Off Idle miss/bog

[naa10104]

Unless you are required to have the EGR and/or switches functional I would simplify it as much as possible. Disconnect and plug/cap everything and see if you can get it running better. You may have to change jets or re-clock your distributor. After you get it running better then connect your vacuum advance directly to manifold vacuum and see how it runs. Then try it connected to ported vacuum.

Hello, on the vacuum tee on the back of the intake manifold there or four small ports I believe two of them are utilized right now. No more than two. Then the big one that goes to the master brake booster. I'd like to keep the set up I have because I spent over $150 on a new EGR valve and a new EGR carbspacer Plate. The car runs well otherwise no pinging, no running on seems to perform well. So I think at this point I'm OK with the timing and the distributor curve. Just want to make sure that everything is hooked up correctly and doing it's job. I do have the timing advanced some ... adjusted by vacuum gauge but not to the point of causing any pinging.

As always I appreciate everyone's input and help. Thanks

 

[Don C]

You can use the 3-port valve as a 2-port valve. Cap off the top port, connect the bottom port to the EGR vacuum port on the carburetor and the middle port to the EGR valve. Connect your single vacuum advance to either manifold vacuum or ported vacuum. I prefer manifold vacuum, others prefer ported vacuum. This is pretty much the same as calibration 3-11E. If you have the double vacuum modulator, connect as in 3-11E.

 

[jbojo]

You can use the 3-port valve as a 2-port valve. Cap off the top port, connect the bottom port to the EGR vacuum port on the carburetor and the middle port to the EGR valve. Connect your single vacuum advance to either manifold vacuum or ported vacuum. I prefer manifold vacuum, others prefer ported vacuum. This is pretty much the same as calibration 3-11E. If you have the double vacuum modulator, connect as in 3-11E.

The bottom port on the 3 port valve is normally closed until coolant temp reaches 215 to 220 degree and then opens to supply manifold vac to try to correct the over temp condition.

He has ported vacuum connected to the top port and the distributor to the center port and that corrected the bog condition and the EGR works correctly now. The 2 port valve controls when to turn the EGR valve on based on coolant temp. As set up now that is being bypassed.

Since he is not concerned with 100% original and the bog condition is gone he should just keep the system as is for now.

EDIT: I was thinking of 3-11A was the original setup

 

[naa10104]

You can use the 3-port valve as a 2-port valve. Cap off the top port, connect the bottom port to the EGR vacuum port on the carburetor and the middle port to the EGR valve. Connect your single vacuum advance to either manifold vacuum or ported vacuum. I prefer manifold vacuum, others prefer ported vacuum. This is pretty much the same as calibration 3-11E. If you have the double vacuum modulator, connect as in 3-11E.

Just curious .. Which port on the carb is the EGR port ? I have two ports on the base of my carb ... driver's side port faces straight forward ... passenger side is near front of carb but comes out the side. THanks

 

[jbojo]

You can use the 3-port valve as a 2-port valve. Cap off the top port, connect the bottom port to the EGR vacuum port on the carburetor and the middle port to the EGR valve. Connect your single vacuum advance to either manifold vacuum or ported vacuum. I prefer manifold vacuum, others prefer ported vacuum. This is pretty much the same as calibration 3-11E. If you have the double vacuum modulator, connect as in 3-11E.

Just curious .. Which port on the carb is the EGR port ? I have two ports on the base of my carb ... driver's side port faces straight forward ... passenger side is near front of carb but comes out the side. THanks

Drivers side

 

[naa10104]

You can use the 3-port valve as a 2-port valve. Cap off the top port, connect the bottom port to the EGR vacuum port on the carburetor and the middle port to the EGR valve. Connect your single vacuum advance to either manifold vacuum or ported vacuum. I prefer manifold vacuum, others prefer ported vacuum. This is pretty much the same as calibration 3-11E. If you have the double vacuum modulator, connect as in 3-11E.

Just curious .. Which port on the carb is the EGR port ? I have two ports on the base of my carb ... driver's side port faces straight forward ... passenger side is near front of carb but comes out the side. THanks

Drivers side

Thanks

 

[barnett468]

So I think at this point I'm OK with the timing and the distributor curve.

For the second tome, the timing curve is not likely optimal for your engine . it is illogical to connect the smog just because you bought the parts and illogical to go to this immense amount of trouble if you don't try to set the timing so it is optimal for your engine.

 

[jbojo]

Just curious .. Which port on the carb is the EGR port ? I have two ports on the base of my carb ... driver's side port faces straight forward ... passenger side is near front of carb but comes out the side. THanks

Drivers side

Thanks

As promised here is the diagram on how I think you can set up the emissions without adding the 2 port switch. That switch disables the EGR valve when the motor is cold and then enables it when the motor is warmed and off idle (driving it). The EGR was designed to reduce emissions by burning some of the exhaust gas again and does lean out the fuel mixture but only while driving so the leaner mixture is not noticeable. That is why it cleared up you bog/miss condition that you had without having to richen up the fuel/air mixture at idle.

The 3 port switch was designed to supply ported vacuum to your distributor under normal operating temperature. If the motor started to overheat then the switch would supply manifold vacuum to try to correct the issue. That switch disables ported vacuum when coolant temp reached 220 degrees. Right now you have that disabled.

Lastly, if your car runs well and you are happy with it I would just leave everything as it. The EGR is working so that part of the emission system is functional right now and meets your goal of using the new parts that you purchased.

 

[naa10104]

Drivers side

Thanks

As promised here is the diagram on how I think you can set up the emissions without adding the 2 port switch. That switch disables the EGR valve when the motor is cold and then enables it when the motor is warmed and off idle (driving it). The EGR was designed to reduce emissions by burning some of the exhaust gas again and does lean out the fuel mixture but only while driving so the leaner mixture is not noticeable. That is why it cleared up you bog/miss condition that you had without having to richen up the fuel/air mixture at idle.

