Holley 600 DP setup - need pointing in the right direction!

[Stuball]

Hi Guys,

Well yesterdays run to the Retro Show was the first time the van has been driven for about 10 months. It started and drove so I went with it! Now I really need to look at setting the carb up a bit better, but I'm a bit of a novice when it comes to this so need a nudge in the right direction as it were..........

305 SBC:
very mild cam
trickflow aluminium heads
trickflow inlet manifold (dual plane)
4 into 1 headers

Holley 600 double pumper (choke horn milled off):
Main jets 66
Main accel pump nozzle 0.28
Secondary Jets 72
Secondary accel pump nozzle 0.32
Idle screw are 1.5 turns out
18-19 inches vaccum at idle (850rpm)

Initial ignition timing is : 10btdc
Cant check what the total timing is, neighbours are very intolerant of noise!, but its running a standard GM HEI distributor

I did have a problem with the engine bogging/backfiring through carb when going to WOT, but i think that was down to very poorly adjusted accel pump screws causing it to go lean.

So, these are the plugs after 100 miles, bit of a mixed bag, the question is where to start?






Cheers guys!

Stu

[kiwicar]

Hi Stu
not very good at this beyond the very basics, but I would say it is over all a bit rich, interesting that 1 and 2 seem close to being correct (though still on the rich side) and 7 and 8 look very rich, with 2,3,4,5 looking just rich from that I would say you were accelerating enthusiasticly on the way home!! I would also guess it all needs leaning out a bit, I would also think you could do with a little more advance on the distributor, may be 2 to 4 degrees. I repeat I am no expert but to me it looks rich and slightly cool combustion.
Actually it also looks as if one half of the carb is richer than the other, 1,4,6,7 look richer than 2, 3,5,8 so I would check the 2,3,5,8 half of the carb for blockages.
Best regards
Mike
Have a read http://www.yellowbullet.com/forum/showt ... p?t=415202

[Stuball]

Cheers mike.

Yeah it does look a little unbalanced. Will strip it down and have a look!
(never know may have stupidly put the jets in the wrong place when i rebuilt it!)

Stu

[Stuball]

Managed to get all confused with the jet sizes??

Mains are 66
Secondaries 72

Stu

[sidecar]

I'm not having a 'go' at anyone here but Vizards book as a great quote in it which I happen to think is true.... "plug reading in order to setup the carburation is less of a black art, it's more of a fallacy"

He goes on to state that if you think that you can get the carb setup well enough for any further tunning to make no difference you are 30 years behind the times!

A lambda probe is the anwser! Having said that it does seem odd that the plugs vary so much in colour.

[Stuball]

Couldnt agree more sidecar!, lambda/O2 sensor would be the best way to set it up, unfortunately I dont have one fitted on the van so having to do it very roughly by the plugs!!

Just cant understand why 5+8 are so black and sooty compared to the rest

Stuball

[sidecar]

Couldnt agree more sidecar!, lambda/O2 sensor would be the best way to set it up, unfortunately I dont have one fitted on the van so having to do it very roughly by the plugs!!

Just cant understand why 5+8 are so black and sooty compared to the rest

Stuball

It maybe worth doing a compression test on those cylinders just to make sure that they are 'pulling their weight'

I guess it could be an ignition fault too, or it could just be that your manifold as a bad fuel distribution issue.

Even though I've just 'spouted off' about plug reading old habits die very hard....your other plugs look quite good to me! (I pressume that the engine was not run at WOT then killed before the plugs were pulled either)

[kiwicar]

"He goes on to state that if you think that you can get the carb setup well enough for any further tunning to make no difference you are 30 years behind the times!

A lambda probe is the anwser!"

Mr Sidecar speaks the truth here, I will not disagree at all.
However it will get you closer than just taking the leaky bucket out the box and bolting to the manifold without doing sanything else, which half the US "tuning" industry still do and if it gets Stu 2 jet changes closer to the correct set up then that has got to save time and money when he gets to the rolling road.
What it does do is let you see problems with the mixture ballance and ignition that can be investigated when you hae the proper kit to hand
Best regards
Mike

[Stuball]

Possible cause of 5+8 being sooted up.......

Found the float on the front bowl to be adjusted all the way up, so....

Looking into the manifold where the carb sits, 5+8 are fed by the rear lowest part (if that makes any sense). Is it possible the fuel was dribbling out of the overflow, through the carb, and down rear of the intake, causing just those 2 cylinders to run rich? (due to the angle of the engine)

I may be spouting complete rubbish mind!!

Stu

[kiwicar]

Hi Stu
that sounds very reasonable as an issue, if there is one thing 4 barrels are good at it is leaking petrol into the inlet manifold if there is anything even slightly wrong with the floats or float levels!
Best regards
Mike

[bigaldart]

The most important parts of setting up a Holley are,

Float Level, first priority as it affects every circuit.

Check that the secondaries are not too far open at idle, for some reason people play with this setting, you should be able to see about a millimetre of the transition slot when the blades are on the idle stop. Adjustment screw is underneath though, so you need the carb off the manifold to set this.

Ensure power valves in place and that they cannot open at idle vacuum, running without power valves is a thirsty business. On a mildly cammed motor the stock 6.5 are fine, if you run a big cam then fit the 10.5 ones.

Stock jetting is pretty close for most applications and you will usually end up only a couple of numbers away if everything else is correct.

Ensure no play whatsoever in the accelerator pump levers, adjust so the plungers just touch the arm, the slightest twitch of throttle should put fuel out of the squirters.

On a vacuum secondary experiment with the spring, it is worth buying the spring kit and the quick change cover for this, start with the softest and progress stronger until there is no bog on acceleration, going too strong will just delay the opening and reduce power.

Clear sight plugs in the float bowls make setting fuel level easy without spilling fuel, it needs to be set with the engine running.

There is a lot of scope for fine tuning on a Holley but these basics will give you a good running and responsive set up.

Alan

[Stuball]

Thanks very much guys!!!!

Stu

[Stuball]

Well having cleaned all the plugs and reset floats etc in the carb, took it out for a 50 mile drive, came back and yet again 5+8 are really sooty, the rest are same as before.

Still have a problem with it stumbling/hesitating when applying throttle, but more concerned with the black plugs



Stu

[JP.]

Just a quick one.........

Holley 600 double pumper (choke horn milled off):

Are the air tube's still untouched.

If these are milled / cut off too you get problems as decribed.

Did some dyno time with the tubes cut off too, and the carb was binned afterwards...

[Stuball]

Are you referring to the vent tubes for the fuel bowls?

This is what the top of the carb looks like:




Stu