1978 70hp Johnson not pumping enough gas

[Tpoorten1]

Motor starts and idles perfect, takes off great to 2000 rpm but won't go higher most of the time. When cold it will go to 3000rpm for a while and then acts like it's running out of gas,
Replaced hose/ bulb and fuel pump,tried another plastic fuel tank and same problem. At 2000rpm will run with out acting like running out of gas, not sure what to do next?

 

[flyingscott]

Try pumping the primer ball when that happens, if that helps could a fuel pump. You also need to do a compression test, and a spark test.

 

[Tpoorten1]

Primer bulb and fuel pump just replaced, starts great idles smoothly, when full throttle after couple minutes it acts like running out of gas surfing, back off to minimum throttle and runs good , pump primer bulb then throttle to 2000rpm an runs good, try to throttle up to 3000 and it hesitates and doesn't go up in rpms, back off throttle to 2000 and will hold 2000. Tried different plastic tank and results are same. Only thing I haven't changed is complete hose.

 

[flyingscott]

What is your compression and spark test results? Is this a good fuel pump or a Chinese knockoff?

 

[racerone]

Think to explain / answer here.----Post your compression numbers.-----Does spark jump a gap of at least 3/8" on all leads ?-----Checked flywheel key ?----Is high speed jet confirmed to be clean on the carburetors.----High speed jet is screwed into the very bottom of float bowls.

 

[Tpoorten1]

What is your compression and spark test results? Is this a good fuel pump or a Chinese knockoff?

Brand new johnson brp pump in the box from marine dealer on lake $82 not Chinese knockoff.
Don't have compression tester, will need to get one. Took old pump apart and it was visually good. First run after install it went right up to 3000rpms. Which cylinder provides vacuum pulse to the fuel pump? Plugs were replaced last year.

 

[oldboat1]

HS jets under screw plugs at bottom front of carb bowls. Don't take out the jets, at least initially. Run a piece of sturdy monofilament through them, followed by a shot of carb spray. Test run.

 

[Tpoorten1]

Think to explain / answer here.----Post your compression numbers.-----Does spark jump a gap of at least 3/8" on all leads ?-----Checked flywheel key ?----Is high speed jet confirmed to be clean on the carburetors.----High speed jet is screwed into the very bottom of float bowls.

Will work on getting the answers!

 

[racerone]

Fuel pumps run on a PRESSURE pulse and not so much on vacuum !----I would never buy a new pump.-----A $7.00 diaphragm is about the only thing that can go wrong on these simple pumps.