I HAVE A REBUILD 4900R FI UNIT. IT WILL RUN FINE , THEN SUDDENLY START LOADING UP ( RUNNING VERY RICH AND NOT IDLE). I SENT IT BACK TO THE PERSON THAT REBUILT IT AND HE DID A FEW THINGS AND RAN IT ON A MOTOR. I GOT IT BACK AND IT ACTED THAE SAME AS BEFORE. FOR PEROIDS IT WILL RUN GOOD THEN ALL OF A SUDDEN IT WILL LOAD UP AND HARDLY RUN, AND BLACK SMOKE IS COMING OUT THE TAIL PIPE. HE SAYS IT MUST BE THE FUEL PUMP BUT IT IS NEW AND WHY WOULD IT BE AN ON AND OFF THING? I AM THINKING IT IS SOMETHING STICKING IN THE UNIT. ANY ANSWERS? OR THOUGHTS? I WAS GOING TO CALL JOHN DEGREGORY TOMORROW SINCE I HAVE BOUGHT SOME PARTS FROM HIM .
FI QUESTION
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What?
Your engine fuel pump is only required to keep an ample gasoline supply in the fuel meter bowl. The engine pump can't cause excessive fuel pressure at the FI nozzles.
You have described an engine that normally runs fine, but occasionally runs excessively rich. There are two ways I can envision the FI unit causing this.
The easier cause to check and fix is a periodic failure of the Cranking Signal Valve. You can test for this yourself. Place a foot long section of vacuum hose between the CSV and the tubing to the main diaphragm. After the engine is started, positively close off this hose by tightening a C-clamp on it. If this positive shut-off eliminates the occassional over-rich condition, then you have a faulty CSV. John DeGregory can sell you a rebuilt original CSV if you need one.
The second possibility is a sticking spill valve. The 4900R series originally came with a so-called "Good Guy" type spill valve. The nickname is a bad joke. This valve design has very tight tolerances and frequently sticks when it gets a grain of dirt or lint jammed in it. The best fix is to replace it with a later '62- 65 nail/thumbtack spill valve. You will then have to recalibrate your unit before it will run properly.
I have some favors to ask of you now. Please turn off the "Caps Lock" feature when you type. Also, please tell me which professional FI rebuilder implied the engine fuel pump could cause excessive nozzle pressure. If you don't want to post his name on this Board, at least e-mail me privately. I thought I knew all five of the guys with FI test engines, and none of them would give advice like that.- Top
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