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Poor performance, gas smell, black smoke...

6K views 71 replies 8 participants last post by  jgs240 
#1 ·
and hard starting (i have to keep it floored to get it to start up).

I have a 305 w/holly two barrel (unsure of anything more than that). This is the first time the car has ran in over 5 years. My father in law helped me go through the carb and remove all the old gas/varnish. I replaced all the fuel line heading up to the carb due to dry rotting, and i replaced the fuel line that runs across the back of the carb. I re-assembled it, and put it back on the car to get things running...now it runs pretty rough.

It idle's high, you have to floor it to get it started, i smell like i have been riding a two-stroke dirtbike after i drive it around awhile, it is really down on power, and throttle response is horrible.

Is this a simple jetting issue? My in-law suggested that the carb on their is a bit larger than what he would like to see for a stock 305, and this would be a good time to move down to a smaller carb.

How do id my current carb? I know their are stamped numbers on it, but i dont know which ones are used for ID.

Thanks!
 
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#52 ·
Ahh...i didnt look closely at the schematic posted online by holley and the one they have in the kit. Opps, i screwed that up.

#13 in my kit is #137 on this schematic. And the picture you posted is exactly what i have, and how things are assembled.

Just to be certain, their are no other o-rings that go with the assembly correct?
 
#54 ·
cobalt327 said:
Correct.

There are, however, thin gaskets (#133 & #135) that go under the lock screw #132 and the adjustment nut #134. Note there are differences in their diameters. See the exploded view.
Thanks for the fyi, i was able to get those as well :)

The good news:

Its back on the bel-air and it runs again!

The bad news:

It runs just like it did before hand (maybe a little better...or it could be my brain tricking me).

In all fairness, i have not done anything to tune it since i have no idea what to begin with. I did set the fuel valves like cook explained in this thread @ 3.5 threads out.

Anyone have a next step for me?
 
#55 ·
Check your accelerator pump adjustment. It should be set with a .010 feeler gauge, between the pump lever, and the adjuster. This clearance should be checked each time you make an idle speed adjustment.

How far out are your idle mixture screws? Turn them all the way back in, and then back out 1 full turn.
 
#56 ·
I put the idle screws all the way in, then backed them out one full turn.

I am not able to check the clearance today on the accel pump since i do not have feeler gauges.

Now that i have made those adjustments however, it wont fire. Just cranks and every now and then chugs a few times but nothing more.
 
#59 ·
Alright first pic is drivers side. These screws are near the front of the carb, about a 1/2" from the throttle plate.





Those are the screws i turned all the way in, then back out one full turn.


After reading what you typed above, i kind of felt dumb...because now i think you mean i should be turning this screw right?



It is on the throttle linkage.
 
#60 ·
The first 2 screws were the ones I said to set at 1 turn out, those are the idle mixture screws. Back these out 1/4 of a turn, at a time, and try starting it.

The last adjustment check was for the screw you are pointing at.

Simply look down through the carb, and look to see how wide the gap is at the throttle plate.

Take the fuel level sight screws out, and see where the fuel level is.
 
#61 ·
Thanks again!

I will make one more attempt at this today, my wife gets out of work in 45 minutes and i have to pick her up.

Could you by chance, tell me what the assembly with the red/pink spring is/does? It is considerably looser (more play) than before i took the carb off and replaced the float bowl gaskets today. Its in the last pic.
 
#62 ·
That is the accelerator pump adjuster. In that picture it looks like it is a little tight. This will be pumping fuel in too fast.

In your earlier pictures, you could see a few threads showing on the top of it. Now it looks like the nut is even with the top of the threads.

Keep in mind, making any adjustments to the idle speed screw, changes this adjustment.
 
#64 ·
I got as far as 2.5 turns out on each one, but it never fired. I am beginning to get a gas smell as well, flooded maybe?

The throttle plate looks like it has about 1/8" opening, but its hard to say. I am judging that based on the angel of the butterfly's, i cant actually see below the throttle plate.

I will adjust the accel pump to match what you are describing if i get time tonight/the next day i get time.

Anything i should be thinking about while i have some down time?

I just realized that i forgot to check the fuel levels in the bowls...something else to look at.
 
#65 ·
ericnova72 said:
Spring is accelerator pump override spring. It should be adjusted so that there is no slop between its head (plus 1/4 turn preload )and the pump lever it pushes against. You did put the spring(different spring) back inside the pump diaphram housing, correct??
I didnt pull the housing apart, i was a little leary looking at the diagram. Sounds like maybe i am due to pull the carb again, and try and do a full rebuild this time instead of just the fuel valves/float bowl gaskets?
 
#69 ·
jgs240 said:
I did set the fuel valves like cook explained in this thread @ 3.5 threads out.

Anyone have a next step for me?
Set the float level by removing the sight plugs (one at a time) and adjust the float level to where there is just a trickle of fuel coming from the open hole at idle.

A bench adjustment should have been made w/the floats assembled into the float bowl, the float bowl is then carefully inverted and the float level is adjusted by setting the float to be parallel w/the bottom (what is now the bottom, w/the float bowl inverted) of the float bowl.

More from Holley HERE.

And a decent page on the Holley, w/details and adjustments HERE.
 
#70 ·
jgs240 said:
No i did not, another cause of this?

Yes, One 'fart' or 'backfire' back through the carb, can cause it's diagram to rupture. This will really make them run rich. They do make a kit you can buy, that will solve this problem on the older Holley carbs. It consists of a drill, a tap, and a plug with instructions.

Switching your linkage back to the correct hole will help. LOL I have done this same thing myself.
 
#71 ·
cobalt327 said:
Set the float level by removing the sight plugs (one at a time) and adjust the float level to where there is just a trickle of fuel coming from the open hole at idle.

A bench adjustment should have been made w/the floats assembled into the float bowl, the float bowl is then carefully inverted and the float level is adjusted by setting the float to be parallel w/the bottom (what is now the bottom, w/the float bowl inverted) of the float bowl.

More from Holley HERE.

And a decent page on the Holley, w/details and adjustments HERE.
Thanks cobalt, ill be reading plenty tonight.
 
#72 ·
carsavvycook said:
Yes, One 'fart' or 'backfire' back through the carb, can cause it's diagram to rupture. This will really make them run rich. They do make a kit you can buy, that will solve this problem on the older Holley carbs. It consists of a drill, a tap, and a plug with instructions.

Switching your linkage back to the correct hole will help. LOL I have done this same thing myself.
I had a pretty decent backfire two days ago while i was trying to start it just before i took the carb off...but then again it was running pretty bad before that as well.

Either way, it looks like i will be getting pretty familiar with this carb :D
 
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