Up untill a few days ago my car was running fine but all of a sudden it started to back fire when I decelerated and starting it became difficult. One thing that has been found is the both the vaccum hoses - light blue and the red to the distributor - both pull vaccum at idle and both lose vaccum when giving the motor some throttle. The red is supposed to have little vaccum at idle and gain vaccum with added throttle - correct? We are thinking that my throttle body has gummed up hole some where but at this moment we don't know how the advance hose nipple is plumbed in the 1976 2.0 throttle body - anyone got any ideas or a detailed drawing of how the advance vaccum flows through it? Thanks, Jim

TB

Advance hose from the dizzy is plugged and just lays on the engine, only the vacuum retard is hooked up to the TB.

I could be mixed up but I think we determined that the red hose from TB goes to where the blue goes on the above drawing and the blue from the air box goes to where the red hose goes to in the above drawing -- and we retimed and dwelled it.

But I am still getting hard starts and back fire when letting of the throttle a when driving a decent pace. -- I have to puch the clutch in before i let off the gas peddle if I want to avoid back firing. What could me problem be? I think it is time to replace the points/condensor,cap/rotor/wires just to rule these things out. Maybe it is a bad fuel injector causing me these problems.

I hate to say this...but check your MPS...pull off the line and put a might vac with a guage on it...see if it hold vacuum...

They do just die...the diaphram breaks...

Rich

I have a spare MPS - I'll give that a try. Thanks, Jim

I still can't get over the fact that my vaccum hose on my trottle body does not get a vaccum increase when I step on the gas peddle and open the butterfly??

I mean it is just a freaking tiny hole under the butterfly that has a nipple the comes out the side of the trottle body - not complicated.

If you connect a vacuum gauge to that nipple with a good piece of hose, clamped if necessary, and still don't get a vacuum reading.... that port must be clogged!

We get a vaccum reading at idle - but it dropps off when we step on the gas.

We also thoroughly cleaned the TB and can see the port is clear and shiny.'

Jim

Vacuum at idle but not at throttle = port below butterfly. Right? The placement of the port determines how it is supposed to act at idle versus open throttle.

QUOTE (jimkelly @ Jan 9 2006, 11:36 AM)

I could be mixed up but I think we determined that the red hose from TB goes to where the blue goes on the above drawing and the blue from the air box goes to where the red hose goes to in the above drawing...

You are mixed up--the drawing is correct. The light-blue and red hoses both go from the throttle body, not the air cleaner, to the distributor dashpot. The retard hose (the only one that you have, according to your picture) will have vacuum at idle and the vacuum will drop off pretty rapidly as the throttle is opened. You do not have the advance fitting on the throttle body, so you won't get the advance vacuum signature (no vacuum at idle, a bunch at a little throttle opening, none at higher throttle openings) anywhere.

In other words, everything is just fine. Disconnect the hose going to the advance fitting on the distributor dashpot (that's the one pointing away from the distributor body) and leave the other end of the hose open to the air.

Look for your problems elsewhere....

--DD

rand - yes - vaccum at idel - it drops off with throttle

dave - the drawing being correct is good to know.

I was refering to the air box - not air cleaner - the air box being the metal container under the throttle body - sorry for my lack of proper jargon : )

I also have two vaccum nipples on the air box just under the TB and this is where we originally had the blue connection as per the drawing. The nipple on the TB is where we originally had the red hose hooked up.

My distributor dashpot does have a retard nipple low position and pointing toward to dist and an advance nipple top pointing away from dist.

Thanks,

Jim

the vacuum advance circuit would only need to produce vacuum in the upper engine range, possibly 3k or higher...

It also does not need to produce to much vacuum for it to pull the canister on the dizzy...

I would suggest putting a guage on that line and watch it from 3k-5k

It will top out in the high 4k range...

Rich

QUOTE

the vaccum hoses - light blue and the red to the distributor - both pull vaccum at idle and both lose vaccum when giving the motor some throttle.

I don't mean to beat a dead horse, but this is normal. A port at the air distribution box, below the butterfly, will have maximum vacuum at idle but drop off as the butterfly opens.

The engine is sucking a lot of air. Put a vacuum port in the intake below the butterfly, close the butterfly, and that port will pull a hard vacuum. Open the butterfly and the path of least resistance is the throttle body, not that little port. Vacuum at the port drops.

The hose at the port below the butterfly should go to the distributor retard. So at idle, it retards the timing. Your car does not need the advance side at all.

Sorry for the rabbit trail... I know this doesn't solve your problem, but it seemed like a worthwhile sidetrack. Your problem may be elsewhere.

QUOTE (jimkelly @ Jan 9 2006, 12:50 PM)

We get a vaccum reading at idle - but it dropps off when we step on the gas. We also thoroughly cleaned the TB and can see the port is clear and shiny.' Jim

The port farthest from the distributor is the retard side, and it goes to the "back" side of the vac can. It has vacuum when the throttle's closed, no vacuum after the throttle's cracked open. The smaller diameter fittings are for the advance side of the can, and that circuit has vacuum when the throttle's opened (no vacuum at idle). The Cap'n

Well I changed the mps and things are better but not perfect.

two questions - is the advance port on the dashpot the one closest to the dist or the one furthest and on top of the dashpot the advance port.

