Holley 650 VS carb. Car idles With 10" of vacuum @ 650 RPMS.

I put 69's in the primaries, with an 8.5" PV. Results were the engine ran perfectly smooth, but rich on the highway and around town.

I drop to 68's with same PV; Now the car STILL runs rich around town and on the highway, but has a NOTICABLE lean-out from about 12" to 10" of vacuum before the PV opens. But its still running RICH ALL THE TIME! my plugs are getting blacker and blacker...

So, I keep the 68's and goto a 9.5" PV, hoping to smooth out the transition. Thats as close to 10" as i want to get, cause thats where I idle. Results were the engine smoothed out a bit, but STILL had a Noticable Lean spot on acceleration between 12-10" of vacuum (throttle position)

But its still running so rich my plugs are slowly fouling. I drop to 67's on the primaries and....
Now it runs super super LEAN on the highway, but Still REALLY rich around town. and it has a REALLY bad lean spot from partthrottle (14") to the PV opening point.

SO I guess my dillema is I cant get the around-town to lean out without a super-lean spot during part throttle occuring, not to mention my highway cruise just leans out so bad the Lights dont even show up on the Air/Fuel guage. After a highway drive the plugs are white as snow. after a city drive they are black and even a little bit sooty almost like oil.

 

Lets get some more info here: What plugs are you running and what do you have your timing set at?

 

The jetting has nothing to do with the "around town"
idle/low cruise, low speed driving AFR. This is controled by the idle circuit. And off idle transition circuit.
Remove the carb and check the throttle blades relationship to the transition slots. Be sure the idle transition slots are not exposed too much at idle. Adjust the secondary idle stop
to even up the fuel flow between the primary and secondary
barrels. Be sure to have a PCV systen hooked up or it will be over rich at idle/low cruise too.

The idle circuit is calibrated rich to start with on a 650 dp.
Remember this is a racing carb, designed for a more radical motor.
The only way to adjust this is to modify the fixed idle restriction
in the metering block. You can use mig welding wire (.025") in the holes to adjust the fuel flow.
Your car will not idle well at 14.7:1 AFR on the guage. It will like around 13:1 afr or so.
It is quite normal for it to "color" the plugs. the insulater should be redy/brown to tan and the threads will have black/gray carbon on the end.
This coloring is more an indicator of the idle circuit calibration than the "jetting".
Get the "jetting" (primary jet) to allow hiway cruiseing
with a AFR betweem 15.5:1 and 14:1. It should go rich when you roll into the throttle to 12.5:1.
Playing with the accelerator pump volume and shooter size
along with the power valve opening point, and secondary jetting will get you there. You may have to adjust the size of the power valve channel restriction if you end up with a primary jet much different than "out of the box". Do this last, after youve perfected the rest of the carb. You won't get it perfrect because you aren't able to mess with the airbleeds or emulsion tubes in the meteriing blocks, but you get it close enough.
Remember a little rich is better/safer than running too lean.

Again, the low speed driving is almost exclusively controled by the idle feed restriction and idle air bleed, not the jetting.

 

interesting.

heres more info: I ran NGK's that were 2 steps cold for the blower, but now im running splitfires that are normal without the blower.

My timing is 15 base, 36 total by 2500, and Highway 48-50*.
I usually run 87 octane...
----

<b>Be sure the idle transition slots are not exposed too much at idle. </b> They are BARELLY exposed.... like less than a throttle blades width....

