under 4 miles to a tank

[skimmer]

My 80s model Mariner 30hp seems to be using excessive petrol I've got a 22.7 litre tank (approx 5 gallons) and i'm not even getting 4 miles on one tank is this normal, my old johnson 70 which was a 90s model used to guzzle but I was sure I was getting more miles out of it and it was more than twice the size.

 

[steelespike]

Re: under 4 miles to a tank

Rule of thumb a 30 would use about 3 gph(gallons per hour) at wot (wide open throttle).You may have some sort of Carb problem.Sticking float/float valve.Choke my not be opening properly.If the fuel pump diaphram has a crack gas could be leaking into the crankcase.
A little more detail on how you use the boat.How does the motor run?
Start good? idle smooth,good hole shot?Does it smoke alot?

 

[Silvertip]

Re: under 4 miles to a tank

At wide open throttle, that engine should burn only 3 to 3.5 gallons per hour. At a 2/3 throttle setting it should be less than that. So - yes, something is very wrong with the engine. Carburetor issues such as a float that is set way too high or has sunk, an inlet needle and seat that are malfunctioning, jets that have worked loose, or a fuel pump with a bad diaphram would be suspects. I'll stick my neck out on this one and suggest looking at the fuel pump. A leaky diaphram can cause fuel to be sucked directly into the engine in large amounts through the pulse line.

 

[Tadd_P]

Re: under 4 miles to a tank

diaphram maybe is the culprit. But a carb kit and gaskets and a good cleaning never hurts in a situation such as this

 

[skimmer]

Re: under 4 miles to a tank

Thanks guys, was planning to do a tune up today now I know what to look for. I try not to use the boat at WOT all the time I usually get up on the plane and back it off, Motor starts first go every time, compressions fine I had tested about a month ago, idles well although it does shake quite a bit. It doesn't blow much smoke although the smoke that it does blow is blacker than i'm used to. Just out of interest if a 30 should use 3gph what would say a 100hp use does it go up accordingly? On the subject of WOT, does it cause excessive wear if you run your boat at full throttle?

Thanks skimmer