Vacuum Advance on multi carb 2.0 liter!! Any experts???

Hi there, this here is a picture of a bosh points dizzy just like the one
i run. Im having problems tuning the carbs i installed on my 2.0 liter banger,
they are 4 mikunis VM 38 one barrel carbs, there are 2 other threads
on this matter but i want to focus this one on ignition and advance.

So, the previous set up was weber 2 barrel carb w/ a hose hooked to
the pump on the dizzy that is the vacuum advance pump.
1st ive been told to just un plug it and run the carbs as they are, but then
a couple o'days ago ive been told by another person that there is
no way i can run w/out vacuum advance.
I tried to hook it to the manifold but the car ran worse!!!!!!
I know they sell non vacuum advance distibutors, but they are quite pricey
and i aint sure they are the solution.

The 1st picture after dizzy shows the holes (plugs) in the intake were
i plugged the advance, i did make a "bridge" so that the vacuum
came from all 4 cylinders.
Second pic is of whole set up.

Any experts here?

Thanx a ton, Nick.

 

After you hooked it up to the manifold vac did you try readjusting the timing? Once it's hooked up to manifold vac. you will have to retard the initial timing from where it was running without the vac. advance.

 

No i didnt adjust it, cause w/ previous set up i ran w/ the advance hooked.
And i was sure i was good w/ that set up.
I dont have a timing gun anyway, if thats what you mean.
Never adjusted timing properly anyway,
I adjusted it by hear turning the shaft, but this aint the right thing to do
in this situation...
Anyone willing to explain the basics, or simply goin into details?
Thanx.

 

Are those black hoses going to that fuel block your vacuum manifold?
Does the distributor use manifold vacuum or ported vacuum?

 

Nope! those are just the fuel lines and fuel block, period.

Your question is most intresting. Idont have the smallest clue!
And i aint happy about it, kinda ashamed also to be honest.
The previous carb had the vacuum advance hose hooked on itself!
not on the manifold. I know some carbs have a sort of valve where
it has to be hooked the advance hose, the previous weber musta've
ben one of those.
Is vacuumless distibutor becoming more and more the next option?

 

Sure looks like Centrifugal advance distributor may be your best solution.

 

There'll be centrifugal advance in there, along with the vacuum.

Another option is manual advance, like they had on many pre-war cars. Remove the vacuum diaphragm unit. It'll hook to a little arm or something coming out of the distributor body. Rig up a cable to a control like a choke knob inside the car or, better yet, idle and advance controls on the steering wheel boss or steering column. You'd have to learn to fiddle with the advance as you drive, but that's what drivers did back in the day.

Now that's traditional!

By the way, are those Mikunis CV or plain-slide carbs? If the latter, the inability to adjust mixture for load might be the cause of your woes. Your car weighs a lot more than a motorbike, and might well need some form of vacuum correction to be drivable.

 

Oh boy! What did i put myself into?????!!!!
Yeah it sure sounds traditional but hell! I wonder how many here do this.
I'd really like to hear from people that chose this option.
Good to know anyway, at least i have an option if anything else fails!

Mikunis are CVs plain slide, totally simple carbs. Love'em! Although the genius
that said they are the shit to soup up a pinto maybe was on drugs
Just kiddin, it wouldnt be fun if it was a bolt on type o'thing.
Yes car weights more than the snowmobile they werre designed for
but Esslinger engineered those kits in the 70s for
this type of engine and if it worked back then i dont see why i cant do it now..
If only there was more people around that still has them that could help.
Back to the advance matter.
I suspect my basics on timing and advance arent all that right.
Anybody willing to explain me what happens to my engine for not
runnin w/ vacuum advance ?
And whats ported vacuum?
im pretty sure manifold vacuum is what i tried hookin it up to all 4 inlets.
Thanx guys.

 

I am using a pair on 45 DCOES on a 2.3 ford (4) cylinder. I am using a port on the rear cylinder intake tube for the vac. for the auto, transmission. Also using a dist. with a mech advance. Dist. is set at 18 degrees int. advance with a total advance of 34 to 36 degrees.
You might be able to find a pair of Weber DCOM that have vac. port built into the carb. if you do not want to use the port opening in the intake.
What size port do you have on the makunis? I would think a 2 liter motor with no work done to head would need chokes in the 30 to 32 mm.
send me an email if you need more mike

 

If you had the engine running w/o the adv. and then hook it up, the vac. will pull the timing further advanced.

