What year is it? Do you have the vacuum advance hooked up? If you have
done mods to the engine and it is a late model B (smog), The part
throttle ping is caused by your vacuum advance unit. Later Bs can
introduce up to 30 deg vacuum advance. When you hit the gas part
throttle, you are not openning the trottle plates enough to lower the
vacuum in the manifold enough to lower the amount of vacuum advance
introduceced at the distributor. Remember that this unit is there to
acount for changes in charge density. When you floor it, you have almost
no vacuum in the manifold and the vacuum introduced advance disapears.
Perhaps the vacuum unit is just sticking. Check for free movement of the
plate in the distributor.
Chris
On Fri, 8 Sep 1995, John M. Trindle wrote:
> I'm still not convinced that my timing is where it could be, optimally.
> To recap, I seem to be able to set either:
>
> Condition A) Timing is set to 5 degrees, car is sluggish off line, but no
> knocking or pinging. Temperatur OK.
>
> Condition B) Timing is set to 8 degrees, car is OK off line, but pings
> often above 3000 RPM in 3rd or 4th gears (light accelleration). Pinging
> lessens or disappears during harder accelleration
>
> Condition C) Timing set to 10 degrees, car is GOOD off line, pings like
> crazy during acceleration in 3rd or 4th gear.
>
> When I am in Condition A) or B) (or right now, in between the two) I get
> plugs with darkish deposits around the outer ring, and whitish deposits
> on the electrode. It's not these strange Champion Premium plugs either,
> since I got a white bullseye / black ring with the stock, recommended
> Champions as well. If I rich the mixture beyond the current setting (1/2
> turn on HIFs richer than starting point) the idle becomes unmanageable,
> and the pinging doesn't go away.
>
> After an extended drive at 20 mph (we have a single-lane touring road, 8
> miles long) the bullseye was brown. I kept the RPMs between 2K and 3K
> the entire way.
>
> My local expert says 1) Since it's a Kent 286 degree cam the timing won't
> be book anyway, and 2) he suspects a fuel delivery problem is causing the
> bullseye, and lean mixture at higher loads causes the pinging earlier
> than would be expected.
>
> I've replaced the fuel filter. The carbs were rebuilt in the last year
> and have worked OK since the rebuild (no bullseye). The plugs in front
> and rear cylinders behave similarly. The compression is even.
>
> Any ideas? My next steps appear to be a fuel pump and a distributor
> re-curved for this cam. The local expert, who sells the distributor,
> says that won't help much. The fuel pump is apparently a real SU, but
> does not shut off ever... it gets much quieter when the system is
> pressurized, but you can still hear it.
>
> Thanks!
>
> John M. Trindle | jtrindle@tsquare.com | Tidewater Sports Car Club
> '73 MGB DSP | '69 Spitfire E Stock | '88 RX-7 C Stock
> Home Page: http://www.widomaker.com/~trindle
> "You are what you is. - Frank Zappa"
>
>
|