Carb Tuning

[joestram]

Hi All,

I would like to put the call out to anyone that has experience in tuning Carb's to see if they would like to come and teach me how to tune my alfetta.

I am located in Templestowe lower and will pay for time / materials.

I can bring the car to a mechanic, however, I won't learn that way so was hoping someone experienced can teach me and show me how to get the most out of my baby.

Not sure if this makes a difference but the car has rejetted Carb's and Pace cams.

Thanks all.

Joe

[LukeC]

This is in two parts, cause it seems the board does not like big posts.

I'd help, but Canberra is a bit far for a house call. But I can give you a few pointers to set you on your way... And for general information:

Getting the most out of your car... When you say the carbs have been re-jetted, I will assume that you mean the car has been dyno-tuned and re-jetted to suit any other mods.

First, make sure everything else is in good condition. Ignition system etc. When you do the timing, check that the spark is not jumping about and stable. If it is not, it is a sure sign that the distributor needs attention. Also check that when you rev the engine, the ignition timing gets full advance and then quickly returns to base setting.

If you do not know when the last time the carbs were kitted, lift the carb tops off and look in the fuel bowls. There should be no dirty residue in there. If so, re-kit time! Also check the condition of the needles and seats (be very careful with the float pin posts, particularly Dellortos... NLA). If you can catch you fingernail on the needle taper: probably time to replace/re-kit. Float height setting makes a big difference in starting/idle quality. It takes finesse to get right. To do it right, you should run the engine, shut down and then measure the fuel height with a vernier... It takes a few goes but in reality, if you are careful with the initial setting when re-kitting, it will be close enough.

Make sure the carbs are getting full throttle. A pretty common thing that they do not, particularly with mechanical linkage cars. I like to install one of these if you still have the old grey plastic type:
http://www.classicalfa.com/products/FL051-ADJUSTABLE-MAIN-THROTTLE-ROD.html
Make sure you order 2 of these:
http://www.classicalfa.com/products/FL050-METAL-THROTTLE-ROD-END-.html
You have to adjust the long linkage and the pedal stop in the car so that the carbs are JUST open when the pedal hits the metal, not hard on the carb stop limit.

[LukeC]

If you are going to get into this stuff on the long term, buy one of each of these:
http://www.classicalfa.com/products/FL024-SCHLEYER-CARBURETTOR-AIRFLOW-TESTER%7B47%7DSYNCHROMETER.html
http://www.classicalfa.com/products/FL024%7B47%7D1-AIRFLOW-TESTER-ADAPTOR-ELBOW-FOR-SIDEDRAFT-CARBURETTORS.html
You do not need the adaptor if you are running trumpets, but useful when doing your mates cars. I have had mine for over 20 years and it is still in perfect working order. I worked in a place with a genuine Alfa manometer kit for a few years, and this was faster, and just as good to get the carbs running smooth.

With the engine warm and at idle, balance the carbs to eachother using the screw between on the steel linkages. Set idle speed at around 900 rpm using the screw on rear carb.

Now the fun bit (that takes feel and a good ear): One by one, screw idle mixture screws in (lean) until that cylinder starts to miss, then out till it comes good. Go back and forth to the other cylinders a few times until you get it as good as you can (I like to richen them up a smidge more as a final setting to help with cold running when you happy). Some model carbs are easier to get idling smooth than others. Reset the idle speed and give it a rev making sure the engine picks up with no hesitation and settles down to a smooth idle. Check balance with flow meter again. The reading should be around 3 3/4 what-ever on the meter scale.

BTW: Weber/Dellorto carbs are VERY tolerant to performance camshafts. A full race Nord engine set up correctly will idle at quite consistantly at 1000 rpm.

[joestram]

WOW - thank you very much for your detailed post Luke!!

I will definitely be giving this a shot!

My car idles at 2500 and anything less will almost certainly make it stall - It also doesn't seem very responsive!

I'm hoping that I wont destroy it while trying to tune it as the last thing I want to do it cost myself a fortune.

Really appreciate the time you have taken to respond.

Thanks Luke

Joe

[joestram]

Hi Luke and everyone else,

Just a quick question regarding the tuning - I am not sure if this makes a difference but I forgot to mention that my car has an electronic fuel pump so does the tuning method change due to this reason?

Thanks

Joe

[colcol]

The electronic fuel pump shouldn't make any difference, just make sure the needle and seats are not leaking and that the float level is the right height.
The reason they use electronic fuel pumps, is that in cold climates, when you turn the ignition key on, the fuel pump goes click-click and fills the carb up with fuel, so that you have fuel when starting, as opposed to having to turn the engine over a few times to fill it up with a mechanical pump, by the time the carbs are full, your battery won't be, Colin.

[joestram]

Hmm there must be something wrong with my fuel pump then.

It usually takes me a good 3-4 tries before the thing starts.

I hear a loud buzzing noise when I turn the accessories on (which I assume is the pump).

The car won't start without choke and I need to pump the pedal a few times.

Thanks for the reply Colin.

Joe

[LukeC]

If the car has Dellortos: after it has been sitting a while (~hour) after running, wipe your hand under the carburettors. If you get some petrol on your hand, then then the accelerator pump diaphrams are cactus and the fuel bowls are draining dry. Rekit time!

Ensure the car has the filter/pressure regulator still present on the right inner guard, and that the filter is not blocked. Ensure that another filter has not inserted near the electric fuel pump. One is sufficient.

[joestram]

Hi Luke and All,

Just went outside to try an tune the alfa and I brought it to operating temperature and noticed petrol dripping from the underside of the carb and there was a wetness under the carb as well.

I am just wondering if it is possible to rebuild carbs from home as an beginner or can people come and rebuild them?

I am obviously very wary of turning the car on now as I don't want it to catch fire!

Thanks

Joe

[Alfapride]

If you haven't done it before I suggest take it to a mechanic that specialises in carbs.... Thornbury carburettors are highly regarded for this hope that helps

[joestram]

Hi Alfapride, thanks for the response I might do a little reading up on it though as I wouldn't mind giving it a shot!

Just a quick observation - can someone please explain to me what happens under the carb when the throttle is depressed?

I was trying to figure out where this petrol leak was coming from so I only had the ignition on so I could have the pump going. I heard the pump fill the lines up to the carb and there wasn't any leaking at that point.

When I used the hand throttle I could feel something opening under the carb and then that's when the petrol started dripping out.

When I closed the throttle the leaking stopped.

Does anyone have any idea as to what that might mean?

Thanks

Joe

[Craig_m67]

Looks like the accelerator pump (squirts in additional fuel) is located on the bottom of the carb.

Buy a kit, have a crack yourself. Do one at a time so you have a working reference.  As an aside, I've found the Nulon carb degreaser from Supercheap to be the most magical thing I've bought in years. Cleans like magic in anycase.

[joestram]

Hi All, just spent about 30 mins trying to tune it before it got dark and have had no luck...
I am not exactly sure what I need to be changing, is it just the balancing screw connecting both carbs (to set idle) and the 4 large screws with springs (one on each inlet)? I have been messing with these screws and can't seem to get the car to idle below 1500. When it gets to that rpm it does start popping out of the exhaust. Does that mean it's lean or does popping from the carb mean it's lean?
The 4 big screws with springs, when it is completely in does that mean rich or lean mixture?