View Full Version : vacum advance on twin carbs,
ok now my nova neva really idles that well. ive seen a few novas on here with the vacum advance connected (to the dizzy) and just want opinions really. been told that its not neccary for twin carbs when the engine is cammed up as it wont help. :|
nathan.
15-01-05, 07:39 PM
vaccum advance is for higher revs, not idling.
i heard that you dont need this for twin carbs
no need on them, mine purs like a kitten with no rough idle or any problems low down
my irmischer inlet manifold has the outlet for the vacuum so im just gonna connect it.
hopefully it shud work fine tho? :|
Custom_Calibra_Nova
15-01-05, 08:35 PM
the vacuum advance is for cold starting and works with the auto choke. you dont need it on twin carbs because you dont have the auto choke like the pierburg. dellortos have manual chokes, so do webers, allthough it is not necessary to connect them. if you have a lumpy tick-over its usually because the mixture is too rich, or the mixture is different on each carb. if you remove the exhaust manifold and start the car you will be able to tell if the mix is balanced or not. if each cylinder pops with a small blue flame, they are evenly balanced. bear in mind though that you will never get a perfect tune, even on a rolling road.
there is a way of locking the mixture screw/s in place, one day ill find the thread, but, you are rite, u cant NEVER get twin carbs perfectly tuned.
Snowface
15-01-05, 10:49 PM
my irmischer inlet manifold has the outlet for the vacuum so im just gonna connect it.
hopefully it shud work fine tho? :|
inlet manifolds don't do vacuum advance. It comes from the dizzy and goes straight to the carb's.
they have a hole for the vacuum brake assistance thingy.
there is a way of locking the mixture screw/s in place, one day ill find the thread, but, you are rite, u cant NEVER get twin carbs perfectly tuned.
Lies lol, and noone can tell me different as i have the evidence sat under my bonnet. Its been well over 18mths since my last tune up, the weekend just gone i checked my plugs for colour whilst at cp's and ALL 4 plugs are still 'brown sugar' in colour which tells me the fuelling is cock on and the balance is as near as damn it cock on.
Not to mention the performance figures i have run between now and my last tune up being within 0.03 of a second each time be it months or a yr apart between attempts.
Sorry if that seems forward but its been done and proven
sorry dan i dont believe you lol
mine needs setting up every month or so.
my plugs are the perfect colour even tho its ballenced badly at the mo and by looking at the exhaust valves they are white showing lean mixture. dont trust just the colour of your plugs mate.
Custom_Calibra_Nova
16-01-05, 10:25 AM
webers need re-tuning every 12 months or so but dellortos need a re-tune every couple of months. dellortos are designed for track use, not road, so they get re-tuned b4 every race anyway.
Snowface
16-01-05, 11:43 AM
if you've got a knackerd thread on your balancing arm then maybe it will lossen, but mines pretty good.
why do you need a re-tune? Do the jets magically change sizes over the course of time so you need to put new ones in?
some carb's might just need a balance every now and then but thats it.
mikey14sr
16-01-05, 12:11 PM
same as on bikes, carbs just need re-balancing now and then, you can get a 4-way balance guage fairly cheap and do them yourself, maybe at every other oil change would be a good idea?
no its just the ballancing of the carbs really.
another thing. does it sound like my timing is too far advance as its a bitch to start unless you just crack the throttle a little. its like its hard to turn the engine over .(sounds like a flat battory but its not)
my plugs are the perfect colour even tho its ballenced badly at the mo and by looking at the exhaust valves they are white showing lean mixture. dont trust just the colour of your plugs mate.
Thats why i use my performance stats to back them up aswell as the fact it purs like a kitten at 800rpm and pulls like a train smoothly until 7k, and the comments of everyone who has driven it etc. It might just be that i am lucky or something but they are defininatly still ok. Also my 14.5 runs were put at the point that it was 13 months after the engine was tuned. An unbalanced car wouldnt be putting them times in in our cc group :wink:
One thing that alot of people i have seen do is have the throttle so it is fully open before the pedal has reached its stop point. With mine i have always had about 2mm travel left on the throttle on the carb end once the pedal is fully down. This stops any extra pressure being put on the spindle and stops them bending or knocking the carbs out every couple of months as you described. Its something very simple but so oftenly not known about or overlooked as not everyone checks for it (every little bit helps)
MD take your car to a proper place to have them tuned then, as it sounds like you go to a muppet (or ciunning git) if they "fall out of tune" lol
dans engine has even been thrown for shell to shell and still has the correct tune etc.
