Fine Tuning After Breaking-In the T/C

[robert kenney]

Guy,
I have to do the break in valve adjustment. I initialy set the valves all @ .016" +/- .001. They are a bit noisy at rpm (2000 +) What would you suggest I finaly set them at? Would like to quiet them as much as possible

I also have one carb barrel that is very rich at idle. It wants to have the idle mixture screw all the way in and never goes lean. The carbs are perfectly synched and the other three idle mixtures are at best hot idle out about 1/2 - 3/4 turn. Any possible causes?

Robert

[Guy Croft]

Noisy GC 3A cams? Perish the thought.

16 thou inlet
18 thou ex

(cold)

To diagnose an IDF barrel unresponsive to alterations to the idle mixture screw you need to get a Colortune device (see Gunsons, links) and fit it in each cylinder in turn. It is the only effective way to set up IDFs.

Thru the colortune window the errant cylinder will show as firing bright orange (way too rich) which means its throttle plate (in that barrel) is not open enough relative to the adjacent barrel or the balance screws on that carb are out of balance - one barrel on one carb must be closed - on the cylinder of the pair drawing the most air, the other screw on that carb is opened to compensate (or fuel is maybe dripping into the barrel from the pump jet), or spark-only which means the cylinder is not firing at all. Naturally when the carbs have been balanced barrel to barrel the carbs pairs must be set against each other via the balance quadrant.

Make sure that the pump jet actuating lever is not rubbing on the inlet manifold by the way, because that makes them drip fuel.. (under the carbs between the barrels).

Check it out and report what you find please.

GC

[robert kenney]

Guy,
I have the valves set at 015-017" .016 nominal on all tappets because of a marginal selection of shims. So you say go bigger EG .018 on exhausts?

The carbs are balanced as I went through them again last night. No accel lever rubbing and no fuel dripping from the pump jets.

The other 3 barrels adjusted normaly and would go rich or lear as I found best idle speed after balancing the carbs. Turning in the mixture screw on the errant barrel will cause an increase in idle speed right up to it is completely closed and not slow the engine at the closed position. Seems like it is recieving fuel from an alternate source. Could the cold start valves (currently blocked) be the source? I saw the poppet valves installed under the covers for the cold start devices.

I will read the header temps with a IR thermometer tonight and see ig the idle EGT's are similer.

Thanks Robert

[Guy Croft]

Rob,

my settings are 16/18 thou, +/- 2thou so you will be OK. I hope you are using new shims.

If the idle speed on the cylinder in question increases as you wind in the idle mixture screw that's the engine responding to an increasingly correct (leaner) mixture. I've hinted at out-of-balance but you assure me it's taken care of. I've mentioned a couple of causes but beyond that I don't know any other bypass routes for excess fuel. The problem is of course either excess fuel from some uncalibrated source or - insufficient air going thru that barrel.

Note that the setting must be done at very low speed, 750-850 rpm otherwise there is a fuel will be pulled from the progression drillings.

I assume you don't have a throttle plate out of alignment (hold it up to the light and check they are seating properly) or an idle jet O ring missing or one odd idle jet?

GC

[robert kenney]

Guy,
Thanks for the reply.
The engine was ticking over @ 1100. I will slow to 750 - 800 and readjust.

I reset the valves .016 in. .017 ex. Most had closed up as the cam boxes were retorqued after first drive / warm up. I used all new shims for the cam bed in and first 100 miles. I used a couple of used good shims for reset due to a better setup than .05 mm increment.


Robert

[robert kenney]

Guy,

After slowing the idle to 750-800 the errant barrel responded normaly to its respective changes in position.

I also increased the air corrector to 190 and this improved a transitional flat spot I experienced after shifting gears.

Plug color is white/off white with a MTBE red cast. Perhaps a bit lean at low throttle but will see how it runs @ altittude.

Valves are fine and I have to realize the cam is way more aggressive (lift velocity and net displacment) and I should expect a bit more valve train presence.

The 409 in my roadster ( .030 X .030 lash) makes a bit of a crescendo much like running water while @ high RPM.

Thanks for the good info.

Robert

[Guy Croft]

Robert hi,

well done for following-thru on the tuning.

One reason for the TC noise is the cambox design, it amplifies the valve train noise like a soundbox - in exactly the same as the body of a violin. Naturally the cam is, as you say, is definitely an aggressive profile but after years of feedback in all forms of competition and fast road too - there's no doubting its BHP potential. Advising cams is one of the most difficult of all the advisory things I do by the way.

GC