engine and drivetrain Engine Idles at 2000rpm and exhaust pops on decel

[silasmoon]

So my car was just tuned before I got her to pass smog and probably needs a valve adjustment. I just changed the oil to VR1 20w50 with extra zinc.

The engine always loved to pop on decel from 4500rpm to 2000rpm (sounds like I ran over a 2 liter bottle). Today however I was poking around and was checking my throttle linkage and just gave her some gas in neutral. Later on I got in and she fired up without needing to give it any gas and idles at 2000rpms. I figured there was still some gas in the carb (32/36) and drove her around a bit. Popped like hell out of the exhaus during some spirited driving.

Was hoping to drive it this weekend. I likely have time to set the timing again trying for idle at 800-1000 at 8 degrees advanced and 3200rpm at max 35 advanced. I have a Bosch 0231170164 vacuum advance dizzy (stock on 49 state 76). Also have an electronic ignition installed. Otherwise engine is stock.

Thoughts and suggestions?

Edited February 19, 2016 by silasmoon

[Simeon]

Might be a silly question but are you describing the action of the fast idle with the choke?

[theNomad]

Perhaps you blipped the throttle and set it to higher idle? 
One pump and then fires up at higher idle until you blip it again and it goes back down.

Backfiring would be rich condition with exhaust leak?

[rstclark]

Sounds like an exhaust leak   I'd spend the time to adjust the valves and see what that does.  but it sound like it's been sucking  air for some time and you may want to check the smug on the exhaust manifold then the gasket from the manifold to the downtube  If tightening the bolts helps  go for it and change the manifold and downtube gaskets  they don't last forever  and sucking air back into the combustion chamber on decell is not really a good thing.

[silasmoon]

Might be a silly question but are you describing the action of the fast idle with the choke?

Not a silly question, as I am not sure what you mean exactly. I didn't inspect the choke, but it's possible it was stuck open or hasn't been set properly. I am just trying to make a laundry list of things to check once I get in there. 

[silasmoon]

Sounds like an exhaust leak   I'd spend the time to adjust the valves and see what that does.  but it sound like it's been sucking  air for some time and you may want to check the smug on the exhaust manifold then the gasket from the manifold to the downtube  If tightening the bolts helps  go for it and change the manifold and downtube gaskets  they don't last forever  and sucking air back into the combustion chamber on decell is not really a good thing.

What do you mean by checking the "smog on the exhaust manifold" - is there a vacuum pressure test I can perform? What's the best way to check for leaks on the exhaust manifold? 

[rstclark]

My Bad  with a typo   Smug should have been Snug   ie. tightness.  see if tightening all the nuts and bolts on the exhaust system helps   You may have to get under the car to reach the lower exhaust manifold nuts  and you will need at least a one foot extension for the ratchet to reach the manifold to downtube nuts  They should be copper and 14mm  you will need a deep 14 mm preferably an impact type that is less likely to slip on the nut.

[Simeon]

You have a 32/36 weber. If it doesn't have a manual choke then it will have either an electric or 'water' choke which will work automatically.

Correct starting procedure for a (working) auto choke is to stomp on the throttle once which closes the choke and sets it to a fast idle. The car should then start and idle at a higher speed (adjustable) until the choke element determines that the engine is warm enough.

As the car warms, operation of the throttle causes the carb linkage to move through a stepped cam which drops the idle speed.

Once the engine is warm, the choke plates will be fully open and the idle should be at the correct speed.

[Cyclone101]

Because race car...

[Hans]

I'd be looking at the fast idle mechanism as described above, and then I 'd be checking points condition, gap dwell and doing timing adjustment ASAP. 35 deg may be a bit too much for a stock setup - maybe back off to 30-32 to start, then add a bit if it doesn't ping and seems healthier.

[silasmoon]

The carb is a Redline K8205 Weber. I just realized this yesterday (only had the car for a week) and knew it likely had some sort of auto-choke mechanism. I will try to find the manual online and double check that today. The car also had a pertronix ignition installed, so points adjustments are out. A few extra questions - I am working all day and likely won't have time to do any big ticket items (tightening exhaust manifolds, futzing with the carb idle screws), but would like to drive it around this weekend again while my brother is in town.

1. Is it way too dangerous to set the timing by ear, if this is in fact the first time I've set the timing on this car? 
2. Is popping from the exhaust going to hurt anything? I know backfires with full fire balls can punch a hole in the exhaust and that some people actually prefer that pop! from an engine decel since it's more mean and grumbly race-car sounding. 

