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Re: Flat Spot/Stumbling at 1800RPM
Posted by: LilRedDevin ()
Date: May 20, 2017 07:54AM

RobertC Wrote:
-------------------------------------------------------
> Have no clue on how Webers work - Is 1800 rpm
> where the carb switches from the idle circuit to
> the main circuit?

2500 RPM is the transition. It was rough when I got the car but once I rejected the webber to the same jets Tom had been using the transition became smooth as silk!


>
> Have any idea on what is in the distributor?
> Shaft? Cam? Weights? Springs?

No idea other than it has the Pertonix II in it. Based on the wisdom of this group it does seem ignition timing is the place I should be looking at most right now. Plan to chat with Seth today and see if one of his Stinger Distributors could be properly set-up to ensure the correct advance at all RPM's.

>
>
> Autocrossing - the only time the engine would be
> at 1800 rpm is when accelerating onto the course
> and when stopping after completing the course...
> I am sure he "managed" the flat spot if it was
> there at that time.

Agreed. I spoke with one of Tom's friends who remembers the car running really strong but also remembered Tom mentioning some fluff in the carbs off idle. What I am experiencing is worse than a bit of hesitation but I have a feeling it is the same issue become worse with the elapse of time and other parameters of the engine being less dialed-in than Tom would have had it in his day.

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Re: Flat Spot/Stumbling at 1800RPM
Posted by: RobertC ()
Date: May 20, 2017 08:23AM

Probably showing my ignorance of Weber carbs, but I thought that they(?) (or some of them?) used separate jets for the idle and the main circuit.

Have you tried going one size richer (or leaner?) in the idle circuit and see if that changed the problem?

As others have stated, maybe the Pertronix is the issue. You could put a point plate in the distributor and see it that changes the problem?



Edited 1 time(s). Last edit at 05/20/2017 08:29AM by RobertC.

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Re: Flat Spot/Stumbling at 1800RPM
Posted by: MattNall ()
Date: May 20, 2017 09:46AM

Once again... please answer!

What Fuelpump are you using? a regulator? if so, what pressure? on a Gauge?





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: Flat Spot/Stumbling at 1800RPM
Posted by: RobertC ()
Date: May 20, 2017 10:26AM

MattNall Wrote:
-------------------------------------------------------
> Once again... please answer!
>
> What Fuelpump are you using? a regulator? if so,
> what pressure? on a Gauge?

Stated an electric fuel pump and pressure regulator in his first post...

Has not stated what pressure the regulator is set at.

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Re: Flat Spot/Stumbling at 1800RPM
Posted by: MattNall ()
Date: May 20, 2017 10:45AM

RC "Electric pump" means nothing other than not mechanical...

We need to know pressure range and flow might help.

"Regulator" we need to know What Model Regulator.

I'm sure Jim didn't use the cheapy Round pancake style...

BUT if he did.... I have found that they seldom flow fuel below 2 psi on the dial...

I always take them apart and flatten the sealing surfaces and then use a correct thickness washer and check calibration with a 0-15 psi liquid filled gauge..on the engine while it's running.. Flow has never been a problem, ever with large 4bbl. on large v8's

This way they work at lower pressures and do not leak..





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: Flat Spot/Stumbling at 1800RPM
Posted by: LilRedDevin ()
Date: May 20, 2017 12:08PM

Fuel Pump: Facet

Fuel Pressure Regulator: Holly Brand. 1-4 PSI Model.

No pressure gauge inline with the regulator so I will need to test actual PSI.

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Re: Flat Spot/Stumbling at 1800RPM
Posted by: MattNall ()
Date: May 20, 2017 12:46PM

Facet is a good pump!! Many of us run them.. But just like Holleys and Airtex's.... there are clones out there..





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: Flat Spot/Stumbling at 1800RPM
Posted by: LilRedDevin ()
Date: October 08, 2017 11:53AM

I wanted to revive this topic and share my progress in case anyone has similar issues. As is the case with problems on 50 year old cars sometimes the issue is not caused by one source but multiple sources.

Ignition:
- I replaced the Pertronix equipped distributor that was on the engine with a STINGER electronic ignition distributor from Performance Corvairs. This solved almost all of the poor idle and low-speed drivability issues I had with the car and really woke the engine up. Best $200 I have ever spent on an upgrade.

