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  Problems.... Idle or Troll, but not both

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Author Topic:   Problems.... Idle or Troll, but not both
newboater posted 12-17-2001 05:16 PM ET (US)   Profile for newboater   Send Email to newboater  

So I got my first Whaler a month ago, but I'm having some trouble with the engine running at slow speeds and idle. The engine is a 75 Evinrude 40 Hp. So far I've rebuilt the carb, replaced both coils and put a couple of sets of plugs in it.

The carb job was last, and now when I set the low speed idle jet, I can make it run nicely in neutral at idle (1/2 turn out), or nicely in gear at "trolling" speed (1 turn out), but not both. It runs strong at half to full throttle, except for when it cuts out after 20 seconds or so. Iím pretty sure this problem is a weak fuel pump not keeping up with full throttle, but I got a new one of those and Iíll be putting it in the next day or so.

Back to the slow speed problem. When I first got rig I did mix the fuel a little heavy on the oil side because the motor hadnít been run in a long time (Now I don't remember by how much). So I'm going to get rid of the fuel in the tank, replace with new (very accurately measured 50:1 (13oz in 5 gal) Mercury oil). Going to put in another set of new plugs too.

Is there anything else this can be? The local dealer thought I ought to check the recirculation system. Iím not even sure I can get to the little thingy without removing the power head. What is it supposed to do?

Any advice would be appreciated.

Dave S.
San Diego Ca

Peter posted 12-17-2001 07:16 PM ET (US)     Profile for Peter  Send Email to Peter     
I've never seen one of those 40s run smoothly throughout the entire operating range. I'd do the fuel pump swap and then play around with the low speed jet.
newboater posted 12-18-2001 08:23 PM ET (US)     Profile for newboater  Send Email to newboater     

Last night I put in the new fuel, replaced the plugs, and went out for a spin.

No change to speak of. Idles well at 1/2 turn, trolls well at 1.5 turns. Doesn't do either well at the other, but half to full speed runs great.

Then I replaced the points and condenser. It might be a little better, but still it doesn't want to idle in neutral.

Does anybody know what this "Fuel Recirculation System" does? The local dealer implied it was used on the "bigger" motors as well. There are two vacuum lines running from the edge of the cylinder walls to the intake manifold. The manual says there are valves and a screen inside the plate, but "service is not usually required".

I'm thinking maybe there is a vacuum leak, but that would make it want the idle setting to be richer, which is backwards.

Any ideas?

How much is a new 40Hp four stroke? (oh I'm dreaming again...)

Dave S.
San Diego Ca

triblet posted 12-18-2001 11:31 PM ET (US)     Profile for triblet  Send Email to triblet     
If this were a four barrel, I'd think the
low speed metering was stuck.


whalerron posted 12-19-2001 12:08 AM ET (US)     Profile for whalerron  Send Email to whalerron     
When you did the carb rebuild, did you spray some carb cleaner into all of the carb ports and passages and then blow them out with compressed air? It sure sounds like you have a passage or jet clogged somewhere in the carb.

- Ron

goldstem posted 12-19-2001 08:16 AM ET (US)     Profile for goldstem  Send Email to goldstem     
when it is having trouble, is it firing on both cylinders???
one possible gotchya: there is a mechanism that kills one cylinder if there is very high vacuum (an attempt to solve a run-away problem). Be careful if you disconnect it as the motor will not want to return to idle when goosed in neutral
also be sure that the timing is correct and the carb pickup is adjusted right. the throttle should NOT be open at idle.
good luck. I had fun with my old 40, but I can't claim to miss it too much!
newboater posted 12-19-2001 01:08 PM ET (US)     Profile for newboater  Send Email to newboater     

I blew through all passages with carb cleaner and can-o-air. Totally clear and clean.

I've also been a little leery about the vacuum runaway circuit. I'm not sure how to easily tell if I'm getting spark to both cylinders when it's running without pulling spark plug wires which is a little hard to do leaning over the spinning flywheel with the boat in the water, and I hate getting shocked.

When doing some of my testing, I disconnected the wire to the throttle position switch. I hooked it up later, and didn't see any remarkable difference in performance. I'll check the timing too. It seems like it gets full advance long before it gets full throttle. Does this seem right?

