
if they do im going to guess yes, but its just a guess.
wait and see if any one else knows for sure

Willyclay · Aug 22, 2010

Re: Slow speed needle - what's the correct shape?

I have a 1973 Evinrude 6HP and my low-speed needle looks like what you described. Another forum member also told me his is the same on a 1975 Johnson. Not sure what is correct.

Daviet · Aug 22, 2010

Re: Slow speed needle - what's the correct shape?

They came both ways, pointed and flat tipped, depending on the application.

Swell · Aug 22, 2010

Re: Slow speed needle - what's the correct shape?

Fair enough, and thanks for the replies. It does look like it's a clean shape as opposed to jagged as it would be if it had sheared.

Only thing now though is that unfortunately I have to look elsewhere to solve my idling problem. It's always handy when you find something wrong as then you know what it is you have to fix!

I will be buying a compression tester as I'm aware that could be an issue, otherwise I'm thinking it could be ignition - which scares me a little as I'm totally unfamiliar with 2 stroke ignition. Is it really necessary to have a special puller tool to remove the flywheel?

Roger

Cofe · Aug 22, 2010

Re: Slow speed needle - what's the correct shape?

If you are suspecting air in leakage, the packing around the idle speed needle gets worn and lets in air. I have used plumber putty, or kid's silly putty to temporarily put on the exterior of the around the needle and carb butterfly shafts to trouble shoot.

Swell · Aug 22, 2010

Re: Slow speed needle - what's the correct shape?

I never considered that. I have fitted new packers, but no harm in trying a bit of extra sealant.

Thinking about it, I don't really understand that needle valve. Is there an air bleed on the threaded side of the needle housing, or a fuel duct? I'm thinking there must be or why have the valve? Not sure if the slow speed needle supplies fuel or air to the engine side of the throttle. Either way, is there another jet to check other than the four beneath the freeze plug?

AlTn · Aug 22, 2010

Re: Slow speed needle - what's the correct shape?

shop2.evinrude.com will have diagrams...BigB9000 has created a website for his 6hp. rebuild...well worth the time to check out...all gas used must flow through the main orfice in the lower part of the carb bowl behind the drain screw..that orfice plug, or jet,must be shiny clean,..as to the 3 jets you're gonna find under that core plug...very tiny holes...I was under the impression they passed a fuel/air mix when the throttle plate was closed, ie. at start, and at idle, however it may just be air that flows through them...either way..at idle, they must be free and clear..

Swell · Aug 22, 2010

Re: Slow speed needle - what's the correct shape?

Cheers I'll check out that site.

I suppose what I'm unsure about is what the slow speed needle valve actually does. If it bleeds air to the engine side of the throttle, where does that air come from if the needle housing itself is sealed using the packers? There must be some sort of duct somewhere within that housing - and the packers are there to ensure it's a controlled flow. I've tried sealing the valve seat i.e. the little hole the needle mates with and blowing down the hole where the needle is fitted to see if air comes out anywhere else and it does seem like there is a slight bleed somewhere, but I can't tell where!

jbjennings · Aug 22, 2010

Re: Slow speed needle - what's the correct shape?

I'm pretty sure the low speed needle controls fuel flow. All the way closed leans it out, opening it up richens the mixture. I would check and see if there is a tiny passage in your fuel bowl which runs up the side of the fuel bowl. It can be tightly clogged and will do what you describe. The opening to this passage is in the side of the face of the bowl.
Good luck,
JBJ

AlTn · Aug 22, 2010

Re: Slow speed needle - what's the correct shape?

you'll see the needle tip when you remove the core plug on the top rear of the carb...those 3 holes enter the rear of the carb throat..I fitted the straw from the aerosol carb cleaner on each hole and got a consistent spray pattern from each

Swell · Aug 22, 2010

Re: Slow speed needle - what's the correct shape?

jbjennings said:
I'm pretty sure the low speed needle controls fuel flow. All the way closed leans it out, opening it up richens the mixture. I would check and see if there is a tiny passage in your fuel bowl which runs up the side of the fuel bowl. It can be tightly clogged and will do what you describe. The opening to this passage is in the side of the face of the bowl.
Good luck,
JBJ

I think I might have seen the opening when I had the float chamber apart yesterday - does it have a brass insert? I did try blasting carb cleaner down it but not sure if it did anything. I'll check again and make sure it's clear - maybe that's the root of my idling problem. Hope so!

Thinking about it, it would have to be a fuel bleed for the slow speed valve cos where else would the fuel come from if the throttle's closed? Also makes sense cos as you open up the slow speed valve it makes it richer, so it must be supplying fuel!

Swell · Aug 23, 2010

Re: Slow speed needle - what's the correct shape?

Just to say that I found the fuel duct from the fuel bowl up the side of the carb to the slow speed needle housing, and it too is clear. I'll try sealing the slow speed needle with something more than just the packers, though I suspect that's not the issue as I had fitted 2 new packers which were a good tight fit.

What else could be causing a lack of idling other than a carburettor problem? (which I'm pretty sure I don't have)

jepstr67 · Aug 23, 2010

Re: Slow speed needle - what's the correct shape?

FYI....the end is not as important as the conical part. Sometimes people will tighten the mixture needle into the seat too tightly and dent the needle. The needle must be a perfect cone, not conical, short cylindrical section, and then conical again. These dented needles make it devilishly hard in not impossible to adjust for a good idle and must be repaired or replaced.

Good point on the leaking needle packing gland. I had not thought of that as a possible air leak!

I had one such needle that was dented from a 1941 33hp Evinrude. I had one of my machinists chuck it up and take a light cut to make it conical again. Totally cured the crazy idle problems.

Swell · Aug 24, 2010

Re: Slow speed needle - what's the correct shape?

I'm just about the replace the freeze plug over the idle jets - does any sealant need to be used? It mentions 'Sealer 1000' in the manual and I've read that there is an equivalent in the states but is there a UK equivalent? Sounds to me like it's basically 'Instant Gasket' which is for metal to metal joins where either there is no gasket or a gasket is missing. I think it's a rubber based material.

AlTn · Aug 24, 2010

Re: Slow speed needle - what's the correct shape?

the core plug is inserted with the "domed" side up and is sealed when the plug is expanded by srikeing it in the center with a flat punch..I used a 3/8" drive extension...if it does not seal completely, some folks use finger nail polish around the rim...as to sealant applied before installation, omc adhesive M was recommended to use around the rim of the plug...you may not need any sealant at all

Swell · Aug 25, 2010

Re: Slow speed needle - what's the correct shape?

I took the plunge and used a tiny amount of Hermetite Red which is a semi hardening gasket adhesive for metal - metal joints which is ok for use with fuel systems. Seems pretty robust stuff. My only reservation was if there was some on the inside rim of the plug which could become dislodged and block one of the jets I'd taken such trouble to clean out! Unlikely as I used so little, but fingers crossed anyway. I also used some to help seal the needle arm where it leaves the carb.

I'll try it out and post the results i.e. if I've fixed the idling problem.

Swell · Aug 29, 2010

Re: Slow speed needle - what's the correct shape?

Didn't sort the idling problem unfortunately, though I'm convinced the carburettor is now fine and it's onto other potential causes. Will leave this post now as it's reached it's end I think.

Many thanks for all the help!

Slow speed needle - what's the correct shape?

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