Fueling:
- Replaced the fuel pump with a rotary pump designed exclusively for low-fuel pressure carbs plus new soft fuel lines and new filter. This solved the issue of fuel expanding and leaking into the intakes after shutting the engine down. The rotary fuel pump allows the fuel to expand and flow backward when the engine is not running.
- Re-jetted and resynchronized carbs for the fourth of fifth time and finally found a pretty good sweet spot. Drivability was much improved but based on the variance in idle adjustment screw settings I was seeing between the left hand and right hand carb I knew something was still not right.
- Exchanged several emails with senior Weber tech at Redline, Bud Pauge. He knows these carbs inside and out and over the course of a few emails was able to diagnose and recommend solutions for nearly every symptom I had experienced. More than that he guessed from my responses to his questions that a throttle shaft on one of the carbs was twisted or bent and suggested a few tests to learn if his hunch was correct. Sure enough he was right on the money, the tests revealed the throttle on one carb was slightly open even when it should be closed. This was the source of most of my frustration. We discussed ways to temporarily tune around the issue for drivability but ultimately the carb will need to be replaced.

WHERE I AM AT TODAY:
- Car is running 80% better than before and is a joy to drive most of the time now. The flat spot is mostly gone with only a very slight sense of firmness in the pedal at the transition from the low-speed circuit to the high-speed circuit versus the brick wall that was there before.
- While I could tune around the twisted throttle shaft I'll probably bite the bullet and replace the carbs because one is always going to be fueling the left side of the engine slightly even with the throttle "closed" and that could lead to bigger problems over time.
- How did the shaft get twisted in the first place? Most likely the home-brew linkage set-up. It was probably adequate when the car was being raced in the 90's but ultimately there are, or should be, better linkage solutions available today.

At this point 80% of the drivability issues are solved. The last 20% will take time, effort, and money. Based on the improvement thus far it should be worth it. I'm sharing this to let anyone else running weber carbs know they CAN be made to work very well on these engines. Seeking out the advice of professionals like Seth at Performance Corvair and Bud at Redline Weber made all the difference in the world. They have the experience and knowledge to diagnose and solve issues us mere mortals can only guess at.

I'll be sure to report back when the engine is at 100% but for now I wanted to say THANK YOU to everyone in this community who provided feedback and helped steer me in the right direction. I am more in love with this car today than ever and having the engine run so smoothly and produce turbine like power feels so much better than the roughness, hesitations, and stumbling that I was fighting with before.

A few parting thoughts based on my experiences so far:
- Webers are happiest and easiest to tune in an INDIVIDUAL RUNNER situation. My engine came with dual Weber 44's on it, each carb on the common plenum fueling 3 cylinders. Not the ideal situation for a Weber but what I have and what I am working with. If someone were building and engine from scratch and wanted to run Weber carbs (or the PMO replicas) then ultimately going with dual triple barrels would be the way to go. More $$$ spent up front but also more tune-ability, reliability, etc. over a span of years/decades. At least theoretically.
- PMO, Redline, and others also have the dual triples available as throttle bodies now for anyone who wants the classic Weber carb look with the modern convince and reliability of fuel injection. Something for fuel injection fans to ponder.



Edited 1 time(s). Last edit at 10/08/2017 11:54AM by LilRedDevin.

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Re: Flat Spot/Stumbling at 1800RPM
Posted by: MattNall ()
Date: October 08, 2017 12:19PM

Great news!! We appreciate the update! Have fun now!





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: Flat Spot/Stumbling at 1800RPM
Posted by: Seth Emerson ()
Date: October 08, 2017 12:25PM

Thanks for the note on the upgrades. Glad I could help. The twisted throttle link had me remembering a suggestion from many years ago. The suggestion was that the actual throttle pedal should have an adjustable limiter stop on it (I have seen a nut welded to the back side of a stock pedal, with an hex-head bolt and a lock nut added. When the "red mist" hits, you try to push the pedal THROUGH the floor. Adding a pedal stop makes sure you won't stress-out the rest of the linkage when you do that.(And you will do that). The stop is set at "just" before the stretching begins, so the links to the carbs, and the throttle shafts themselves, don't become the stretch point.

Seth Emerson

Check my new Performance Corvair Web site [www.perfvair.com]

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