Dizzy problem with twin carbs

[Nailen]

I have probes wi my 1600 8valve with twin 40s. When the dizzy timing is set perfect with timing gun it bogs down wi sharp revs and drives like a pile of crap. But when I turn dizzy back a good bit it revs great and has power but dies at 4500 rpm I have black dizzy with vac advance but no air pipe connected don't know if that would be problem

[autoworksnovasport]

have you tried putting a vacume on and then trying it??

[Nailen]

i dont have anywhere for it to connect to on ma inlet manifold, do you think thats the problem before i satrt drilling hole in it

[Royston]

Ignition needs to advance as the engine revs rise, I would check the vacuum unit it working by sucking on it, if it creates a vacuum it is OK, if you just suck air, the diaphram has failed and needs a new one! no point connecting it if its broken, if to are going to create a vacuum point, make sure you put it in the right place;)

I think that will certainly be part of the problem, has the car/carbs been set up properly, suspect not if it isnt running well.

Another alternative is to fit some form of ignition/spark control, but I'm not the one to ask.

Before you do anything you could advance the ignition to @ 34 deg BTDC (my sport had the ignition fixed at 34 deg BTDC when it came, ran like a sack of hammers until the revs were up, before I fixed it) and see if it drives better up the rev range, that will tell to it is an ignition advance problem;)

[garyc]

The vac advance is just an economy device. Try setting your advance at 34degrees at 4500 rpm. Drop it down to idle and see if your ignition advances. Dont forget the timing mark is at 10 degrees so on an adjustable timing gun will need to read 24.

[Royston]

My Sport with 34 deg advance at tick over would sting your eyes with the hydrocarbons from the exhaust, it went off the scale an the gas analyser (10,000+ ppmlol)

Was alot better with a working distributor (had been fixed, no advance mech)and vacuum advance and the carbs set up properly

[Nailen]

My vac diaphram is burst just checked it there when I advance the timing the car is hard to start but revs like hell then runs out of puff at 4500 but when I set the timing dead on it will rev past 6000. Does anyone know where I could get a new vac advance unit am running a 1.2 dizzy the big black one

[Royston]

Got my last one off fleabay

[tony-the-muss]

Hi , I had a similar problem with my 20 seh Sr running on 40' s , so bit the bullet and purchased a new ignition set up from h and h ignitions , inc New custom dizzy , coil , leads etc and do away with vac , cost around 250 but well worth it imo

[Nailen]

I just spOke to a boy who sets up carbs and he said I have wrong dizzy he has always saw them wi 2 pin bosh dizzys and mine is a delco and he says if I get the vac advance to work it won't run right cause no matter what I do it will advance it to much surely this can't be right is it and is there no way I can just keep my own dizzy on I have blew a fortune on this already should have just put an xe in it to begin with

[garyc]

It should still work properly without the vac advance working, it just won't return best mpg round town. You may want to check if the belt has jumped a tooth. Is the mechanical advance working ?

[Nailen]

I went out today and took twin 40s off put twin45s set timing to 32degres btdc and it's a flying maching now 6500rpm 5th gear and still pulling like a train ran it of road over the moon wi the result time for rolling road and few little adjustments thanks for all your help boys

[autoworksnovasport]

what you doing with your 40s???

[mowgli]

so you came on here & asked for advice about dizzy's then chose to ignore it & swap the carbs which seemed to make it go faster..... 6500 isn't exactly fast revving on an small block engine.... so your carbs were at fault .....

if your old dizzy was running right (as in the diaphragm fixed) it would have been fine. as the sport novas never had any trouble with them

[Nailen]

Think about selling them

[Nailen]

And mowgli I always had a feeling the carbs weren't right but wasn't sure was getting told all sorts. Then ma mate kindly donated the 45s so put them on and ma problems are away and am not saying 6500 is fast but compared to 4000 it is a big difference it will be going on the rollers to get set up right. And as you were saying about getting vac advance sorted and it would be fine.bull **** cause the jetting was all wrong for what I was running.you never gave me any advice on this thread so whats your problem......

[Royston]

Many people do not understand that twin 40's must be set up for the individual engine

I suspect that your 40's are not set up for 1600, the chokes are probably too small and the jets/emulsion tubes will be in correct. (sport 1300cc chokes are 33mm)

40's are cabable of running up to 2.0l engine (depending on spec)

45's you have probably are specced for @ 2.0l hence it breathes better than before and there will be alot of restriction at the cab/inlet manifold unless it's been port matched. I suspect you will have other issues with them once on the rollers, not sure but I suspect you can't spec the 45's down to suit your engine correctly, 45's may run properly on a full race spec 1600

I did ask earlier if the carbs has been set up properly......

You will find a wealth of knowledge if you ask the right questions.

[mowgli]

And mowgli I always had a feeling the carbs weren't right but wasn't sure was getting told all sorts. Then ma mate kindly donated the 45s so put them on and ma problems are away and am not saying 6500 is fast but compared to 4000 it is a big difference it will be going on the rollers to get set up right. And as you were saying about getting vac advance sorted and it would be fine.bull **** cause the jetting was all wrong for what I was running. you never gave me any advice on this thread so whats your problem......

nailen, i watch some threads and if people are giving advice that i agree with, i don't see the point in repeating it. you had a timing issue when you started this thread, then suddenly you 'fixed' it by swapping your carbs

a delco dizzy with a shot diaphragm will still provide a reasonable spark as long as you advance it enough, as a short term measure that it, i should know, as i had to do it to get home from a long trip when mine went (back in the day).. anyone who sets up a carb engine with no form of advance simply doesn't understand how an engine works, because they all need advancing as the revs go up, what you need to do is get the 40's set up properly for this engine, and get the dizzy sorted out. 45's are too much unless you have spent about 2 grand on uprating everything else.

[waggygsi]

wouldent help that ure 40s were jetted for your old 1.2 engiine buddy