Basic tuning - timing and carb settings

[yabadaba]

The 383 2bbl in my 66 Polara is bone stock and runs okay I guess, but I've got nothing to compare it to and no experience of what one that's properly tuned is like...so for all I know it might be running like a dog

On one hand there's no 'pinking', but on the other it smells like it's running pretty rich, so I'm pretty sure a few tweaks here and there would make for an improvement. Problem is I haven't got a clue what I'm doing . Not sure whether to try and learn some of the basics myself or take it somewhere, so would be grateful for either some advice/info on where to start, or recommendations on who could tune it for me....preferably somewhere not too far from SE London.

[John]

Been doing the same over the last couple of months,

Had some great advise and it`s very satisfying to have a go yourself and see results imo

I will hopefully see any improvements over the shakey weekend

[Dave-R]

They will all smell rich until you have a lot more initial ignition timing than stock. You need to sort that out before adjusting the carb.

Even with a completely stock engine you will need at least 12 degrees initial and maybe as much as 20 degrees. If you advance the timing as the car idles, find the spot where the engine revs start to level off. That will be about the spot you want for initial.

There is only two ways to get that kind of initial without also giving the engine too much total advance at higher revs.

The first and most simple way is to use manifold vacuum for the vacuum timing on the dizzy instead of ported vacuum as stock.

The second way (which I prefer) is to limit the amount of timing in the distributor either by welding the weights in the dizzy or by fitting a plate made by FBO.

Only when you have the timing right can you start adjusting the carb. Set the idle speed to 800rpm and adjust the manifold vacuum to JUST to the lean side of max vacuum.

After that look up the tuning tips somewhere on here for tuning the jets.

[yabadaba]

They will all smell rich until you have a lot more initial ignition timing than stock. You need to sort that out before adjusting the carb.

Even with a completely stock engine you will need at least 12 degrees initial and maybe as much as 20 degrees. If you advance the timing as the car idles, find the spot where the engine revs start to level off. That will be about the spot you want for initial.

There is only two ways to get that kind of initial without also giving the engine too much total advance at higher revs.

The first and most simple way is to use manifold vacuum for the vacuum timing on the dizzy instead of ported vacuum as stock.

The second way (which I prefer) is to limit the amount of timing in the distributor either by welding the weights in the dizzy or by fitting a plate made by FBO.

Only when you have the timing right can you start adjusting the carb. Set the idle speed to 800rpm and adjust the manifold vacuum to JUST to the lean side of max vacuum.

After that look up the tuning tips somewhere on here for tuning the jets.

Ah okay thanks...I had heard something before about the problem of getting too much advance at higher revs - something about modern fuels being different to the ones available when these things were designed (??). If I'm honest I don't (yet) understand the difference between manifold and ported vacuum, but will go with the second method you describe anyway. Don't happen to have a link to those FBO plates do you?

Like you said, I'll get that sorted first and then worry about the carb afterwards. Just bought a Gunson Advance Xenon Timing Light, so hope that is up to the job....it was the only one they had in Halfords!

[Dave-R]

Ported vacuum is on the side of the carb and is above the throttle blades so you don't have vacuum at idle when the throttle blades are closed. Or at least you shouldn't.

Manifold vacuum is usually taken from the base of the carb below the throttle blades or from the manifold itself. In this case you have high vacuum at idle because the engine is trying to suck air past the closed throttle blades.

You can get FBO parts from MMA member Turnip on here.

http://fbo-uk.com/

[yabadaba]

Thanks Dave, I'll get in contact with 'Turnip' tomorrow.

[Adrian Worman]

I got an FBO advance plate kit from Jon, it worked ever so well, super easy to install and he's a nice guy to deal with too

[yabadaba]

Thanks for all the info/advice - I received my FBO plate yesterday and will be fitting it soon...would have given it a go tomorrow, but don't want to risk it in case anything goes wrong because I'm aiming to go to the Brookland event on Sunday!

It seems that it can be fitted in one of 3 or 4 different positions (in terms of degrees of advance) so does anyone know which would be the correct one for me?

[Adrian Worman]

You'll work that out from your own engine when you set the initial advance. If you have it set at say, 18 deg and it does'nt kick back at that, then you would use the plate marked at 14 deg, that gives you 32deg. You're aiming for 34-36 deg ideally, follow the instructions they give you, the chart is very good.
Its pretty easy tho mate, gives excellent results too

[Dave-R]

Plug the vacuum line for the distributor at the carb.

Use your timing light to see how many degrees advance it has now.
Then increase the engine speed to 3000rpm and use your light again to see what the timing is at that point.

Note the two figures and subtract one from the other. That is the number of mechanical degrees your distributor has built in.

Now advance your initial timing by rotating the dizzy until the rpm increase rate just starts to level off.

Then lock it there and re-adjust the idle speed back down to normal.

Now see if the engine still starts OK without a struggle. If it does struggle or kick back, just back the dizzy off a few degrees and try again.

When you are happy the engine starts ok, use your timing light to check how many degrees initial you have now.

Lets say you find the engine likes 18 degrees initial and you found that your dizzy has 26 degrees advance built in.

With that amount of advance your total advance will now be 18 + 26 = 44 degrees! That is 10 degrees more than you want in the dizzy because ideally you only want 34-36 degrees at 3000rpm.

So you use the plate to remove 10 degrees. Now you at 18 degrees initial and 34 total. Jobs a goodun and she will rev better and smell nicer.

PS
If you decide to re-connect the vacuum line (optional) you can do so but make sure the engine does not start to "pink" under some conditions like part throttle going up hills etc.
Most vacuum cans are adjustable so you can back off the vacuum advance if you have too much.

[Adrian Worman]

Can't go wrong with them instructions Daveman..............you got a way with words aintcha?

[yabadaba]

You guys are superb...thanks for the help and clear instructions. As it happens I didn't get any instructions or chart with the plate, just a disc with some oblong holes and round holes in it!! It did however come with a bit of paper on which someone had traced around the disc and holes and written 10, 0, 14 and 18 against some of them...but as it happens I can see these same numbers lightly stamped into the plate itself.

Is there any benefit in reconnecting the vacuum line then? Doubt I'll bother unless it's actually needed.

[Adrian Worman]

I kept all my inst sheets and charts for that disc, I can fax 'em or post em to yoiu mate

[Dave-R]

A bit of vacuum advance might give you a tiny bit better mileage and help keep the plugs cleaner but because you have got more initial timing at idle the effects will not be noticeable really. So you can just as easily do without. I doubt you would notice any difference.

[Anonymous]

Hi guys, jus been reading this post as my timing is a problem also, i advanced the dizzy as Dave said but the rpm's kept increasing even though i was now at 25 initial, i set it at 18 and the dizzy has a setup of 17 advance but when i raised the rpm to 3000 i was way past 36 deg ! should i lock my dizzy at 34-36 and get a start retard ?