This thread is getting long, so a quick recap:
1991 Sea Ray 170BRLTD with a Mercruiser 3.0, replaced in 2003. I bought it last fall. It runs great for the first 5 – 10 minutes off the trailer but then starts to bog and pop through the carb intermittently. It seems to be worst at WOT and eventually will not get over 3000 rpm. However, it always starts easily and idles fine. I can also confirm that it doesn’t overheat. My temperature gauge is solid at 150 deg.F.
Here’s what I’ve tried up to my last post:
When I winterized last fall, I changed the oil, replaced the spark plugs and fuel filter and cleaned/regasketed the carb.
This spring I’ve taken the carb back apart and verified everything is still clean and correct. I’ve replaced the distributor cap, rotor and coil (all appeared to be fine). Confirmed that the choke is working properly. Drained the gas out of the fuel filter (no signs of water). Compression test, all good. Drained the fuel tank. I didn’t find any water, but the old fuel was a little darker than what I consider normal and didn’t smell fresh. Refilled with 91 octane, ethanol free. Also, on the suggestion of a forum member, I sprayed carb cleaner down the carb while running for a couple of minutes.
With all this there was maybe a slight improvement, but the bogging and periodic backfiring was still there. So, here’s what I’ve done over the last couple of weeks:
While it was acting up on the water, I checked the spark at the plugs using a tool with an adjustable gap. The spark seemed to be fine and similar to what I’ve seen in my driveway on the muffs.
While I was testing the spark, I thought I heard an air leak at or around the fuel pump. So when I got it home I removed the fuel pump, the anti-siphon valve and the fuel pick-up tube. The tube and anti-siphon valve were fine, but the threads galled when I took them apart, so I had to replace both ($#@%!). I also replaced the fuel hose from the tank to the pump.
I took the pump apart, and it was disgusting inside! All gummy and dirty, I’m blaming it on ethanol. I cleaned it up as well as I could, but the check valves were still suspect. I couldn’t disassemble those, and the elastomers seemed stiff. I put it back together, reinstalled and ordered a new one.
While running it on the hose, I sprayed carb cleaner around the base of the carb and where the manifold attaches to the cylinder head. While spraying along the top of the manifold at the head, it would noticeably affect engine speed. So, I removed the manifold and inspected the gasket. It looked fine with no signs of leaks or damage, and the mating surfaces of the manifold and head looked good as well. No dings, scratches or visible cracks. I bought new gaskets (destroyed the exhaust elbow gasket during disassembly) and put it back together. I tested again, and the issue remains (engine speed drops slightly when I hit it with carb cleaner).
We took it to the lake anyway to see if anything I’d done helped. There was improvement although the underlying problem remains. But it ran well enough at lower speeds that I was able to teach my son to water ski. We’re getting some enjoyment out of this tub regardless of how it runs!
View attachment 399697
Since that outing, I received and installed the new fuel pump. The wife and I went back out this weekend, and it still runs the same. I checked the manifold gasket with carb cleaner while it was on the water and acting up, and it seems to be maybe a little worse than on the hose, but not significantly. This is my prime suspect, so any suggestions are welcome. I installed the gasket dry, so maybe some sealer might help?
I’m also wondering if there’s something in the carb that isn’t quite right. Float maybe?
I appreciate any input or ideas. I’m still groping around. Thanks!
