66 Big Twin won't throttle up, Carb Issue I believe

[juicebronco]

So this summer I picked up an Evinrude 66 Big twin model 40652B. After rebuilding the carb and replacing the fuel pump I got it running. I can start it, it idles fine, and can drive around at low speeds no issue. However, when I try to get on plane it starts to rev, then the rpms come back down, and it may stall, if I reduce the throttle, I can keep it running. I have the carb in the Auto position, and if I reach back and open it while trying to plane out, it will cut out. I was adjusting the choke spring thing on the side, that has an arrow one direction that says lean, and I could get it to where the motor would kind of surge when I gave it gas. It would start to rev up and go, then come back down, then rev up again, and back down.

To me this indicates an air fuel mixture issue, am i correct? I'm more of a carb novice, so I'm not exactly sure where to start.

 

[RCO]

You could have the float too low, or lack of flow from the fuel pump. Try squeezing the bulb at WOT throttle to see if the symptoms improve. Run the choke manually until you get the motor running right, it should not come into play at all when you are accelerating. Did you remove the high speed orifice and clean it VERY well when you had the carb apart? Also make sure your tank is venting properly and there are no leaks in the connectors of lines anywhere.

 

[juicebronco]

I was trying to squeeze the bulb, it seemed to help maybe just a touch, but hardly noticeable. I did remove the high speed orifice plug, and clened it when I rebuilt the carb. The tank is venting properly, it runs my 20 horse with no issues.

I tried manually operating the choke, and didn't have much luck. I was trying to find a happy medium between closed and open, while accelerating, and just didn't seem to get much accomplished, but I could try some more.


Would the float not being set right effect high speed operation? I can adjust it up a little so it brings more fuel into the carb.


Thanks

 

[F_R]

Sounds like a fuel supply issue. That is, it does if the high speed jet is truly clean as you claim. Fuel supply can be anything between the level of the gasoline in the tank and the fuel pump (sucking air). Or yes, a bad fuel pump or an obstruction in the carburetor.

Until you get it figured out, once you get it started, flip the choke to manual off position. You don't need any choke on a running motor after the first half minute or so.

Stop right now and check the compression and ignition system. No sense in beating a horse with other issues.

 

[juicebronco]

I did a compression test when I picked up the motor, I think it was around 120, I don't recall the exact number, but both cylinders were pretty close.

So you are thinking it's fuel delivery, I'll double check the high speed orifice for being clean.


I had the engine warm, and had the choke held wide open and it still wouldn't wind up, it actually did better with the choke semi closed. So that would indicate too much air, not enough fuel, so I need to be looking at fuel getting into the carb. Thanks.

Hopefully I can attack it tomorrow or Tuesday.

 

[racerone]

Sounds like it is running on one cylinder check for 1/4" spark or more on both leads.

 

[juicebronco]

PROGRESS! Thanks for the help.

What I did: I adjusted the float about a mm, to let more fuel in, and I pulled the orifice out and cleaned the tube again, which did happen to have some crud in it. Which isn't that surprising being I had the bowl off a ton of times getting the float dialed in.

The Results: I was able to get it on plane with the carb manually opened. It started starving for fuel, so I pumped the bulb and I was able to maintain plane as long as I kept pumping the bulb.

So, to me that sounds like the carb isn't having an issue asking for fuel, but having trouble getting fuel to it. I did replace the fuel pump, but it's not like a part has never been faulty before. Anyway, my suspect is the fuel pump, any thoughts?

 

[F_R]

Was it a new pump? If yes, check for air leaks as I already suggested.

 

[juicebronco]

It wasn't a new pump, it was a tested used pump. Even had a guarantee with it. The only reason I bought it was because I dropped part of the original pump in the barrel of water, and never thought I'd find it and get it back together. Although I did, and I'm pretty sure I have it together correctly. So I have that one I can try as well.


What is the best way to go about checking for air leaks?