Also - do I plug the hose coming off the advance port of the dashpot or do I leave it open to the air.

pic

QUOTE

two questions - is the advance port on the dashpot the one closest to the dist or the one furthest and on top of the dashpot the advance port. Also - do I plug the hose coming off the advance port of the dashpot or do I leave it open to the air.

Your questions have already been answered...

QUOTE

Disconnect the hose going to the advance fitting on the distributor dashpot (that's the one pointing away from the distributor body) and leave the other end of the hose open to the air.

Captain wrote opposite Dave - I had to ask despite feeling very confident with Dave's reply. Also the advance hose plugged or unplugged seesm to be not fully in agreement but again I am going with what Dave advises - but want to thank everyone for their replies!!! Jim

Gotchya...

I have read the factory left it UNplugged.
Not sure how much it matters.

QUOTE (jimkelly @ Jan 9 2006, 11:36 AM)

I could be mixed up but I think we determined that the red hose from TB goes to where the blue goes on the above drawing and the blue from the air box goes to where the red hose goes to in the above drawing -- and we retimed and dwelled it. But I am still getting hard starts and back fire when letting of the throttle a when driving a decent pace. -- I have to puch the clutch in before i let off the gas peddle if I want to avoid back firing. What could me problem be? I think it is time to replace the points/condensor,cap/rotor/wires just to rule these things out. Maybe it is a bad fuel injector causing me these problems.

The drawing is correct!

If you have a real 76 TB there is no port on the TB for the Vacuum advance and don't worry about it.

From the Factory a hose was plugged into the dizzy advance port and plugged and stuffed under the runners, it didn't go ANYWHERE.

The dizzy is mostly a mechanical advance unit and the vacuum advance isn't really needed.

Time to due a full maintance on the car, adjust valves, oil change, plugs, points, cap, rotor and retime it. Then see whats up.

pic

QUOTE (jimkelly @ Jan 9 2006, 03:34 PM)

Captain wrote opposite Dave ...

Actually, I think that the Cap'n agreed with me. He was, however, talking about the fittings on the throttle body, not those on the distributor dashpot.

--DD

Lookat the 73 2.0 Throttle body with the two ports!

Thanks to you guys my baby is feeling a lot better now!

this is interesting! I've had the advance side of my 76 hooked up to the TB forever. Mine is a CA car with EGR, so it has the same ports as the 73 above. Vacuum at mid throttle for the EGR. Guess I just assumed it needed to be hooked up to the dizzy too. This explains why I have to run a tee in the line to hook up the EGR when I smog it. Think I'll go mess with it a bit and see if it improves light-throttle driveability.

Also my $.02 on your backfire on decel. Thanks to Headrage, I eliminated 95% of my pop on decel by leaning out the CO adjustment on the brainbox. I have always kept it about 3/4 rich just to be on the safe side. Don't wanna burn a piston. Allan was following me one day and clued me in to the rich condition causing the backfire. Couple of test drives and adjustments and viola! no more backfire. thanks again Allan.

My understanding is the adjustment screw on the ecu is for idle only and does not effect motor at above idle ?? Jim

My problem has been solved - thanks to rtowle - my mps was BAD : ( but I had an extra : )

QUOTE (jimkelly @ Jan 10 2006, 04:15 AM)

My understanding is the adjustment screw on the ecu is for idle only and does not effect motor at above idle ?? Jim My problem has been solved - thanks to rtowle - my mps was BAD : ( but I had an extra : )

The ECU screw only adjusts the mix at idle but it can affect the mix when the throttle is closed on decel IIRC.

On my 1976 2.0L I changed my bad 043 mps to a good 049 mps. While things appeared at first to
me much better - and are in fact much better - because back firing is esssentially
gone - I have noticed this problem. Maybe I did not notice it immediately because
my drive to work is extremely short - 5 miles. I have taken two bit longer trips recently
and found that after letting my car warm up in the garage for 5-10 minutes - for the first 10-15 minutes of my drive everything seems fine - I can rpm up too 4000 smoothly but after another 10 minutes or so it starts to hesitate at 3000-3500 rpms. If I come to a complete stop _ red light or stop sign - a few minutes later - coming off the light I find that the hestiation starts even earlier that 3000 rpm. I have one problem that I know of - my FI plug to one of my fule injectors is lose-ish ut tis does not appear to have been my problem causing this hestitation problem. Any idea if this could be being caused by a bad head temp sensor or position switch? Note problem does not occur withing first few minutes of driving but does become apprent after 10 or so minutes of driving and them worsens.

http://members.rennlist.com/pbanders/DJetP...tm#troubleshoot

Its because in the first 10 mins of driving the engine is running rich as its warming up due to the CHT. After 10 mins the leaner A/F mix of the 049 is causing you the missing/hesitation. You should get the proper MPS for your car-a #043.

I would also change out those rubber vacuum hoses to the proper ones and look for vacuum leaks. Its like a dog chasing its tail if you have vacuum leaks.

geoff,

I have a 043 mps that I got from skline and another from root locally but for some reason my car won't idle nicely with these : (

It idles fine with the 049 : ) but bucks like a bronco under throttle : (

There is no question the 043 previously in my car was bad - my car backfired like crazy and I can suck thru it with my mouth.

Do you think it could be a timing issue that is not letting the 043's allow my car a decent idle even though my car will idle fine with the 049??

Jim

If the 043 is bad then its waay to rich so the motor can't handle the extra fuel to idle. If the MPS is bad the engine can't pull the diaphram back with vaccum to the inner stop so it runs too rich.



Geoff