Bog / Hesitation off Idle - 65 Corsa Turbo

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rarroyo
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Bog / Hesitation off Idle - 65 Corsa Turbo

Post by rarroyo »

I need some help solving, please.

Setup: Stock 180HP engine with new 40 DCOE and exhaust system, spark plugs set to .030, timing is at 24 degrees (timed with vacuum line on.


The Problem:

1. The car does not accelerate off idle, if I do not ride clutch and slowing accelerate.

2. Throttle does not return, sticks slightly until I tap gas peddle or pull on the throttle linkage up.

Fixes to try to solve this issue:

1. Rebuilt Original Carter YH Carb
2. Replaced Throttle Body and linkage (From Clarks)
3. Replaced all lines from and to carb
4. Replaced gaskets from carb to turbo
5. Replaced intake gaskets to chrome crossover
6. Replaced tube from chrome crossover to turbo
7. Replaced exhaust system and packings from logs to turbo to exhaust
8. Replaced fuel pump and fittings.

Still nothing...

8. Replaced Carb with Weber 40 DCOE (stock jetting: 30mm venturi / choke?115 main jet?F11 emulsion tube?200 air corrector jet?50 pump exhaust valve?45F9 idle jet?40 pump jet?1.75 needle valve?, 85F9 starter jet, 150 starter air jet)

Hesitation still persists...

What I discovered today, will post photos tomorrow.

Driver side exhaust manifold had a stripped bolt and a loose packing ... it is not flat left side is closer than the right side of the donut. Not sure if this is the cause of what seems to be a vacuum leak.

Thoughts?
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acarlson
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Re: Bog / Hesitation off Idle - 65 Corsa Turbo

Post by acarlson »

I had a similar throttle sticking problem with my ‘66 turbo. Turned out the throttle linkage at the bracket on the transmission was not aligned correctly and was slightly bent.

Disconnect the linkage from the Carter. Pull the linkage forward and see if it still binds on the return. If so, check the linkage under the car and adjust so that it slides smoothly.
Alec Carlson
Dahlonega, GA
1965 Regal Red Corsa 4 Speed Turbo Convertible
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larry202br
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Re: Bog / Hesitation off Idle - 65 Corsa Turbo

Post by larry202br »

You completely replaced the carburetor, and no change? I would look hard at the ignition then. Do you have the correct distributor, and the correct vacuum "retard" module? Are you running points and condenser? Have they been replaced?
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bbodie52
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Re: Bog / Hesitation off Idle - 65 Corsa Turbo

Post by bbodie52 »

Image


Looking at the centrifugal advance timing curve on the turbo engine distributor, I don't see how the advance curve could impact initial acceleration off idle. The turbo engine starts with initial timing advance of 24° BTDC. The centrifugal advance does not dial-in any additional timing advance until 4000 RPM, and then adds 18° for a total advance of 42° at 4900 RPM. There is no vacuum advance on a turbo distributor — only a pressure retard device that subtracts 8° of timing advance at 3.7 psi of turbo boost. None of this would impact off-idle engine acceleration. The base timing setting starts at 24° and the distributor is not designed to add any timing advance until the engine is over 4000 RPM.

The correct 1965-66 turbo distributor number is 1110329. I did have a problem with a non-turbo distributor many years ago that produced bog/hesitation. I made an error in reassembling a Corvair distributor when I reinstalled the centrifugal advance weights upside down. In that case I had created a centrifugal RETARD mechanism, which retarded the timing as the engine speed increased. It idled fine, but trying to accelerate felt like I had run into a wall of Jello! On that engine the base timing was 13°, and the vacuum advance was giving me some low RPM timing advance, but the centrifugal advance was reversing the timing. More throttle disengaged the vacuum advance, and negative centrifugal advance just killed the horsepower.

The basic design of the turbo Corvair distributor centrifugal advance mechanism is the same as that found on non-turbo distributors, so it would be possible to flip the weights upside down ad create a centrifugal retard device. But the weights and springs are set to only engage above 4000 RPM, so eve an incorrectly assembled distributor would not impact the timing until the engine reached 4000 RPM. I doubt that timing is causing your off-idle power problems, as long as you have the correct distributor model and the base timing is set to 24° BTDC.

