High RPM Surging

[Blu]

Hi,

I'm having trouble tracking down an engine issue. Boat is a 1986 Sea Ray with a 5.0L 230HP mercruiser engine.

The problem is that the boat will only run above 3000 RPM for about 10 seconds before it starts to hesitate and buck. I don't hear an electrical miss. Watching the tach - I will see it drop several hundred RPM and then bounce back up and all over until I drop the throttle back and get it under about 3000 RPM. The water seperater/fuel filter only has about 20 hours on it. The in-lin fuel filter is brand new and the cap/rotor/wires/plugs all look like new.

Can a fuel pump just get weak or something? Any suggestions?

Thanks for looking!

 

[bustermin]

Re: High RPM Surging

Sounds like a fuel restriction or a bad float adjustment. did you also check your water seperator? when was the last time the carbs were rebuilt?

 

[Blu]

Re: High RPM Surging

The boat had a full tune up 3 years ago. The water seperator only has about 20 hours on it.

It starts/idles and runs great as long as I keep the RPMs down under 3000.

 

[bustermin]

Re: High RPM Surging

The boat had a full tune up 3 years ago. The water seperator only has about 20 hours on it.

It starts/idles and runs great as long as I keep the RPMs down under 3000.

3 years is a long time for a carb, and 20 hours doesn?t sound like much but it only takes a second for it to become restricted, did you check it for water? Remember, marine motors do not like to sit unused, which unfortunatly is what they do most. It may be time to have the carbs cleaned again, and it sounds like it to me. You do not say where you are, was the motor winterized, when was it last used when it ran properly?

 

[cooter2506]

Re: High RPM Surging

Run it on a remote tank and see what happens. If it runs ok then it will be a fuel pick up problem at tank or your vent line to tank is blocked.

 

[Blu]

Re: High RPM Surging

3 years is a long time for a carb, and 20 hours doesn?t sound like much but it only takes a second for it to become restricted, did you check it for water? Remember, marine motors do not like to sit unused, which unfortunatly is what they do most. It may be time to have the carbs cleaned again, and it sounds like it to me. You do not say where you are, was the motor winterized, when was it last used when it ran properly?

OK I'll remove the water seperator and check it for water. I'll was also thinking of adding some sea foam to the fuel, just in case it is water.

Does spraying some carb cleaner through the carb count or do you usually remove it and have it serviced at a marina?

I'm located in Michigan, so yes it was winterized. I filled the fuel tank about 7/8ths full and added Stabil. It ran fine the first 4 outings of the Spring and then started acting up on a return trip in rough seas.

Where do you tap into the fuel line to run it off of a remote tank?

Thanks for all the replies!

 

[Don S]

Re: High RPM Surging

http://forums.iboats.com/showthread.php?t=167561

 

[Blu]

Re: High RPM Surging

I finally had a chance to work on the boat today. I believe I found the problem. There is a wire mesh filter inside of a fitting that is on the fuel tank pick-up tube (the fitting the anti-syphon valve screws into). It was about 90% clogged. I could barely see light through it. Got it all cleaned out (marina didn't have a replacement) and put back together just before I needed to go pick up the kids . So, I will water test tomorrow morning. Keeping my fingers crossed.

 

[Blu]

Re: High RPM Surging

Good news. I made it out tonight for a test run and she ran like a champ! The clogged pick-up tube filter was the culprit. Thanks to everyone for their input One good thing came out this, I learned a lot about the fuel and electrical system...