rneoaz82

my 83 is one hell of a gas guzzler and it sucks bad.. I drive to school which to and from school is about 16 miles. I can have a half tank of gas and when i go to school and then come back home i have only a quarter tank, so basically this bastard is getting horrible gas mileage. Can anyone give me some suggestions on what the hell can be going on with this. My fuel filter is new, so i can x that problem out.

I have this crazy idea that my motor might be dieing because on the highway to school the car only hits 65mph tops with the gas pedal to the floor. Maybe it might be wasting that much gas because my secondaries are opened as though like passing a car, but i can't if i tried. Maybe its feeding a crap loud of gas and the 83 still tops 65mph. Not cataylic converter because its strait pipe from front to back.

Any help would be greatly appeciated

candyassmiler

fuel filter my friend.

rneoaz82

You really think it might be the fuel filter? I had to replace my gas tank like a month ago because it was rusted and was also leaking. the rust had clogged my old fuel filter, but now my new one is a month old.

Mark S

iTrader: (1)

It sounds to me like a clogged exhaust. You say you are running a straight pipe, are you running one cause your cat went bad? If so, sometimes as the cat breaks apart, pieces of it are chucked up into the muffler -clogging it to.

A cheap test would be to disconnect your muffler and go for a drive (a loud one) and see if the car runs better.

If it's not the exhaustr, my second guess would be a prob w/ the carb.

LongDuck

I would take a very close look at fuel leaks from the tank, filler, pump, and the filter location, not to mention looking down the carb when the engine is idling.

Using that much fuel (1/4 tank in 16 or 32 miles, even) is WAY too much and you should be seeing black smoke out of the tailpipe due to the rich mixture.

Since you're describing some performance problems in addition to the fuel consumption, it may well be that your carb needle valves and seats are allowing the fuel pressure to flow past them, overflowing the bowls, and running down into the intake. This is pretty common when either your needle valves and seats need to be replaced, or if your fuel pressure regulator has gone out. An aftermarket fuel pressure regulator (adjustable from zero to 9-10 psi) is a cheap fix for this, and most Mikuni carbs in the 1st Gen should be run at about 4-6 psi for best performance. Any more than this and you may be overflowing the fuel bowls in the carb.

As a check, put some fresh cardboard under the car, fill it up with gasoline to Full, and then let it sit overnight. If you have a fuel leak, you'll notice the stains on the cardboard, and this could be part of your problem - that is a LOT of gas to be running through your engine.

Also, the fact that you stated you were working on the fuel tank in the past may mean that you forgot to hook up a vent line or connector that may be leaking the fuel out under pressure as you drive - it's probably something simple.

rneoaz82

Thanks longduck see now thats the kind of answer i was looking for im going to check that out this weekend!

rneoaz82

can someone tell me where the fuel pressure regulator is located?

LongDuck

There is a fuel pressure regulator located internal to the fuel pump, but this can go out after an indeterminate period of time, which bumps up fuel pressure considerably. The only way to find this out is to get a fuel pressure gauge (for carb'ed engines) and hook up a T-connection in line from the feed from the pump, going to the carb. There is also a return line going from the carb back to the frame tubing, but this will not register much pressure, as it's only for overflow.

On that note, something to think about would be your fuel return line from the carb back to the tank not hooked up, kinked, or possibly clogged, which would lead to the fuel bowls overfilling and flooding the engine - you did mention that your last tank was rusty and your fuel filter was gummed up - could be that some crap made it past and worked it's way into the carb, or even into the return lines. However unlikely, it's something to check. A clogged return line would definitely cause flooding and high fuel usage. Check this by removing the return line and running the pump to see how much fuel is returned to the tank in a fixed amount of time - do this at the carb, and then again at the return line at the rear of the car to be sure that it's the same flow. If not, you've got a clogged return line.

A good bet is still verifying that you're not overpressuring the carb. If you don't want to buy a fuel pressure gauge and all, just spend $15 bucks on an aftermarket fuel pressure regulator and put that in-line between the frame tubing and the feed line to the carb (in the engine bay, obviously). This will allow you set whatever pressure you want, and works better and more reliably than the internal fuel pump restrictor. I think most 1st Gen Mikuni (stock) carbs work best on 4-6psi - going by the Racing Beat catalog. Dial it in to 4psi and give it a run and see what happens. If you get fuel starvation at high rpm's and high speed, bump it up 1 or 2 psi further to ensure that you get good high volume flow - this will be evident through the car 'topping-out' at a specific rpm or vehicle speed.

What I've suggested will not fix a fuel leak issue that's in the tubing on the frame, or the fuel filler or tank, of course. If that's the case, you're going to need to find that leak and fix it to get good performance and fuel mileage. You've got your work cut out for this weekend.

rneoaz82

For the time being im going to replace the both fuel lines going the carb. I think your pretty much right that maybe some crap got stuck in the lines and could be clogged because yup before i replaced the gas tank i had to replace the fuel filter twice. One more thing in reading the hynes manuel it says that the fuel cut off can be it for loss of power. Should i replace this also since fuel was running though there also.

LongDuck

I doubt it - the 'check-and-cut' valve is usually either good or bad, i.e., it flows or it doesn't. This valve is designed to cut off fuel flow if the car is rolled over as in an accident.

It would be the last thing on my list to replace and only then if you've done everything else in your power to figure it out. HTH,