Image
Centrifugal Advance Weights
Centrifugal Advance Weights
A vacuum leak might cause your lack of power. inspect the clamps and hose between the turbo outlet and the intake manifold tubing for cracks or leaks. Also inspect the PCV system vacuum connection and the vacuum hose connection to the distributor pressure retard device to eliminate any possibility of a vacuum leak.

Image

You should also confirm that your harmonic balancer outer ring has not slipped. The outer ring is pressed on and held in place by a rubber ring between the center hub and the outer ring. The outer ring can loosen with age so that it begins to slip, which can make your timing mark inaccurate. Check the slip-check reference marks on the harmonic balancer to ensure the accuracy of your ignition timing setting.


Harmonic Balancer
Harmonic Balancer
Harmonic Balancer.jpg (26.61 KiB) Viewed 1600 times
Attachments
1965 Corvair Assembly Manual - TURBOCHARGER SUBSYSTEM.pdf
1965 Corvair Assembly Manual - TURBOCHARGER SUBSYSTEM
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Brad Bodie
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61SuperMonza
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Re: Bog / Hesitation off Idle - 65 Corsa Turbo

Post by 61SuperMonza »

I would first deal with the linkage issue. Have you checked the accelerator pedal pivot? They get loaded up with debris and stick. If that is okay then check the pivot under the car. That should fix the linkage issue. Has the turbo been looked at or rebuilt? If that has been done the next issue would be as stated a vac. Leak in the system. Has the DCOE been converted to a progressive set up? If not you will never get rid of the bog/hesitation of idle. Each turbo engine will require different set up for proper operation depending on the individual engine. Very difficult to get right. I should say time consuming. I would reinstall the YH since you have rebuilt it. Get the original set up working properly and linkage fixed. At that point you can upgrade to the DCOE with progressive operation. Good luck.
First corvair in 1985
Have owned 4 corvairs since
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flat6_musik
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Re: Bog / Hesitation off Idle - 65 Corsa Turbo

Post by flat6_musik »

I would also perform a compression check on all cylinders, right out of the gate. Make sure the engine is warm, ignition coil hi-voltage wire grounded and throttle blocked open. If the compression checks out on all cylinders, then make sure your turbo can spin freely. If it is froze up, that would be a source of exhaust blockage/sluggishness.
rarroyo
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Re: Bog / Hesitation off Idle - 65 Corsa Turbo

Post by rarroyo »

Thanks, everyone for the prompt and detailed responses... boy I have a busy weekend!

Plan to tackle:
- Throttle linkage, review and fix

- Re-examine exhaust connections as recommended (please note that I am using the original inlet pipe to y exhaust clamp.... inlet pipe repro has a straight pipe but I did notice that the one I took off had a small adapter allowing the donut packing to be held between clamp, donut, y pipe, clamp... not sure if this is the cause... it seems once I tightened bolts to sandwich packing it seemed fine.

- Re-check bolts from carb to turbo, turbo to crossover
- Re-check vacuum lines to see if I have any cracks
- Perform compression test and check turbo
- Check distributor number and retard
- replace packing donuts on the short and long intake manifold.

Weber is stock with stock jetting...no progressive conversion

30mm venturi / choke
115 main jet
F11 emulsion tube
200 air corrector jet
50 pump exhaust valve
45F9 idle jet
40 pump jet
1.75 needle valve

85F9 starter jet, 150 starter air jet

Thanks
rarroyo
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Re: Bog / Hesitation off Idle - 65 Corsa Turbo

Post by rarroyo »

Quick update...

Decided to focus on the throttle linkage at the trans and sure enough, it was all dried up and rusty... I cleaned it up and greased and now no sticking... unfortunately still have the bog.

Discovered that at 850 RPM's it bogs but if I engage the choke 1/2 way and raising RPM's to 1000... bog is gone? I know have not changed any of the stock venturies, jets... but would that really prevent it from at least revving up without the hesitation?]