and im sure jims will stay in tune as it was setup right etc.
also you dont need the vac advance as the dizzy gies all the advance you'll ever need automatically. the vac is really for low end advance etc but you set that up on the dizzy.
also the vac advance can come off the carb, but tis still AFTER the butterfly as thats where the vaccum is (untill over about 15% torhttle opening) so the fact that the webber one is in the manifold is because there is no vac line out of the carb. ALSO to be properly accurate (if you really ust have the vac advance) you should put a hole in all 4 inlets and t piece them up to get a decent "average" vaccum.
so, i am rite that the outlet on the 3rd cylinder inlet pipe IS the vacum. it is DEFINETLY not for the brakes because thats on the side of the inlet manifold.
:roll:
btw, my inlet is the old skool irmischer manifold, not aftermarket stuff??
You've just got to find the right person for the job. After all, there are alot of B/S garages out there today.
I don't just trust any-old person to fix/repair my car, and i doubt many people do.
if your in the north west area, i can recommend a chap that will strip,rebuild,tune webers/dellorto's, plus he can use Corner balances properly and works absolute wonders with coilovers.
That's where i'm taking my dellorto's to.
nah mate, im down in the west midlands. already got me place sorted to setup/tune and rolling road mine when its done.
place up by the merry hill shopping centre in netherton/dudley
i take my car to one of the most respected rolling road tuners in the south west. Allan Jefferys. hes won many votes for his accuracy and abilities. but to be fair he does not believe that a 1.6 8v that is still driveable on the roads can acheave much more than 130 140 bhp. in na form
he also said that my piss pore last rolling road figure of 150bhp and 120 ft lbs of torque was very good. :roll:
i believe it should be more like 170bhp and 150 ftlbs of torque with the mods ive done.
ive spoken to him via email today and hes going to have a good look at the car this week to see what can be done
krobinson
16-01-05, 08:44 PM
Agreed, anyone who says you cant setup T40's is lieing.
Mine is setup perfect, idles at 600rpm when cold and 800rpm when warm, and runs smooth right through the rev's!
Keith
Snowface
16-01-05, 09:44 PM
i take my car to one of the most respected rolling road tuners in the south west. Allan Jefferys. hes won many votes for his accuracy and abilities. but to be fair he does not believe that a 1.6 8v that is still driveable on the roads can acheave much more than 130 140 bhp. in na form
he also said that my p**s pore last rolling road figure of 150bhp and 120 ft lbs of torque was very good. :roll:
i believe it should be more like 170bhp and 150 ftlbs of torque with the mods ive done.
ive spoken to him via email today and hes going to have a good look at the car this week to see what can be done
is that the guy in Plymouth who built that 250+bhp N/A escort engine?
He specialises in Vauxhall engines doesn't he?
I heard he's good.
nova---chris
16-01-05, 09:59 PM
Oh please.
If your car needs setting up every month theres a fucking problem. Its not that hard to work out is it?
To me if its out of sync ect ect. you must have a bent spindle in there.
Something i myself might have. But not to a severe degree.
Or theres something out with the linkage that needs altering.
I run webber 45s on a 2L 16V and again i think its been years since ive seen a rolling road for a setup. So why dosent mine need setting up every month? 1/4 time of 13.8 with a car setup on rollers around 2 years previous. Its not blown up yet nor does it run shite. Idles sound starts in cold with no (that was NO) choke! So please ask your tuner what the crack is mate?
pffft it's all lies chris, trust me i am a class example :roll:
nova---chris
16-01-05, 10:05 PM
Oh another thing. Talking of lies i must be a fucking liar to? Having witnessed your car for most of the year running sweet. Not needing a setup . not even needing to remove the air filter to set it up.
So i can confirm your not a liar. and that if carbs need setting up every month im trading my car in for a escort van deisel.