Side note - here is the 1986 California Document legalizing and setting stipulations for the Redline Weber 32/36 I found in my research online. 

Edited February 19, 2016 by silasmoon

[Mark92131]

I am fairly confident that most of your issues will go away when the car is setup properly.

 

If any of this seems beyond your current skill set, post a request for someone on the FAQ in the Bay Area to help you with these adjustment in exchange for the beverage of their choice.

 

1. I would start with the timing using a timing light to set it to 25 degrees at 1400 RPM using the flywheel ball, Basically you warm up the car, use the idle adjustment screw on the Weber to adjust the idle to 1400 RPM, disconnect the vacuum hose to the distributor and plug it, connect your timing light to the battery and the number #1 spark plug wire, slightly loosen the distributor, take a #2 pencil and stick the eraser down the timing inspection hole at the back of the engine to clean off the ball (you'll feel it hit), pull out the pencil and shine the timing light through the hole, if you are lucky the ball will be there jumping around, if not, slowly turn the distributor back and forth until the ball appears in the hole, when it does, re-tighten the distributor without moving it, hook up the vacuum line and go for a test drive to see if the backfire goes away.

 

2. Next, set your Weber Carb up for Best Idle using these instructions...  http://www.carburetion.com/Weber/adjust.htm.  If you can't get a best/fast idle with the carb's current jetting, could be #3, or you will need to make jetting changes.  Take if for a test drive, if still backfiring, see #3

 

3. Most likely an exhaust or vacuum leak somewhere.  Look for open/cracked vacuum hoses/connections, tighten exhaust/thermal reactor and intake manifold bolts, look for cracked manifolds, check all smog connections.

 

Good luck,

 

 

Mark92131

[silasmoon]

Alright - went out this morning to peek around again and pulled the air filter off for - GRATUITOUS WEBER SHOTS! Forgive the first handful of images, as I was trying to also document all the vacuum lines and setups. The last bunch should show a lot of detail for the weber currently. 

This morning the car was idling at around 1,000 again, so my guess is me playing Mr. Engineer with the car off, testing the throttle linkage, messed with the carb choke / idle / what-have-you and it decided to idle higher. This time around it was fine idling at 1,000 rpms when I didn't futz with it prior. I then of course began futzing with it once I took the air-filter off. When I pressed the throttle linkage down with the engine off, the butterfly valve (which was open) sprang closed with both wings closing at the same time and fully. 

So a few questions then:

• How does the electronic choke work exactly? What triggers it to come off and on? 
• When inspecting the vacuum lines I noticed that the intake manifold has some open holes in it - see here at the top right. What are those and should I plug them? And how to plug them?
• The vacuum line seems to be setup according to this weber spec. But I noticed my carb was connected via a t junction to the base of my air-filter as well as a cylindrical motor(?) on the driver's side wall of my engine bay that had a perforated end. You can see it here right above my brake fluid reservoir. What is that? A/C motor? should I unplug the vacuum?

I plan on doing the valves this weekend if I have time and then hitting up the timing. I need to get a new gasket for the job likely. Thanks everyone for the help as always! 

Edited February 19, 2016 by silasmoon

[Mark92131]

1. You have a water choke, when the engine is cold the butterfly valve will close when the throttle linkage is pressed, as the car heats up, the water heats up a bi-metal spring that slowly opens the butterfly valves.

2. That hole doesn't go all the way through the manifold, I think it was used to mount the dash pot on your original Solex Carb

3. That cylinder is your charcoal canister that absorbs fumes from your fuel delivery system.

 

 

Mark92131

[Mark92131]

This picture shows your idle adjustment screw, yours is screwed in way to far, which means the carb is not adjusted correctly.  You need to warm the car up and then turn it off and back this screw off until it just makes contact (moves) the brass lever, then turn it clock-wise 1.5 turns.

 

Then under the water choke housing (two water hoses attached to it) in the second picture is your idle mixture screw, you need to turn this screw clockwise until it barely seats, but not tight so you don't damage it, once it is seated, turn it out (counter clockwise) one turn.

 

Try and start you engine, it should idle really low and rough.  As long as it does idle, you can slowly turn the idle mixture in and out to achieve the best smooth idle, should be between 1.0 and 1.5 turns from seated, if not you may need to install bigger or smaller idle jets.  When you have the best fast idle, go back to the idle adjustment screw and adjust it so the car idles at 800 RPM.

 

You should be good to go.

 

 

Mark92131