Another Carb vs. Air Leak/Fuel Delivery Problem

[jadoty]

Still trying to diagnose loss of power on my 1976 70hp Johnson. It will go almost indefinitely in the tank at idle, but dies quicker on the water in gear. At higher rpms, it dies off quicker or dies right off if I gun it. If I back off to idle quick enough before it dies, it will kick in again and idle. I can keep it running longer by pumping the primer bulb. I've checked and rechecked the floats half a dozen times and am pretty confident they are right. My ultimate question is, since choking it (after it's warm) kills it instead of perking it up, doesn't that imply that the carbs are working properly, and that it is just not getting fuel to the bowls? And that I can rule out floats and other carb issues and look exclusively at the fuel lines/pump? Correct or faulty reasoning?

 

[rickdb1boat]

Re: Another Carb vs. Air Leak/Fuel Delivery Problem

That sounds like a plan. If you can keep it going by pumping the bulb, then I'd be looking at a fuel pump/fuel supply problem. ..At least for starters...

 

[JUSTINTIME]

Re: Another Carb vs. Air Leak/Fuel Delivery Problem

That sounds like a plan. If you can keep it going by pumping the bulb, then I'd be looking at a fuel pump/fuel supply problem. ..At least for starters...

8)

or u need to sync and link

 

[OBJ]

Re: Another Carb vs. Air Leak/Fuel Delivery Problem

Couple of quick tests for the pump.....

Pull the pump lose with the hoses still connected and squeeze the primer bulb. If fuel comes out the port that sits next to the block, the pump diaphram is bad.

Or, take the pump off and drain it. If you can blow back through the pump from from the pumps outlet nipple, pump is bad.

Edit: Are your hoses in good shape? Are they still soft and plyable? Replace any that have become hard.

 

[jadoty]

Re: Another Carb vs. Air Leak/Fuel Delivery Problem

I've already done and redone the link and sync til I got it right - it only took me about 6 times but that is a dead issue. I had already replaced all but one hose which I have since replaced but have not restarted it to see if that made a difference (freezing weather here). I did have a question about fuel line in general though, because I originally replaced my 5/16" fuel line with some Sierra 5/16" line but it had a way thicker outside wall to it - is there any way that could affect the fuel flow? Otherwise I have replaced everything else including the fuel pump, except for the primer bulb/line. I guess I should still check the new pump and make sure it's working properly. But if that isn't it and it still does the same thing at this point, I am really going to be at a loss. I was going to put some clear line in to see if I could see flow problems, but can't seem to find any here. Anybody know a good source for clear/transparent fuel line?

 

[jadoty]

Re: Another Carb vs. Air Leak/Fuel Delivery Problem

Problem solved, I think - cold weather preventing putting it back in the water. Problem #1 - the brand new fuel pump I just put in was bad, it worked but had some kind of restricted flow, so I put the old pump back in and it eliminated cutting out after running at at higher rpms. Problem #2 - a piece of grit had somehow gotten into the needle valve seat of the top carb, so it wasn't getting full flow to it.