Vacuum advance or centrifugal advance?

[nxp]

Today I've tuned up my 121 hatchback (carbed 4spd) because she was missing somewhat - the spark timing was off and the plugs were burnt. Replacing those made her run pretty well again.

Unfortunately this didn't stop the hesitation she had when flooring the pedal. And I'm suspecting this may be timing related because what happens is that the spart first RETARDS and only then advances as I would expect when revs increase.

Would this be the cause of the hesitation or would it be a byproduct of such hesitation? I know that during hesitation vacuum is lost because the manifold gets full of air/gasoline, but if my eyes don't deceive me here I'm getting momentarily a spark that is retarded with respect to when I disconnect the vacuum line and let the engine idle (base timing of 15*).

Could it be that the vacuum advancer is overshooting when I press the pedal? Or does anyone think it could be a bad advance mechanism in the distributor? Is there anyone who thinks it's the carb and accel pump (which by the way is actually spraying fuel) and this spark retard is just a symptom?

I hope some of the smart guys in here have some ideas on what's going on!

Nath

[FestYboy]

be sure your vac lines to the carb are in the correct positions. also be sure you're not over spraying with your accel pump (can cause engine to bog and look like spark retard).

[nxp]

Thanks Festyboy.
I have checked the vacuum connections and found...

The normal(or nearly normal) stuff....
There is a vacuum line and a fresh air line from the carb and the air cleaner to the vacuum advancer.

A vacuum line to what I believe is the second throttle plate actuator (high pressure side is open to the atmosphere).

The obvious brake booster vacuum line.

A line from a small aluminum canistar to the left of the carb (when viewed from the front) to the manifold - I am assuming this is part of emissions control.

The crankcase ventilation port thingy? - from the top cover to the air cleaner and from the top cover to somewhere in the carb.


The nasty stuff....
A vacuum line that splits into two from the manifold close to the cylinder head, splitting into two - one going to the hot air/cold air actuator before the air filter, and the other to what looks like a bimetallic strip with a plug on top of the line after the air filter. The strip is always open and looks like one of its metal bands is BROKEN! How bad is this? (note that here we never get temperatures below 10 degrees Celcius)

What looks like a solenoid on the back side of the carb, on the left when looking from the front, at the top of the carb. This has NO PIPE CONNECTED! The connector seems to be for a larger pipe than the ordinary vacuum lines. Both when opening the throttle and at idle there is no suction felt from here but it must serve for something - and I have no idea what creates the signal to open it!

A blanked line coming out of the manifold after the carb.....

Does this setup seem acceptable at least for engine running if not for emissions?


The second thing you suggest, the accel pump - does that have any way to set it? Is there any way to change volume or rate of squirting? A friend suggested that the nozzle may be partially blocked, but how realistic is that?

I appreciate the help!
Nath

PS:
Regarding EGR, I have no idea if previous owners disabled EGR - How do I confirm the presence of the EGR valve and that it is operating? Would its absence have an effect when going from idle/very little throttle (when I assume it should work) to WOT?

[IL4Festiva]

egr valve is a valve to let hot air out of the crankcase and cool air in, it is there for a reason, i suggest leaving it, you won't gain any benefits by removing it.

[FestYboy]

egr valve is a valve to let hot air out of the crankcase and cool air in, it is there for a reason, i suggest leaving it, you won't gain any benefits by removing it.

umm what? Sorry there IL4, but you're WAY off on that one. EGR (exhaust recerculation) sends metered amounts of exhauts gasses back in to the intake durring certain conditions to reduce the formation of NOx (typicaly durring cruising speeds). it can also have a side effect of improving MPG by effectivly reducing the engines dynamic displacement (exhaust gas is "dead" and takes up space in the cyl. therefore reducing the actual charge volume per stroke)

[benms79]

im prob way off,but i had a similar prob, ended up being o2 sensor.

[nxp]

Yep festyboy - I agree with your definition of EGR, but my question is not on how to remove it. I asked how to locate it on the manifold and what problems it could create if missing - this because a few cars that I've seen here that were messed with by inexperienced "mechanics" had the EGR removed.

Also I'd really appreciate if someone could enlighten me on how to change the accel pump stroke as you say that it may be squirting too much and causing bog.

(It would also be nice if someone could tell me whether there's something nasty with the setup of my vacuum lines on the carb!)

Nath

[WmWatt]

I wrote up an account of cleaning the EGR valve on my car and put it in

https://www.ncf.ca/~ag384/Cars.htm

EGR - Exhaust Gas Recirculation

[WmWatt]

EGR - Exhaust Gas Recirculation. The solenoid at the left of the carb operates the EGR valve. (There are two EGR solenoids, a Mazda feature I think.) There is a large diameter red hose on the bottom which goes to the EGR valve. There are two normal diameter hoses from the top. The one with the red dashed line goes to the carb. It goes into a T-connector at the back. The hose it plugs into goes from the carb straight down somewhere. The vacuum outlet it uses is right beside the bent, plugged outlet. The other hose from the solenoid (green dashed line) goes down behind the engine somewhere close to where the first line goes. I ca feel the ends but not see them.
The aluminum solenoid at the front top of the carb is part of the deceleration control anti-backfire system.
Chapter 6 of the Haynes manual is devoted to emission controls but is very limited on the feedback carburetor. I just hope nothing ever goes wrong with mine. Haynes also publishes an emissions control manual of which our public library used to have a copy.
I don't know about the bimetal strip. However please post any other question you might still have.

[Pgh5spd]

I'm very interested in this thread- symptoms sound like what my 88L just started doing - bogging on attempted acceleration, especially in 2nd, and especially when taking off from a rolling stop in 2nd, which previously was no problem, and at first, anyway, acted like the accelerator pump wasn't putting out. It came on suddenly, just a few days after a great 600mi trip - at first I thought it was a clogged fuel filter - symptoms were a bit like that from the past on this one, but changing it didn't help much. I'm particularly interested in the EGR cleaning (thanx Wm! Looks very well described.) and the O2 sensor, which I need to read up on. Do O2 sensors typically fail without much warning, or do they go more gradually, or is that the wrong question to be asking?

It's probably irrelevant, but the last gas I got on the trip (7gal, and re-filled with 4gal since, of which over half now gone) was 10% ethanol.

[m715]

It's strictly my opinion, but my carb cars are acting up with the gasoline that is out there too......from certain sources, that is. Even my FI Vulcan Taurus is complaining about some of the fuel I seem to end up with lately. The base fuel, before the additive package that is being delivered is what I believe to be inconsistant, and sometimes more Ethanol concentrated, like it is not mixing very well. Fuel economy is erratic too! Your next tank, and some carb cleaner, may be all the fix you need.
BTW, O2 sensors are *supposed* to be changed about every 50,000 miles, but I believe it has more to do with the sensor staying clean to measure the gasses than anything in my experience. Unburned additives (ash like deposits), and oil pass through contaminating the probe. The probe, sensing a false reading, throws off the fuel metering causing poor economy/performance. The worse the deposits build up, the quicker the sensor gives the false reading.
JMO..... for what that is worth.........

Michael