Question for the MFI tinkerers

[jkeyzer]

Hey guys -

I took the MFI pump off the car today to look it over, change the belt, and do the gumout routine to clean up the rack.

I have noticed that the throttle lever on the pump does not always return freely back to the idle position. It will spring back 3/4 of the way, and then requires an extra push. This is most pronounced if you release the lever slowly and don't let it snap back.

Is this normal?

Possibly related, how "springy" should the rack be when pushing on it? Should it snap back quickly or be a more slow, fluid motion?

I am letting the pump soak overnight with B12 poured into the fuel inlet. I tried pushing the rack in and out while rotating the input shaft for a while but the behavior has not changed.

Tomorrow I am going to hook up all the fuel lines and injectors while the pump is on the bench and see how the spray patterns are. I tried this with a single injector tonight and it seems to work pretty well. I'm going to get a few small vials also and see if the quantity of fuel from each injector is similar.

The sprocket is somewhat worn on the leading edge of its teeth. I hope this is not a big deal. The belt never slipped while I have had the car. I imagine these sprockets are NLA anyhow.

[Early_S_Man]

Jeff,

The 'degumming' procedure with B-12 to free up the rack motion is done in the lower 'crankcase' of the pump ... where the engine oil resides and is probably easiest to do if you take off the right-side cover. If your pump's rubber gaskets for the crankcase covers are damaged and leaking oil, they can be replaced by locally available O-rings of 1/8" cross-section. You can guesstimate the needed length by taking the covers to the Beraing & Seal supply store.

Or, as an alternative, you could use Dow Corning 730 Sealant, or Loctite 518 ... after the crankcase is cleaned up and dry, and ready to reassemble. The pump should be refilled with oil up to the overflow fitting before reinstalling on the engine ... and any oil leaks can be checked & found if you let it sit for a couple of days on the bench with all of the orfices covered and tied off to keep dirt/dust out of the works!

[jkeyzer]

Thanks for the advice Warren.

Both articles I have read refer to adding gumout to the fuel inlet to clean up the rack. Using your method, where would I pour in the B12?

I have removed the side covers and can see the plungers and springs but not much else. Opening one of the other covers reveals a bunch of levers and springs near the thermostat.

Am I correct in assuming that the throttle not returning freely is a problem I need to solve?

Thanks again.

[Early_S_Man]

Jeff,

Yes, the sticking rack needs to be resolved. In Check, Measure, Adjust, it is recommended that gummed-up pumps be replaced with reconditioned or new pumps!

With all three crankcase covers in place and the pump laying with the right side cuver up, you can pour the B-12 into the oil return (overflow) fitting, or its' tapped porthole, if the barb fitting is off. After the B-12 has set overnight ... you will probably want to pick up the pump, cover the oil return porthole or fitting with a thumb ... and shake the pump vigorously a few times, then drain out the 'used' B-12 with contaminants immediately into a clear glass container ... a clean pickle jar works well. Remove the crankcase covers and examine to see if all 'gunk' has been removed and check to see if rack motion is now 'free.' Further soakings with clean B-12 may be needed to completely free up the rack. Blow out the crankcase area after draining ... with filtered compressed air line to remove all resicual liquid B-12 Chemtool from the crankcase. Allow to 'air' out and dry for a couple of hours on the bench, preferably while covered with a clean inverted trash can or cardboard box.

Replace all covers, and fill with clean engine oil ... and recheck rack return action. If the 'degumming' has been successful, rack return wil be smooth, and complete, without sticking!

[jkeyzer]

The rack movement is pretty smooth and complete, just a little slow. It's the throttle lever on the pump (the one that is connected to the stack crossmember by a linkage) that does not return completely if released slowly.

I've got the pump soaking overnight thanks to your instructions.

Zzzzzz....

[jkeyzer]

Warren -

Could you tell me if the throttle return spring is in the correct location in this photo?

Even after soaking the pump twice I couldn't get the throttle to spring back fully until I wound the spring around another half turn - originally it was hooked onto the other side of the throttle lever. Was it correct before?

Now that I have increased the spring tension the throttle snaps back nicely.