fuel mixture too lean

[GGR]

Hi all,

my fuel mixture seems to be a bit too lean. The spark plugs are very lightly colored and the engine does not seem to respond exacly as it should when I floor it at highway speeds. Also highway cruising is a bit as if an invisible rubber band was holding the car back a bit. Ignition timing is correct and spark plugs are the correct non resistance ones.

I have ordered a fuel tank filter (the big alen bolt at the bottom of the tank) as well as a fuel filter as they may be clugged and are old anyway. Are there any other filters in the fuel circuit I should replace? In the fuel pump or the injection pump?

Also, in my experience, fuel mixture tends to get richer when these injection pumps wear out. Anything I should look at before intervening on the main rack adjustment, in case replacing the filters do not solve the problem?

[wwheeler]

Have you done the split linkage test at higher rpms? That will tell you if you are lean or rich at higher engine speeds. It is not exact, but gets you pretty close. I wouldn't mess with the adjustments on the injection pump until you are certain about your mixture.

You can also check the output volume of the fuel pump. There are plenty of posts here about that. If you do need to adjust your mixture, you might think about shimming the BC instead of the main rack screw. It is easier and easier to reverse if needed.

[GGR]

Thanks.

I did a search with the "split linkage test" words and though I got many threads refering to it I was unable to find a description of the procedure. Could you please direct me to the right place, or describe the procedure?

Thanks in advance!

[Raymond]

Search for Linkage Tour by JA17 and you'll find this:

http://www.sl113.org/forums/index.php?topic=5003.0

[Jordan]

Linkage Tour I believe is only available with a paid membership.  Very worthwhile.

[GGR]

Search for Linkage Tour by JA17 and you'll find this:

http://www.sl113.org/forums/index.php?topic=5003.0

Thanks. I went through all the thread and though all is described about rod lengths I did not find a description of the split linkage test procedure (one reference is made about it by ja17 but no description) . Unless it consists in making sure the butterfly closes properly and that other rod is 233 mm? Or I missed it?

[glenn]

Hi, The test procedure, roughly...   1. Engine warmed up to normal temp, etc.  (fresh from a spin)  2. Detach  vertical rod between the Fuel Injection Pump and crossover rod.  Detach at top.  3. Slowly push rod down about a 1/4 inch or so,(this adds more fuel slowly) If rpms go up at first, the engine was lean.  At some point of more fuel, it will become too rich and rpms will decrease and eventually stall).

Next with FIP rod back on stop(but still detached)....   Slowly open the butterfly on the venturi.  If the rpms go up more than 50 rpms, engine is too rich.  As it is opened more, it will lean out(rpms will fall and eventually stall.  If rpms fall immediately, engine is lean.

[GGR]

Hi, The test procedure, roughly...   1. Engine warmed up to normal temp, etc.  (fresh from a spin)  2. Detach  vertical rod between the Fuel Injection Pump and crossover rod.  Detach at top.  3. Slowly push rod down about a 1/4 inch or so,(this adds more fuel slowly) If rpms go up at first, the engine was lean.  At some point of more fuel, it will become too rich and rpms will decrease and eventually stall).

Next with FIP rod back on stop(but still detached)....   Slowly open the butterfly on the venturi.  If the rpms go up more than 50 rpms, engine is too rich.  As it is opened more, it will lean out(rpms will fall and eventually stall.  If rpms fall immediately, engine is lean.

Thanks, I got it. wwheeler is talking about doing the test at higher rpm (which makes sense as at idle idle richness adjustment kicks in). Should I actuate the linkage so that the engine revs at say 2-3000 rpm and then diconnect the vertikal rod while keeping the engine revving and do the test?

[wwheeler]

What I did for the higher speed test is to pop the IP socket off the ball in advance but hold it together while opening the throttle. Once you reach your RPM you want to test, hold the arm attached to the crossover rod steady and slowly move the IP rod and socket off the ball. From here, you can add more or take away fuel and determine if it is rich or lean. You must hold the crossover rod arm steady so that you won't vary the engine speed with it. I would think that 2-3000 rpm would be sufficient.

Concerning the linkage tour: I took my car in to adjust the automatic trans for better shift quality. The mechanic is highly regarded in this area and he was amazed at how good the linkage was set up and adjusted. That just shows you how good the linkage tour is because I followed it very closely.

Hope this helps.

[ja17]

Hello,

Yes, that is the correct description of the "split linkage test".  Some basic logical thinking.  Pushing down on the rod going to the injection pump increases fuel. Pushing open the rod to the intake venturi increases air.  Listen to the engine........it will tell you what it wants, fuel or air. The procedure can be conducted at different rpms, and engine temperatures.  Make sure that all engine tune up items are in order or you may just be getting everything out of adjustment.

Maybe we can do a video and document "The split linkage test" at PUB "11"

[GGR]

Thanks all, this is very useful. So I should first follow the linkage tour and make sure all is in order there and then do the split linkage test. Will try and do that this week end.

Maybe we can do a video and document "The split linkage test" at PUB "11"

That would be great!