(mind you will that need a setup every month ? )
8)
WTF..........
i told you what was happening with MY car and made a light hearted joke saying dan was lying about never getting his carbs set up all the time hence the LOL.......
i know a fair bit about tuning, and building of engines as ive ported my own head, and have ported many others with good results every time. and aside chaning the jets i can roughly set up carbs and time up an engine too, infact there is not a lot i dont know about the vauxhall 8v engine. so dont talk as if i know fuck all because you are wrong.
aside the piss taking.... i have thaught about the bent spindle idea and i am currently thinking of getting the webber linkage rather than the not so good dellorto one that i use now in the hope that it will be more stable over time.
the bloke you are talking about is john read i think snowface but he just builds engines now as he sold his rolling road site (carberation and injection)
nova---chris
17-01-05, 10:57 AM
So your giving us your version of events with your car.
So when another user gives his events(and its the same as many other cabr owners) whats the (i dont beleive you thing) The best part about it the member you say it to is actually one of the most trustworthy peeps on here as well as being very knowledgeable about engines.
So before you get the hump think what your saying mate!
And i stick by what i said. Theres no need for them to be set up monthly.
if there is take them back to webber and buy throttle boddies .
The only time ic ould see this possibly happening is in full on motorsport hobbies ect.
OK, I?m going to ignore the arguments and state the facts:
As mentioned, if setup properly, carbs will never go out of tune. If they do, there is a fault, it could be one of two things, and normally is the balance screw unwiding due to excessive vibration. My carbs went through a phase of going out of balance which wasn?t a problem as I had gauge to sort it. I worked out pretty quickly what the problem was and dabbed some nice blue nail varnish on the thread to stop it happening. Never went out of balance again. The other possibility is that the spindle is bent, and this is caused, as Dan mentioned by the throttle not being setup properly. You need to ensure that the pedal stops at the same time as the spindle or the extra leg force on the spindle will bend it. If this happens, you?ll notice as no amount of balancing will resolve the problem.
Slight imbalance will effect idle and will hardly be noticeable when on full throttle, so imbalanced carbs will have little effect on ? mile times. Mixture screws once again only effect the car at idle, so incorrect mixture will not affect ? mile times. IF you do have a problem with mixture screws moving, and they rarely do, try a dab of nail varnish in there too.
An engine on Twin carbs does need the vacuum advance, but unfortunately it doesn?t work as the pulsing from one cylinder alone would throw it out. Therefore you should disconnect it. The standard weighted dizzy will do the job, but not perfectly. If you were to look at an ignition advance map from an ECU, the ideal advance curve gives maximum advance at lowish RPM?s combined with heavy load, and tails off slightly as RPM increases. The standard dizzy can?t do this. The sprung weights in the dizzy are moved in a linear fashion with increasing RPM giving maximum advance at maximum RPM. A rr operator will set the dizzy to the point when no detonation occurs at top rpm. And what you?ll find is that the ignition is not advanced enough low down under hard throttle action. The vacuum advance is designed to work here. An engine will have the greatest vacuum under load at low rpm?s and the vacuum advance would advance the ignition accordingly. At high rpm?s the gasses are flowing fast and there is far less vacuum, so the vacuum advance would be backing off. Peak horsepower is not effected, but low end power is.
To overcome the problem of not having a vacuum advance, you can modify the dizzy. You need to place a small blob of weld on the moving section inside the dizzy that would hit the stop when at full advance. This would effectively reduce peak advance. You then rotate the dizzy around by the same distance to restore peak advance. The only difference now is that the advance starts off higher at low RPM?s going some way to shallow the advance curve and mimmick an ECU map. There is only so far you can go though before it becomes difficult to start the car.
MC
thankyou MC, thats exactly what i asked for.
rather than being told that im talking bollocks just because what i had a problem with was not the same as someone else with twin carbs.
and to nova chris. IT WAS A JOKE as i just said!!!!. :roll:
i admire both yours and dans cars for what you have done. they are very good examples of how to do it properly. its just lucky that you have the space to do such a thing. ive had to build mine by asking favours from friends with garages and doing the rest in the rain outside my house on the road. so when i have problems due to lack of time space and money then you can see why i get pissed off with people saying i know nothing.
