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I have a problem I can not solve. confused smiley
Posted by: red64vair ()
Date: March 10, 2017 02:46PM

I have posted this problem before but since I have investigated farther I am posting it again.

Since rebuilding A 65 110 engine with everything new except the crank and valve seats I have had a miss and suck-back at the exhaust. I have tried everything I can think of to find the problem with no success. This is most noticeable at idle and up to about 60 mph. I think engine rpm is high enough at 60 that I just don't notice it. Driving at a steady speed it produces a lunging effect. The problem goes away with heavy acceleration at any speed but returns with steady speed or deceleration.

My efforts to solve this are.

1. Readjusted valves. Even ran them loose to the point of click.

2. Replaced all components of ignition system.

3. I have tried AC 44ff and Bosch 7902 plugs gaped at .030. Currently running
Bosh and they appear very slight straw color.

4. Timing at 14 Deg.

5. Points dwell 31-32 Deg.

6. Checked rebuilt harmonic balancer markings still aligned.

7. Replaced fuel pump and Carburetors. Jet size is.051. Already had new tank
and lines.

8. Fuel pressure 2-3 lb.

9. No vacuum leaks.

10. Pulled engine and verified cam and crank gear timing marks aligned and key
position correct.

11. Verified no shearing of cam or crank gear key.

12. No worn down cam lobe.

13. Removed heads and returned to rebuilder. Rebuilder said no problems
but did lap valves.

14. Before reinstalling I tested valve to seat seal by filling with lacquer
thinner and had only one valve show a slight leak.

15. Recently I pulled the engine to installed new piston rings because the
previous rings did not seat well. While I had it apart I installed another
set of heads because I still suspected that was where the problem was.
No luck, the problem still exist.

16. Recent compression test four at 150 one 145 one 130. Rings probably not
well seated yet. Only about 200 miles on them.

17. Cylinder pressure test on compression stroke with exhaust manifolds off
indicated a slight leak at all exhaust ports. I could not detect a leak
through the carburetors. There was more leakage by the rings than exhaust
or intake.

18. Engine vacuum at idle connected to both choke pull off ports is 11"-12".
Pinching either side tube gives a needle flutter. At 2000 rpm needle is
steady at 17". Pinching either side tube drops vacuum to a steady 15"

19. Very little difference shorting spark plugs.


Could a cam lobe be ground wrong or the key machined out of correct location? The cam is Clarks C785. Clarks said they had not had any complaints with that cam.

Larry Blaylock
Saltillo, Mississippi
64 convertible
66 customized Corsa coupe


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Re: I have a problem I can not solve. confused smiley
Posted by: MattNall ()
Date: March 10, 2017 03:02PM

Even though you've changed heads.... weak exhaust vale spring.... the suckback tells the tale, and you checked valve sealing..





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: I have a problem I can not solve. confused smiley
Posted by: Brizo ()
Date: March 10, 2017 03:03PM

Its tough to diagnose this since we cant feel it, but the symptoms that get my attention are :"lunging effect at steady speed" and "goes away on acceleration" and "fuel pressure 2-3 lbs" It sounds like a lean surge. The first thing I would try is increase the main jets to 53 or 54, A/O, increase the fuel pressure. The pressure/ output may be erratic and dropping at speed.

Dan Brizendine,
'64 8door Greenbrier 140 PG. "In beautiful Wanamaker Indiana...with one stop light and 5 pizza shops"

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Re: I have a problem I can not solve. confused smiley
Posted by: Ratt643 ()
Date: March 10, 2017 03:28PM

Agree with Brisk, go up two jet sizes and see if the surge goes away. As Matt mentioned, you may have weak exhaust valve springs. Sounds like you have had two separate problems. I would change jets first and see what happens.


1964 Monza Coupe

Maryville, TN
U.S. 129 The"Tail Of The Dragon"

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Re: I have a problem I can not solve. confused smiley
Posted by: BobV66Vair ()
Date: March 10, 2017 03:44PM

Could there be a problem in the carb(s)? Erratic delivery of fuel at idle could be a dirty idle circuit couldn't it?

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: I have a problem I can not solve. confused smiley
Posted by: Wagon Master ()
Date: March 10, 2017 03:53PM

Can you get the miss/suckback to happen in neutral in the garage? Tell us what the vacuum gauge readings are at that point. Any Chilton's auto repair manual will have several pages of vacuum gauge readings and procedures in the troubleshooting section. Should be able to pin it down from there.

'64 Monza Coupe 140 4 speed
'61 700 Lakewood 95 4 speed
'69 Monza Convert. 140 Auto.

Been aircooled since 1973
Northwest Ohio

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Re: I have a problem I can not solve. confused smiley
Posted by: kenzen ()
Date: March 10, 2017 06:05PM

Out of sequence firing? (plug wires swapped?)

kenzen
66 Monza Coupe 110/PG
Bel Air, MD

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Re: I have a problem I can not solve. confused smiley
Posted by: 66vairman ()
Date: March 10, 2017 06:19PM

BEFORE you change the jets you need to verify your fuel pressure with a different gauge.

Non-turbo carbs have a float setting based on the man. spec. of 4-5 PSI. At 2-3 PSI you could have a lean run and surging due to low fuel levels in the bowl.

