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Weak/Plugged Idle Circuit
Posted by: TomW ()
Date: April 16, 2017 06:15PM

1962 Monza 102/4.
Been troubleshooting a coming-off-idle "lurch" for awhile.
Based on the March 2017 Tech Topics, I checked the Idle Circuit in both carbs.
Covering the Inlet of the Right-Side Carb stalls the engine.
Covering the Inlet of the Left-Side Carb sligtly slows the idle,
but completely blocking the air into the left carb, the engine continues to idle.

So, I assume a left-side Idle-circuit blockage which I'll try to clear tomorrow.

Question is:
The Right-side (Good-Side) has strong "suction" at the Carb inlet.
The Left-side (Bad-Side) has weaker "suction" at the Carb inlet.
Both sides have similar "suction" under higher Revs.4

Since each "Inlet Stroke" should be drawing 24 cu.in. of air per cylinder
on the left or right bank (whether or not they're firing)
why does the Left Bank (Bad) suction feel "weaker" than the Right Bank (good)??

Puzzled in Preston, CT.

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Re: Weak/Plugged Idle Circuit
Posted by: MattNall ()
Date: April 16, 2017 07:38PM

Carb's air flow is not equal / Balanced....

Do You know how to Balance the carbs? Have the Tool?





MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Weak/Plugged Idle Circuit
Posted by: Chilly Willy ()
Date: April 16, 2017 08:11PM

Definitely synch the carbs. Also look for a vacuum leak on the left side and check for throttle shaft play.



Will
Northern California

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Re: Weak/Plugged Idle Circuit
Posted by: TerribleTed ()
Date: April 16, 2017 08:20PM

I would first accelerate the engine to a mid throttle say 2500-3k rpmish and slap my hand over the weak carb a few times insta-blocking it. See if it makes a difference. This will sometimes dislodge debris causing this type problem. then I would try balancing with the Unison tool. If not fixed at that point time to pull the carbs and rebuild them.

Avid Corvair hobbiest since 1984. Have personally restored 20 or more Vairs a number of them ground up.

Located in the Atlanta Georgia area.

[www.facebook.com]

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Re: Weak/Plugged Idle Circuit
Posted by: Chilly Willy ()
Date: April 17, 2017 05:46AM

Not sure what you've tried so far, but a quick and easy. Is to raise the idle slightly on the left carb. Then adjust the mixture.if you don't get a response and no vacuum leaks. Then its internal.



Will
Northern California

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Re: Weak/Plugged Idle Circuit
Posted by: Chilly Willy ()
Date: April 17, 2017 06:05AM

Also, have you done a compression test?



Will
Northern California

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Re: Weak/Plugged Idle Circuit
Posted by: TomW ()
Date: April 17, 2017 07:44PM

I've Sync'd and Re-Sync'd the Carb several times.
Even built a test rig with a Vacuum Gage, Tee, (2)-Valves, and (2)-Hoses,
so I can hook-up to both Carbs and switch Left/Right Banks
by opening/closing the Valves.
Will work on the Left Carb idle circuit tomorrow.
Under power, both side are pulling and performance is good.



Edited 1 time(s). Last edit at 04/17/2017 07:45PM by TomW.

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Re: Weak/Plugged Idle Circuit
Posted by: Chilly Willy ()
Date: April 17, 2017 08:21PM

How did you synch the carbs if the left side has less vacuum ? I've learned the first thing to do is check the compression then for vacuum leaks.



Will
Northern California

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Re: Weak/Plugged Idle Circuit
Posted by: TomW ()
Date: April 18, 2017 12:44PM

Today, I cleaned-out the Left Carb Idle Tube using a piece of 0.020" Brass wire as described in the March "Communique" Tech Topics. That's all it took to solve the problem! Runs much better now.

Next I'll check for any vacuum leaks on the balance tube hoses and do a new Re-Sunc of the Carbs.

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Re: Weak/Plugged Idle Circuit
Posted by: MattNall ()
Date: April 18, 2017 01:05PM

Yup... although not in our FAQ's... that hasbeen discussed here many times...


Now tell us how you go about balancing the carbs..

Instructions are in our FAQ's... and in your case I think it's all in the crosslink adjustment...

The idle siphon tube has nothing to do with Total airflow thru the carb at idle or open throttle..





MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Weak/Plugged Idle Circuit
Posted by: Chilly Willy ()
Date: April 18, 2017 05:23PM

Nice!



Will
Northern California

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Re: Weak/Plugged Idle Circuit
Posted by: TomW ()
Date: April 19, 2017 06:24PM

During my post-cleanout test drive, I stopped at a local gas station to put a few gallons in the tank. Of course, the Corvair attracted some attention.

I learned that this station sells 110-Octane Leaded Gas!!!
Only (1) problem: It costs $10/gallon eye popping smiley
I asked them how the State of CT allows them to sell it.
They said:
"We can't pump it into a car. We must pump it into a gas can."
"After you drive-off with that can, they/we don't care what you do with it"

So, here's my thinking:
#1. Get (2)-gallons of 110 Octane Leaded.
#2. Mix (1)-gallon on 110 Octane with (4)-gallons of 93 Octane Unleaded.
That should give me (5)-gallons of 97 Octane sorta-leaded gas that my 102Hp should LOVE!

Any thoughts on this????

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Re: Weak/Plugged Idle Circuit
Posted by: MattNall ()
Date: April 19, 2017 06:30PM

Foolish thought!!

Our engines have never needed LEAD as with all aluminum heads..... STEEL Valves eats... not soft cast iron..