<b>650 dp</b>
Its a 650 Vacuum secondary carb. I recently added the quick change spring to it, and even with the lightest one in, it still has a noticable bog and then suddenly i can HEAR the secondaries opening! it sounds like a blow off valve for a small turbo!
----
I HAD a 650 Double pumper on it, But went with VS carb for fuel economy reasons, and both do the same thing, have this lean spot...
----
The deal with the idle is depending on RPM it may or may not pull enough fuel, for instance if I get the motor Idling good in neutral then put it in gear it wants to die from lack of fuel. if i get the idle good in gear then it wants to foul my plugs in neutral.
----
<b> It should go rich when you roll into the throttle to 12.5:1</b>
Well lets say im cruising down the highway and my A/F guage is reading almost perfect 15:1 where I've got it. I check my plugs and sure enough, they are perfect. Now lets get back on the highway and cruise again, but this time lets start to step into the throttle. Right off cruise, as SOON as i Start to move the throttle, it leans out SO BAD the engine stops making power, rather it just instantly leans out and trys to die. this gets WORSE as i move the throttle to the floor, until about 9-8" of vacuum it finnaly jumps over to RICH and begins making power again. I cruise at almost 20" of vacuum, so from 20" of throttle position to 10" there is a gigantic flat spot of lean ness where the motor stops and wants to die. If i fix this by bringing up the jets it just runs rich as crap while cruising, black plugs that begin to miss.
----
<b>Be sure to have a PCV systen hooked up or it will be over rich at idle/low cruise too</b>

I dont have PCV, it was going to the exhaust but i disconnected it because it was sucking oil into the exhaust. Whats PCV got to do with being rich? I've never used it. this isnt a factory setup.. i dont even have the PCV breathers...
----
<b>the insulater should be redy/brown to tan and the threads will have black/gray carbon on the end. </b>
Latelly from city driving they are so black they begin to miss in gear. I have to sand blast them about once a week...
And i cant get it to NOT run rich around town, no matter what i try... I guess I have to change the <b> idle feed restriction and idle air bleed</b> Right? and how would i go about doing that?

 

Somehow I missed the fact that this is a supercharged motor.
Is it a B&M 144?

You cannot run a blown motor on 87 octane gas.
use 93 or better or lower the boost before you destroy the motor.
You should be limiting the total mechanical advance to about 28/30 deg @WOT unless you are running racing gas or water injection on a blown motor. But a blower motor likes lots of initial advance. Total advance under cruise should be
normal 40/50deg. less if you cruise under boost. (more density needs less advance)
You may need to recurve the distributor.
Use non projected tip plugs a little cooler than a stock plug. Split fire plugs are not for a blower motor.
You're looking for trouble.
The blower has a lot more internal volume than a manifold that needs to be enrichened (pump shot) when you roll into the gas. This is the cause of the lean out while rolling into the throttle. Get a 50cc accelerator pump kit and some .042 .055" shooters (alcohol carb parts)
and the hollow shooter screw.
The idle is rich because of the fact the carb is on a blower
and there is no PCV. Hook the PCV to the base of the carb and
vent the valve cover. Get a book on holleys and look where
the Idle feed restriction is. Try a piece of .035" wire stuffed in the holes to lean out the idle circuit.
Run big jetting in the secondary side. Like 88's to start.
You don't want to be too lean at WOT with a blower.
Primary jetting should be near normal but you may need to drill out the PVCR a little for enough WOT fuel.
This is not the cause of the lean spot when you roll into the throttle. That is the accelerator pump volume and shooter size.

The powervalve must be a little lower then the vacuum guage reading at idle while in gear or the carb will also run real rich.
What does the vacuum guage say at idle (in gear)?

15:1 is probabily too lean for a blower motor at cruise.
especially if you cruise under boost. ( boost guage reading)
You may need to Boost reference the Power valve to get the right
powervalve action too, if you want it tuned that close.
Hook a vaccuum guage under the carb and another to manifold
vacuum (on the intake manifold) and see the difference in the two guages, while you roll into the throttle on the hiway and the car transitions from vac/ cruise to boost.

 

Your Pan evac system was probabily sucking oil into the headers because the holes in the valve cover are right over top of a rocker
and or there is no baffle in the valve cover ( aftermarket).
If you hook up a PCV system to these valve covers you'll suck oil into the motor at high vacuum too. (deceleration)
Fix the valve covers. You may have to build a remote oil breather separator canistor. Run the PCV hose from the valve cover to the canistor/ oil separator and then to the carb/base.
Vent the other cover with a baffled and raised filtered PCV breather.

 

Its not a blown motor now. it was, with a fuel infection setup, but now its a carbed N/A motor.

