db's 66 Belvedere ***FOR SALE***

[Guy]

Not a good idea to plug the PV on a street car. you would have to jet up 10 sizes to compensate. Basically you would be disabling an enrichment circuit giving yourself even less tuning options.

Yup tell me about it You want to try my combo Paul two carbs with No PV's, one 2 one linkage only one accelerator pump per carb, one shooter for all four barrels and no choice of shooters available its great fun

[db]

This carb seems weird Blue- I'm about 10 sizes DOWN on what I feel it should be!
Changing primary mains doesn't seem to have much effect.
I started with 77's in the primaries which gave AFR 11-ish and have come down to 64 mains (smallest size in my kit), AFR is still 12- 12.5 at wot.

I had 73's in the vac sec primaries, with AFR in the 13's.

[Pete]

My 440 +6 has #64 jets on the centre carb.......77's sounds huge.......

[John]

I had to do a similar thing with my 750dp Paul. It seemed strange to me too but I have ended up with 66 in the front and 82 in the rear to get an overall acceptable reading. I`ve settled with a 6.5pv and the blue pump cam though but still get a very minor bog when mashing the throttle.

My vac at idle was only 5 but 12 at cruise by the way. Power brakes too by the way but for some strange reason they work fine......... Well as fine as drums can of course

[db]

i'm wondering if your masking a problem by having the secondaries permantly shut?

Arrgh!!

You are not trying to tune a bog out with the secondaries closed are you db??

Holding the secondaries closed is ONLY for setting the primary jet size at a steady RPM. You have to have the whole carb working for everything else including acceleration mixture and ironing out a bog. In particular with a DP carb.

Ummm

Yeah, I get easily confused with complex problems like this.
I started searching for info because I don't like to feel like you lot are doing all the work for me but all that does is confuse matters with conflicting information

So, how does this sound...

1. Get motor hot.
2. Re-check timing, note at 500rpm intervals.
3. Re-check float levels.
4. With secondary transfer slot open so a square is visible, set idle mix screws to achieve maximum vac, set idle speed to 800, AFR should be around 14..
5. Fit suitable PV.
6. Wire secondaries shut. Drive at steady 2500, (PV will be shut) re-jet so AFR is 14.
7. Release secondaries. Do full throttle run, jet secondaries for AFR 13 at wot.
8. Try every pump cam I have to try to cure the off-idle bog.
9. Sulk. Re-read the last few pages of this thread and realise what I forgot.
10. Start all over again

[Dave-R]

Something like that. But I'm getting bored reading about it now. I am going to wait until the Ron Howard movie version of this epic tale comes out. That will be easier to follow.

[Pete]

I ASSUME this is a DP and you are disconnecting the secondaries?

Unless you have a fault with the carb it is not really that difficult.

Given that you have a Vac gauge on the car, selecting the PV should be a POP.

Get the car in the ballpark first and then worry about the AFR for fine tuning.

The key to this is how it DRIVES.

Starts easily.
Idles cleanly.
Comes off idle with no Bog.
Cruises ok.
No flat spot when you accelerate gently off cruise.
No flat spot when you Bananarama!.

You will not know the Secondary jets (and maybe even the primaries) until you get a few runs in at the track and establish a baseline; and then jet up for maximum MPH.

[Dave-R]

What Pete said. I have only ever used an Air/Fuel meter to tune for steady cruise speeds. Which is why you wire up the secondaries. To get the jet size for the primaries which is what you drive normally on.

So when doing the primaries drive at good steady speeds. 3000rpm. 4000rpm. You need good steady airflow through teh carb.
Use a lower gear to keep your MPH down. Jet for your 13:1 at all the steady rpms.

Then re-connect the secondaries and do it again. STEADY speeds only.

THEN you start using the pump shots to get rid of the bogs.

THEN you need the track to tune the SECONDARIES ONLY to max MPH in the quarter.

Then re-visit the pump shots to see if you can come down in size at all now that the secondaries have enough fuel.

But as Pete says. The A/F meter is for cruise mixture at steady speeds to get the jets ballpark. Mainly the primary jets.

[db]

I ASSUME this is a DP and you are disconnecting the secondaries? YES IT'S A DP

Unless you have a fault with the carb it is not really that difficult. YES IT HAS A FAULT- FUEL LEAKS OUT OF THE THROTTLE BLADE SHAFTS SO AIR MUST LEAK IN. NEW TEFLON SEALS SHOULD BE WAITING FOR ME WHEN I GET HOME

Given that you have a Vac gauge on the car, selecting the PV should be a POP. YES, EXCEPT BLUE SAYS GO HIGHER AND DAVE SAYS HOW INACCURATE THEY ARE!

Get the car in the ballpark first and then worry about the AFR for fine tuning.

The key to this is how it DRIVES.

Starts easily. YES
Idles cleanly. YES
Comes off idle with no Bog. NO
Cruises ok. YES
No flat spot when you accelerate gently off cruise. NO
No flat spot when you Bananarama!. NO

You will not know the Secondary jets (and maybe even the primaries) until you get a few runs in at the track and establish a baseline; and then jet up for maximum MPH.

Thanks, I'll start from scratch with this new advice and the right priorities as soon as my carb is rebuilt and fitted and my clutch is done, hopefully by the weekend

[Pete]

Air Leak.
Pump incorrectly set up.
Incorrect PV.

I would sort spindles first, then PV and finally Pump cam, adjustment and Shooter selection.....

[db]

Big thanks to Mike (Mad Machs) for a replacement fuel bowl, I also picked up some Teflon seal strips so my 750dp is back on the car, no leaks so far and the car starts fine. All ready for the next tuning sesh...

NEW CLUTCH ARRIVED! Gearbox out and clutch off last night.
The old clutch and the flywheel are already showing signs of abuse.. Santa Pod may well destroy them

[MilesnMiles]

Just for shxxts and giggles, why not fit an auto with all the right internals. Give your left leg a rest


I'll get me coat, I know how much you've suffered with setting that gearbox/clutch up

[Pete]

That flywheel looks kippered to me, but I am sure you are going to re-use it

Welcome to the world of swore-speed transmissions.............

[Blue]

The flywheel is fine, rough it up with some emery and git 'er done. I'd be more worried about that aloominum bellhousing if anything did let go, do you like your feet?

[correct direction]

Four speeds are great if you use a good quality clutch,used a centre force diaphram cover on my Satellite never missed a gear,even in anger.plus not as heavy as the spring type units.