Twin Webers & Ignition Timing.

[Guest elgey7]

I just spent my hard earned cash on twin weber 45's 152's for my pinto which has been running on a DGAS.

I am having the normal problems - setting the idle mix, exhaust popping, balance etc.

I am getting there, slowly, but my question is: do I run vacuum or not?

It is an injection head with a std inj cam.

 

I believe the static (idle) timing is to be 12 deg (vac disconnected) & the max advance to be 35deg @ 3500.

Does this mean that the static timing with vacuum on at idle would be 12+the 15 of vac = 27deg?

I am correct or missing something?

What's the advice - use the std vac distributor or get (or mod) a new curve without vac?

 

Also does repacking the exhaust help reduce the overrun popping?

 

Jim - I've read your many posts about keeping away from Twin Webers on a pinto I feel like a victim.

However I hope you can help me resolve my problems.

 

Thanks

Colin

[Guest gavinc]

i am by no means an expert on webbers but from what you have described (head and cam)

 

i think you will find it very hard to get the jetting right..you will need to down jet it quite alot

 

a personally feel you would have been better of with 40's,as you have not really increased the need for

 

more fuel with the standard injection head and cam.

 

depending what you using the car for if its for road use onlyi would use the vacuum advance.

 

if doing sprints, time trials etc i would remove it , this is only my opion and i might be wrong thou.

[Snapperpaul]

think you will find it very hard to get the jetting right..you will need to down jet it quite alot

 

a personally feel you would have been better of with 40's,as you have not really increased the need for

 

more fuel with the standard injection head and cam.

 

I agree with Gavin, but don't give up just yet as the 45's will be OK when you do the next mods or swap them for some 40's.

 

 

This may give you a start.

Twin 40's 34mm chokes, 135 main jets, F11 emulsion tubes. 190 air correctors, 35 accelerator pump jets,

40 F9 idle jets. 4.5 auxiliary venturies, float shut off height 7.5 mm, float at full drop 15mm, idle screw out 7/8ths of a turn, 12 degs advance @600rpm and 38 total mechanical. vacuum can be used.

 

and for the 45's, this is for a modified engine so someware in between the 2 settings may get you going.

Twin 45's 38mm chokes, 145 mains, 180 air correctors, F16 emulsions, 40 accelerator pumps, 45 F2 idle, 4.5 auxiliary venturies, floats as the 40's, idle screw 1 turn, 50 accelerator pump inlet. 18 degs @ 1200rpm, 38 total mechanical.

 

Just to add more confusion to the mix i found this in the weber manual for twin 40's conversion kit for the Capri pinto 2000, so pretty standard non injection engine.......

32 choke 4.5 aux venturi, main jet 125, emultion F16, air correct 180, idle jet 50F9, accelerator 40, pump ex valve 50.

 

Give it a try and see how you go.

[Guest Simon cooper]

Hi Colin,

Firstly, are your carb's new?

Is your linkage new?

They can be a real pig if your linkage is old.

Are you familiar with setting carbs in general?

I intend to write up instructions over the next night or so on how to set up and balance on twin carbs and as it is a common topic on here. If you can hold on, I will get it posted.

Secondly, ditch the vacuum advance. It has one perpose in life, to hold on advance at low throttle openings, ie cruising in the lower rev range when centrifugal advance is low. This aids fuel consumption slightly.

However, since you have gone the 45's route, I assume that consumption is not a concern to you. If it is, then start thinking otherwise.

Vacuum advance is a neusance and has no place with twins. That is why on 99% of twin carb setups, there aint any.

The jet settings earlier mentioned are a good starting point, but all engines are different and you will need a rolling road session to get the best out of them. BTW, when you do go to the rollers, find someone who knows what they are doing with Webbers. There are a lot of people who claim to know, but you come out the other end with stacks of power at top revs but undriveable low down. Pay a little extra for a good 'un.

Regards

Simon

[Guest hypermick]

Just one thing to check. Make sure when you bolt the DCOE flanges up that the spring washers are correctly set and dont squash the rubber sealing rings on the flange spacers.

