Extreme high idle

[maxellus]

Hey guys I need help!

Rebuilt 110 motor, with new pistons, cylinders, mild cam, precision valve job, roller rockers, careful by the book assembly. I am using a Clarks 4-carb conversion with their performance exhaust headers and a Crane electronic ignition system, with a rebuilt 330 distributor. Timing is set statically at 8 degrees BTDC, all idle screws backed right off, mixture screws at 1-1/2 turns out, unused vacuum ports on secondary carbs are permanently blocked and the vacuum advance is hooked to the vertical port on the right side primary carb. Hope I haven't forgotten anything.

Problem is that the engine starts right up and idles at 2000 RPM and nothing in do will bring it down. Choke cams are not on a step and throttle plates on all four carbs are closed, with no light visible using a flashlight down the venturi.

Any suggestions??

[Scott V]

disconnect the linkage from the carbs so your sure thats not part of the problem.

look for a vacuum leak - that would cause a high idle.

what carbs did you use for the conversion? all primary carbs? that could be part of the high idle problem.

-Scott V.

[bbodie52]

Are the chokes in the primary carbs (and their associated fast idle cams) engaged? Are the choke mechanisms on the secondary primaries disabled?

[maxellus]

Thanks for the quick replies guys. Yes I am using four primary carbs, with the chokes completely removed on the ones that are the secondary's. Yes the cams are also removed on the secondary carbs. Good suggestion about disconnecting the linkages, I will try that tomorrow. I have checked carefully for vacuum leaks and no issue there.

Thanks again.

Maxellus

[terribleted]

Are all 4 carbs idle circuits complete and active? Could make it idle fast, would be like holding a light foot on the pedal:) If so try closing the mixture screws on the "secondaries" or set leaner mixture on all 4 maybe?

[66vairguy]

What year are the carburetors?

Primaries on secondary positions can make for a "slightly" higher idle, but certainly not 2,000 RPM.

Only two things - fuel or timing causing this.

Are these carburetors newly rebuilt? The 65 and later primaries aren't good choices for use as secondaries - IMHO.

Steve Goodman at Rear Engine Specialists in Colorado has recommended the 62-63 bases on secondaries for the idle circuit (the drivers side tends to misfire at idle with the stock secondary - long story) and in Colorado 60's Corvairs have to pass air quality testing (and folks think Calif. is tough). I seem to recall he sets the throttle plates closed on the secondaries and the mixture screw out about 1/2 turn. Primaries are set up normal.

The 62-63 bases are simple, no hot start vent, no mixture enrichment, a good choice for a secondary.

[bbodie52]

Did you leave the accelerator pump mechanisms in-place on the 'secondaries'? The spring tension is needed to ensure positive closure (through the external linkage) of the secondary butterflies -- otherwise they might drift partially open and increase the idle or create what amounts to a vacuum leak.


The two carburetors with rubber cups on the accelerator pump plungers are the two PRIMARY carburetors. These have active accelerator pumps. The SECONDARY carburetors do not use accelerator pumps, but the plungers — with their associated springs — still utilize the external linkage to exert spring pressure to close the throttle butterfly valves. The secondary carburetors do not even have accelerator pump passages drilled in the venturi area to permit fuel to squirt into the carburetor throats — unlike the primary carburetors, which have a complete accelerator pump system. The secondary carburetors lack many of the vacuum ports, passageways, choke systems, idle circuits, etc. that are found in the primary carburetors.
(The above comment refers to a 140 hp engine with factory secondary carburetors. However, using two primaries as secondaries may still need the accelerator pump springs to ensure that the throttle butterfly valves fully close).

Also, try temporarily disconnecting your vacuum advance hose from the distributor and plugging it. Then start the engine see if your extreme high idle speed goes away.



There is a comment here about careful bonding of the carburetor adapter piece to the head. I could possibly be a source of a vacuum leak...

Re: 4 x 1 CARB Kits
Posted by: steve goodman
Date: May 18, 2006 07:48PM

Hello all: I have done several of the 2 carb to 4 carb conversions through the years and probably reviews are mixed. The downside is that you still have small intake valves and small exhaust tubes even if you chose headers or a dual exhaust system. The larger valves and larger exhaust tubes on the 140hp is what gives it the extra ump after 3500rpm.

