Evinrude question

[carbineone]

Heres the deal.I have a 1974 50HP two cylinder Lark..I was doing some testing to see if the top cylinder is maybe not putting out the power it should.If I remove the top plug wire and just run the motor quick on the lower cylinder my Tach says the bottom cylinder is running 3000RPM.When I pull the bottom one off and run it on just the top cylinder I am only getting 2000RPMs.

Things I tried are I swapped the top and bottom coils to each other and still the same low RPM on the top cylinder.I checked the spark in the top cylinder and it jumps a good 1 inch blue consistent spark..The motor has 160PSI in each cylinder..It may be carb adjustment but I have messed with that and still always get the 1000RPM descrepancy between cylinders.I also cleaned the Carbs and even before cleaning them they were very clean..Both plugs are new but they are champions so theres a possibility that could be it but you would think even a brand new Champion would work a little while.No I guess I swapped the plugs between cylinders and still the same.

Any thought what may be going on? The only other thing I can possibly think is there a possibility something in the way the electrical is set up that may cause the top one to run low RPMs when the bottom plug wire is unhooked but you would think that would go both ways if so.I do not know if that a possibility but who knows...Any thought appreciated...Thanks

 

[Bob_VT]

Re: Evinrude question

I have never heard of testing an outboard by disconnecting a cylinder. Where is this test originated?

Are you saying that the cylinders are turning at different speeds???........ which is impossible.....

Are you doing this while out in the boat? OR are you doing this test on muffs or in a drum full of water.

 

[carbineone]

Re: Evinrude question

Just running in a tank.actually its a common test to pull a plug wire off momentarily to see if a cylinder is running on all kinds of engines...Not that uncommon at all...You pull one off a multi cylinder engine at a time and see if it makes a difference in the way the motor runs and if it makes no differance you more likely found your bad cylinder....Been done for probably as long as engines have been around...

No I am not saying the cylinders are doing revolutions differantly as that is impossible but one that runs at only 2000RPMs at the same throttle setting as one running 3000RPms at the same throttle setting obviously does not sound right to me and the lower RPM one has to have a miss in the cylinder either eletrical or fuel related to have a lower RPM reading at the same throttle setting..Got me why one cylinder reads lower RPM on my tach than the other thats running the same identical throttle setting and thats why I asked!

 

[bassfearmee]

Re: Evinrude question

Your fuel pump pulse is drawing power from the area of the top cylinder. This would explain the difference you're seeing. But I've never heard of intentionally pulling plug wires and running an engine like that. It makes no sense to me. If you have even compression and engine runs good, be happy.

 

[1946Zephyr]

Re: Evinrude question

Just running in a tank.actually its a common test to pull a plug wire off momentarily to see if a cylinder is running on all kinds of engines...Not that uncommon at all...You pull one off a multi cylinder engine at a time and see if it makes a difference in the way the motor runs and if it makes no differance you more likely found your bad cylinder....Been done for probably as long as engines have been around...

No I am not saying the cylinders are doing revolutions differantly as that is impossible but one that runs at only 2000RPMs at the same throttle setting as one running 3000RPms at the same throttle setting obviously does not sound right to me and the lower RPM one has to have a miss in the cylinder either eletrical or fuel related to have a lower RPM reading at the same throttle setting..Got me why one cylinder reads lower RPM on my tach than the other thats running the same identical throttle setting and thats why I asked!

I totally agree with this gentleman. This is a trick that I myself learned way back too. It's a good way to also check on your car engines to see if you have a cylinder with a burned valve. If you pull a plug wire and no change is made in the idle, then it's a good way to find the problem cylinder. As far as your outboards go, running it on each cylinder, is a good way to see if it's firing and running equally. A lot of these old twins will run okay one one cylinder but won't have the guts to wind up the way they should. Pulling each spark plug to run each cylinder alone, is a good and quick way to find the problem quickly.

As to why his RPM's change? That's a mystory to me.

 

[Tim Frank]

Re: Evinrude question

I totally agree with this gentleman. This is a trick that I myself learned way back too. It's a good way to also check on your car engines to see if you have a cylinder with a burned valve. If you pull a plug wire and no change is made in the idle, then it's a good way to find the problem cylinder. As far as your outboards go, running it on each cylinder, is a good way to see if it's firing and running equally. A lot of these old twins will run okay one one cylinder but won't have the guts to wind up the way they should. Pulling each spark plug to run each cylinder alone, is a good and quick way to find the problem quickly.

As to why his RPM's change? That's a mystory to me.

I don't think anyone is disagreeing with popping a plug lead to confirm that both cylinders are firing...most everyone knows that trick.

But I would never expect the two cylinders to operate independently at exactly the same RPM. There are just too many contributory factors that will work against it, but the motor will still perform fine.

OP does not say what his performance concern is; if if he is testing "just because", I think he does not have a problem and is wasting his time. JMO.

But I've never heard of intentionally pulling plug wires and running an engine like that. It makes no sense to me. If you have even compression and engine runs good, be happy.

^^^ Well put.

 

[carbineone]

Re: Evinrude question

Well it just seems that I am not getting the power I should out on the lake.it does run fine at higher RPMs but maybe has a miss at low idle in the top cylinder for sure and maybe that top cylinder is just not developing the power it should.We are going to take it on the lake today and do some carb adjustments that we read about here.It appears that these are not really adjustable for high speed setting as they are factory set but there is a needle for setting the low speed I believe.Bassfearme,maybe you are correct on the fuel pulse thing and like the other fella said maybe you will not ever get the same RPM reading on each cylinder and I am just overeacting to it..By the way Bass do not fear me they sit down there and laugh at and taunt me,DEVILS...Thanks

 

[tx1961whaler]

Re: Evinrude question

What are the RPMs at wide open throttle on the water?
This may be more of a motor set-up issue (prop, motor height, etc....) than anything, but do make sure that the carb is adjusted and synched correctly.

 

[carbineone]

Re: Evinrude question

Carb is synched correctly and the throttle plates open fully.Yes you are probably right that I have a problem I have been fighting since mounting this motor.Today we took it out using a 17 pitch prop and ran only 4500RPMs and 30MPH on the GPS....That 50 should atleast approach 40MPH on the little ten foot boat..What I think is going on is as you say the motor has drag as its just not high enough..The cav plate sits even with the bottom and cannot raise it any higher right now..I tried a 19 pitch too that I have and it ran the same speed but even lower RPMs.I also have a 15 pitch here and that seemed to make it a rocket and if it was car it could probably burn rubber at 60MPH..The 15 pitch had great throttle response and take off but only achieved 26MPH top speed..I may just be stuck with what we have for this year but will running it at 4500 hurt the motor you think or maybe any suggestions on what may be going on that I am not covering here? Thanks