The other weird thing is the plate that the points and stators bolt to seems like it has a lot of "float" and play in it. I would have thought it wouldn't move around so much. Any comments on that?

I've never had this much trouble with a 2-stroke before. Usually it's just fuel and spark and they run great for me. Thanks again for the comments and advice.

Dave S.
San Diego Ca

Bigshot posted 12-19-2001 03:05 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
you have never owned an mercury:) Try a couple other things. At cruise squirt gas or carb cleaner in the carb throat and see if it either picks up speed or bogs down. If it picks up speed it is gas related. If it bogs down, your fuel is oK. I am wondering about reeds that is why I ask. If a reed is stuck closed or bent open, she can act up on you. 1/2 turn is tooo lean and 1.25-1.5 sounds pretty good. I think you might still have some carb issues(could just be worn out). Try running it on straight techron mixed with oil 50:1. When the solution is finished, let it sit a day or so and then start it on ether. This will clean anything in the carb and decarbonize the crap out of it. Adjusting timing on these is tough and is 99% never the problem. Points, etc might be. Try the above and get back to me. Now it is a case of trial and error.
Bigshot posted 12-19-2001 03:06 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Ps what is the compression? Low compression will give shitty idle.
newboater posted 12-19-2001 06:05 PM ET (US)     Profile for newboater  Send Email to newboater     

Thanks for the ideas. I didn't even think about doing a compression test because the motor runs so strong at full throttle. The squirting fuel down the carb when it is running is also a good idea.

I'll play with it some more over the holidays while we are out on our trip and report back next year.

Thanks again,

Dave S.

goldstem posted 12-20-2001 08:42 AM ET (US)     Profile for goldstem  Send Email to goldstem     
With those old 40s, it should be pretty obvious if it is only running on one cylinder.
as for the advance, you will definately get full advance before full throttle.
however, there should be a mark on the stator plate that shows where the throttle cam should pick-up.
also, the motor should run as rich as possible at idle, not lean, adjust the lowspeed jet toward the rich side when you get max rpms. you may also have a vacuum leak.
swede5 posted 12-27-2001 12:37 AM ET (US)     Profile for swede5  Send Email to swede5     
Hey Dave, I'm curious as to what your definition of having the carbs rebuilt is? Where the plugs in the carb pulled, cleaned and repaced. Also this may seem crazy but I've worked on a 70hp Johnson, replaced one of the carbs twice, only to find out that the O-ring on the adjustment needle (original carb) was faulty and was fouling up the air fuel mixture. Good luck!
newboater posted 01-07-2002 04:45 PM ET (US)     Profile for newboater  Send Email to newboater     
Hello all,

As Iím sure you recall, in December I was having problems with my Ď75 40 Hp Evinrude. It ran rich at idle, if I leaned out the slow speed adjustment so it would idle, it wouldnít run in gear at trolling speeds. I had rebuilt the carburetor, replaced coils, points, condensers, and multiple sets of plugs. I had convinced myself I must have a cylinder low on compression, as the top cylinder seemed to always be much richer than the other.

I fixed it and it runs great. (At least as well as anyone could expect from a 27 year old motor.)

The Solution:

Any guesses?

Dave S.

kingfish posted 01-08-2002 10:03 AM ET (US)     Profile for kingfish  Send Email to kingfish     
Aw, come on, somebody guess, or Dave, tell us what it was - the suspense is killing me. (It's winter in Michigan - I think I have cabin fever!)


Bigshot posted 01-08-2002 11:20 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
newboater posted 01-08-2002 01:03 PM ET (US)     Profile for newboater  Send Email to newboater     
Ok, Ok,


Fuel Pump.

I never would have thought a bad fuel pump could make something run rich. There was a small hole in the diaphragm and since the pump is operated by vacuum and bolted directly to the side of the crankcase, the top cylinder was getting flooded by extra fuel. It's hard to believe it ran ok at moderate speed with the bad pump.

Anyhow I'm a happy Whaler owner now, and over our vacation we put over 250 miles on it. (ok, 180 miles of it was being towed behind our sail boat, but we probably Whalered around 70 or 80 miles)

Thanks for all the help guys, and I think it was "Peter" who first recommended R&R of the fuel pump.

Dave S.
San Diego

Bigshot posted 01-08-2002 03:35 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Glad you did not screw with the timing now?

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