On the good side, you get good linkage with the Clarks kit, buy the air cleaner setup and it looks great when you pop the lid and yes you do get some more go off the line. Typically you need to work with the distributor and of course the exhaust system. Be very careful in bonding the adapter piece to the head, any tiny air bubble etc will be an air (vacuum) leak and will drive you crazy trying to find it later. Also a set of 90 degree plug wire boots are very handy to clean the left hand carbs. The choke rods are a bit sticky to bend, I made a pattern from coat hangers after the first install so the later ones don't make me work as long. Keeping the cutting of the various sheet metal pieces to a minimum is important too, a nice clean job looks like that, if you miss then there are gaps that look funny.

My last observation: since only 'knowing' Corvair owners would realize that there was a kit in place instead of just using the 140 heads, build at least a top end that uses the 140 heads to their advantage. 1965 cylinders and 140 heads on your 64 engine will fit perfectly, use a standard 140hp distributor and the factory exhaust system unless you want headers.

I realize there is some money differences here between using your original pieces and buying lots of parts. Budgets are often the deciding factor of course. If you chose the 110 conversion I think you would like it but not as much as a real 140hp. Good luck in your choice.

Best, Steve

[maxellus]

I really appreciate all the quick and detailed replies guys. I'm new at this forum thing so bear with me. To answer a few questions, yes the carbs are all 65/66 primaries and with fresh rebuilds. I will try that adjustment/suggestion on the accelerator pump re the secondaries.

I had some success on the weekend with disconnecting all the linkages which did partially bring the idle speed down and I actually found a linkage issue which I have corrected, but idle is still too high at around 1200 PRM today. I have also added a second return spring on the secondary carbs (Clarks C1916) which seemed to help as well. Oh, and yes I have tried disconnecting the vacuum advance as one of you suggested, but no change in idle speed resulted.

My next step is to really do an in depth look for vacuum leaks again.

Thanks again guys I will try to keep you posted.

[66vairguy]

With four carb's isolating an issue is tough. If all else fails I'd install block off plates on the secondary positions and that gets you down to working with just two carburetors and you have two spares to swap on and see if you have a bad carburetor. It only takes ONE carburetor to cause an issue.

A word of caution about the 66 carburetors. I had an idle issue with one and after taking it apart (and having the "experts" examine it) NOBODY could get the idle speed stable. I read Bob Helts book and discovered the 66 and later carburetors (all, not just the Calif. emission control carburetors) had a revised idle circuit that added a port to produce an "idle mixture emulsion" that provided a better idle mix with a slightly leaner mixture - smooth idle with less emissions. It works well until it DOES NOT. The circuit has an internal path that will not tolerate any dirt or corrosion. The only way to access all the internal paths is to pull a few casting plugs. My carburetor had corrosion in the internal path that was not repairable - junk in spite of a nice looking external appearance. I went with the 65 bases on primaries and 62-63 bases on the secondaries. That got the idle down to about 900RPM which is acceptable. My next experiment will be to replace the slotted throttle plates in the secondaries (from 62-63) and install the solid throttle plates from the secondary carburetor bases. Note that the secondary 62-63 idle mixture is set to about half the primary setting to get a smooth idle. Basically the 62-63 emulates the latter secondaries that had a "fixed" idle circuit added. Why? The drivers side on a 140HP engine does have a tendency to miss at the cylinders near the secondary (where the vacuum balance tube connects) unless you run the primary idle mixture rich. In Colorado this will cause an emissions test failure (yes old Corvairs have to pass emissions test there) and Steve Goodman used the 62-63 bases on the secondaries to emulate the later secondary idle mixture circuit and was able to tune the cars to pass the emission test. No idle miss and cleaner idle emissions - what's not to like.

[maxellus]

Hey that was great advice from 66Corvairguy. I think I know where I can find some 62/63 bases which might be a good starting point if all else fails. Kind of a winter project. Today I readjusted all four carbs float levels per Bob Helt's book, one of the primary carbs had a dribble from the cluster. I'm away for a week, so I will get back on applying some of these suggestions next week.

Thanks again guys.