Inconsistent running w/ throttle and secondary air flap sticking issues

[1970Bonneville]

I have a 1970 Pontiac Bonneville with a 455 I recently purchased and did a rebuild with a SR kit and new choke pull off. (Used the book as a guide as well) Motor is stock from California. I have had 2 problems with it since the rebuild.

The first problem is the secondary air flaps I can feel catching / rubbing while opening them by hand. If i position it right I can actually get them to catch at an almost full position. I've also once pulled back into the driveway after a test drive to them stuck open on their own. I had a cracked Hanger Lever which I replaced, as well as a replacement of the Cam and spring. There is what felt to me like very minimal play left to right (pretty much similar to the primary air flap). If i push all the way left or right it rubs either way. It almost feels like it is the air flaps rubbing against the bore, and I can see some signs of rubbing on the bore that would make me think that is true, however I'm not 100% sure that's what causing the sticking.

My though was to remove the air flaps and possibly sand them down a little (2000 grit paper) and the bore. I'm also thinking maybe when i put the flaps on the shaft the shifted enough to grab the bore. However, I wanted to check here before I went to far with anything. If that is a logical step or there is something more common that would cause that.

My second problem was just inconsistent running that was happening before the rebuild and got a little better but didn't really get fixed after. My thought before the rebuild was a bad accelerator pump.

Basically, idle runs great and revving in park runs great as well. However, under load I get inconsistent driving. When doing about half throttle it really seems to bog down sometimes. At full throttle it will sometimes not feel like its getting full power. But of course, sometimes it runs perfect.

The only real consistent issue is when i do get a strong run at WOT once it gets to a certain RPM it just doesn't have anymore go to it - almost like its not getting enough gas. I plan on checking the fuel pressure at some point in the near future. I suspect if the secondaries are getting stuck that has to be part of it, but I feel there may be more to it - especially the lack of power after a certain RPM.

I squared away the points, wires, plugs, and timing this weekend to in theory eliminate the chance of it being an ignition issue. I am stumped and might be in over my head at this point (this is my first experience working on a carb car ever), but any help would be appreciated!

[Cliff Ruggles]

We run into sticking secondary air flaps on occasion. 

Sometimes it's from a bent shaft, other times re-adjusting the flaps will cure it.

We also have ran into a few that required removing a little material from the inside edges of the airhorn to gain adequate clearance.  It's not uncommon for the two long screws in the rear to "push" some material forward and causing interference with the air flaps no matter how you set them.

For sure you need to work with the parts and clearance everything so nothing rubs anyplace and the flaps open smoothly and return to the closed position without sticking.

To correct running issues you need to make sure fuel delivery is adequate.  If you have installed the high flow N/S assembly from our kit and still having issues at WOT, the fuel supply to the carb needs some help.......Cliff

[1970Bonneville]

Appreciate the help and quick response!

Makes sense, I will hopefully find some time this week to get that sticking solved.

I did replace the N/S assembly with the one in the kit. Sounds like I'll have to do some tests on the fuel supply line.

[1970Bonneville]

Update

I took back apart the carb to see what was going on with the fuel delivery and found a bunch of little rubber pieces inside of it. My understanding is that's probably the fuel line disintegrating, probably a big part of the problem with the running issues.

However, I noticed 1 thing I wanted to ask about. I attached a photo of the part as I'm not sure what its actually called (circled in red). I apologize for quality. When I fully press the throttle and the accelerator pump is all the way in, the circled piece only goes down about a quarter of the way. So the rubber air flap doesn't really open. Almost as if the spring that attaches to it has gone bad.

Is that spring something you can adjust or is that available to purchase new? I tried a quick search online of a handful of websites and didn't see that piece available for purchase

Thanks

[Cliff Ruggles]

I would disable that system so the vent is open all the time like the non-California models and the 1972 and later models.

if the bowl doesn't vent at there may be fuel delivery issues as it may not fill quickly.  That was basically a one year only design (1970) and Pontiac only.  It is designed to vapors to the charcoal canister instead up thru the big vent into the air cleaner assembly. 

You can simply remove the big rubber piece that seals off the large vent, and plug the large hose leaving the carburetor.  All the parts can be left in place and look functional.......Cliff

[1970Bonneville]

Very interesting that its such an oddball part only being 1 year.

Thank you for the info, this will end up killing 2 birds with 1 stone as I found all the pieces getting into my carb was coming from the canister so I was going to disconnect it anyway.

[Cliff Ruggles]

Common problem as the canisters deteriorate over time, and they are not needed anyhow.....Cliff

[1970Bonneville]

Sorry to bring up an older post. Figured I'd close it out for anyone who finds this thread in the future.

I was able to do everything discussed and car is running perfect now!

Thank you Cliff!

[Cliff Ruggles]

Good news and thanks for the update!

[tayto]

Cliff how do you bypass the charcoal can? Just plug @ the carb? I had a carb where the bowl was full of, what looked,black pellets. I had heard that it might be the rubber fuel lines breaking down,but I suspect the charcoal can. I have run them on all my vehicles because I was under the impression it gets rid of the gas smell @ shutdown.

[Cliff Ruggles]

Not sure if they would "get rid of the gas smell at shut-down" since they wouldn't purge without vacuum.  At a minimum install a 3/8" in line filter between the carb and the charcoal can to keep anything from migrating up into the carb bowl, and new lines to make sure the innards of the lines aren't flaking away and putting some crap in the carb as well.......Cliff

[tayto]

Excellent idea. I can use one of those cheap see through plastic fuel filters.

[Cliff Ruggles]

Yes, as long as you keep it away from the heat of the exhaust manifolds.  I'd put it down out of sight as close to the charcoal canister as possible......Cliff

[1970Bonneville]

If it helps your decision, I just unhooked the rubber vent line from the gas tank to the canister and I did not notice any difference in smell in my garage.

Also if it helps, for identifying if it is charcoal or fuel line pieces sort of the big tip off for me was disconnecting the line from the canister to the carb and seeing what came out of it. It may not be a definitive answer but in my case the same black pellets found in my carb came pouring out of the rubber line when i unhooked it. I also found a big pile of it from the exact spot that line went into the carb when taking the air horn off.