Different between a Evinrude 3hp and 4hp carburetor?

[cajuncook1]

How can you tell the difference between a 1968 Evinrude 3hp carburetor and 1969 to 1974 Evinrude 4hp carburetor? They are identical in appearance.

I purchased a Evinrude 3hp folder complete lower unit and gear case. I was able to get a 1968 Evinrude 3hp completed power head with magneto and starter with very good compression. The power head was missing the carburetor.

I found what appears to either a 1968 Evinrude 3hp carburetor or 1969 to 1974 Evinrude 4hp carburetor in a box of parts from a past deal.

??? Would I have to measure the venturi throat of the carburetor to distinguish between the 3hp and 4hp???

– Does someone have the internal diameter of the 3hp carburetor venturi ???

Thanks for any help. Piecing together a 1968 Evinrude 3hp Power head to 1966 Evinrude 3hp complete lower folder unit to make a full motor.

Cajun

[frankr]

Don’t know, but I think you are on the right track with the venturi size.

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cajuncook1

[outbdnut2]

If you compare part numbers for parts in the carb at Marineengine.com or similar place, you will fined that the nozzle Part #28 (the venturi) and the throttle valve part #3 (butterfly) are different part numbers. I think the rest is all the same. Since the high speed jet is adjustable, the 4 HP carb may work OK on your 3 HP – I’d try it! Not sure, but my guess is the small holes in the throttle valve are probably a different size. I ran across similar differences a few months ago between a 7.5 and a 9.8 Mercury carb. The holes in the throttle plate control how much air it gets at minimum idle where the throttle is closed all the way, so on your 3 HP, the 4 HP carb may not idle down quite as slow as the 3 HP carb – but if that’s a problem, plugging one hole may help. Let us know what you find – you’ve got me curious now.

Looking again – part #23, the high speed needle valve is also different part number, but that could just be a different length or knob attachment detail.
Dave

Trying to post a pic below:

http://www.marineengine.com/parts/evinrude-johnson-parts-diagrams/EVINRUDE/39864.gif

• This reply was modified 3 years, 2 months ago by outbdnut2.

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cajuncook1

[cajuncook1]

Like Dave stated there are only minors differences. All parts are the same except 4 parts

1968 Evinrude 3hp Carb …………………… 1970 Evinrude 4hp Carb

Part #3

0302983 – Throttle Valve ………………….. 0315172 – Throttle Valve

Part #12

0383008 Float Chamber Assy………………….. 0383755 Float Chamber Assy

Part #23

0312824 – High Speed Needle………………….. 0315174 – High Speed Needle

Part #28

312971 – Nozzle High Speed ………………….. 0316598 – Nozzle High Speed

The carb that I have has a casting number on it found on the Float chamber assembly that I can’t match up with anything. 315175

• This reply was modified 3 years, 2 months ago by cajuncook1.
• This reply was modified 3 years, 2 months ago by cajuncook1.

[JOHN HOLBIK]

If memory is correct intake manifold on 4 has larger holes and I think the throat hole is larger.

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cajuncook1

[fleetwin]

Well, this is an interesting topic, something I have wondered about before….
I compared the 68 3hp to the 69 4hp also on marineengine.. They do list a part number for the stripped carb upper body (no shafts/butterflies), and that number is the same for the 3 and 4hp models. So, it would appear as though the venturi size is the same for both models. The throttle valves, nozzle, bowl and high speed needles are different though. I really don’t think the length of the needle valve is the issue, the pans are the same for both years, the low speed needles are the same as well. I guess it makes sense that a change in the design of the high speed needle tip would require a change in the bowl to accommodate it…
Would love to see the bowls/needles and be able to identify the differences. Mixing this stuff up would probably create a nasty carburetor gremlin…

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cajuncook1

[JOHN HOLBIK]

I may be wrong but the memory of me fifty years ago when my dream was to make a 3 go as fast as a four.I had a 4hp carb and I can clearly remember filing the reed plate intake opening larger with a rat tail file.I think some American tourist girl at the resort convinced me life was better with out the filing.I always liked the tank on the top 3hp weed less having the extra zip of the four would have been great.I could not due the power head swap because the 4hp did not have the holes for the 3hp recoil also my tool selection was severly limited.I was just a 12 year old kid and kept those motors running at the resort with a few screw drivers a couple wrenches hammers and a 1/2 set of 1/2 sockets and my most used tool feeler gauge and my prized possession a pair of vise grips.I must have changed 15 or 20 water pumps on CD12s half in pitch dark millions of biting mosquitos no flash light .I don”t know how many clutch cones I reversed on the cd5/2s those customers had some terrible shifting tecniques.We had lots of other motors with there own little Quirks.Thank god we had hydro electric when we got our MQ 9.5 great motor but a real treat to work on.

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cajuncook1

[cajuncook1]

Sorry guys, I didn’t mean to vanish from the post. I was stuck at the hospital all weekend. Work load has increased much more these past 3 weeks.

Just to be clear, I an not trying to make a Evinrude 3hp into a 4hp motor.

I am trying to figure out how to identify a 1968 Evinrude/Johnson 3hp carburetor from a 1969 to mid 1970’s 4hp carburetor.

I found a carburetor in a box of parts from a past deal. It looks like it maybe a 1968 Evinrude 3hp carburetor.

I will try to compare to a known 4hp carburetor and keep in mind the stated findings from the post above.

Cheers,

Cajun

[dave-bernard]

early 3’s had choke pull on right side later 3”s and 4’s was on the left.

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cajuncook1

[cajuncook1]

You are correct.

The 1968 3hp carburetor has the choke linkage on left just like the 4hp motors. Quite the challenge 🤔

There are no physical embedded part numbers distinguishing the two carburetors.

I will have to examine/measure the Venturi throat and the high speed needle. Hopefully I can find a distinguishing part and properly ID the carburetor.

Cajun

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