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Set carb idle mix, now hesitation, advice?
Posted by: Mark M ()
Date: September 15, 2011 08:05AM

Finally fixed the hang-up on the left carb linkage. Balanced following the Handy video, setting initial idle and then adjusting the swivel on the left carb until balance was correct. Perfect and it ran great! Wasn't happy with how this method seems to twist and torque the cross shaft some (somehow that doesn't seem right), so started over last night and balanced again by checking vacuum, disconnecting the left carb swivel, adjusting the idle speed screw and adjusting and reconnecting swivel to test vacuum until carbs were balanced. Had to adjust right carb once to get it right. At 1100-1200 RPM carbs are within 1", right side just slightly higher. Idles at 550-600.

At idle, the left carb idle speed screw is just touching the throttle lever - maybe 1/2 turn in - and right is about 1 1/4 or so. When I put my hands on top of carbs at idle, left carb has noticably less vacuum. But, reading is balanced at 1200 RPM.

I set the idle mix screws per instructions and think I got it pretty good. In until stumble, out very slowly until no additional increase in RPM, in 1/16 to 1/8 turn. Idles smoother and engine seems more quiet. Dwell is 32, vacuum advance working, no vacuum leaks and accel pumps are good. But, on acceleration - especially at the lower end of RPM range - I get a hesitation. It's just for a split second. I know it's not point bounce. Wasn't there before this last adjustment.

So, do I need to get better at setting idle mix, or maybe go back to the Handy method of balancing?

Mark M
Project: 64 Spyder Vert running 80 hp heads and carbs
1st Vair: 65 Corsa 140
St. Louis, MO
Show Me Corvair Club &
CORSA member

"If it's not broken, you're not driving it hard enough"

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Re: Set carb idle mix, now hesitation, advice?
Posted by: MattNall ()
Date: September 15, 2011 08:09AM

Change you balancing method... suction should be thesame





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: Set carb idle mix, now hesitation, advice?
Posted by: Mark M ()
Date: September 15, 2011 02:24PM

ggg....somehow, I knew you would say that.

Mark M
Project: 64 Spyder Vert running 80 hp heads and carbs
1st Vair: 65 Corsa 140
St. Louis, MO
Show Me Corvair Club &
CORSA member

"If it's not broken, you're not driving it hard enough"

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Re: Set carb idle mix, now hesitation, advice?
Posted by: cnicol ()
Date: September 16, 2011 10:38AM

I have only one thing to say...grinning smiley

Click here!

Craig N. Coeur d'Alene ID.
66 Black Monza 4dr, 4.2L V8 49k
61 Seamist Jade Rampside 140 PG
60 Monza coupe (sold, sniff sniff)
66 Sprint Corsa convt - First car! Re-purchased 43 years later
2+2 gnatsuM 5691

+17 Tons of parts

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Re: Set carb idle mix, now hesitation, advice?
Posted by: Mark M ()
Date: September 16, 2011 11:38AM

cnicol Wrote:
-------------------------------------------------------
> I have only one thing to say...grinning smiley
>
> Click here!

Aw heck! Before I do that I will go back to my homemade yadrdstick manometer. ggg

Mark M
Project: 64 Spyder Vert running 80 hp heads and carbs
1st Vair: 65 Corsa 140
St. Louis, MO
Show Me Corvair Club &
CORSA member

"If it's not broken, you're not driving it hard enough"

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Re: Set carb idle mix, now hesitation, advice?
Posted by: bill darcy ()
Date: September 16, 2011 12:32PM

I'm curious why there is that much difference in the idle speed screws.If I am reading this right left side 1/4 turn right side 1-1/2 turns.You may be slightly uncovering the transition slot in the right carb which makes mixture adjustment difficult.I have seen many carbs where the throttle plates will not close completely even after the speed screw is backed off the stop.Most of our carbs have been subjected to at least one overhaul, some good some not so good in their lifetimes.I make it a practice to check by holding the carb up to light with the speed screw backed off the stop to assure plates are fully closed.Many times I've had to loosen the plate screws slightly to center the plate in the throttle bore.It can also be the case that the throttle lever on one side is bent.Never discount anything on a 40+ year old car.From many years of Triumph,MG,Jaguar ownership I still use a 3ft length of heater hose to the ear to balance carbs although I do own a unisyn just don't use it often.I also don't quite understand the twist,torque cross shaft thing.Should't be tension on the cross shaft if everything is aligned properly.Maybe I'm just misreading what you're saying.Hope this helps some.

