1955 25hp Evinrude BigTwin wont idle

[D_B]

The motor ran decent 6 years ago, then sat unused. I overhauled it last summer with all new wiring, gas lines, impeller, coils, condenser, and carb kit but she absolutely will not run at low throttle. I adjusted the needles several times and even went through the carb again thinking there was a blockage. Slow speed needle looks ok, and new packing didnt help. Motor will fire up pretty good, then as soon as I pull throttle back it immediately dies. Using a trolling motor to get around the dock, I took her out on the lake and ran 1/2 tank of gas at medium-high throttle. No improvement.

At this point, I am close to throwing in the towel and buying a new motor but I was convinced by the restoration forum to see if you guys had any ideas to fix the Evinrude. The compression is decent (115 and 113) so I think she has life left. Im definitely a weekend mechanic, but I can follow a manual and any help would be much appreciated. BTW, my boat is a 57' Lonestar King Commander and the motor is model RDE-17.

 

[oldcatamount]

Re: 1955 25hp Evinrude BigTwin wont idle

chances are good you are running on one cylinder. check spark with an air gap tester. should jump a quarter inch or more.

 

[HighTrim]

Re: 1955 25hp Evinrude BigTwin wont idle

...Can also try pulling plug wires.

You should hear a noticeable drop in RPMS when you pull a wire. If there is no change in RPMS, that cylinder was not running. Then if you pull the other and it dies, proves the point.

 

[D_B]

Re: 1955 25hp Evinrude BigTwin wont idle

Huh, I never thought it might be running one cyl. I did a spark test initially, both cylinders sparked but I didn't test 1inch (maybe a 1/4). However, the engine runs like a bat out of hell under full throttle (every bit of 30 mph). Could the dead cyl kick in under high rpm?

I'll try to test spark and pull one plug this weekend and report back.

 

[nwcove]

Re: 1955 25hp Evinrude BigTwin wont idle

if yer running like a scalded cat at wot, dont give up on the motor! do the drop cyl test at idle, and get an open air spark tester to make sure it will spark across 1/4 gap with a good audible snap! could be as simple as a coil being set a bit back to far to fire with a strong spark at idle. jmo

 

[Crosbyman]

Re: 1955 25hp Evinrude BigTwin wont idle

did you check the slow speed carb circuit up to and including the upper drip chamber under the dime size plug on top of the carb.

you need to pull the core plug (drill a centered hole and remove it with a pick) then clean the chamber, check the tip of the l/s needle
insert a new plug, punch it closed and seal it with finger nail polish.

 

[Will Bark]

Re: 1955 25hp Evinrude BigTwin wont idle

Be careful drilling that hole just go thru the plug and don't hit the bottom!

 

[oldboat1]

Re: 1955 25hp Evinrude BigTwin wont idle

+1 ^^. I’m with Crosbyman and Will bark on opening up and cleaning out that chamber. Along with potentially solving some problems, it also gives you a chance to see and feel how the low speed needle seats. Get out any bits and pieces up there, and screw in the needle just to test – get to see from the top how it fits, and how it feels to gently seat. When it’s all closed up, you have to do that by feel.

Thing is, you need an expansion plug to put back up there, so best to have one before pulling out the old one. Think I would first check your tank, lines, clips for leaks. If a pressure tank, needs to hold pressure (cap tight). If a one-line system, vent has to be open and working, and fuel pump has to be in good shape (no holes in diaphragm, for example). The fuel mix is 24:1, according to specs. Running at high rpms, I would at least hold to that mix initially. Plugs are J6C, gapped to .030.

Points: .020 gap, and clean.

There is a safety switch on your motor that shorts out a cylinder when you quickly throttle down from high rpms (safety feature). If it malfunctions, it’s one of a number of electrical gremlins that can cause some issues. Shouldn’t assume that’s your problem at the moment, though.

Good rig!

 

[D_B]

Re: 1955 25hp Evinrude BigTwin wont idle

Carb chamber: the 2nd time I overhauled the carb I removed plug and cleaned well including fine wire through all small passages. Did not think to seat needle while open (doh!).

Tank pressure: thumb button stays hard, which I assume means no pressure loss. But I have always assumed the no idle problem was lack of fuel.

Gas/plugs: I always go by the sticker inside cowling 16:1 (I think) and 0.30 gap.

Cut-off switch: I bypassed this switch already, but it didn't help.

Argh!!!

 

[HighTrim]

Re: 1955 25hp Evinrude BigTwin wont idle

All the thumb button on the pressure tank does is send fuel to the carb bowl. Has nothing to do with pressurizing the tank, the motor does that.

Did you try pulling the plug wires?

 

[oldboat1]

Re: 1955 25hp Evinrude BigTwin wont idle

that cylinder drop test that H.T. describes -- should do that.

Also, I had a problem dialing in one of the '50s motors I tinkered with, and it turned out to be a broken reed -- one of the petals was broken off (nothing subtle). I think the symptoms were similar to what you describe. I was unable to tune the motor until I replaced the reeds/reed petals. Maybe with a heavy fuel flow drawn through, high speed operation wouldn't be affected (guessing at that). But I know idle operation was definitely affected. btw -- thanks for the note on that 16:1 instruction shown in the cowling. On that basis I would run with the richer mix too, rather than the 24:1 ratio I mentioned.

 

[D_B]

Re: 1955 25hp Evinrude BigTwin wont idle

Motor update: I picked up a spark tester, and got equally good spark both plugs. After some fuss, finally got her started (its been 6 months) and pulled each wire under high throttle. Pulling either wire caused bad sputtering, ergo both cylinders firing fine. Since motor dies at low rpm, I couldnt try pulling wires under idle speed. Not sure what to do next, I dont see any twisting of plug wires when cam plate is turning that might short out one wire at low throttle. Also, I made a mistake on fuelil. The cowling says 1qt oil per 6 gal gas = 24:1 (sorry oldboat). Where are the reeds? Is these the flower-looking things inside the crankcase? I already checked and cleaned the V-shaped bleeder valve on the side of the motor.

 

[oldboat1]

Re: 1955 25hp Evinrude BigTwin wont idle

Hi D_B. Sounds like maybe you’ve already been back to the reeds, but maybe not. Carb is bolted to the inlet manifold. The reed plate and reeds are in behind – will be a gasket on the front and back of the reed plate. You can see the reeds (reed petals) through the front of the plate. I would check and see if you can see the reed behind each of the openings in the plate (tot of seven in each of two circles on your motor, I think – not sure.) Reeds have to be straight and flush against the plate. If petals are broken, you should see that from the front of the plate. I usually close it back up at that point if it looks good – flush and unbroken, but you can remove the plate and check further (reed stop(s) on the back of the plate).

 

[lindy46]

Re: 1955 25hp Evinrude BigTwin wont idle

Carb chamber: the 2nd time I overhauled the carb I removed plug and cleaned well including fine wire through all small passages. Did not think to seat needle while open (doh!).



Argh!!!

I've seen the casting where the needle seats chipped/broken from someone tightening the needle too much. That could cause idle problems.