L20B Stock Carb - Power dropoff after short period of acceleration [Fixed]

[kidatari]

Howdy everyone,

 

Ran into a weird issue on my $500 PL521. When I accelerate heavily, after 4-5 seconds of accelerating the engine falls flat on its face--all power goes away. Shortly thereafter the engine dies. Afterwards, the engine starts after a few cranks and idles OK. I can easilly replicate the issue, and I'm thinking fuel, but I'm not sure.

 

Thinking this may be related to off-idle hesitation; I press the throttle, and there is a significant hesitation before the RPMs increase. I can actually see fuel squirting into the carb as soon as I go off idle. Not sure.

 

Anyone have any ideas?

 

1970 PP521

L20B (Est. from a 1975 620) with all smog parts removed

Stock Carb

EI Distributor

[datzenmike]

Change the fuel filter. It partly plugged and can't supply enough gas for full throttle and the carb runs dry. Do it anyway even if it doesn't fix it. They are cheap and it's probably 15 years overdue anyway.

 

 

Hesitation: Check valve lash and timing... also probably due to be done.

[greybeard]

I think Mike has it nailed,

 

for sure a fuel issue, when it dies, open the hood and look at the carb, can you see fuel in the sight glass?

 

if not the filter, plugged line or the fuel pick up sock in the tank is plugged.

[kidatari]

I think Mike has it nailed,

 

for sure a fuel issue, when it dies, open the hood and look at the carb, can you see fuel in the sight glass?

 

if not the filter, plugged line or the fuel pick up sock in the tank is plugged.

 

I can see and look into the sight glass, but I can't see the level fuel, I think it may be over the level of the sight glass, oddly. I'll have to check it out.

 

Thanks for your help, folks. I'll update as I check items off the list.

[Braden]

i have almost the same problem with my truck, when the truck isnt moving i can give it gas and it has good throttle response and will rev right up but when under load like when i try and take off it has zero power, i have a fresh rebuild on the carb, new plugs, wires, rotor, cap, and a timing job, it suck ass cause when i go to take off i have to revv it up really high and slip the clutch alot to get going otherwise if i let out on the clutch like normal and give it gas it will puke out and about die then it will catch up a little bit, the same thing happens if the truck is already moving and i stomp it it will bogg down then after about 10 seconds it will catch up and really go

[datzenmike]

I can see and look into the sight glass, but I can't see the level fuel, I think it may be over the level of the sight glass, oddly. I'll have to check it out.

 

Thanks for your help, folks. I'll update as I check items off the list.

 

Most common is a dirty/plugged fuel filter but the float could also be set too low. Idle the motor and look at the glass sight level. If there is fuel in the carb it is golden color, no mistaking it. It should be at or near the horizontal line on older carbs and on or near the dot on the newer ones.

[kidatari]

Well, I've managed to fix the issue.

 

A change of the fuel filter made no difference. I opted to replace the stock Hitachi carb, as the old carb was wonky. 6 hours later, I now have a Weber 32/36 DGEV (Electric Choke) using Redline kit K660. Now my 521 runs great! :D

 

Thanks to everyone who contributed to helping.

[racerx]

Can never go wrong with those 32/36 webers.