:lol: that was a lively debate! Anyways lads you can avoid any hint of your carbs going of tune quite easily - buy TB's get an ECU and get a properly tuned engine :P ! ( oh yeah and some more valves and an extra camshaft whilst you're at it) :lol: :lol: just jokin!
BTW when I had twin carbs ( back in the old days :wink: ) the only time I noticed them going "out of tune" (not idling very well and a bit rough low down) was once when they tried to depart from the inlet manifold and air was getting in round the seals ( what type of seal kit do you use m.d. ?). The other time(s) was the difference between the engine being hot and cold which obviously changes things a lot mixture wise?
Just a thought?
FFS mark what took you so long :lol: :lol: :lol: :lol: :lol:
As for the rest of the thread tbh i agree it has gone abit out of shape, what with me being a grumpy git (yes more than normal) the last few weeks etc so even my banter came acroos as kind of but not :? . *holds hands up to that one*
ive had to build mine by asking favours from friends with garages and doing the rest in the rain outside my house on the road. so when i have problems due to lack of time space and money then you can see why i get p**s off with people saying i know nothing.
That is my life also 8) , mine was built 120 miles away from where i live and meant travelling every weekend to and from with no sleep in the middle each time (hence we had such a tight time limit) and others helped out with alot of stuff after some begged and owed favours were called in etc.
Also same with money, if budget was a persons name i would be known as budget budget, and my middle name would be budget lol.
If i'm not in admin mode and just come across as miserable just ignore as no offence intented. If i am in admin mode then normal rules apply :lol:
lol i like my 8v and single cam, less things to go wrong.
im going to check the ammount of travel the pedal has and if its bending the spindle on full throttle when i have chance. ivaspoken to my local tuner again and hes going to have a look at the jet sizes im using now that he knows the problems i have. but he (as i do) does agrea with what your saying that they should not become unbalenced once set up properly.
i looked at my idle correctors today with the engine running and they are moving with the vibrations of the engine, explaning most of the probelm.
and the main linkage is just crap so ill be changing that asap.
CP when you say what type of seal kit im asuming your referring to the seal between the manifold and the carbs yes, im unsure really. it consists of a plastic carrier with an o ring either side that each flange seals on. seems very good and ive never had a leak there so im hopong its ok.
thanks dan. :D
good to know someone else is in the same boat.
Ok thats the sort of seal kit not to have! I had them and they are shite! The rubber seals deform and degrade and the whole lot is more likely to come loose and leak. Go to a weber dealer and get the sort that are made out of zorst gasket type material with rubber seals moulded on both sides. It looks a bit like a rubber doughnut with the gasket material sandwiched in between. Use nylock nuts instead of the spring washers things they sometimes flog and do it all up pretty tight. Never known this sort to be wrong and they aren't too pricey. Any little amount of air getting in after the carbs will fook up the mixture so its worth making absolutely sure of this first before examining other stuff?
Snowface
18-01-05, 03:35 PM
'side stepping the topic'...
my carb's are letting in air at seal i think. It whistles a bit when you accelerate below 3k rpm, and when its really bad it lags when i put my foot down at 3k.
thy stop whistling when i tighten it up a bit but then i was told by the r/r guy that it would cause the float chambers to froth.
i've got both types of seal kit (mISAB rings and the plastic ones) and i'm currently using the plastic ring + 2 rubber at the moment, with thackery washers on the bottom bolts and rubber grommets on the top lol.
still leaks slightly but when i used the misab ones it was even worse.
i think i need to get my inlet manifold skimmed because its one thats been made from a mould or something not a proper irmischer one.
Take your carbs off and using a steel ruler or a level place it across the manifold to see if it is warped. If its ok put your carbs on use nylock nuts and the mISAB rings and do the fucker up tight! Rolling road guy not helping you there. I've never known fuel frothing to be a problem on any nova engine with 40's or 45's! Its not like these engines are running bonkers revs and anyway they are made well enough not to vibrate badly.
Snowface
19-01-05, 04:35 PM
havn't got a steel rule but last time they were off i used the back of a hacksaw blade. it seemed fairly level, the blade was only long enough to reach over 2 1/2 inlets though so not ideal way to see. think i will just tighten them up a bit more. see how it goes. i think i know which inlet is whistling.
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