A timing light won't be any help when getting your unique combination of parts dialed in. You will need to do it the old fashioned way by the seat of your pants. I like to advance the distributor as much as I can until the engine starts to ping under a load. I back it off until it will pull under load and not ping anymore. It may take 2 or 3 trips up the road trying different settings until the best compromise is found. This will also account for the gas that you are using and any changes in octane. Then you can mark the location of the distributor so that you can repeat the setting if needed later. Short of dyno test runs that is about the best that you can expect. IMHO

Your dist. was made to use both the mech. and vac adv. systems that it was made with. It can be altered to work on mech. only by someone with a distributor machine but you will get better mileage if you can keep the vac adv.

Ported vacuum is for pollution controlled engines mostly. Your car will idle cooler in traffic with manifold vacuum also.

Not very scientific. but it works....for me, a backyard mechanic, anyway.

 

Mike c ,I know those type of carbs, they are good quality carbs indeed, but i see them in every strret machine ford or VW in europe and i wanted something diffrent, that could deliver power and still look more of a hot rod piece than anythingelse.
The Mikunis have the means to do so,i only need to be patient and keep trying, at some point i will have a good enuff result and can move to the next step.
They are 38mm, but dont work like webers. 38 is the actual aperture of the carb, it has a single slide and no variable venturi.
If you think its over carbed that aint the point. were alredy went trough that.
Just a question: from what you said it seems like you hooked vac advance on 1 inlet, not on all 4. can you do that? I thought the dist needed to get vacuum from the whole 4 cylinders not just one...lemme know..thanx.

Tommy mate, that is scientific enuff for me! a backyard butcher...
your explaination of the old fashion way to set timing advance is clear
i suppose....but? what does ping means??? i got the overall point but aint sure about that one word.,and i will try it asap.
Just a question. How would you hook the dist to the manifold?
Is using them tapered holes alright? or is there a better option in your experience? like hookin thenm to the carbs someway or ????

I think i will not modify the dist, in that case i would buy a non vacuum one. Only now its too much for my broke pockets to spend more than 300 Euros for it, which translated are about 500 bucks! yeah 500!
So, ported vac isnt my case, if i can hook it to the inlet i'll do so.
Now the car is at the local shop for inspection, we have to do that every 2 years here otherwise they can inpound the car if find you driving.
I hope its gonna pass, i have so many things that are illegal that it cant pass "legally", the mech needs to do some tricky stuff.
he said leave it 1 week and i see what i can do, no ok or no chance answer from him, which is worst in a sense.
Im relly nervous about it. pray for me guys!

 

Getting a clean vac signal with a setup like this is half the battle. Each individual cylinder will only produce vacuum when the intake valve is open, so without a common plenum to even out the pulses, you can give the dizzy fits as the timing shoots all over the place from an inconsistent signal.

Do you have any pics of the "bridge" you made? It should be tapped into the runners from those plugs, then go to a vacuum canister. Pull the signal for the dizzy off that vacuum canister. It's a similar concept to using the fuel block to distribute fuel, just in reverse I put a pic of a vac canister below. It's for an EFI setup, which is why it has those extra ports on top for emission controls, etc. It will give you the basic idea though.

 

Yes, thats exactley how i did mine, only in shitty T-joints and fuel line instead of that cool piece there, but i was plannin on machining my own very similar to that if it worked out.
I had a problem w/ it thoug, other than runnin crap. cause i have front discs, i have a brake booster and its hooked to the manifold too.
Now, imrunnin w/out vac. advance and its hooked to one cylinder, but when i had the "bridge" hooked up w/ vac advance, it was on the opposite side but still connected to the bridge.
The problem was, that 1st braking went ok, then i would loose front brakeing, and more weird of all if i kept pushing the brake pedal it would rev the engine up?????
Any clues? is it simply cause carbs and advance are outta tune?
Or if i make the vacuum plenum the booster vacuum hose has to go somewhere else?

What do you personally suggest?
Plug the vac advance or get a non vacuum advance dizzy?
Thanx for taking the time to read this.
Nick.