Ill ignore all of that stuff you just said

SO back to the littlr 650 VS carb, I will probably be: <b>Try a piece of .035" wire stuffed in the holes to lean out the idle circuit. </b>

To see if it leans out my around town driving. Vacuum in neutral @ 900 RPMS is 15", in gear at 650 RPMS is 10". Always super rich, of course, because if i lean it out any, it dies. Only has front idle screws....

Im ready to throw the TPi setup on this thing. im getting sick of fouling plugs for no reason.

 

Vacuum leak.

And the PCV has lots to do with it.
The carb is calibrated to work with a PCV system.
Costs you nothing in power and will make your oil last longer.
Without it the idle and low speed curcuit will be rich.

You've tried two carbs and still got the same tuning problem.
Not likely the carb (s). I'd suspect a vacuum leak.

 

hmm. a vacuum leak where exactly? My carb is connected to my brake booster, from the back, and thats about it. could it be leaking there?

and why does PCV have anything to do with the air/fuel ratio a carb spits out?

and its also confusing me because I have the lightest vaccum secondary spring in the darn thing, but there is STILL a very noticable bog and an audiable hiss when the secondaries open.

and im getting a strange response around 12-10" of vacuum during acceleration. if im driving at about 45 MPH, 17-18", and begin to step into the throttle SLOWLY...
From about 17" to 13" it stays rich.
But right as i get to 12-11" it begins to have a noticable lean spot, the A/F guage goes red. When it hits 10" the engine stops making power and the A/F guage goes off the chart (super lean) as if the carb has simply stopped adding fuel. If i hold the throttle right there, it will sit like that for about 6 seconds before suddenly kicking up and back to rich again (vacuum drops below Power valve opening point)

So its not an accelerator pump issue, because it occurs with VERY little throttle movement, and if i STAB the gas it just gets up and goes as if nothing was wrong. like i said it will sit there if i hold the throttle open at about 10" and try to die. i let off and it goes back rich, i step further and it opens the power valve. it was alot worse with a 6.5" PV.

 

The brake booster is a possibilty. So is the vacuum modulator line on a th-350. Id look real hard for a intake manifold leak.

The PCV is part of the system. The little air leak of the PCV valve at idle is part of the total airflow into the motor.
The carb's idle circuit is designed to provide the right AFR
with a functioning PCV system. If you plug ithe PCV, the mixture
is richened and you have to open the throttle more to feed the motor the same air. The motor don't care how or where it gets the air and fuel. BUT it does matter that the throttles are in the right position at idle relative to the idle and transition fuel passages.
If you don't under stand it, just trust me and hook it up.
Your motor will run much better. Be sure the valve cover has a baffle below the PCV valve and is between the rockers not over them. be sure to Vent the other cover.
A replacement lawnmower muffler makes a neet Vent /baffle/oil separator.
Even a radical street strip motor will run better and last longer
with a functioning PCV system.
Here's cool trick. On some radical motors with big cam timing the carb has to be too far open to allow enough air at idle. this is caused by the lack of manifold vacuum.
One cure is to drill the butterflies for more airflow at idle.
Another one is to just hook up two PCV valves. The extra airflow through the extra PCV is usually just right and lets you close the throttle back down to the proper idle position without drilling the butterflies. Now I'm giving away secrets.

 

Even this radical '68/69 corvette l-88 427 hs a fully functional PCV.

 

Guess I should post the picture eh!!!

 

Hook up the PCV check for a manifold vacuum leak and up the primary jetting 2 sizes. Blow out the air bleeds in the top of the carb with compressed air. Check the little cork gasket that is between the vacuum diaphram housing and the side of the carb.
This may be leaking and causing the noise and bad secondary response.
What is the carb model#?

Any carb that has a 3/8" vacuum port is designed to be used with a PCV. If you plug the PCV off, it will run rich "around town"

 

Could he not drill some small holes in the throttle blades and do the same thing as a pcv system without having to adjust the idle stop screw? This would give him more air at idle and not uncover his idle transition slots. I also agree that he needs a little vacuum on the valve covers as well. Maybe an oil separator and then to the exhaust.