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Re: Set carb idle mix, now hesitation, advice?
Date: September 16, 2011 01:58PM

I have the same problem with hesitation. All of the electrical parts are new and the carbs have been rebuilt. I assume I need to set up the carbs as per the above discussion. What causes the hesitation...idle speed, mixture or balance?.

Corey Pedersen
Amston, CT
1962 Monza 102 HP Convertible - Restoration Complete
1964 VW Beetle - Restoration Complete
1981 Chevy C-20 - Better Than New!
1951 MG-TD - Newest Addition
Member of Bay State Corvairs and CORSA

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Re: Set carb idle mix, now hesitation, advice?
Posted by: cnicol ()
Date: September 16, 2011 02:04PM

connecticutcorvair Wrote:
-------------------------------------------------------
> I have the same problem with hesitation. All of
> the electrical parts are new and the carbs have
> been rebuilt. I assume I need to set up the carbs
> as per the above discussion. What causes the
> hesitation...idle speed, mixture or balance?.

Balance can be a factor but more commonly it's a lean condition caused by inadequate accelerator pump volume or late pump timing or low float level.


To some extent, you can check the pump volume and timing by observing the accelerator pump ouput as the throttle is advanced.

Craig N. Coeur d'Alene ID.
66 Black Monza 4dr, 4.2L V8 49k
61 Seamist Jade Rampside 140 PG
60 Monza coupe (sold, sniff sniff)
66 Sprint Corsa convt - First car! Re-purchased 43 years later
2+2 gnatsuM 5691

+17 Tons of parts

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Re: Set carb idle mix, now hesitation, advice?
Posted by: Mark M ()
Date: September 19, 2011 07:53AM

confused smiley Okay, I am crazy or stupid, or both.

Went at the balance again this weekend. Driver side linkage unhooked, set both idle speed screws 1 1/2 turns in after contact with lever. Idles at 550 - 600. Using hand on carb method, adjust right and left slightly to get them as close as possible. Connect right linkage, adjust left swivel until it just goes in hole on lever. Hook up vac gauge to both choke pull offs with a "T".

At idle, with both carbs pulling on the gauge, reading is 14. Rev to 1200 and reading is steady just above 16. Pinch either off at idle and the needle varies too widely to pick a center point. Rev to 1200 and pinch one side at a time, left is 15 and right is 18. Swap the vac lines just to be sure something is not stuck in a hose and get same result.

Pull vac gauge and hook up homemade manometer with 6" of water in each side. Bingo, almost perfect balance at idle. Tweak it just some. Rev to 1200 and water on right side pulls up 4 or 5". Matt's instructions say, "Water level is HIGHER on the right. Back out IDLE SPEED screw on RIGHT carb." I do that at 1200 rpm and the water on the right goes higher. That makes sense to me since the throttle plate would close off and the carb would pull more vacuum from the choke pull-off. Typo on Matt's instructions? I return the idle speed to where it is balanced at idle. Idles great and runs well.

I can get the carbs in balance at 1200 rpm, but only if the left carb is backed off of idle almost completely. Doesn't make sense. I'm hoping to get away for HACOA Corvair Round Up. Maybe somebody there will see the problem I am missing.

I adjusted valves cold a year or so ago. Adjusted left side hot when checking for something else. Any chance I could have the right side so off that it is causing the problem?

Mark M
Project: 64 Spyder Vert running 80 hp heads and carbs
1st Vair: 65 Corsa 140
St. Louis, MO
Show Me Corvair Club &
CORSA member

"If it's not broken, you're not driving it hard enough"

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Re: Set carb idle mix, now hesitation, advice?
Posted by: MattNall ()
Date: September 19, 2011 08:08AM

Your engine is weird!!!


Disconnect Both Downlinks and try again..





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: Set carb idle mix, now hesitation, advice?
Posted by: Mark M ()
Date: September 19, 2011 08:22AM

MattNall Wrote:
-------------------------------------------------------
> Your engine is weird!!!>
> Disconnect Both Downlinks and try again..

Ain't that the truth! I think I did that once, but will give it another shot.

You sayin' your instructions are not a typo?

Mark M
Project: 64 Spyder Vert running 80 hp heads and carbs
1st Vair: 65 Corsa 140
St. Louis, MO
Show Me Corvair Club &
CORSA member

"If it's not broken, you're not driving it hard enough"

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Re: Set carb idle mix, now hesitation, advice?
Posted by: cnicol ()
Date: September 19, 2011 08:23AM

I have only one thing to say... (again)
Cheaper this time...

