Anyone ever have problems running the stock TPI pump with a regulator?

My cars getting barely 8mpg....I've been advancing and retarding the engine like crazy trying to find a spot it likes with no success. The pressure out of the mallory 3 port regulator is a steady 7PSI....which should be fine. I dunno...I'm just trying to find any reason why I might not be getting good fuel milage....thought it might be possible the TPI pump is just sending way too much fuel into the carb even though the pressure seems right.

 

6 psi would probably be better. But, as long as the fuel bowl levels are staying where they should be, it isn't sending too much fuel to the carb.

Places to look include ignition (proper spark, proper mechanical and vacuum advance), jetting, and right foot pressure.

 

The only question mark I have is vacuum advance....I don't understand how it works. It says it came set for 10* @ 10"WC...and it's adjustable...but I have no idea how much the adjusting it does. I don't know if 1/4 turn retards it 1* or 5*, and accel was no help whatsoever. The car was pinging, so I retarded the intial timing, now there is no pinging at all any time, my MPG went from like 7.7 to like 8.5 But that is still crap....the engine does ping....do I need to keep retarding?

 

Kind of a far out idea but I know my 81 camaro needed colder plugs. It use to ping when it would run hot. Also check your choke to make sure it isn't closing.

 

running a carb, you need more volume with less pressure. the fuel bowls need to be full, not under pressure. a carburetor uses the venturi priciple where it pulls what it needs from the bowls. if you run this setup you can have the right amout of pressure (6-7 psi) but not enough volume. this is how I understand it. if anyone knows better, please correct. it's very possible that it will work, but not very well.

-Mike

 

Nothing wrong with the volume produced by a stock in-tank pump. If pressure is being maintained, that's not the problem. (Think about it: How would too little volume cause poor gas mileage?)

On the vacuum advance: What you're adjusting is the force the spring places on the diaphragm, or to put it another way, how much vacuum it takes to produce the full advance from the vacuum. Adjusting it in means it takes more vacuum to produce the 10 degrees advance, adjusting it out means less vacuum. The only way it would keep it from giving the full advance is if you adjusted it in so much that the engine doesn't produce enough vacuum to give full advance.

The basics of timing adjustment: You set the total mechanical advance to produce best WOT power (adjustment made with the vacuum advance disconnected). For SBC's, that's typically in the 34-36 degree range. You adjust the base or idle advance to keep the starter from kicking back and produce a good idle - this is typically 8-12 degrees, again without the vacuum advance hooked up. (Obviously, in order to get the proper advance at both idle & high RPMs, you need to adjust the amount of mechanical advance the distributor produces, which is easier with aftermarket distributors such as an MSD ProBillet than it is with a factory HEI.) You adjust the vacuum advance to give the most low-load advance possible without pinging on light load - this is typically a trial & error process.

Improperly adjusted vacuum advance, or adjusting the idle or total advance to compensate for an inproperly adjusted vacuum advance, are good ways to produce poor mileage. You want the most cruise advance possible without pinging to maximize economy.

 

Someone told me that the advertised 10* @ 10" was camshaft degrees, which is HALF of engine RPM. Meaning it's 20* full vacuum advance at 20" WC.

Basically, I have base timing around 7*, WOT is fine, but MPG is bad. I had been changing the initial timing since I couldn't understand how the vacuum advance adjustment works.

Does that mean if I keep screwing the vacuum advance chamber in, I can essentially limit the amount of vacuum advance the distributor will give out? I'm not pinging under cruise or WOT, but I'm guessing I still have too much vacuum advance at cruise. I don't want to mess with initial that much, since WOT is where it should be, with 24* mechanical, and 7* initial, I'm right around 31-32* @ WOT, which is where I want to be.

I appreciate your post 57, it was very helpful. (and everyone else)

 

Half the crankshaft degrees, yes.

20 degrees vacuum advance is about right. You can limit it mechanically (someone had a post on that somewhere on this board, recently), but that shouldn't be necessary.

 

Well my screwing the adjustment in, it should allow me to lower the total advance I get correct?

 

If you're not pinging under cruise, why do you want to reduce the vacuum advance?

As previously stated, screwing in the vacuum adjustment more will only limit the amount of timing if the vacuum required to provide full advance is higher than what the engine produces. It doesn't provide a direct limit in timing.

 

Ahh....so what should I do so I can exactly control my total vacuum advance?