 

hey without timing light and vacuum gage you will not get it right. I would say that you need to hook dist uo to ported line, that means above the slides in the carbs. manifold vacuum probably exceeds what the advance on dizzy needs at base timing, and pulls it on to early. you need to set your base timing at about 6 degrees before top dead center then check total advance with out vacuum hooked up. hook up vacuum n see where it is at idle should be the same as unhooked or close to it. check total advance at around 1800 rpm and see that it doesn't exceed about 30 32 degrees this is just the basics for setting up timing on anything for street driving and mileage
hope it helps ya
Ken

 

Ping...pre-ignition, detonation, spark knock....are all the same thing. It's a light tapping noise in the engine that usually occurs when the ignition is advanced too far. You won't hear it cruising but lugging the engine in high gear (pulling a long hill) will produce the noise. Letting up on the gas (load) and the noise goes away...then you know it's "pinging" or detonating. Not good! If you advance it too far and lug it in a high gear you will hear the new noise. Back off on the timing until it will pull smoothly without the noise. I never lug an engine. I grab another gear so do your testing like you would be normally driving it.

The high compression motors from the early 60 often developed this problem when the high octane gas that they were built for disappeared. Using a timing light to set the engine to 1963 specs for an engine designed to run on 103 octane gas will often produce the same symptom with today's fuels.

If you ever have an engine overheat on the road, you will often hear the same noise under load until the cooling problem is fixed. The timing is too far advanced for those temperatures.

Since you don't have a common intake plenum I'd make a vac manifold connected to all the runners to average the vac signal. If you plug it into only one runner you are only sensing that one cylinder. The vacuum signal does not increase (add up) with more cylinders but you will average the highest cylinder and lowest signal with all the rest. It may not make any difference but that's what I'd do.

 

What do you mean by a vacuum gauge?
I built my own vacuumometer for tuning the carbs, but i suppose it aint
what you mean here.
How do i read total advance?
I understand setting base timing 6° b4 TDC but how to read advance is
still bit of.......how?
Another bit of a question that i thought of. Im having flooding problems, as in: raw fuel exiting by the tail pipe!!!
I ordered smaller pilots and mains(just in case), but do you think this can also be related to timing and advance?
Or am i right to also think i have enormous jets for my engine?

Im goin home now, im at work, i know im very bad, but i moved to a new home
a couple of months ago and still didnt make a connection. So is either here or nowhere!
thanx to everybody for the super clear and useful responses
Talk to all of you guys tomorrow.
Nick.

Edit: Tommy! we probably posted togheter or very close!
OK, i see! Now its definiteley very clear, and i might recognize the noise already!
Thanx a lot mate! talk to you tomorrow.

 

The dizzy signal does come from the manifold between the carb and the head. Those plugs are definitely the ideal location to use. ou will get a very strong, violent vac signal from whichever cylinder is open, but the idea is that by averaging the 4 signals you get a consistent output. You shouldn't be producing too strong of a signal for the dizzy unless something is seriously fubar'd.

I think the only way you will know for sure is to put a vacuum gauge in the dizzy line for tuning. If the needle on the gauge is jumping around at all, so is your timing.

Now as to the brakes, there should be a vacuum reservoir somewhere to prevent the issues you described. Nothing fancy just a container to "store" vacuum for brake use. That's my only thought there, maybe someone else can help more?

P.S. that picture above is a stock part from a Toyota Levin. I don't know what they called them in Europe, but you may be able to grab that piece out of a JY. It's the 1.6L with 4 throttle bodies from the 90's. The A101 chassis iirc

 

Here's a good article. Not my words, I copy and pasted to try and help out:

TIMING AND VACUUM ADVANCE 101

The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.

The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.

At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).

When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.

The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.

Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.

If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.

What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.

Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.

For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts.

 

Hey im back!
Today is gonna be a hard one so i cant "chat" all day
Mr Sinister: Thanx a lot, that made my mind straight about advance!
A really helpfull article. Just a question? Is there a way to calculate
the righty size of a vacuum advance can?
Be back later. Thanx again, this place is the best!

 

no problem!!

i don't know that you can calculate the right size can for your particular setup, its one of those things that you might have to just buy a few different ones and see which one works best. you're not exactly running a common setup there!!

