Distributor - vacuum tube

[Goki]

My Felicia "coughs" on small gas (not on petrol - but on LPG)... I went to change the LPG system filters, and they said the problem is in the distributor...

So, they pulled out the vacuum tube, adjusted the distributor - and left the vacuum tube not connected. They said that 90% of Felicias run this way...

Is this true? What exactly is the role of the vacuum tube, for the distributor?

HELP... :confused: A new distributor costs 120euro back here...

[cjb]

It's to advance the ignition timing as revs rise.

[Goki]

So, do I need to put the tube back, or leave it like it is (NOT connected)?

[cjb]

Well, I'd put it back and set the timing correctly, but I know little about LPG conversions. If it stays disconnected you should plug it as there will be an air leak.

[Goki]

They plugged it on the chasis...

...And also said that they can't set the timing better, because of a bad distributor. But I've been to a Skoda service garage, and they said that there's nothing wrong with the distributor itself...

I really don't know what to do...

[Phil-E]

Is this a 1.6 engine?

[KenONeill]

I know the engine won't run properly on petrol without the vacumn advance connected.

Take the distributor cap off, get hold of the rotor arm (or timing sender), and feel for any side play in the distributor shaft. If there is any, you may well need a new distributor (which will give you better running and fuel economy on petrol and LPG).

[daverapid]

Is this a 1.6 engine?

:)The 1.6 doesn't have a vacuum unit on the distributor.

The 1.3 engine is fairly prone to pinking anyway, but running on LPG it will be even more likely to pink. Disconnecting the vacuum advance pipe means the timing isn't being advanced at part throttle, therefore reducing the likelyhood of pinking. That's OK, but the pipe needs blocking off or there will be an air leak...which may lead to pinking!!

[Phil-E]

I'm guessing this is the MPi? As I don't recall seeing a vacuum pipe on the dizzy on mine.

Phil

[auroan]

Mpi doesn't have a dizzy

[Goki]

It has a 1.3 engine - carburator type...

[Goki]

Well, I put the vacuum tube back... So far, so good...

I'll test it on petrol tomorrow, and I'll see what she'll say... Let's hope for the best...

The best thing I learned is that a brand new distributor goes for 40euro in Germany, and 110euro back here... lol Those vulchers...

[Phil-E]

Mpi doesn't have a dizzy

Hehe... I realised what I had typed shortly after while at the gym! Wasn't thinking straight and forgot it's just got a coil pack thingamy!

Ah right... is it just the carburettor engine that has the vacuum hose on then?

Phil

[KenONeill]

Whether a Felly MPi does or doesn't have one, there is no technical reason why a fuel-injection petrol engine should not have a dissie. Just an observation, and a note as to why people might occasionally get confused as to whether or not a specific induction arrangement has a dissie.

For the OP, I stand by the statement that the engine (esp now I know it's carb and clockwork) will not run correctly on petrol with the vacumn advance pipe disconnected, even if the carb take-off is plugged which at least stops the hole causing lean running.

[Phil-E]

Hehe... No you are right but I did know that it doesn't have a dizzy but had a dizzy moment! lol

Obviously on the injected models the ECU does the advancement of the timing hence no vacuum hose to the dizzy.

I know absolutely nothing really about the carb models.

Phil

[Goki]

For the OP, I stand by the statement that the engine (esp now I know it's carb and clockwork) will not run correctly on petrol with the vacumn advance pipe disconnected, even if the carb take-off is plugged which at least stops the hole causing lean running.

So, I should put the vacuum pipe back, right?

Today, I drove it on Petrol, and it caughs on high gas (with the vacuum pipe installed)... Strange...

I guess it's time for a new distributor... :S

What do You think?!?

Edited 30 April, 2009 by Goki

[KenONeill]

So, I should put the vacuum pipe back, right?

Today, I drove it on Petrol, and it caughs on high gas (with the vacuum pipe installed)... Strange...

I guess it's time for a new distributor... :S

What do You think?!?

Yes, reinstate the vacumn advance!

You might be able to get better running by having the points gap set using a dwell meter rather than feeler guages, and better advance setup either by ear or by strobe light than static alignment of timing marks, but I suspect the distributor bearings may be worn out in which case it's time for a new or exchange dissie.