The 3 port switch was designed to supply ported vacuum to your distributor under normal operating temperature. If the motor started to overheat then the switch would supply manifold vacuum to try to correct the issue. That switch disables ported vacuum when coolant temp reached 220 degrees. Right now you have that disabled.

Lastly, if your car runs well and you are happy with it I would just leave everything as it. The EGR is working so that part of the emission system is functional right now and meets your goal of using the new parts that you purchased.

Hello,

Thanks for all your help and constructive information, and the diagram ...really appreciate it. May leave it as is but might route the vacuum as you have shown. Will let you know when I get to that point. Take care.

 

[Jeff73Mach1]

If you are only using two hoses on the 3 port switch you lose all vacuum advance when the switch opens. If you aren't going to use all 3, then run your vacuum advance line straight from the carb fitting to the distributor vacuum advance cam.

 

[jbojo]

Good point Jeff.

I would just run a line from the capped port to manifold vacuum. I believe he said he was going to route the vacuum lines as suggested.

thx

 

[Jeff73Mach1]

Actually that three port switch is something that I almost think is worth adding to most street driven cars. I can't comment on EGR systems as I would rather throw one away than fix it, this is an interesting read on vacuum advance and ported vs manifold vacuum. I've read it before, but in reading it today, it gave me something specific to check on my car.

http://chevellestuff.net/tech/articles/vacuum/port_or_manifold.htm

 

[jbojo]

Actually that three port switch is something that I almost think is worth adding to most street driven cars. I can't comment on EGR systems as I would rather throw one away than fix it, this is an interesting read on vacuum advance and ported vs manifold vacuum. I've read it before, but in reading it today, it gave me something specific to check on my car.

http://chevellestuff.net/tech/articles/vacuum/port_or_manifold.htm

Yeah, I have read this article a few times too, its a good read. Curious as to what you are going to check.

 

[Jeff73Mach1]

Vacuum advance canister. Because I have a very lopey idle and sometimes it seems to "wander" a hundred rpm one way or the other, I'm thinking a VAC that responds to a lower vacuum level might be worth considering.

 

[jbojo]

Vacuum advance canister. Because I have a very lopey idle and sometimes it seems to "wander" a hundred rpm one way or the other, I'm thinking a VAC that responds to a lower vacuum level might be worth considering.

Yes I think that It'll help. My motor makes low vacuum too but I am able to simulate my needs by programming my ECU for the fuel system for the timing curve that I want. If I were still using a carb I would have put in a new vac advance on the distributor to compensate for the low vac. This is my distributor now, no springs, weights or vac can.

 

[Jeff73Mach1]

it looks lonely in there

 

[barnett468]

Vacuum advance canister. Because I have a very lopey idle and sometimes it seems to "wander" a hundred rpm one way or the other, I'm thinking a VAC that responds to a lower vacuum level might be worth considering.

If you have a holley style carb, set the gas level so it is just below the inspection hole at idle.

Plug your dist vac hoses.

Set your fuel mix screws to highest idle.

Reset idle speed.

With the car idling, advance the timing 4 degrees and see if the rpm goes up noticeably and if it still runs smooth.

Retard timing 4 degrees to previous level.

Rev engine to around 2200 rpm or 1.3rd throttle and advance timing 4 degrees and see if the rpm goes up noticeably and if it still runs smooth.

If the rpm goes up with both tests, leave it advanced 4 degrees and test drive it.

After drive, turn it off for 5 minutes then try to restart it . if it still turns over easily leave it there.

If your vacuum advance can is not adjustable, buy a standard moors products p/n VC31 or borg warner p/n V311 . summit sells the VC31 . any auto store can get either.

Set it to increase timing by 6 degrees . connect it to PORTED vacuum.

The Chevelle post is partially WRONG.

 

[Jeff73Mach1]

I'm currently connected to ported vacuum. I just backed off my timing a bit a few weeks ago to deal with a run on issue. My idle is smooth enough, it just sometimes seems to vary from day to day. It doesn't cause any problems nor do I have any flat spots or driveability issues.

I had a very talented builder tune my carb and distributor, but he is prone to setting up cars for the track rather than the street. I'll check with him id he changed the vacuum canister.

I'd be interested in your take on why the article is "partially wrong"

I was actually thinking of PMing you on a cam/ rear gear compatibility issue.

 

[barnett468]

No prob.

Run on is often caused by high float levels or having the throttle open to far and reducing the timing to cure it is often addressing a symptom instead of the root cause of the prob.

If your cranking compression is around 18 or more, i would try an autolite heat range 4 plug if your current plugs are hotter.

Also, high engine temps like above 195 can contribute to run on.

I would look at all these issues firsy . it is sometimes necessary to drill holes in the throttle plates to reduce or eliminate the problem.

Here's a tip . if you have vacuum at your ported vacuum port at idle, your throttle plates are open to far . if it dies when you close them more you need to increase the timing and/or drill holes in the plates.

One thing the article is wrong on is that is states that vacuum was connected to manifold vacuum for 30 or 40 years before the mfg's switched it to ported vacuum . well it was NOT . even the 1955 corvette had it connected to ported vacuum . there may be a few instances where this was the case but i have never seen it in my over 40 years of building cars for a living.

.

 

[Jeff73Mach1]

Well my throttle is set up with a solenoid and closes well, but I'll look again. My engine temps tend to run to the cool side. No vacuum at idle from the ported source. I don't recall which plugs are in it, I'll take a look this weekend.