1957 7.5 evinrude starving for fuel at high rpm

[BlackoutBill21]

So This motor was seized and I tore the block apart for education purposes. after honing the cylinders i realized The block was in great shape. so I ordered some new rings, and put her back together.

SHe idles like a boss! runs really well otherwise.. Now the problem is at high speed after about 30 sec, she cuts out and dies.

putt the choke on she starts right back up, and after putting the choke back in, she lean sneezes like crazy then eventually riches out and goes back to the best idling motor ive ever heard. I had it idling for 2 hours straight.

side notes. new fuel pump, i converted it from the duel line tank to single using the vacuum cap method.

also new fuel lines/ carb kit/ coils plugs and condensors. spark jumps over 3/8. Also tried a brand new primer bulb with same results.

This test was all in the barrel. never on the water.

any ideas?

 

[oldboat1]

Did it run on the dual line tank before conversion to fuel pump?

 

[jimmbo]

Does it suddenly quit, or does it slowly die?

 

[BlackoutBill21]

id say suddenly.. like 5 seconds... you can hear it when it starts to die then stalls before a 5 count

 

[BlackoutBill21]

Did it run on the dual line tank before conversion to fuel pump?

i have no idea. picked it up from a dude who didnt know it was locked up
i only bought it cause he gave it to me for 25 bucks

 

[Crosbyman]

so it is starving for fuel... does it keep going if you keep pumping the bulb to feed it … if yes then the issue is a fuel feed issue ( assuming the electricals are ok)

will it run if you keep the fuel supply ABOVE the engine
how far away and lower is the fuel supply (tank) ....to far ??

is the side connector sucking air instead of fuel (bad oring ) does it leak gas ?
is the vent open on the tank (sorry to ask)
tank pick up clean ???
what pump are you using ? maybe the fuel pump is bad / inadequate (low fuel rate) I used a round B&S/Mikuni pump on my 5.5 using the block channel method
Is the glass bowl filter 0303133 - Filter Element clean ? remove the filter element and retest
is it rebreathing it's fumes...try running a fan to feed it fresh air … how is it on the water ??


the 7.5 has side covers … why not used a square pump on a plate method instead of the channel/cap method .
just cut a plate mount it over a drilled out side cover and mount a square pump& gasket over it

 

[BlackoutBill21]

i believe it would stay running if i squeezed the bulb...

tank was vented, no gas leaks, side connector brand new, tank being too far could be an issue.

don't have the means to hold a tank above the motor but i could look into it.

fuel pump is brand new rated for 15 hp and above

glass bowl is clean but i can check it out... retest with the filter element off?

cant/afraid to take on the water lol i will try the fan method I ran it full speed without a prop for about 5 minutes... it stalls before the 5 minutes just giving perspective.

I haven't tried the square plate pump method cause i dont have means to cut out a plate. ALso the motor was already disassembled so I just figured when i put it back together id cap the intake manifold.

Thanks for the tips! its supposed to be warm in NJ tomorrow Ill test and get back to you!!

 

[racerone]

You ran it full throttle with no prop ?----Why ?------I would say you are lucky it did not blow up !----Gas and oil mixed at 24 :1 ?

 

[BlackoutBill21]

gas oil is 24-1.... ever run an outboard in a barrel full of water at full throttle.... good bye water.. goodbye cooling source

 

[GA_Boater]

You ran it full throttle with no prop ?----Why ?------I would say you are lucky it did not blow up !----Gas and oil mixed at 24 :1 ?

gas oil is 24-1.... ever run an outboard in a barrel full of water at full throttle.... good bye water.. goodbye cooling source

Full throttle with no prop means no load and way over revved. It's the same as full throttle in neutral, a pretty good way to put a rod through the block.

I didn't see an impeller replacement in the first post. Overheating?

Is it dying after 5 seconds or 5 minutes? You say both.

Another novel thought - The motor may be revving so high with no prop that the fuel pump can't supply enough gas. Having to use the choke on a warm motor and the lean sneeze kinda points to not enough gas in the carb on the restart. That shouldn't happen. Try a bigger barrel and a cover to keep the water inside and a hose to keep it topped off - With the prop on.

 

[achris]

... Try a bigger barrel and a cover to keep the water inside and a hose to keep it topped off - With the prop on.

Or just take it to the ramp, reverse it in and run it with the boat still on the trailer.

 

[GA_Boater]

I don't think the motor has been mounted on a boat. Is it?

 

[F_R]

1. Deal with the over-revving issue first
2. Most often seen cause of fuel starvation is a partially clogged fuel filter in the glass bowl, as already mentioned. Simply temporarily remove it as a test.

 

[Crosbyman]

"glass bowl is clean but i can check it out... retest with the filter element off? "



just unscrew the glass bowl remove the filter element and reinstall the glass bowl/gasket​

 

[BlackoutBill21]

Ok LOVE the responses.

The 5 minute remark from me was kinda embellishment like to mean I didn’t overrev it long. But I won’t run it without the prop anymore..

it dies before 30 second of full throttle.

it has a brand new water impeller. Def not over heating. I’m thinking the overreving could be starving the fuel out of it.... I will remove the carb and check the filter element to test.

i did inspect the high speed needle and in taking it out apparently the packing material has disintegrated. So the carb has to come off anyway so I’ll take care of the filter and needles together.

No the motor has never been mounted to a boat... I never thought I’d make it this far lol Motor was a locked up junker

 

[oldboat1]

After cleaning and using a kit on the carb, I would switch to 15:1 with the 7 1/2. Work on low speed running in a "tank" -- nothing over high idle. OK, maybe a short burst or so to see if it throttles up right. Initial settings for mix needles is 1 1/2 open (top) and 3/4 to 1 open (bottom).

 

[Rook66]

Now the problem is at high speed after about 30 sec, she cuts out and dies.

Try putting your car in neutral and running it wide open for 30 seconds.