Steve

 

Why not just hook up the PCV and kill two birds with one stone.
The motor will run right, and the oil will last longer.
You really want to avoid drilling . this motor does not need it.
The PCV will not cost you any power. There really is no good reason not to run it and lots of good one in favor of it.

 

whats the idle transition slots got to do with running rich around town but super lean between 12-10" of vacuum part throttle?

and how do i fix THAT? It was fine with the big cam, a 234/244 @ .050 on this carb. but this new cam pulls more vacuum and is so much nicer, but its freaking lean at part throttle and rich the rest of the time!

thats my main concern. I will hook up the PCV system, if you insist, and see what happens. But from what your telling me the rich idle will go away with a teeny vacuum leak, pulling more air and less fuel. it makes sense, of course, but i really dont think thats the problem with it running rich "around town" I have a feeling that has to do with it being an old POS more than anything. well, its not super old, but im picking up a TPI setup tommarow... hrmm...

 

Normally that carb with stock out of the box jetting would be real
close. But because you dont have a PCV hooked up the idle circuit is now a little too rich, So ya got the idle mix screws to far in to compensate. Now when ya get off idle its too lean, till you get into the power circuit then its ok.
Hook up the PCV as it should be . Forget the hows and whys for a moment and see how it works from there.

Check to see if the secondaries are sharing the idle too. The secondary butterflies should be at least part way to the sec ondary transition slots and so fuel is balanced between all four barrels at idle. (fuel for the secondaries idle circuit comes partially from the primary side thru passages in the base plate and partially from the sec metering block.)
(If this passage is blocked for some reason {dirt, wrong gasket}
the idle will never be right)
When ya got the 4 barrels set right and sharing the idle and the PCV hooked up the mixture will be right at idle and off idle.
The transition will be nice and smooth. If you get away from this set up things get wacky.
What intake manifold is this and what is the carb #?
It's actually quite easy to get this out of wack.
And even more so if one cylinder has a vacuum leak. It will only show up at a certain throttle position. And no amount of tuning and fiddleing will get it right till the vacuum leak is found and the carb throttle blades are in the right spot at idle to start with.

 

I will do exactly as you suggest, and i beleive its a 4150 but i could be wrong....

Its one of those holley 650 VS Shiny Carbs for like $249 they sell new. very cheap as carbs go, in my opinion, especially since the blower carbs are like $650 and ive got one sitting around with all the goodies like adjust a jet and titanium needle etc...

The intake is a Performer RPM. it was a single plane when i had the really lumpy cam in it, maybe that helped somhow?

I noticed when i initially pulled the blower off the big ol' blower carb made it very hard to drive. throttle response went piff, as did fuel economy and everything else. ah, well its an 850...

I am going to get that TPI setup put on this motor, i beleive, since i dont think this carb can support 20+ MPG...

but ill fix it first, or die trying. thanks, Im leaving for a week, be back in a week, ill try it then. ill let you know how it goes, and take some pics...

 

I have the same manifold and it's one of the best I've ever had.
I'm not real big on those Shiny Holleys. Especially the ones with
the removable top that look like a Motorcraft carb.
My friends have never had good luck with them.

The only VS carb worth buying in my book is the 3310.
Although the 600 1850's seem to work well too.

 

okay ive got the PCV hooked up to 1 valvecover, and it...

Idle speed came up, so i re-adjusted. idle got leaner, so i re-adjusted. It was like creating a small vacuum leak, almost exactly like it.

but its running a SLIGHT bit leaner around town, good highway, but stil annoyingly rich. now rich enough around town to leave smoke but rich enough to foul my plugs after a 40-50 mile town drive. doh. I tried making the hose to the PCV a bit bigger but it didnt help (hoping for a bigge vacuum leak.. heh..)

I also noticed it leans out much quicker when i step into the gas slowly. now it starts to go lean and sputter with a lean mis-fire around 12" of vacuum. I bring the idle jets up real rich and it goes away, but of course then its SUPER rich around town. D'oh

I got that TPI Setup... all i need is injectors, fuel pump, ECU, and a MAP sensor... and some common sense.