Evinrude Big Twin: runs on choke only


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Typically loose reeds (as in not properly installed during a rebuild) will give you a very hard starting engine that requires a lot of fuel and will only run at well above idle. You should also experience backfiring through the carb......Yours did not. Up to you if you want to check while the carb is off.
My setup was different than yours - I was working on a Merc, where mine weren't seating tight and I could see light through them. They certainly weren't loose, I did not have backfiring through the carb - that's something you won't miss by accident.

I did post about it with pictures when I fixed it...here's the link:

Okay, this thread is going a bit off topic.
Seeing light through the reeds (typically near the tips) is not necessarily something that has to be corrected "immediately".
You have to remember a couple things.
1. The crankcase has both positive and negative pressures going on as the piston travels up and down in the bore.
2. A slight opening in a reed will immediately close with the positive pressure and seal against the reed cage. This is why you never had a backfire through the reeds and out the carb.
Hi everyone - an update.
. The idle mix needle washers are all fully compressed.
. Idle mix needle out 1 turn to 4-1/2 turns (1/4 turn at a time, run on choke for 15 to 20 seconds before trying to open the choke) didn't do the trick.
. Tomorrow I'll remove the starter, remove the carb, confirm the nozzle gasket at the bottom of the bowl is compressed to create the right vacuum. Will also confirm that high speed orifice is clear.
. If all that looks right, will re rebuild the carb (r&r plugs, float valve needle/seat, every hole and passage, make sure idle mix needle is fully seating, etc.) as soon as the kit arrives. Hopefully tomorrow.

I really appreciate everyone's help with this. Will keep you posted.
The only other basic idea I'd have is that somehow the float is not opening the valve. It can appear to function without the bowl attached, but a gasket that compresses can protrude and jam the float in the closed position... etc... I'd look hard at that...

Beyond the horses the next step is zebras.... is it possible that someone might have tried to re-assemble the motor before you with mismatched parts ? Based on what we found in the parts diagrams.... The mid year parts changes could have resulted in improper parts being matched to the motor ?
All indications are that you are NOT getting fuel up and into the idle circuit. The choke by-passes the idle circuit and shows you that the engine will run and is properly sealed as it runs pretty evenly and smooth on the choke.
This may have to wait until Monday but I have a carb at the shop for one of these or maybe another at the warehouse that I can check today. Will look at one or both and see if there is anything I am missing.
Note the differences between carburetors from 60 to 61. It's possible that you're working with mixed parts...



1960 Lark:

Note that the 1961 carb shows a donut on the main jet... 1960 doesn't.... etc...
Here's a 61 with some good photos to compare.... an unmolested second carb would be the easy way to figure out if the one you have is kerfuffled….


a 62:
I always try to keep a 2nd parts motor of anything that I have in service for me.... a 2nd carb brings to mind a similar story.... my 58 35 hp ran ok... but just seemed to be lacking that full throttle anger that I expected... on a whim one day I took the carb off a 59 35hp parts motor I had in the stable... cleaned and rebuilt it... put it on the 58 and it suddenly ran like a scalded cat... never could figure out why....

A second carb would be a cheap addition to your arsenal...
Thanks again to both of you; it's nice to know you're out there trying to help me get this one put to rest.

I looked through marine engine.com, my manuals, and some photos. Looks like I do have the 61 carb, so at least it's matched and I was looking at the right schematics, etc.

I pulled it off this morning. It was a lot dirtier than I expected, for something I rebuilt in October. High speed orifice was oozing dirty fuel mix, and the cavity behind the idle Welsh plug was nasty. If I hadn't taken the photos, I would have thought I just imagined having rebuilt it. Bowl was clean, oddly. Cork packing gaskets were falling apart. Idle mix needle hole (where the brass needle seats) was plugged with some kind of goo. Looked like caulk... Surely not. Although my original photos show the 3 main holes and 5 smaller ones leading to the carb body were completely clear, I don't remember checking that mix needle hole the first time.

Fuel filter and pump screens clear. Nothing visible in the tank or lines (this is the setup I use regularly on another engine). The only 2 things I can think of:
1. That idle mix needle seating hole might have been clogged all along. I didn't see anything else like that during the initial rebuild, and I don't remember checking it (and no photos of that hole, so I bet I didn't look at it).
2. After the power head rebuild and carb reassembly, I put the engine on a stand on the back of my truck to take it to the lake. Didn't put the cowling on, and my truck bed usually has dirt and mulch in it from a yard project. Could that much dirt have swirled around and then made its way into the carb? Never even heard of such a thing, but I can't think of any other explanation.

Back together now. One question before I install and try again. The schematic shows the following order for the idle mix packing: cork, plastic, plastic, cork (with the bushing under all that, and the nut on top). I had installed plastic, cork, cork, plastic. Does that matter? Which way is correct? My 70s ones all have a squishy red plastic one -piece, so this one isn't as familiar to me.
All good. Thanks to everyone who encouraged me to stay focused on the fuel.


Plastic cork cork plastic is fine as the plastic is acting like a bearing surface and the cork will compress.
Glad you got it running without going to some of the extremes that were suggested. BTW - I was down at an antique outboard meet today and had a chance to look at a 57 35hp carb. I was looking for anything I had missed and found nothing yet we knew it had to be in the idle circuit.
What did the debris look like? By chance was it the same color as the diaphragm in the fuel pump? Just an educated guess that the diaphragm in the pump may be on it's way out and what it is shedding is going through the carb. check it.
Thanks Pappy. The debris was more sludgy and brown than synthetic and black. I checked the fuel pump today even though it was rebuilt and the diaphragm was replaced in October (I agree it made sense given all the dirt I found today). Everything was clean in the pump.

I still need to get it in the water with the prop on and get the carb tuned (right now it's only 3/4 turns out and idling a little high and rougher than I'd like), but I'm really happy that it's running at this point.
It's a good lesson for all. No matter how diligent and well informed, as you certainly were, there should always be the first assumption that you likely just need to redo something you thought you did properly.... Then move on to zebras only after you've triple checked the obvious...

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