135 4cyl evinrude fuel problems

[iwannagofast]

Had my 73 135 evinrude out on the lake this weekend to try and do some trouble shooting for my horse power issues and this is what I found.

With the lid off the motor and under full throttle it seems that my top two cylinders are receiving a steady stream of fuel from the carbs. On my bottom two cylinders only one is receiving a nice flow of fuel and the other one is barely getting a sputter. I tore the carbs off again and made sure they were all clean and also that the tube from the bowl that feeds the fuel upto the cyl was not blocked. For some reason fuel just does not want to flow up that one tube.

Not knowing too much about this stuff just sort of figuring it out maybe someone can tell me what might cause this to happen? What exactly causes the vacume that is required to pull the fuel up through that tube in the carb?

Just a note if I have someone sit at the back of the boat and feed fuel using a spray bottle directly into that one cylinder the motor cooks I mean if the boat had wings it would fly out of the water.

 

[tashasdaddy]

Re: 135 4cyl evinrude fuel problems

possibly a weak fuel pump, or a blockage in the line. the fuel pump pushes the fuel up. the float only controls it's one carb, does not stop the flow to the other carbs. top float needle may not be opening all the way. did you remove the fixed jets and clean them?

 

[iwannagofast]

Re: 135 4cyl evinrude fuel problems

Not so sure its the fuel pump. Each carb is for two cylinders the top carb seems fine the bottom carb is feeding one cylinder but not the other properly. 1 fuel line goes to each carb and both seem clear, the float and need seems free and clear and operating properly. I had a mechanic look at the motor and he says he put new jets in but I found later that the guy is a moron so maybe I sould check this. Where are they located on the carbs on my 25 horse mariner I know its just a screw on the side of the carb that adjusts them For this motor I have no clue.

 

[iwannagofast]

Re: 135 4cyl evinrude fuel problems

Just to add to the info about the retard mechanic he says that he replaced the jets without removing the carbs not sure if thats possible or not?

 

[ezeke]

Re: 135 4cyl evinrude fuel problems

The fuel pump fills the float bowls and no more; the fuel is drawn from there through the carburetor by the vacuum created by the pistons.

If your float valves were to fail, the pump would push fuel into the carburetors continuosly and you would certainly know it because gas would be running out into the engine compartment.

The capillaries above the low speed jets need to be soaked clean and blown out with compressed air, as well as those for the high speed jets. You really can't do much for your carburetors without a complete disassembly and new carburetor kits.

You asked if you could remove the jets without removing the carbs. Yes, it can be done.

If the carburetors are thoroughly cleaned and there are no air leaks, the vacuum created by the pistons will be all that is needed as long as your leaf valves are good and various hoses are all connected tightly.

 

[F_R]

Re: 135 4cyl evinrude fuel problems

If you look at the bottom of the carburetors, you will see 4 hex-headed plugs, two in each carb, one on each side. The high speed jets are deep in the hole behind those plugs. Takes a special screwdriver to get them out. You can make your own. The little short one is for the ones that you would otherwise have to take the carb off for. http://i155.photobucket.com/albums/s311/frankr_photos/FixedJetScrewdriver2.jpg?t=1186506709

 

[iwannagofast]

Re: 135 4cyl evinrude fuel problems

So i guess another thing would be that if my compression was low on 1 piston it would not pull enough fuel through the carb for that one piston. Is this correct?

And would a piston with low compression perform if fuel was injected in through the carb manually like I did with a spray bottle?

 

[ezeke]

Re: 135 4cyl evinrude fuel problems

That is not necessarily correct. Much would depend on the nature of the lower compression and what is causing it - for example it could be a blown head gasket.

The compression and vacuum are both necessary. One to create a condition for successful burning of the fuel, the other to draw in the fuel for the next cycle. At some level, neither will function and the piston will just drag.

For simplicity, all troubleshooting should begin with a compression test, no matter what the problem is.

 

[iwannagofast]

Re: 135 4cyl evinrude fuel problems

What should the compression be on a 73 evinrude 4cyl `135 anyway??

 

[ezeke]

Re: 135 4cyl evinrude fuel problems

At sea level, 135 on all cylinders after new rings and honing.

 

[iwannagofast]

Re: 135 4cyl evinrude fuel problems

So is there a formula for calculating compression if you live above or below sea level. I guess the first step would be to find out how far above I am in Timmins Ontario Canada

 

[F_R]

Re: 135 4cyl evinrude fuel problems

Don't get all hung up on the details. If they are anywhere near the 135 and more or less equal, that is not your problem. Now if you have three at 135 and one at 50, then you gotta problem. That's what it would take to not draw Any gas from the carb. Once you determine the motor is not dead (no/low compression), then move on to those jets. The one with no flow is plugged up.