Quarter Coin TBI Mod

[trenchwarfare]

Has anybody ever heard of placing a coin I believe near the fuel regulator to improve performance???

[chevymotocross]

Yup, the coin puts pressure on the regulator spring increasing the fuel pressure.

Best way is to first tap in a fuel pressure guage at the TBI to see what you are currently running. Stock should be 9-13. 13-14 is what you really want for a close to stock tbi engine.

Coins are kind of annoying though because you have to constantly use different coins to get the pressure needed when you can just install an adjustable regulator. Check out CFM-Tech or ebay.

[trenchwarfare]

Thanks. Finally a quick and accurate response for once!

[78 Chevyrado]

I don't remember where I found this, I found it like 5 or 6 years ago. I did do this to my '87 and it worked quite well. The coin works too, its just a simpler method.

You can change the setpoint of your stock regulator by roughly +/- 2psig, quite easily. Sometimes without even having to disassemble it. Remove the whole fuel meter cover and regulator assembly from your TBI and flip it upside down in your left hand. You should note a rectangular window cut in the side of the regulator can, with the end of a tang visibly located somewhere between the extreme ends of that window. The tang is attached to the spring perch within, and it's relative up/down position is roughly proportional to the setpoint of the regulator. Move tang up, more pressure, move tang down, less pressure. Now, look at the bottom of the can and you will probably see a beefy collar with what appears to be a screw tack welded in the middle. You can either dremel away the tack Weld and manipulate the screw, or, you can try this next approach. Firmly grasp the collar with a good set of vice grips or channel-lock pliers, and gently attempt to force the collar counter clockwise. Chances are pretty good that the tack welds between the can and the collar will snap, and you can then proceed to turn the whole collar assembly counter clockwise to raise the pressure slightly. If this does not work for you, or if your regulator does not have a collar (as some don't), then you'll have to disassemble the regulator to modify it. Again, spin the perch counter clockwise on the screw shaft to compress the spring and raise the pressure.

I just dremeled the tack weld away so I could use the screw with a regular screw driver... worked great. I mounted a schrader valve right to the top part of the TBI for a pressure gauge, but I can't remember exactly what part I installed it in.

[bigblock73]

Originally Posted by trenchwarfare

Thanks. Finally a quick and accurate response for once!

Nice attitude...

[68 TT]

Originally Posted by 78 Chevyrado

I don't remember where I found this, I found it like 5 or 6 years ago. I did do this to my '87 and it worked quite well. The coin works too, its just a simpler method.

You can change the setpoint of your stock regulator by roughly +/- 2psig, quite easily. Sometimes without even having to disassemble it. Remove the whole fuel meter cover and regulator assembly from your TBI and flip it upside down in your left hand. You should note a rectangular window cut in the side of the regulator can, with the end of a tang visibly located somewhere between the extreme ends of that window. The tang is attached to the spring perch within, and it's relative up/down position is roughly proportional to the setpoint of the regulator. Move tang up, more pressure, move tang down, less pressure. Now, look at the bottom of the can and you will probably see a beefy collar with what appears to be a screw tack welded in the middle. You can either dremel away the tack Weld and manipulate the screw, or, you can try this next approach. Firmly grasp the collar with a good set of vice grips or channel-lock pliers, and gently attempt to force the collar counter clockwise. Chances are pretty good that the tack welds between the can and the collar will snap, and you can then proceed to turn the whole collar assembly counter clockwise to raise the pressure slightly. If this does not work for you, or if your regulator does not have a collar (as some don't), then you'll have to disassemble the regulator to modify it. Again, spin the perch counter clockwise on the screw shaft to compress the spring and raise the pressure.

I just dremeled the tack weld away so I could use the screw with a regular screw driver... worked great. I mounted a schrader valve right to the top part of the TBI for a pressure gauge, but I can't remember exactly what part I installed it in.

Tapping a schrader valve into the TBI regulator housing is a good idea. Was it accessible with the air cleaner installed? Where on the regulator did you install it?

I'm thinking maybe tapping into the bottom of the supply side and plumbing a 90 degree fitting out to where the schrader valve would be easily accessible for tuning with the air cleaner in place.

[78 Chevyrado]

I tapped my valve in here where the BLUE arrows are. I tried it where the Red arrow is and it Didnt work. Where the blue arrows are is the tunnel where the fuel goes from the regulator to the injectors. You have to tap in somewhere in there between the regulator and injectors. So you'll have to remove the air cleaner lid to check pressures. If you mount it so it's externally accessible, You will get a fuel PSI reading of the fuel pump, but not the regulator.



When I installed the schrader valve, I used a threaded one and screwed it into the TBI. I drilled and tapped a hole in the TBI's top plate (blue arrows) I put epoxy on the Schrader's external threads as well as in the TBI's new threaded hole. You have to remove that top plate off the TBI to install the scrader, if you don't metal shavings will get to your injectors and the epoxy might block the cavity. I wish I had a photo, but i never took one of that mod.

[68 TT]

Originally Posted by 78 Chevyrado

I tapped my valve in here where the BLUE arrows are. I tried it where the Red arrow is and it Didnt work. Where the blue arrows are is the tunnel where the fuel goes from the regulator to the injectors. You have to tap in somewhere in there between the regulator and injectors. So you'll have to remove the air cleaner lid to check pressures. If you mount it so it's externally accessible, You will get a fuel PSI reading of the fuel pump, but not the regulator.

I think it will work either place as the two different pressure adapters that are out there for testing the TBI both hook up before the regulator.

The test port on my other vehciles are also before the regulator from the factory too.

If the regulator is working right the excess pressure in the supply line should be bled off into the return line and both sides of the regulator should be equal pressure.