I'm working on building a late model "170" carb, let's say an Olds front inlet from 77-78 application. My goal is to take advantage of larger fuel bowl capacity hoping to not run out of fuel @ top end of track. Car noses down about 50' before the speed trap & definitely costing me a tenth or two when losing acceleration for the last 100 feet or so.

I am trying to avoid electric fuel pump but will eventually add it if this simple experiment doesn't do the trick. I am running 1/2" from pickup to carb (#8 AN) w/ Robbmc pump & filters so I'm a bit surprised that bowl doesn't seem to be staying full. Usually run a half tank or slightly more so I don't think I'm uncovering the pickup, but problem does appear to be delivery. Carb is a modded 7040258.

1) Can additional bowl volume be gained in "170" by removing the plastic shot glass?
If so, can I remove some of the casting material that walls off that well?

2) Idle bypass air is being added to base plate fwiw. I have been unable to locate a ported vac nipple on these model carbs. The nipples in body casting seem to supply manifold vacuum despite their location. Am I missing something or is there a mod I can do to create a ported vac nipple for my distributor & lockup circuit?

 

Seems odd you would have fuel starvation issues with what appears to be a very good fuel pump setup. Maybe you need a high flow needle and seat? Anyway, talking to Cliff Ruggles on the subject of fuel starvation;

I asked him about making more space for fuel in the carb by removing the round plastic insert for the aneroid cavity which some carbs have. In a nutshell, he basically said that such mods would only delay fuel starvation by a very minute amount so it wasn't worth it. He said it's all about fuel flow volume. With that said, I have heard others remove some of the material off the bottom of the plastic insert over the fuel bowl ( though removing it completely is not recommended ).

Your carb should have a ported vac source on the front drivers side of carb which would've been for the EGR valve. If that port is giving you full manifold vacuum then I'm at a loss.

 

If the ported vacuum nipple is giving you manifold vacuum at idle it means your carb is not running on the idle circuit; your primary plate has opened up past the port slot, showing that slot the manifold pressure. A confirming symptom of this is limited, or no, idle response when the idle screws are turned in or out.
This happened to me because of the engine rebuild put in a slightly bigger cam than stock. Cliff Ruggles will be modifying my idle circuit this winter to give it more umpf.

 

I also had fuel delivery issues with a RobbMc pump, finally installed a Holley 125 electric.

 

Depending on the fuel pump you have RobbMc recommends running their 1100 models at 12#s and then regulating them down to 6-7 before the carb.

Some of his articles:

http://www.robbmcperformance.com/news/news_v2i2.html

http://www.robbmcperformance.com/news/news_v3i1.html