Jackpot!
You were right on about the EGR system leaking. I sprayed carb cleaner on
the EGR connections and sure enough the idle speed increases indicating its
leaking. Apparently leaking at the EGR valve to exhaust manifold mounting,
on the plunger rod on the EGR unit, at the other end where the pipe connects
to a banjo bolt on the intake manifold.
How do I improve on the sealing of the these joints?
Also seems to be leaking at the carb to manifold gaskets. This is
surprising as the gaskets are new and the nuts are tight.
I put a vacuum gauge on the carb vacuum port for the EGR control. Its not
dead as I thought. Seems to be no vacuum idle but when I open the throttle
it then gives lots and gets stronger depending on the throttle opening.
So it appears that the rough running is caused by a few vacuum leaks, but
I'm not sure how I can improve upon them.
Peter S
----- Original Message -----
From: Bob Sykes <stan.part@worldnet.att.net>
To: <alfapete@pacbell.net>
Cc: <spitfires@autox.team.net>
Sent: Saturday, June 26, 1999 2:42 PM
Subject: Re: carb - (ZS tuning problems)
>
> Sorry I missed the beginning of this thread and I'm not sure exactly
> what model car(b) is in question here but I'll give it a shot:
>
> Peter S. wrote:
>
> > Ok listen up out there! Car still runs a bit rough. (recap - ZS carb
> > leaked gas and ran rough - then rebuilt carb and no gas leaks but still
runs
> > fairly rough. Did the following today:
> >
> > 1. compression check - All cyl. at 109lbs.
>
> OK
>
> > 2. Ensured timing was correct and operates smoothly. Discovered advance
> > vacuum pipe was melted and replaced.
>
> Good
>
> > 3. Attached a vacuum gauge. Reads steadily and changes smoothly.
> > Discovered vacuum port for EGR - (top rear section of carb nearest
manifold)
> > appears to be dead (checked good when carb was on the bench). No vacuum
(or
> > pressure) measured. I remember wondering which way the carb-to-manifold
> > gasket should be since it has a notch. I put it where the old was which
was
> > pointed to the front of car and downward. THIS CORRECT????????????
>
> There's a gasket and there's a 3/8" spacer here. The important thing is
> that the notch aligns with a corresponding hole in the carb flange. The
> spacer is not symmetrical, so it's possible for it to be pointed to the
> front of the car and downward and still not line up with the hole. I'd
> check this.
>
> > 4. Ran engine from new gas in gas can instead of cars gas which may be
old.
> > 5. pinched off temporarily various vacuum hoses while engine ran to see
if
> > there was any change. Virtually nil on all of them. Discovered large
> > crankcase breather pipes leaking and replaced with new hoses.
>
> This is good. It's important for the crankcase breather hoses to be
> leak
> free (or will be too lean and impossible to tune). For troubleshooting
> purposes, you can just run a single hose from the rocker cover to the
> appropriate port on the carb. This bypasses the evaporative lines and
> cannisters which could be a source of further vacuum leaks.
>
> > 6. Ensured Choke control operated properly.
>
> Not sure what you did here. ISTR this was a water heated choke?
>
> > 7. Replaced dashpot oil with 3-in-one.
>
> OK
>
> > 8. Used ColorTune. NO color changes when turning idle mixture screw.
Can
> > see/hear no difference at all despite many turns. Always slightly
> > blue/white.
>
> Could be a little lean. Possible vacuum leak. It sounds like you are
> turning
> the *fine* mixture adjusting screw. This will have little/no effect if
> there
> are other problems. As Atwell noted; you probably want to adjust the
> carb
> needle with the "special tool" for more effect.
>
> > 9. Ensured Lucas distributor had gap as specified in manual. Noticed
dist.
> > shaft seems to move somewhat preventing decent measurement. Cap and
rotor
> > are new.
>
> Probably OK. A "points type" distributor and water heated choke are
> mutually
> exclusive wrt to originality. They'll work just fine together, but I
> cannot
> deduce the model year of the car based on these items.
>
> > 10. HT plug wires all measured 6-10 ohms.
>
> Should be OK
>
> > 11. Plugs cleaned and regapped to 25 thou. Splitfire plugs.
>
> I have no experience with these sparkplugs.
>
> > What am I missing? All of the changes had little or no effect to the
> > running of the car though the new vacuum advance pipe does appear to
give a
> > little more power than before.
>
> Possible vacuum leak(s). Did you check for play in the throttle plate
> (butterfly)
> shaft bushings when you rebuilt the carb? This is a common source of
> air leaks
> when the carbs get some age on them. I'd (temporarily) plug the vacuum
> port on
> the carb. Fit the single hose from rocker cover to car (mentioned
> above). Then
> check the EGR valve for vacuum leaks with the car at idle. We're not
> checking
> the control port here (I remember you said this won't hold a vacuum).
> We want
> to make sure the "business part" of the EGR valve is not leaking air
> directly
> into the intake manifold. This can be accomplished by spraying carb
> cleaner,
> WD-40 or other flammable fluid of your choice in and around the EGR
> valve.
> If this causes the idle to change, then you've probably got a vacuum
> leak here.
> You can perform the same test on the throttle plate shaft ends to check
> 4 leaks.
>
> FWIW I'd recommend having a fire extinguisher handy while doing this.
>
> Hope this helps,
> Bob
>
>
> --
> Bob & '78 Spitfires
> (one of them mine for 21 years)
>
|