[Goki]

I drove it out on the open today, and the situation is following:

She snags on both low and high gas (pedal), even on 100km/h in fifth gear... :(

She does this on both petrol and gas... So, a faulty gas injector is out of the question (plus it was cleaned 2 weeks ago).

Should I still look for the problem in the distributor, or should I suspect for something else?

Please understand me - I don't wanna end up changing half of the parts, and still have the same problem. Service people back here try to persuade me to change everything, and spend around 1000euro...

[Cepheuz]

The Vacuum that goes to the distributor is one of the component in the vacuun advance system;

as rev go up, the vacuum force increases from 1200 to 4000 rpm, vacuum will degrade after that point

as rev go up, little weights in the distributor will advance the timing from 800 until 6000 rpm.

initial timing on a skoda felicia 135 engine is 2° btdc +/- 2°, meaning from 0° to 4° of basic advance @ 650 rpm.

when the engine is on load (accelerating bipassing, carring more weight) the vacumm will decrease, providing moro torque (cus it will burn all the fuel at the right timing) and when is traveling light will provide better FE (cus it will advance the timing more due to higher vacuum)

since both the vacuum advance and the weight advance work together, if you reomve the vacuum the egine will not advance the timing as needed when speed increases, if initial timing is set to compensate you will ping on load and will not have adecuate timing throu the rpm range (worst FE and performance) if you do not adjust initial timing to compensate you will feel the car "hesitate" or feel lazy due timing not advance enough to burn all the fuel (unburned fuel on the exaust, over cooling of the combustion chamber, high CO emition)

recomendation. Tune your car with the basic advance it needs, humidity, elevation, air temp play a role in this (thou not a bigh one, since is a 4° range) my recomendation, set to 4° with no vacuum, let idle for 10min, turn off, remove a plug, if you see a ring at the top of the seramic, your golden, if not derease timing by 2° and repeat, after timing (you should be adjusting idle to maintain the engine @ 750rpm) adjust idle mix reduce the mix until your engines rpm go down, then increase by 1/2 turn and go back to the idle adjustment and set engine idle to 850 +/- 50 rpm there you will have perfect timing, perfect mix, and perfect idle (smooth, quiet) and good throtle responce

after that, adjust the LPG settings, there are two screws (if the system resembles the ones here) one in the tube, represent the low setting, and the one in the converter the mx setting, you start with the low, if you have 2 tubes (one conected to each of the carb barrels) start with the low barrel, turn off completly both LPG feed tubes, then increment 1/2 turn on both and star testing, incrementing by 1/2 a turn on the low side until you get decent idle

is an ofset system (meaning the two feed hoses will not be calibrated equally) and every time you increase the feed on one is going to offset the other so you have to compensate by increasing more on the other. (gas is like water, it will go to the path with least resistance) and it work by balancing the vacuum of the intake with the push of the gas the push of the gas is calibrated by the high screw on the converter, and the pull of the vacuum is calibrated with the individual low screw on the feed hose.

if you cant calibrate it, blame it on bad instalation.

best of luck mate.

i like to point out that i'm not a mechanic or engineer, and my statement does not reflect the views of one, i'm just a simple joe who like fixing thing (and get away with it most of the time)

[calderscot]

Ignition timing for lpg and petrol is different.

See this page for a good explanation:

http://www.acl.com.au/web/acl00056.nsf/0/359683e8a538a3e64a2566c0007bb33e?OpenDocument

[Goki]

I checked the distributor cables that lead to the sparks...

The spark No.1 cable is almost totally busted... Could this result in ineffective performance and sudden shocks while running?

[Goki]

Problem solved... Car runs like a baby now - smooth that is, not slow...

[KenONeill]

A touch late with this reply, but yes. In fact, if you have HT leads, they are the first things to check in the case of an actual or suspected misfire, not just because they're easy to get at, but because they're amongst the least reliable components in the ignition system! This does not mean that they are always the cause of the fault, but they're easy, and (used to be) cheap to replace.

[Goki]

I too forgot to chek that...

But, when my starter finally died Saturday (and I didn't knew what it was), while checking the leads - I found the fault...

Now:

repaired starter + fixed HT leads + fixed timing + tuned a bit = happy Felicia owner

[KenONeill]

My bad; I forgot to ask about the basics because I thought you knew what you were doing well enough to have covered them!