Hey Guys, I am trying to determine what the correct Carter mechanical fuel pump is for my 1967 Pontiac Firebird 400 /4-speed. Please note, FWIW, I suspect that I have a 67' 400 from a GTO transplanted in my Firebird.
I am having fuel delivery problems and working my way through the fuel system from rebuilt carb. I searched online and its appears that M4522, M4684 and M4523 could fit - but the vehicle fitment specs conflict across Summit, etc.
I do not care about keeping car 100% stock - just want a high quality pump that will not require adjustments. Thanks in advance.
For a fairly stock motor all you need is a stock delivery pressure/volume pump if everything is set up correctly. There is no need to guess by replacing parts unless you cannot duplicate the problem during testing. With some digging for volume specs and testing the pressure you can tell what shape it's in. That said one of the main differences you will find in stock replacement type pumps is whether or not it has a vapor return line or not. Just look on your pump for a third nipple that has a hose going back to the tank. The vapor return is also very effective in helping with the dreaded vapor lock/fuel starvation during hot weather which unfortunately is much more common with todays alcohol gasoline. Ames performance engineering Has some nice replacement pumps and also detail exactly what you need based on your setup. I trust them mostly because I have been using there parts for many years and they are Pontiac only dedicated.
I'm not sure how deep you have gotten into it yet but one often overlooked fuel starvation problem is the gas cap. Our 7s & 8s use a vented gas cap if you use a non vented voila starvation problems. A lot of crappy venders will sell non vented 69 and later as stock for 7&8 and are so poorly made that they fit loosely and you can kind of get by because it can vent through the loose fit. The problem is it can still cause intermittent problems. Also if you have the correct vented cap the valve can get clogged causing the same issue. in extreme cases you will hear whooshing noises when removing the cap for refueling. To test just use your mouth a little gas never killed anyone. Good luck.
Given that I have a 400 originally from a 67' GTO transplanted into my 67' Pontiac Firebird (which presumably originally had a 326) I likely have a mismatch between 2-line and 3-line configurations. I currently have a 3-line after market pump on the engine where the vent line was blocked off and I cannot find a vent line - so either there was a vent line originally on the 67" Firebird and it was removed or there never was a vent line.
I have the options of installing a two-line pump (Carter M4523/vertical female input or M4689 /lateral female input) or installing a 3-line and new vent line. I live in CA and the car will be in hotter temperatures so having vent line may be beneficial. Note that I did have the gas cap issue previously and did get the correct vented cap through Ames which solved the issue.
Hi Sean, back in the day people that would get the wrong configuration pump from the parts store would just block off the extra nipple just like yours and it would be fine except for the ugly factor. As far as the pump line angles I really don't remember but it mostly hinges on what you have for lines on your car, stock or hand made. what I almost always see is that the line from the pump to the Carb. is hacked and rubber line is clamped on with worm clamps up to the Carb. sometimes with a filter in between, I know a lot of people do this but it is defiantly not the safest setup especially with todays poor rubber hose quality. As far as the vaper return If your car was a 326 it would not have come with one unless it had a/c because of the hotter under hood temps associated with it and also the higher performance 400s because of the same. But that means nothing on a 50+ year old car because the only difference is the sending unit and it's extra line. When replacing this back in the day that was another thing people got wrong just like the pump and would just block it also. To see if yours has it look on the passenger side top right front of your tank. Ames has the 67 pumps listed specifically for v-8 with or w/o vapor return they don't seem to designate between 2 and 4bbl either but don't worry about it the psi was the same for most configurations and the volume will be plenty for your setup. they state no differences in inlet angles but possibly they are different depending on with or without the vapor return. They are a good company and if you called one of their techs they either would know or pull them and compare. As far as your last question that's a tough one, does having the factory vapor return help with keeping the fuel temps down with the hotter under hood temps associated with Higher performance engines especially with todays alcohol fuels having a lower boiling point ultimately causing more vapor lock problems? Definitely. The hard part for me to discern is whether you were having vapor lock to begin with and is it worth it for you if you don't have the extra line on your sending unit to buy one and have to drop the tank and make (assuming you have a tubing bender and know how to use it to make the little flares on the ends for the hoses) the associated line up to the pump or buy that also. I guess if you don't have the extra vapor return line on your current sending unit you could buy a pump with it, block it off and if it solves your fuel starvation problem wait till next summer and see if you have any vapor lock problems and add if needed. By the way another symptom of this is when the under hood temps are at their hottest because of heat soak after the car is shut off. When you try to restart while still hot it will take a lot of cranking before it fires. What happens is the fuel boils in the Carb. and the line from the pump to Carb. causing it to expand pushing past the needle and seat causing the engine to flood at a point when it almost needs no gas because of the high engine temps. To verify if someone has this issue the next time you have a hard start because of long, not slow cranking of the motor just hold the accelerator pedal to the floor while your cranking and if it starts you can be pretty sure that's the problem. Sorry about the run on sentences I guess I have that train of thought writing thing.