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Re: I have a problem I can not solve. confused smiley
Posted by: red64vair ()
Date: March 10, 2017 06:23PM

Changing jet size is one thing I have not tried but I will. I hadn't considered too lean of a mixture because the exhaust always smelled rich and the spark plugs were always black but that may have been burned oil. The first set of heads had Clarks new springs. When I sent those heads back to the shop I asked him to test the springs and he said all was ok. The engine does miss and suck-back at Idle with a vacuum reading of 11-12. Idle jets are on either carburetor will kill the engine if screwed in too much and run very rough if screwed out too much.

Before new rings the exhaust tubes were black now they are white. The spark plug photo was after a 20 minute drive

Larry Blaylock
Saltillo, Mississippi
64 convertible
66 customized Corsa coupe


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Re: I have a problem I can not solve. confused smiley
Posted by: MattNall ()
Date: March 10, 2017 06:27PM

Yup too lean...

Also you may need to raise the floats....very common with our current gasolene....but nothing to do with Ethanol...





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: I have a problem I can not solve. confused smiley
Posted by: jjohnsonjo ()
Date: March 10, 2017 06:31PM

Get the fuel pressure up to 4-5 first. Most folks say a turbo should run at 2, mine like 3.5 or I get lean surge.

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa

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Re: I have a problem I can not solve. confused smiley
Posted by: red64vair ()
Date: March 10, 2017 06:44PM

Float level 1 1/16. Fuel 97 octane Ethanol free.

Larry Blaylock
Saltillo, Mississippi
64 convertible
66 customized Corsa coupe


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Re: I have a problem I can not solve. confused smiley
Posted by: Lane66m ()
Date: March 10, 2017 07:26PM

His is a 110. But agree he checked pressure being delivered to carbs at 2-3 psi. I would deal with new carb filters first.

Al Lane
Ellabell GA

1966 Monza Coupe, 110 hp, 4 Spd
1966 Corsa Turbo Coupe, 180 hp 4 Spd
1964 Greenbrier Deluxe, 6 dr, 80 hp car engine, PG
2015 Chevrolet Malibu 2LT
2015 GMC Sierra SLT Crew Cab
1968 Camaro SS Coupe 350 CI 295+ HP PG
1947 Farmall A tractor 15 hp


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Re: I have a problem I can not solve. confused smiley
Posted by: Frank DuVal ()
Date: March 10, 2017 08:46PM

2-3 psi sounds low. Take out the regulator to test. Only YHs really might need a regulator, unless you got a bad fuel pump. I know no club members here running a fuel regulator on their Rochester carbureted Corvair.

Check vacuum at the balance tube. Only easy to do on Powerglide, need adapters on manuals, or you can join both choke pull off hoses to one gauge. 11 to 12 sounds really low for idle, but that might just be the three cylinder reading.

Frank DuVal

Fredericksburg, VA

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Re: I have a problem I can not solve. confused smiley
Posted by: Max Roeder ()
Date: March 11, 2017 01:27AM

Long shot here but you mention a head shop that does work for you. If by chance the guides were changed/ sleeved and or spring seats were not spot faced with new centerline or checked with old, your valves may not be seating properly under load. I have this thing about bad head work!

Newly installed springs on "seated" valves on the bench can appear to seal but when the valves start getting hot and rotating a spring rotating and pulling unevenly can cause a valve to "wobble" in it's seat. Will also cause early guide wear.

Does sound more like a lean issue though so I would pursue that line of thought first. You did mention "miss" in your original post. A misfire is usually a lean issue but can be an after fire or a backfire. If you have anyone with an O2 sensor on a probe and can insert it into your tailpipe you may find a A/F to be above your target (above choke temp) idle of somewhere in the 12's maybe.

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Re: I have a problem I can not solve. confused smiley
Posted by: Bob Helt ()
Date: March 11, 2017 01:32PM

Larry,
It sounds like a bad vacuum advance can to me. Pull and plug the hose going it and see what happens.
Bob Helt

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Re: I have a problem I can not solve. confused smiley
Posted by: Spectre ()
Date: March 12, 2017 10:14AM

Bob Helt Wrote:
-------------------------------------------------------
> Larry,
> It sounds like a bad vacuum advance can to me.
> Pull and plug the hose going it and see what
> happens.
> Bob Helt

I agree with Bob, I've had bad VA's cause a weird steady state cruise pulsation.

David Clamp


1965 Corsa convertible - 140 4spd/3.55/AM-FM

2013 Mustang GT convertible - 5.0, 6spd auto, Procharger i-1

2003 Miata SE - 6spd manual (wife's toy)

"Victory is mine!" - SG

Warner Robins, GA (15 miles south of Macon)

Click for Warner Robins, GeorgiaForecast


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Re: I have a problem I can not solve. confused smiley
Posted by: red64vair ()
Date: March 15, 2017 06:48PM

I installed .053 carburetor jets, increased fuel pressure to 5# and verified that vacuum advance was working properly. Missing problem still exists.

Larry Blaylock
Saltillo, Mississippi
64 convertible
66 customized Corsa coupe





Edited 1 time(s). Last edit at 03/15/2017 06:49PM by red64vair.

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Re: I have a problem I can not solve. confused smiley
Posted by: 63turbo ()
Date: March 15, 2017 06:58PM

Try running without the va hooked up, next easiest thing to try!

------------------------------------

Kevin Nash
Friday Harbor Washington
63 Spyder, Daily driver, EFI read about my project here: [corvaircenter.com]
first test start on EFI here:[www.youtube.com]
first official EFI boost test here:[www.youtube.com]
engine less 62 Spyder
Canadian 64 Monza Parts car



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Re: I have a problem I can not solve. confused smiley
Posted by: MattNall ()
Date: March 15, 2017 07:03PM

Ill 2nd that!





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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