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Old 08-02-2009, 11:31 PM   #1
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Default V-Spec not holding a tune [resolution]

I posted up a month or so back that my v-spec wouldn't hold a tune. I think the thread got deleted in some forum issue a while back, but regardless, I'm posting up my resolution in the hopes that it will help somebody else having similar issues.

I have resolved the issue and determined what it was. I will reveal what it was near the end.

First off, the symptoms: The car would accept a tune, run well, and then out of the blue it would suddenly get excessively rich. You could re-tune it (more than a turn on the high speed needle and similar on the bottom end) and it would be perfectly fine... until it would swing the other way, coming off the track so lean it temped at 306F when it had gone out a little fat if anything. Some times it would be fine, then bog everywhere, then fine again, all in the course of a few laps. Some times it would be rich bogging, then landing off a good jump would trigger the tune to come back in.

I tried all of the standard stuff. I sealed the carb with ultra grey. I sealed the back plate. I replaced all my tubing. I removed my in-line filter. I replaced my header gaskets. I rebuilt the carb (as in, tore it down, cleaned it, nothing appeared to need replacement.) I switched tanks (I have 2 cars, one d8 I run, and one I use for a parts buffer). I tried different glow plugs. I tried different plug heats. Nothing resolved the issue. Obviously, I thought each time I had solved it... until it came back.

Then one day, I had tore the carb apart at the track (after pulling it during a qualifier because it had switched back to mega lean mode on me half way through the race) and was cleaning and inspecting it as a last resort before tossing this v-spec in the garbage thinking it's just cursed. During this tear down, I noticed that there was some dirt in two places: under the slide boot on the carb side and IN THE FUEL BANJO on the high speed needle. Turns out the sealing washers above and below the banjo were damaged -- probably from the initial time I moved the nipple to the right location initially. The sealing washers are steel covered in a rubber coating. Tighten them too far and the rubber coating gets damaged, creating a potential leak. Having been out of it for 12+ years, this being the first motor I have touched in that long, I didn't realize how sensitive they were and over torqued the HSN when changing the nipple direction. I thought they were simply black metal shims. If I had realized they were rubber coated, I would have torqued it down far less!

So what was happening was basically that the car would normally have an air leak in the fuel supply before entering the needle after the nipple and whenever dirt would clog it the car would suddenly suck fuel like it should. When it wasn't clogged, it was getting far less fuel because sucking air is easier than sucking fuel. I went to the hardware store and got some aluminum washers and replaced the busted up coated steel ones with the crushable aluminum ones -- this is how full size cars seal fuel banjos. I could see after inspecting the marks on the washers that it was mating and sealing well and I've had no problems since with the tune changing on me.

Sucks that it took 3 gallons to determine this was what was giving me random issues.
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Old 08-03-2009, 03:43 AM   #2
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Thanks for the info, I would have never thought about that being an issue.When someone posts a resolution it should be archived !....???
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