Posted video for reference and photos.

video
https://photos.google.com/share/AF1QipO ... JRc251Rk5n

https://photos.google.com/share/AF1QipO ... JRc251Rk5n

photos
https://photos.google.com/share/AF1QipO ... JRc251Rk5n
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flat6_musik
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Re: Bog / Hesitation off Idle - 65 Corsa Turbo

Post by flat6_musik »

Bogging is generally overly lean. Make sure your accelerator pump is squirting correctly and then richen up your idle mixture screws (turn out) an extra turn or less....just to see if that helps. As was stated, a vacuum leak will cause it to be lean.
rarroyo
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Re: Bog / Hesitation off Idle - 65 Corsa Turbo

Post by rarroyo »

Thanks for the replay flat6! ...

Got it, ordering the recommended base jetting today.

Current Stock setup:

30mm venturi / choke

115 main jet

F11 emulsion tube

200 air corrector jet

50 pump exhaust valve

45F9 idle jet

40 pump jet

1.75 needle valve

85F9 starter jet, 150 starter air jet


Recommendation:

34mm venturi / choke

195 main jet

F16 emulsion tube

220 air corrector jet

50 pump exhaust valve

50F8 idle jet

1.00 pump jet

1.75 needle valve

Mixture screws are two full turns out
Fuel Pressure set to 2psi on cheap regulator

Regarding fuel pressure... I do have a regulator and gauge to install this weekend as well.

Cheers,
Rafa
rarroyo
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Re: Bog / Hesitation off Idle - 65 Corsa Turbo

Post by rarroyo »

UPDATE: Still have not determined if vacuum leak or poor timing or exhaust leak... is the cause the bog, hesitation and poor acceleration of the Corvair but decided to take it down to the block and heads and start to check every bolt and line again... During this, I decided to replace the exhaust gasket on the turbo between the hot and cold side where the clamp is and found out that there was a crack on the hot side of the turbo and it did not move freely took quite of bit of finger strength to make it move...

Question: What would be the effect of this if any? Would it cause poor acceleration and bogging?

Any insight will be greatly appreciated.

Photos: https://photos.app.goo.gl/5Pf23PcfLA4aE6t77

Cheers,
Rafa

Image

Image

Image
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bbodie52
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Re: Bog / Hesitation off Idle - 65 Corsa Turbo

Post by bbodie52 »

:coolphotos: :goodpost:

Your 3 images at the bottom were not displaying properly. I edited your post and corrected the URL for each image so they can be viewed.

Image
To get the image URL, go to the Google Photos image location to view each image. Right click the selected image to display a menu, and then select Copy image address to copy the URL to the Windows clipboard. Then paste [Ctrl+V] the URL between the image markers on the Corvair Forum.

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Brad Bodie
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rarroyo
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Re: Bog / Hesitation off Idle - 65 Corsa Turbo

Post by rarroyo »

Thanks Brad!
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thewolfe
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Re: Bog / Hesitation off Idle - 65 Corsa Turbo

Post by thewolfe »

If the turbo is seized it will certainly cause problems with acceleration. You should be able to easily turn the wheels with the housings on. If you try to spin it, it should spin about a turn or turn and a half. With the exhaust housing off you will not be able to spin the wheels easily. I would start with a turbo rebuild and your stock carb and go from there. Also check for vacuum leaks. Whoever told you 34mm choke tubes gave you bad advice, unless you are running a progressive secondary which you aren't. Stick with 30mm. Going bigger will make any off idle bog worse.
Nate Wolfe
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rarroyo
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Re: Bog / Hesitation off Idle - 65 Corsa Turbo

Post by rarroyo »

Thanks Nate. So the crack on hot side does not effect performance?
joelsplace
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Re: Bog / Hesitation off Idle - 65 Corsa Turbo

Post by joelsplace »

Yes the crack will hurt performance hence the suggestion of a rebuild which would include replacing the cracked housing.
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