5200 carb vac. diagram & vac. advance ?'s

[Mikel89us]

Im serious about the 20* advance though. I used to run fixed timing at 32* in my street car untill i realized it was hurting my overall performance.

 

[rab]

i got the truck ideling at 1000 to 1100 rpm, 20 inch vacuum, and advanced it roughly 6-8 degres inititial timing, the timing i just moved it about a 1/2 up from the pointer (on the 78 timing cover there is only a pointer and no marks.

the truck free revs great sounds healthy comes down to idel nice,ect,ect, but when put under load/driving at 2000 to 2500 ish rpms it hesitates and stumbles, again only under load.

anyone have any ideas?

 

[flaminranger]

try to find a timing light that you can dial in the timing with so it fires on that mark by what you set the light at. then set it at around 12 and leave it. if you want more power mill the head. I have tryed alot of timing on mine and it killed power and mileage also around 16 initial I started getting spark knock.
you just need to deal with the fact that these engines are weak.
I do sympathize with you though. but the head is where the power is mill, port,polish, three angle valve grind ect. then when you get that done yank the engine and replace it with a bigger one.lol
Duane
good luck I am rooting for ya

 

[Mikel89us]

also have the combustion chamber reworked around the intake valve. make it to where it slightly flows away fromthe valve. factory castings actually flow back towards the valve. i did this with a flow bench to test with and i got 10% better flow out of the intake valve with that modification alone. which makes it 76% crossflow (intake to exhaust) which is almost perfect for naturally aspirated engines. also everyone says to ort and polish, but a polished finish anywhere that fluid(fuel) flows will actually show better mixture properties with a slightly rough finish.

 

[rab]

i got the truck ideling at 1000 to 1100 rpm, 20 inch vacuum, and advanced it roughly 6-8 degres inititial timing, the timing i just moved it about a 1/2 up from the pointer (on the 78 timing cover there is only a pointer and no marks.

the truck free revs great sounds healthy comes down to idel nice,ect,ect, but when put under load/driving at 2000 to 2500 ish rpms it hesitates and stumbles, again only under load.

anyone have any ideas?

anyone

 

[Mark_88]

It sounds like you have a vacuum leak somewhere...high idle and no power under load is similar to what I had on mine...discovered a vac leak at the base of the carb...to find a leak spray brake cleaner or something similar around the carb with the engine running...if you notice the idle changes when you do this, you have found a leak...

Be careful though...and don't breathe that stuff in if you can avoid it...