[74Grandville]

I just got my 455 running, but it seems i'm starving for fuel when i get on the gas. I believe my setup shouldn't need an electric pump. Please give me your thoughts.

455 (.040 over), stock, 6X-8 heads (9.1:1), 068 cam (212/225 .407/.408).
th400, stock converter, 3.23 posi.

i'm using a 1981 SR Q-jet ment for a 68-69 400. 72/41 primary, K hanger with CK rods on secondary. {this carb has a big float, so i know it doesn't hold as much fuel as the later carbs}

Carter fuel pump (0-3000 ?), not sure of the model, but it's a single line pump. stock 3/8 fuel line from tank.


this is in a 1979 firebird, had a 301\th350 originally.


I was trying to work on the full throttle shift, but I can't even get the motor to get up to 4,500 rpm with out choking out. I would like it it shift around 4,800/5,000 rpm.

Your suggestions are appriciated.

[thadeal4real]

whats the psi cause probly aint the pump??

[74Grandville]

I have no idea. I don't have a guage on it.

[goatwgn]

I dont like the single line pumps. They dont allow you to run a vapor return line. I would check your fuel pressure, (it should be 5 or 6 psi or so, but most importantly, it shouldn't drop off a lot when you open the throttle) I've run a factory type (with the big canister) high volume pump with 3/8" outlet and a vapor return line for years on a 455 with no fuel starvation. Make sure that you also have 3/8" line coming from the tank, as well as the pickup. Some were only 5/16". I did run a Carter high volume pump without vapor return line before this and had vapor lock issues in hot weather. I think the Carter pump is a good unit, but running a return line seems to keep the fuel from picking up excess heat before entering the carburetor. Just some ideas, hope this helps.

[74Grandville]

I was looking at the large can stock units. If I where to go that route, which one should I choose?

[goatwgn]

I would get one for a 1971-72 455 HO "F" body car. These should be High Volume large canister types with the lines in the correct position for your car. If you have trouble at your local parts stores I beleive our host may have them.

[PontGuy]

I have a very similar 455 setup to yours but running a stock-style Airtex 40710 big bowl pump with a vapor return (listed for early 70's 400/455s). I installed a new tank and the new stock-style 3/8" pickup is plumbed through the original 3/8" tubing to the pump. I figured it would be enough but now not so sure.

I am about 800 miles into the engine since the initial break in and so still tuning, but have come a long way with it. The shift point feels "right" around 4800 RPM or so but this is just at the ragged edge of fuel delivery. Sometimes it pulls through the shift just fine and sometimes it bogs right at or just after the shift. Also I sometimes get a bit of vapor lock on hot days so having a return line isn't an instant cure in itself.

I am thinking about trying a Robmc pump, but if the original 3/8" fuel tubing is the problem (either restricted somewhere or just too small) then a better pump probably won't solve my problem. I don't want to go electric- been there, done that. It works but at a cost- noise, etc.

Just some food for thought...

Walt

[74Grandville]

Does anyone know the minimum requirement to supply an engine like mine? I would think a stock setup would be enough.

is 3/8" to small of a feed line for a mechanical pump?

[PontGuy]

I asked the same question when I was initially working out the bugs on my new engine and got a wide variety of answers. The street guys had mixed opinions and the racing crowd was unanimous in saying stock is not enough.

I don't think there is a simple answer. Just doing a simple ratio, a 455 spinning at 4900 RPM is sucking approximately the same air/fuel volume as a 400 spinning at 5600 RPM, or a 350 spinning at 6400! So we are probably at the ragged edge for stock components, and it depends on condition of the fuel line, head flow, jetting etc. Going with an OEM style big-bowl 455 pump should help, but it may or may not get you all the way there.

By the way I tried two of the Airtex pumps and never returned the first so I have an almost-new spare that I probably will never use. I'd be happy to drop it into the mail for you to play with, but the inlet/outlet positions are probably not right for your FB.

Walt

[Evil Stu]

Any chance you have a small leak on the suction side of the pump? It may not drop fuel, but will draw air, like trying to drink through a straw with a hole. A small one may only draw air at high flow rate, like you're seeing.

BTW, stock pump (large) and lines(3/8") have proven adequate for me thus far.

Stu

[lust4speed]

You definitely have a fuel problem, but it's not the wrong parts - just something wrong with one of the parts. Check everything in the delivery system. I'd start at the rear and insure that the tank is properly vented. Next check the gas line from the tank to the steel line. Everything this side of the pump is critical because the pump is pulling a vacuum and sucking fuel is a tough job even when everything is working correctly.

Easiest way to check the fuel pump is with a gauge - even if you have to borrow one. Easiest way to check out the carb is to substitute a known good one.

[74Grandville]

Thanks for all the reply's. I did some checking and made a couple changes. The line is the stock line (from 79), so it may have a leak somewhere that is not visable.

i'm going to test tonight and see if what I did helped the problem.

things I did:

- removed the stock fuel filter from the carb and installed a steal can before the carb.

- removed the steal line from the pump to the carb and installed 3/8's rubber fuel line. It had some sharp bends in it.

- shorten the line going from the steal line to the pump. It was calapsing the line i think being to long. Creating to sharp an angle.

--------

If I still see an issue, i'm going to check the seat size of the fuel inlet in the carb. sounds like it should be .125" and check the lines at the tank.

[bluzurb]

I had the same problem. When my TA was on the dyno she wouldn't go above 4500 rpm's. It has a stock 400 with an 800 carb and edelbrock intake. Lunatie BMII cam (.490/.490 llift) AC delco fuel pump. We tried quite a few things on it. The major things we did was stopped getting it to run rich. We jetted down the primaries in the carb one size. Also, the cam was out of place with the crank. The crank gear was 3 teeth too retarded. We turned the crank 3 teeth forward and took her for a drive. She was great. I took her to the track and was shifting about 4800-5000 rpm. Also upgraded quite a few things. new plugs, 8.8 wires, ignition coil, etc.. How do you know you are starving for fuel? Another thing you can try is hooking up a fuel pressure (i can't even think of the word) dial thing...LOL....hook it up between the carburetor and fuel filter and run a hose into the car and hook the fuel pressure dial thing to the end and take it for a drive and get it up to 4500 and see where the fuel is at. Then go from there.

[74Grandville]

Thanks for all the replies. for now my issue has been resolved.

[PontGuy]

Good point bluz. We'd all like to think that a fresh engine will always run like a banshee right from the start but that doesn't always happen for a variety of reasons. Mine ran strong on the bottom but wouldn't come up and run on the secondaries properly, and I started chasing fuel as just one of the possible causes. Some adjustments to the carb and a quicker distributor curve worked wonders, and then my Cliff Q-jet finally arrived which completely eliminated any sort of bog. Still running the same fuel system I started with- not sure it is quite enough, but not ready to start throwing money at it quite yet especially since I am so close to where I want to be.

74Grandville, what does your timing curve look like? Also is it pulling into the secondaries strong and then falling off?

[74Grandville]

when i built the engine a couple years ago, i put in what made sense to me and what I had learned. The engine has only been in use now for less then 2 weeks, so I know things like timing and carb still need to be looked at. At this point the engine is running strong. Someday i'd like to make my way to a chassis Dyno to really see what is going on and tune it.

tonight i was working on the shifting again. I almost have it dialed in where i want it, 4,800 shift. I'm just happy to have a running pontiac again. This time with some nice power for the street.