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Misfire above 1/4 throttle
Posted by: joelsplace ()
Date: January 29, 2019 11:56AM

'61 Wagon automatic. Unknown engine PO said it's a 110. Has '61 chokes but unknown carburetors other than that.
Idles great and is very peppy up to about 1/4 throttle. Misfires pretty badly above that. Runs good at about 50mph but any more throttle and it misfires progressively worse.
What should I be looking for when I tear into the carburetors? I've never had this symptom before on one that runs so flawlessly below 1/4 throttle.
It has a Pertronix 1 and it ran the same with points.

Joel
Northlake, TX
4 Ultravans, Lost count at 100 Corvairs...

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Re: Misfire above 1/4 throttle
Posted by: 7004doorL ()
Date: January 29, 2019 11:57AM

Secondary Ignition?

Mike 1960 4 Door
80 HP PG

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Re: Misfire above 1/4 throttle
Posted by: TerribleTed ()
Date: January 29, 2019 12:13PM

Fist thing is to find out exactly what the engine is. Look at the block and head numbers to determine this. Next check the distributor. Is it correct for the engine? (could be getting too much advance perhaps causing detonation/misfire). How is the ignition system wiring, and coil? Low voltage or weak coil to the ignition could cause an issue like this. Could also be leaning out do to a carb or fuel flow issue? Start with the basics and re-check and verify everything one step at a time.

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

Avid Corvair hobbiest since 1984.
I have personally performed ground up restoration on over 20 Corvairs.
I currently work full time at restoring and repairing Corvairs.
Located in the Atlanta Georgia area.
[www.facebook.com]

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Re: Misfire above 1/4 throttle
Posted by: joelsplace ()
Date: January 29, 2019 12:21PM

More information:
It wasn't running great before so I set the idle mixture and balanced the carbs. I noticed that one venturi cluster has a broken finger so I replaced that and then balanced it again. Took it on about a 20 mile trip down the highway and it ran perfectly. Stopped for gas and then this started.
Good thoughts on advance and timing but with this extra information I doubt that is the issue unless a spring broke. Worth checking anyway since I don't know what I have. I have looked at the plugs and they look good.
I think my fuel flow is fine because it has an electric helper pump with the stock pump. It runs the same with the electric pump on or off. I guess it's possible the electric pump is bad. It will fill the carburetors when they are dry.
Thanks!

Joel
Northlake, TX
4 Ultravans, Lost count at 100 Corvairs...

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Re: Misfire above 1/4 throttle
Posted by: RobertC ()
Date: January 29, 2019 01:46PM

Basically, everything Ted stated...

Carb filters been replace?

And, carbs should be a matched pair, jets, cluster



Edited 1 time(s). Last edit at 01/29/2019 01:47PM by RobertC.

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Re: Misfire above 1/4 throttle
Posted by: joelsplace ()
Date: January 29, 2019 02:05PM

I don't think miss-matched parts are the issue. It ran great for a little while.
I haven't looked at the carb filters yet.

Joel
Northlake, TX
4 Ultravans, Lost count at 100 Corvairs...

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Re: Misfire above 1/4 throttle
Posted by: JohnVan ()
Date: January 29, 2019 03:16PM

joelsplace Wrote:
-------------------------------------------------------
> I don't think miss-matched parts are the issue.
> It ran great for a little while.
> I haven't looked at the carb filters yet.

It sounds to me like some small piece of dirt, gasket or something is blocking the fuel flow in one of the carbs. Something in the high speed circuit?

Ignition issues can be a bear in that they can create symptoms that "feel" like carb issues. I had problems with my Corsa sputtering and backfiring through the carbs at certain speeds. Turns out it was an intermittent ground on the ignition points plate. I ended up changing over to a Pertronix ignition which had a new plate and a separate ground wire and have not had any problems since.

The thing that finally tipped me off was I was able to vary the engine speed while watching the distributor vacuum advance. When the advance moved a little I'd sometimes get the misfire. The vacuum advance moves the points plate.

My rule of thumb is that a misfire that comes on suddenly and is somewhat intermittent is likely ignition while a misfire that is more consistent is likely fuel (carb) related.