And current 93 octane / R+M/2 is more than adequate...

Have you "decarbonized" your engine yet?


Also you still haven't fixed your airflow problem!!

Tell us your procedure / hook up for Balancing airflows...





MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Weak/Plugged Idle Circuit
Posted by: BobV66Vair ()
Date: April 20, 2017 09:50AM

De carbon the engine. While HOT and running, put some Marvel Mystery Oil down each carb. It will smoke like crazy but that's just the carbon burning off. I used to put about a quart into the full fuel tank and burn through that too. In the old days, cold water was used. I cannot imagine that is good for an aluminum engine though.

Sync them.

Bob Vinnacombe
Sandy, Oregon
1965 Corsa 140 stock
1966 Monza Soon to be race car
1968 Monza Parts for now

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Re: Weak/Plugged Idle Circuit
Posted by: corventure Dave ()
Date: April 20, 2017 12:20PM

Go to "search" here.
Look for... Often overlooked on a carburetor rebuild...Tip.

Corventure Dave

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Re: Weak/Plugged Idle Circuit
Posted by: TomW ()
Date: April 24, 2017 12:23PM

Tell us your procedure / hook up for Balancing airflows...

I've attached a couple photos of my Carb Balance rig.
Single Vacuum Gauge that tees-off thru (3) valves to (3) hoses.
One hose to Left Carb Choke Pulloff port; one hose to Right Carb Choke Pulloff port.
Third hose to Vac Balance Tube port.
Easy to change measurement port by opening/closing valves.

Did a re-balance after cleaning-out the Carb Idle Tubes w/ 0.020" brass wire.

Setup:
1. Warm-up to normal operating temp.
2. Hookup Carb Balance Rig.
3. Disconnect/plug Vacuum Advance Hose.
4. Check Dwell and Timing.
5. Disconnect Cross-shaft Link at Left Carb.

Initial Readings:
1. 900 RPM
2. Left Carb: 19" Vac
3. Right Carb: 17" Vac.

Adjustments:
1. Adjusted Left Carb Idle Speed screw for 18" Vac
2. Adjusted Right Carb Idle Speed screw for 17.5" Vac
3. Idles at 900 RPM
4. Backed-out both Idle Speed Screws to reduce Idle to 700 RPM (I set idle a little high)
5. Left Bank = 18" Vac; Right Bank = 17.5" Vac.
6. Adjust Left & Right Idle Mix screw for best idle (*)
(*) Halfway between Too Rich and Too Lean; look for highest Vac reading.
7. Reconnect Cross-shaft Link to Left Carb (**)
(**) Had to lengthen (1) turn to align to Cross-shaft Lever

Disconnect Carb Balance rig and reconnect Vac Advance Hose & Test Drive moody smiley

Note that I do not use the yellow plastic Caps on the (2) unused Vacuum Ports
because they LEAK! For the Left Carb horizontal port and the Vacuum Balance
Tube port, I use a 2" length of Vacuum Hose with a plug made from round bar.

Attachments:

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Re: Weak/Plugged Idle Circuit
Posted by: MattNall ()
Date: April 24, 2017 01:05PM

With that setup you are as close as you can get!


Why many of us use a Unisyn is because it measures ABOVE the throttle plate, thereby eliminating the Balance tube...


You might try disconnecting one side of the balance tube and plugging it and the tube on that head.... see what difference that makes..for a test...





MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Weak/Plugged Idle Circuit
Posted by: JimBrandberg ()
Date: April 24, 2017 02:30PM

I use Sea Foam instead of Marvel's Mystery oil for carbon treatment down the carbs.
I would want to run to run a 102 on 89 octane, maybe 91 if I wasn't driving it much. 110 is for high compression race engines.
Jim Brandberg
Isanti, MN
CorvairRepair.com

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Re: Weak/Plugged Idle Circuit
Posted by: TomW ()
Date: April 24, 2017 06:25PM

You might try disconnecting one side of the balance tube and plugging it and the tube on that head.... see what difference that makes..for a test...

Matt:
I'll give it a try!
I'm not sure that the Vac Balance Tube is really needed, except as an input to the Powerglide Vacuum Modulator. Think it's unnecessary for a stick shift.

I would want to run to run a 102 on 89 octane, maybe 91 if I wasn't driving it much.

Jim:
I always run 93-Octane Sunoco in my 102/4.
I buy 5-gallons at a time and add (1)-Oz of Blue Sta-Bil, and
(5)-Oz of TechRon to each 5-gal.
I drive less than 1000 miles a year (April thru October), so 5-gallons could
last me a month of driving.
The idea of adding 110-Octane was to allow more spark advance at minimal cost,
with less chance of ping/detonation.
I know that I don't need the lead in the gas.

At the Oil/Filter Change last Fall, I went to BradPenn 10W30 Semi-Synthetic.
So far, the "102" sounds better, runs better, and (for the first time) it
started-up in April 2017 with NO rapping Lifters!
I know that it's all "seat of the pants" judgement but
I've run 20W50, 10W40, and 10W30 "Dino"-oil (Castrol-GTX) for years, and
this change to Semi-Synthetic is the most dramatic change I've seen.



Edited 1 time(s). Last edit at 04/24/2017 06:28PM by TomW.

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Re: Weak/Plugged Idle Circuit
Posted by: MattNall ()
Date: April 24, 2017 07:15PM

The Balance tube is there so you do not have to have the carbs in Perfect balance.


A Turbo engine has no B/T...one carb!





MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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