High Idle Pressure, Slow Fuel Shutoff

Have a C-Rotor PSI on a BBC. Have about 20LBS fuel pressure at 2K idle RPM. When I push the fuel shutoff, it takes over 30 seconds to kill the engine. Have a Gorr ditribution block that has built in check valves for the dribblers and the mains. Anyone have an idea why it takes so long for the engine to die and how to get the idle pressure down? Very rich at idle, thinking that the poppets in the Gorr dist block are sticking open and supplying too much fuel? Not sure but wanted to get some input. The advertised pressures are set for 5 LBS on the dribblers and 20 LBS on the mains from Gorr. Thanks.


Tom

 

The idle return is usually #20 with a screw blower but the idle pressure should be less than#10 at low idle at the distribution block. Whats the barrel valve leakdown? and make sure the spool isn't in backwards. The secondary ports should be at #25 so they dont open staging at #20.


Marty Creech

 

To expand on what Mike posted, my shut-off had small by-pass leak and would not completely stop fuel flow and my motor would rev up pretty high and stay there for quite sometime.

Rebuilding it and cleaning-up the action solved my issue, good luck with yours.

 

Thanks to all for the input. The rich idle was cured by a barrel adjustment. We have checked the shutoff and that is not an issue.

When I had an 8-71 I used to kill the engine with just the ignition, never had an issue. When I shut the engine off with a 14-71, I hydrauliced it because of the extra fuel so I always shut off the engine with the fuel shutoff. It would normally take 5-10 seconds to kill the engine. With this thing, it takes way over 30 seconds to shutoff which makes it very dangerous if I need to shut it off in a hurry. Running the lines out hydraulically, they seem to be the same as the 14-71 so I'm having a hard time to see what the difference here is. I have four lines into the blower; the front two have 30LBS checks in them. The back two are open to the backside of the barrel valve and I believe that is where the fuel is getting sucked in. The ports are at 25LBS and the dribblers are at 5LBS.

Do I just need to shut this down with an ignition kill and back the engine down after that or is there something I'm missing? Just can’t believe this is that different from the roots but am open to doing things differently. Thanks.

Tom

 

fuel set up on a PSI screw blower

Tom, The fuel set up is completey differant then what you had for a 14-71, I have been running a 206D on a BBC for some time now, and when I got started I had some of the same issues. what is you idle check set at ?
The way we kill the motor is to first pull the fuel shut off and when the rpm's start to increase, us the mag kill switch to kill it, it takes about 15 seconds, and before we restart the motor we pull the plug and spin the motor over to make sure there is not fuel left in the cylinders, for us #2 always seams to have a little fuel that comes out, just my 2 cents.

good luck

Butch

 

Hi Butch, thanks for the reply. I got the differences down but why this is taking so long to shut down has me puzzled. I can understand that the fuel in the line is being sucked into the blower; I'd like to find a way to stop that. I changed from a -8 to a -10 main line for the screw so I know it added more potential volume in the line but with no pressure after I hit the shutoff, I would think that it would shut down faster than it does. I did get a hold of Spike Gorr and he said it was classic with the plate to have the fuel puddle when idling and to rap the throttle just before hitting the fuel shutoff to clean the excess fuel out. I thought more folks on here would know about this and chime in. If something is messed up it would be great to know about it but if it is normal, how does everyone else deal with it?

Tom

 

PSI shut off

Just like Will said very common for a screw blower. There is a lot of fuel volume in the lines that has to feed out before the motor will die. Go to the shutdown area when there are screw blowers running and that is what you will hear most of the time. I only know of a couple of funny car guys on the west coast that let it really run on the fuel shut-off.

 

Thanks guys, really appreciate the input. I just wanted to know what was "normal" so I didn't chase my tail and now I know. As always, the input from this site is great.

Tom