4 corner idle help please

db · Post by db » Tue Jul 28, 15 10:42 pm

What's the order of busyness... Fronts then rears? All 4 together?

Adrian Worman · Post by **Adrian Worman** » Tue Jul 28, 15 11:05 pm

All four together, gently seat them and back them out 1&1/2 turns.
Connect ya vac gauge & keep going till you get the highest reading.
Check linkage adjusted right, throttle blades not open etc.
Obvious bollux to bear in mind, timing bang on, fuel pressure stable, motor fully up to temp blah blah blah.

Oh & don't trip over anythin while you're balancing on one leg

db · Post by db » Tue Jul 28, 15 11:44 pm

Cheers medarlin!
Now I just need a dry day tomorrow and North Wales gonna lose it's ozone layer

db · Post by db » Tue Jul 28, 15 11:48 pm

Rear blades just showing a square of the transfer port yah?
Lets see if Les was right about an 850 to wake this Bananarama! up!

Mick · Post by **Mick** » Wed Jul 29, 15 8:20 am

Les knows his onions but he looks at everything from a racing perspective.
I've seen 1150 dominators on small blocks working fine, it just depends on the combo and who did the carb, remember 340's came with an 850 thermoquad in 71 anyway. However, if you're looking for decent economy dont use an 850, personally i would use a 950 over an 850 because the 750 base gives you a better signal and shift recovery.

Guy · Post by **Guy** » Wed Jul 29, 15 9:07 am

Mick wrote: personally i would use a 950 over an 850 because the 750 base gives you a better signal and shift recovery.

Clear as mud that

I agree with Mick assuming he meant 750 instead of 950. The 750 over the 850 will recover better on an auto but yours being on a stick I think you will be just fine and if you ever want economy just drive on the primarys..

db · Post by db » Wed Jul 29, 15 10:55 am

If want economy what the hell am I doing here?

Blue · Post by **Blue** » Wed Jul 29, 15 11:36 am

I think what Mick is getting at is the 950 uses the same size butterflys as a 750 and that keeps the air speed up. The 850 has larger butterflys so airspeed is reduced. You can get 750 based Holleys from the aftermarket that flow nearly as much air as a Dominator, applications such as this is the reason they exist.

Adrian Worman · Post by **Adrian Worman** » Wed Jul 29, 15 1:05 pm

Yeah never knew about the 750/950 base anomaly till mick put me straight on it.
The only part of tuning you are gonna have some work to do is off idle to part throttle. I think an 850 is going to have a poor low speed signal on that small block & that will show up as a slightly lean condition at part throttle & low rpm steady state cruise as the low venturi air speed struggles to pull the fuel thru.

Your AFR meter is your friend there

db · Post by db » Wed Jul 29, 15 3:54 pm

Funnily enough that's exactly the point I've just got to!

Idle is happy, mid-throttle is a clean steady 13.7-ish, full noise is low-mid 12s.
I just have a hole coming off idle!
Vac at idle is low, as it was with the 750. If I set it high, 1100ish, vac is 9. My normal idle, 800ish, vac is 5-6. This caused power valve issues with the 750, I ended up with a 4.5. I think I have a 6.5 in this carb so I can swap that, see what happens.
I've not played with pump cams yet.

db · Post by db » Wed Jul 29, 15 7:11 pm

Yaay, 4.5 has got rid of the stumble off idle. I fine tuned the idle screws after and raised the idle speed a touch to 8500, this gives a vac reading of 6 or 7 so it keeps the pv shut.

I have both carbs pretty good now. When the clutch is bedded in I'll compare the two.
Three actually, I forgot the spreadbore! Though that's a pain to fit and I have to leave the spacers out so I'll lose some torque anyway.

latil · Post by **latil** » Wed Jul 29, 15 8:49 pm

I fine tuned the idle screws after and raised the idle speed a touch to 8500,

Blimey

db · Post by db » Wed Jul 29, 15 8:51 pm

Whoops!

Pete · Post by **Pete** » Wed Jul 29, 15 8:58 pm

Yep, them Small Blocks are real screamers!!!!