Craig N. Coeur d'Alene ID.
66 Black Monza 4dr, 4.2L V8 49k
61 Seamist Jade Rampside 140 PG
60 Monza coupe (sold, sniff sniff)
66 Sprint Corsa convt - First car! Re-purchased 43 years later
2+2 gnatsuM 5691

+17 Tons of parts

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Re: Set carb idle mix, now hesitation, advice?
Posted by: Mark M ()
Date: September 19, 2011 08:25AM

cnicol Wrote:
-------------------------------------------------------
> I have only one thing to say... (again)
> Cheaper this time...

Did that too - way back. Why would the results be any different than with my manometer?

Mark M
Project: 64 Spyder Vert running 80 hp heads and carbs
1st Vair: 65 Corsa 140
St. Louis, MO
Show Me Corvair Club &
CORSA member

"If it's not broken, you're not driving it hard enough"



Edited 1 time(s). Last edit at 09/19/2011 08:26AM by Mark M.

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Re: Set carb idle mix, now hesitation, advice?
Posted by: MattNall ()
Date: September 19, 2011 09:24AM

They won'y be... but you have something strange going on... some part of the carb / linkage is being held.





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: Set carb idle mix, now hesitation, advice?
Posted by: bill darcy ()
Date: September 19, 2011 12:23PM

From what you've described and all the carb adjustments made I would seriously consider rechecking valve adjustment.Low vacuum signal usually indicates valves that are too tight.Adjusting one bank by a different method than the other bank can lead to different results.Yes I'm old school and yes it's messy but I've been adjusting them running for well over 40 years and find it most effective as it allows all dimensions to stabilze.Course I also think that everythings a hammer except a screwdriver...thats a chisel.

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Re: Set carb idle mix, now hesitation, advice?
Posted by: Mark M ()
Date: September 19, 2011 12:47PM

Bill,

I was thinking the same thing, except it's the left carb that is showing low vacuum and that's the side I adjusted running. Sure, I may have done it wrong. But, I found the running method easier and more fool-proof than the cold method - so I am pretty sure the valves are adjusted well. Now, that could mean I am too loose on the right causing a higher reading on that side.

One more idea to try and then I may adjust the right side hot. I just hate having to pull the heat shield. If I remember, it also involves the muffler hanger and that's a pain to get back into place.

Mark M
Project: 64 Spyder Vert running 80 hp heads and carbs
1st Vair: 65 Corsa 140
St. Louis, MO
Show Me Corvair Club &
CORSA member

"If it's not broken, you're not driving it hard enough"

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Re: Set carb idle mix, now hesitation, advice?
Posted by: bill darcy ()
Date: September 19, 2011 01:22PM

I think I'd leave the right side alone and recheck left side.Try backing off each rocker 1/8th turn to start.If one or more are tight you'll notice a change in idle as you loosen them.Don't know what your initial setting was but I have had good success with just 1/2 turn down from zero lash.

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Re: Set carb idle mix, now hesitation, advice?
Posted by: Mark M ()
Date: September 19, 2011 01:30PM

Bill,

On the left side running adjustment I followed the advice here and from Clark's tech pages. Both said: after backing off slowly and then back in slowly until noise just stops, wait for it to settle. Then, turn in 1/2 - 3/4 turns. I split the difference.

Mark M
Project: 64 Spyder Vert running 80 hp heads and carbs
1st Vair: 65 Corsa 140
St. Louis, MO
Show Me Corvair Club &
CORSA member

"If it's not broken, you're not driving it hard enough"

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Re: Set carb idle mix, now hesitation, advice?
Posted by: bill darcy ()
Date: September 19, 2011 01:56PM

Hey Mark,You may try this method when adjusting.Loosen until clack is loud, turn down just enough to get quiet on each valve.When all are JUST barely quiet shut off engine and have a beer or two.Once you've finished your beer,without starting engine turn down all 1/2 turn.Have another beer while engine cools then put cover back on and start it.This has worked for me on many occasions although I have also done it with coffee.

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Re: Set carb idle mix, now hesitation, advice?
Posted by: Mark M ()
Date: September 25, 2011 06:58PM

Finally! Replaced the cross shaft with a good old one I cleaned up and added o-rings and ferrules to. Per a CORSA Tech guide article I bent the right lever some so both levers were about the same distance above the top of the sheet metal at base of carbs. Found where the left carb linkage was hanging up. Broke the rod trying to bend it, but found a spare. Set the idle speed screws, checked vacuum, left was lower. Adjusted left swivel and the carbs are balanced. Set the idle mix and all is good.

Thanks.

Mark M
Project: 64 Spyder Vert running 80 hp heads and carbs
1st Vair: 65 Corsa 140
St. Louis, MO
Show Me Corvair Club &
CORSA member

"If it's not broken, you're not driving it hard enough"

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