...but I've been wrong before smiling smiley

John Van Valkenburgh
Knightdale NC
'65 Corsa 140

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Re: Misfire above 1/4 throttle
Posted by: TerribleTed ()
Date: January 29, 2019 05:09PM

If it was running well and this just started something changed it could very well be some crap in a carb.

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

Avid Corvair hobbiest since 1984.
I have personally performed ground up restoration on over 20 Corvairs.
I currently work full time at restoring and repairing Corvairs.
Located in the Atlanta Georgia area.
[www.facebook.com]

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Re: Misfire above 1/4 throttle
Posted by: MattNall ()
Date: January 29, 2019 05:28PM

Please change the coil.... so easy!





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: Misfire above 1/4 throttle
Posted by: 63turbo ()
Date: January 29, 2019 05:37PM

Too wide of a plug gap can also cause that.

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

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]
My new fan! [corvaircenter.com]
engine less 62 Spyder
Canadian 64 Monza Parts car



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Re: Misfire above 1/4 throttle
Posted by: Ratt643 ()
Date: January 29, 2019 05:42PM

MattNall Wrote:
-------------------------------------------------------
> Please change the coil.... so easy!


What Matt said, change the coil. Sounds like a voltage drop off to me. Even if one carb wasnt getting fuel, the engine would still rev above 1/4 throttle, just not very well..


1964 Monza Coupe

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

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Re: Misfire above 1/4 throttle
Posted by: Ratt643 ()
Date: January 29, 2019 05:50PM

The coil could be the cause of your tachometer problem also.


1964 Monza Coupe

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

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Re: Misfire above 1/4 throttle
Posted by: RexJohnson ()
Date: January 29, 2019 06:28PM

Something else to try if it acts like you are running out of fuel is to by-pass one of the fuel pumps. Most of the time you can run pumps in series but sometimes the second one will restrict flow. I had a '63 that could only get to about 55 mph but otherwise ran good. A coworker told me about a motorhome he had with the same problem and that it was the two pumps in series. I by-passed the mechanical one and it ran great at all speeds.

RJ tools
Salem,Oregon

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Re: Misfire above 1/4 throttle
Posted by: vairmech ()
Date: January 29, 2019 06:28PM

Here's my 2c!

This sounds very much like a plug or a wire breaking down under pressure. Especially since it is repeatable at a specific throttle position.

Ken Hand
Handy Car Care
248 613 8586

Vairmech@aol.com

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Re: Misfire above 1/4 throttle
Posted by: vairchet ()
Date: January 29, 2019 07:16PM

Could be stock resistor wire is breaking down. Suggest bypassing stock resistor and install an external resistor such as this: [www.ebay.com]

Chet in Ramona

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Re: Misfire above 1/4 throttle
Posted by: American Mel ()
Date: January 29, 2019 08:33PM

A LOT of good suggestions on here.
BUT, you really should try the simplest ones first.
Do what Matt & Rex said, if that does not take care of the problem them move on to the next item that is cheapest or easiest for you to do.
But I would start with those two since they are not HIGH $$$ or difficult at all.

.
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
WA. state, 1 mile south of the Canadian border,
I am not at the end of the world, but you can see it from here.
'66 Monza Coupe - 4spd, 140 Daily driver beater
'67 Monza Vert. - PG, 140 Daily driver beater
'67 A/C Moredoor Monza - 140 4-spd. driver

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Re: Misfire above 1/4 throttle
Posted by: MattNall ()
Date: January 29, 2019 09:16PM

Don't forget the Resistance wire...as Vairchet mentioned... it's over 50 years old is as just a small/weak heater...





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: Misfire above 1/4 throttle
Posted by: Frank DuVal ()
Date: January 29, 2019 09:26PM

If it is not backfiring through the carb, drop a capful of gasoline in each carb while it is misfiring and see if it improves or gets worse. Or add propane.

Watch engine run in the dark (not so dark you can not safely rev throttle) and see if there are sparks from ignition parts.

Frank DuVal

Fredericksburg, VA

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Re: Misfire above 1/4 throttle
Posted by: The Stig ()
Date: January 29, 2019 09:38PM

Ignition switch?

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Re: Misfire above 1/4 throttle
Posted by: joelsplace ()
Date: January 29, 2019 10:13PM

I'll try to check some of these things tomorrow. Thanks!

Joel
Northlake, TX
4 Ultravans, Lost count at 100 Corvairs...

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