Fuel line size

[redlinj]

My 21' sylvan supersporster originally came with an 88 Hp johnson spl which ran fine albeit not as fast as I would have liked. I replaced it with an 1982 evinrude 150hp. It runs ok but seems like it has more to give but for some reason, just can't! I eventually replaced the fuel line and bulb from the tank to the engine. Fuel line is 3/8 but the end fitting/clip that connects to the engine is 5/16. Could this slight restriction be the potential cause of the power loss? After all I went from an 88hp 4 cylinder to a 150hp 6 cylinder. Thanks!

 

[interalian]

If you've got 3/8" from the tank to the motor connector and it's 5/16" inside the motor, that's probably the way the factory plumbed it. If you suspect fuel starvation, try pumping the primer bulb when you're at WOT and see if it makes a difference.

 

[redlinj]

I don't know for sure that the original hose was 3/8. It could have been 5/16 just like the connector to the engine. Remember, the original factory setup was an 88hp Johnson. So wouldn't going from a 4 cylinder 88hp to a 6 cylinder 150 Hp need more gas? I will try squeezing the bulb next time at wot and see what happens. If rpm 's shoot up by 3-4 hundred, then I have a bottleneck somewhere right?

 

[interalian]

Right. Give the bulb a few pumps and see if anything changes.

But what I meant was that on your 150, the fuel line size inside the motor, whatever it may be, must be enough for it based on design. I was referring to the new 3/8" line from the tank.

 

[gm280]

You can try pumping the primer bulb, but I find it amazing to see the fuel delivery being the problem. I mean if your fuel pump is doing its job, I think you have plenty of fuel available. But what do I know. :noidea:

If you like, you can do the math and see what difference the two sizes offer. Calculate the volumes from each diameter and length of the fuel lines and see what volume you have available. But remember the fuel pump is pulling the fuel from the tank and feeding it to the carbs under force. You can also check the fuel pressure out of the fuel pump. JMHO

 

[redlinj]

Ok, let me put it this way: there are 3 different size hoses and connectors that I know of. 1/4, 5/16 and 3/8. Wouldn't it stand to reason that low hp motors would have the smallest diameter and 4 cylinder motors have 5/16 and 6 cylinder motors have the largest diameter? Also, if I squeeze the bulb at wide open throttle and the engine speeds up, what does that mean? Is the bulb defective or the fuel pump a bit weak? Or possibly a restriction between the tank and the carbs.

 

[interalian]

If you squeeze the bulb whilst at WOT and the motor picks up, your fuel pump(s) is(are) weak, or you have an air leak between the tank and pump.