 

Also on the NW Robin Hood site theres an article on distributor modifications, which might help you. Its very interesting, particularly the comments on altering the advance curve (by changing, omitting springs)

 

 

Mick.

[Big Jim]

Souldn't have fitted them in the first place, I did tell you!

[Guest hypermick]

Mind you, when they are set up properly, they do sound bl**dy teriffic, even if you do pay through the nose at the fuel pumps in return !

[Guest elgey7]

Many thanks for all the information

It's funny how another day always lets you look at problems differently and sometimes better.

I went into the garage tonight and started again! I instantly realised that the throttle linkage rod was pulling

on the butterflies especially on the front set. I released it & re-balanced the back & front.

This meant it was a simple case of the front to throttles not being fully closed.

Hence when I was taking my foot off it was still letting air/fuel in, the result - exhaust popping.

The differnce was amazing and the popping has gone. (or should I say no different than with the old DGAS).

The car drives so much better I had a big smile on my face tonight.

 

Once again thanks for the advice.

There is a lesson here - I don't know how many times I read ' make sure the throttles are closed & balanced'

 

Simon thank you - I am still very interested to get the set up info you have, including the timing curves.

 

 

Regards

Colin

[Guest Bob Green]

Setting up DCOE's is not a black art as people seem to think. The keyword here is patience.

 

Try to get hold of a wideband meter that will significantly assist once you understand what is happening at various throttle openings and engine load.

 

If you have 3D ignition with a TPS, this will make it easier and more accurate.

 

Bob

[Guest Bob Green]

Quoting Snapperpaul

"and for the 45's, this is for a modified engine so someware in between the 2 settings may get you going.

Twin 45's 38mm chokes, 145 mains, 180 air correctors, F16 emulsions, 40 accelerator pumps, 45 F2 idle, 4.5 auxiliary venturies, floats as the 40's, idle screw 1 turn, 50 accelerator pump inlet. 18 degs @ 1200rpm, 38 total mechanical."

 

 

 

 

 

 

38 mm chokes are for a highly tuned engine. Chokes need to be 36 mm. The rest of the jetting is a good starting point though.

[Guest yosamite sam]

pay no attention to them if they say twin carbs are no good - they are just fine! lots of people have them.. may not be the most upto date in engine management / fuelling but dont you think they look and sound superb when set up right? - they are really very simple if you dont keep fiddling with them.. lots of people do and tend to muck it up from what they had.. iv been running 45's for 3 years now and once they are balanced and somewhere near get it rolling roaded.. best person i know would be an old racing driver - someone who has been racing since the 70's.

[Guest vacinc]

pay no attention to them if they say twin carbs are no good - they are just fine! lots of people have them.. may not be the most upto date in engine management / fuelling but dont you think they look and sound superb when set up right? - they are really very simple if you dont keep fiddling with them.. lots of people do and tend to muck it up from what they had.. iv been running 45's for 3 years now and once they are balanced and somewhere near get it rolling roaded.. best person i know would be an old racing driver - someone who has been racing since the 70's.

i"d totaly agree, had mine balanced about a year ago, running a bit rich, but it drives perfect

i"d go for the old school, ( but there getting harder to find ? ) and there not that hard on the mothion lotion

if you drive it normaly, its a tenner every time you go out (at least)

[Guest MrSandman]

Lots of sensible advice on the carb set up but I would question the advice on ignition timing.

 

Vacuum advance helps with mid range/cruising ecomony by virue of the additional drivability. Basically it fires the mixture while it can still produce power, rather than straight down the exhaust port. This gives better throttle response and drivability when not using full throttle.

 

Using vacuum advance is difficult if using twin carbs but if using a standard dizzy you will suffer. Fitting webers is supposed to be a performance option. This is no good on a road car if the only gains are at the top end. most of your driving will be at mid range and part throttle openings.

 

My advice would be to either get a modified dizzy with a suitable curve or go the mapped route with megajolt or some other programmed ignition.

[Guest elgey7]

Update - Thanks for all the advice so far.

