5.0GL-C won’t get on plane

JR6424

Seaman Apprentice
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Oct 20, 2018
Messages
35
Hi all,

Freshly rebuilt 5.0GL-C in a 22’ cuddy cabin walk-around starts up and runs like a dream in the driveway, but won’t go above 2600 RPM when in the water. She hesitates a little coming off idle but then revs up but just falls on her face between 2,000-2,600. Sometimes it’ll backfire and stall, other times just rev but won’t make any more power under load.

Everything is new or rebuilt except for the fuel pump, all fluids and filters fresh. Timing (Delco EST, new dizzy, new coil) was set as per the instructions found elsewhere here, using the proper shunt tool. The carb was rebuilt and tuned but there is some play in the accelerator pump lever which might explain the initial hesitation but not the lack of WOT power under load, no?

My troubleshooting plan is this:

-Change fuel filter in case I sucked up some gunk from draining and putting in fresh fuel.
-Verify timing and make sure the electronic advance is working properly (how?)
-Fix or replace accelerator pump lever on carb
-Test/replace fuel pump

Am I missing anything? I’m praying for a simple fix here, or something I may have overlooked during the rebuild/reinstall. The WOT troubleshooting thread in the sticky above links to a thread about a Yamaha stalling issue, does anyone have the updated link to the original thread?

Thanks for the help!
 

Bondo

Moderator
Staff member
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Apr 17, 2002
Messages
69,297
Ayuh,...... Sounds like it's goin' lean,.....
When ya change the fuel filter, examine the contents of the old one in a clear vessel, for anything but clean fresh gasoline,.....
I'd try runnin' it on a remote tank, hooked right to the new fuel filter, to diagnose that side of the fuel system,....
 

WIMUSKY

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Sep 26, 2009
Messages
18,668
Possibly a bad coil, I know you replaced it but.... Had a 5.7 Volvo in a 24' Cuddy. Ran fine off plane. Tried to get up and it would spit and sputter, but no go. After that I carried a spare....
 

alldodge

Supreme Mariner
Joined
Mar 8, 2009
Messages
37,046
Verify timing and make sure the electronic advance is working properly (how?)
Using an advance timing light or having the damper marked so advance can be seen. Set base timing at 10* then remove shunt and verify

5.0GL-B/C/D/E Models1
Engine RPM. . . . . . . . . . . . . . . . . . . 89 AKI Fuel
Initial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10°
600 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19°
800 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22°
1200 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25°
1600 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26°
2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27°
2400 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28°
2800 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28°
4000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28°
4800 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28°
 

stresspoint

Cadet
Joined
Sep 19, 2022
Messages
23
how did you set the valve lash ? ,if you fitted new lifters try backing them off till they click / clack then down 1/2 a turn and see if the problem disappears ..

check all the lead are on the correct cylinders. IE: you haven't crossed a couple.
 

JR6424

Seaman Apprentice
Joined
Oct 20, 2018
Messages
35
Thanks for all the replies. I changed the fuel filter last night and drained the old one and the gas looked perfect, no water and no debris.

Thank you for the advance curve info alldodge, I’m going to check that next. My gut is telling me it’s the electronic advance on the distributor, even though it’s brand new when I plugged the shunt tool in to set the initial timing nothing really happened. A few YouTube videos on this system said there would be a drop in RPMs with the shunt in place and that didn’t happen making me think that’s the problem. It’s brand new so hopefully it should be covered under warranty.

I still have the old coil so I guess I can swap that one in if the timing looks ok.

As for the valve lash I set it to zero lash plus 1 turn as per the service manual and rechecked it twice before buttoning everything up. The valves don’t clatter at all and she starts up on the first crank and idles perfect, and she revs all the way up to redline in neutral. If everything else checks out is it possible the lash is set too tight?

I also noticed the outside of the flame arrestor is pretty gunked up so I’ll clean that too, can’t really think of anything else that would be causing this.
 

stresspoint

Cadet
Joined
Sep 19, 2022
Messages
23
if set at 0 +1 lash you should be fine , however , the lash could have tightened once the lifters settled with oil pressure , ,you may possible have a couple or more tight ones that will cause a backfire and lack of high RPM performance under load (lifters pumping up).
for the sake of it and the fact it is a fresh motor i would remove the rocker covers and check with the motor @ idle , easy to do , just back them off one at a time till it ticks then tighten half a turn , this will insure you are at the correct lash .
the time it takes to check is a lot less than burned up valves.

if you are not getting any change to the timing with the shunt , then it could very well be the advance curve not changing as alldoge suggested., which will also not be good for the motor if you continue to run it .
 
Last edited:

stresspoint

Cadet
Joined
Sep 19, 2022
Messages
23
have fun ! a strip of cardboard box strategically placed in the head behind the rockers will help stop the oil from going onto the exhaust .
also if you want you can set 0 lash @ 1 turn if you want .
 

JR6424

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Joined
Oct 20, 2018
Messages
35
Well interesting development, I went out to work through these troubleshooting steps and it wouldn’t start. It fired up for a second and then stalled and then wouldn’t restart at all. The only thing I had done so far was to replace the fuel filter and the new filter still looks dry so now I’m thinking it’s the fuel pump. Or it’s ALSO the fuel pump… I’m waiting on a replacement pump and then we’ll go from there. I’ll report back next week!
 

JR6424

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Oct 20, 2018
Messages
35
I’m solo so I can’t hear or feel the pump while I’m cranking, the fuse is good. I’ll have help on Monday which is when the pump is supposed to come so I’ll have someone to crank while I check.
 

alldodge

Supreme Mariner
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Mar 8, 2009
Messages
37,046
Maybe use jumpers and hot wire the pump directly. If it runs and fills the filter/carb then would be another issue
 

JR6424

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Oct 20, 2018
Messages
35
Did you replace the power valve in the carb?
Yes, everything in the carb was cleaned/replaced EXCEPT the 2 little cork washers for the idle mixture screws. My rebuild kit was missing them so I left them alone and didn’t back them out since I was worried the washers would fall apart and I’d have nothing to replace them with.
 

JR6424

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Oct 20, 2018
Messages
35
Ok, another new development. I still don’t have anyone to help but when I got home from work I tried starting it again and still no good. I pulled the fuel filter and it was about half full. I pulled the line off the carb and it was dry, then I pulled it from the fuel pump side and it sort of “popped” once it was loose and grimy looking fuel went everywhere. I blew out the hose with compressed air and reinstalled it on the pump and ran the other end into a clear container and cranked it and a steady stream of clean fuel came out. I reinstalled the line to the carb and it started right up.

I thought maybe I’d solved my problems, however when I rapidly advance the throttle it stumbles and sometimes stalls, plus there’s a steady tapping sound now that wasn’t there before. So I think my no start issue was a clog in the fuel pump outlet or line to the carb, but the lack of power under load problem probably still exists.

On Monday when I have help I’m going to reset the valve lash with the engine running and confirm the timing is set properly and that the timing advance system works. If I still have issues after that I’ll look at the accelerator pump lever and maybe put a fuel pressure gauge inline and see what my pressure looks like under load.

Am I missing anything else? Thanks for all the help fellas, it’s greatly appreciated.
 

alldodge

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Mar 8, 2009
Messages
37,046
If pump wasn't pumping because of some crud inside which is now clear, some of that may have made its way into the carb
 

stresspoint

Cadet
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Sep 19, 2022
Messages
23
interesting you are getting tapping after a stumble , it could mean the engine is running very lean from lack of fuel pressure, have you checked the filter where the pipe enters the carb , some carbs have a fine mesh filter there .
 
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