57 Rochester FI - any experts?

**Byron** · 08-20-2016

Hi I am trying to dial in a 57 Vette 283 FI. I have a few questions.

**1project2many** · 08-20-2016

I'm not an expert. I can try and help based on RFI manual and experience with EFI and limited experience MB Mechanical FI. I have heard these systems are finicky so my help may be worth no more than the cost of membership here.

**Byron** · 08-23-2016

OK here is the story.
I work at Major Corvette shop in Riverside Ca.The Car came in with a carb and high rise manifold on a 1960 283 / Turbo 350 and all the original 57 FI parts in a box - everything from Manifold to distributor.
I went through every FI item - Replaced all gaskets, seals, and diaphragms. Made sure that all injectors and lines were clean and clear.
The car actually runs quite well until you shut it down. Upon restart it is always flooded and needs 1/2 throttle to start and clear out. At times the cylinders are so full of gas that it will Hydro lock damn near. I removed the upper manifold and any intake valves that were shut have that port full of gas.
Question is --- What id used as say a check valve to keep the system from draining into the cylinders? Is it the spring tension on the spill valve that would shut the fuel off? Could i have damaged the spider when I blew air and carb spray through the spider? Is there a check valve in the Fuel spider?
I have done several others with no problems on restart - this car is got me baffled.

**myburb** · 08-23-2016

We are talking a lot of years ago but I had a couple of friends with the old rochester fi. I think there was a check valve that failed a lot. I can't remember how it was done but they both put in manual shut offs after hydro locked bent rods. l haven't talked to them in a long while but could try and get ahold of them if no one else chimes in.

**Six_Shooter** · 08-23-2016

I haven't played with the Rochester FI, but I have played a little with Crower mechanical FI, and on those systems a valve is installed in line with the main feed to shut the fuel off to the barrel valve and circulate it into a return for shut down. The Crower system uses open "constant flow" injectors, which I believe the Rochester FI does not, so the need may be slightly different but could work as well.

**1project2many** · 08-23-2016

Today's fuel creates more vapor pressure at a lower temp so you may have the unit assembled properly and the problem is caused by the fuel vaporizing. The spider is a good place for fuel to heat after shutdown and it will force fuel into the manifold. But the amount of fuel in the spider is nowhere near enough to fill a cylinder so the next consideration is fuel getting from the bowl to the engine. There should be a small valve in the bowl to prevent fuel from siphoning from the bowl into the spider and manifold. If you have an original '57 unit the valve will be gravity only, no spring assist. It's not known to be extremely effective. Later designs used a spring assisted valve that may or may not be better. But there's even more to consider: The amount of fuel in the bowl can cause problems but if you're getting a massive amount of fuel it's possible that the tank is pressurizing enough to continue to push fuel into the bowl as it leaks past the anti-siphon valve. If the tank vent is restricted then pressure will build until the fuel cap vents. Old fuel caps would limit pressure to about 2 psi but newer replacements can allow pressure to build as high as 7 psi. This could be enough to push fuel into the bowl as it drains.

Checking the tank is easy: Open the cap after the car has been running and see how much vapor pressure exists. There should be none. Checking the anti-siphon valve is tougher. I'd remove as much fuel as possible from the system then connect a hose from the bowl outlet line to a container. Refill the bowl and see what comes out into the container. If the fuel flows out as fast as it's put in then the valve isn't effective. If fuel drips out then IMO you're dealing with old Rochester FI design issues. If originality isn't top priority then you could install an electronic isolation valve. This video shows an installation: http://www.youtube.com/watch?v=a5sKNCT5SZ0&noredirect=1

Here are two good resources I've used to learn about RFI operation and to help folks troubleshoot:
http://www.oldcarmanualproject.com/m...0Injection.pdf
http://jerrybramlett.net/tips.html

**Byron** · 08-27-2016

Figured it out finally. The spill valve/fuel control valve was sticking in the bore. 1000 grit to the piston and the bore - now piston moves smoothly in the bore. Also float level was slightly high. So far running great without any more starting issues.