I now have fixed: the Exhaust leaks, Re packed my box, Vac leaks, Balanced the throttles,

set the idle mix screws and now modyfied the disti mech advance curve per the NW club.

I am just about there. I have zero exhaust popping on the overrun (better than it was with my DGAS)

Power is much better than I expected.

Economy is down a little but nowhere near as much as I was led to believe.

 

So I'm happy - well not quite !

I have the odd random inlet spit back poping when doing 30 at around 1500 when just lightly touching the throttle. I'm pretty sure the idle mix screws are OK now. As anyone anthing to suggest that might cure this?

All I am reading suggests too lean at but I don't think this is the case.

If it is too lean why does this cause spitting back?

 

By the way do not set DCOE 45 152 carbs per most instruction you read on the web.

The idle mix screws need to be out 3.5 turns as a starting point not as the older carbs which start at 1.5.

This issue caused me big problems until I found an american web site which gave the correct procedure and starting point for adjusting 152's.

 

Choke 36, Main 145, Air Correctors 185 (were 155), Emulsions F16, Idle 50f9

 

Thanks again

Colin

[Guest Simon cooper]

Hi Colin,

Sorry mate but you is a touch too lean. It only takes a little bit on one screw to do it. Try and re-create it with your air filters off and holding the throttle just open. It can be caused by as little as 1/8 of a turn.

Arm yourself with a 2 foot length of 1/4 inch ID fuel pipe. Run the engine up hot, not just warm, but HOT.

Put the end of your pipe about 2" into the carb and the other end in your ear.

Listen to each one in quick succession. They should all sound the same.

You are listening for a sharp POP from all of them.

DO NOT put your pipe into the venturis if the carbs are popping back continuously. It can burst your ear drum; at best you go deaf for 5 minutes.

If they do not all sound the same, they are not set right. (Obviously).

For those who are not familiar with setting twins, take this as a quick guide. It is not hard once you know what to listen for.

Back off all idle screws and the screw on the balance bar so that all throttles are shut. On one of the carbs, the throttle will stay open until you hold the linkage shut. Whilst holding it shut, turn the balance bar screw until it just touches the balance blade. If you turn it too far, the other carb will start opening so back of so that both are both shut. You are now “Statically Balanced”.

Turn the ONE idle screw that acts on the balance bar that opens both throttles till it touches the linkage and then 2 further turns.

Turn all mixture screws till they sit LIGHTLY on their seats and then open about 3 turns.

If you now start the engine and adjust the idle screw to idle at about 1200 rpm.

If there is a lot of spitting back through the carbs, open all mixture screws 1/2 turn until it stops.

At this stage, whatever you do to one, you do to all.

When you have a half descent idle, you can proceed.

Using your tube, get one from the front sounding as close as possible to one of the back ones by using the balance bar screw in the middle. Then re-adjust the idle.

Then work on one pair at a time.

You are trying to achieve the loudest, sharpest, crispest pop that you can.

If the mixture is too weak, the pop will sound “Puffy”.

If the mixture is too rich it will sound “Slushy”

That is the best way I know of describing it. You will hear it for yourself.

Keep the tube in the venture that you are working on, all of the time. It will help you hear the change in revs more clearly and the “Slush Puff” effect.

As you get the mixtures right, the revs will also pick up so you will also have to keep adjusting the idle back down.

As you go past the ideal mix, the revs will drop off. I suggest you turn mixture screws ¼ turn at a time and listen for the change.

When you have each one the best you can, start again by checking back with front and go through the whole process again but this time you will need smaller adjustments to get the rise and fall in revs.

When you have it as close as physically possible, open all mix screws by a further 1/8 turn.

Depending on what cam you have fitted, dictates your idle speed. For set up, use an idle of 1200 rpm and adjust to about 1000 rpm when finished.

WHEN (not if) you get it right, you should be able to Snap the throttle open quickly and get a smooth hesitant free acceleration. If it hesitates, you are not right OR you have an Accelerator jet fault.

You will find it very rewarding when it is right and wonder why people make such a meal of it and shroud it in mystery. It’s a piece of cake.

Good luck

Simon