 

I had a set of Mikunis set up for my inline six at one time. One of the tuning issues I discovered was that the Mikunis did not like high fuel pressure. I had to install a regulator that would keep it down to 1~1.5 psi in order to get a decent idle.

 

I would make sure my carbs are in sync, then I would create a vacuum source manifolded from all cylinders and hook the vacuum advance back up and the re-time the motor and have fun.
You can run w/o vacuum advance, but its there for a reason, it gives better low end power and better gas mileage and performance due to the timing change at certain rpm's.

 

Mustangsix, i have a fuel pressure regulator, its recommended setting for this set up is 4 to 5.5 psi.
At the moment im runnin at 0.5 to maybe 1.5 psi, because
of the very high consumption im gettin. I see you have diffrent type carbs than mine.
Mine are VMs, yours look like CVs or something.thanx for taking the time to reply.
Turbo mate, carbs are totally in sync. Its been the 1st thing ive done after boltin the manifold.
Then i realized the sync was crap and re did it more accuratley. I tell ya, it aint easy to sync those bastards,
each cable is of a diffrent lenght, so if turnin the retainer 2 turns places one slide to WOT ,
the same on another bareley moves it from idle position....?!?!?! I did it well though.
Now im waiting for smaller jets and im already lookin if i can get a vac. can from the Junkyard.
But first i have to get my car back from the garage that is doing the inspection (called MOT? in the USA?)...until then im stranded. Hope all goes well,
w/ the laws we have here car aint totally street legal....fingers crossed.

Thanx to everyone who helped me out. this has been most helpful.

 

if your head isn't swimming enough, here's another great read, but grab a coffee, you'll be a while.

http://www.streetrodstuff.com/Articles/Engine/Detonation/

 

I spoke with a guy at Esslinger Engineering who pioneered the use of those Mikuni's on 2.0 Ford oh so many years ago. They felt the vac can on the stock dist would be fine for your application. You MUST run the vacuum being connected to all 4 intake runners, it will not work on just 1 or 2. Otherwise don't use it.
Set inital around 12* BTDC and look for about 36 * total at 2000-2500rpm.

 

Hey Don, thanx a ton, i contacted them too, askin for a non vac. dist, and then askin what is best,if the non vac. dizzy or the vacuum canister.....
they didnt reply yet, but apparently you beat me to it!
Thanx a lot, as soon as i get the car back i have enuff to keep me busy i recon!
Mr Sinister thanx for those other articles. Theres never too much "basics" when you
spend half of your day on the car....and those seems very well written.
You guys have been great.
Thanx for your intrest.

 

Hi all!
I just recived an email from Esslinger which said that w/ this Mikuni set up i dont wanna use Vacuum advance???,
but i should get a non vac. dizzy.
The one they have is Mallory unilite.
Is anyone familiar w/ this unit?
Plus, they are always very "short" on their answers,
and i'd like to know your opinion.
I do not think they're trying to make a buck on me, as they have a pretty serious
name w/ a long history, and suppose a reputation to keep.
But this still seems to go the opposite direction than everybody else pointed me to.
Im also considering they have diffrent opinion themselves as hotroddon
spoke w/ someone there saying vac. can will do good.
Im confused. actually, more confused!

 

I can't add any specific info about your particular set up.

Generally race cars do not have vac adv. Street drivers often do. This may help in deciding which way to go.

Race cars don't get caught in traffic and over heat. Race cars don't care about fuel mileage while cruising on the highway.

Street drivers often get caught in traffic and getting better mileage on the street can be as important as the maximum HP output considering the amount of times that you actually use the maximum HP available on the street.

There can be lots of confusion on lots of subjects when trying to apply racing principles to a street driver. Running a vac adv is not going to damage your car.

Deciding how the car will be used is the first question that you need to answer. IMHO

 

I've been running a Uni-Lite on my 462" BB Buick for about 50,000 miles and 15 years.

No problems.


I'm of the opinion that the complainers haven't read the instructions, didn't set it up like it should be and have a poor ground at the ground terminal.

 

I recently pulled the MSD dizzy no vac advance off my 390 FE motor and reinstalled a stock with vacuum advance because it is street driven I have not had a chance to drive it yet, but will post any difference I noticed on it. Was told same thing that it is better for the street.