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RPM's jumping anywhere from 900-1700!!

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Discussion starter · #23 ·
Re: RPM's jumping anywhere from 900-1700!! UPDATE!!!

Well,

We put the Jet stage 2 Q-jet on tonight...hooked up everything....said a little prayer, and started her up.....
She is running!!!! She went to about 1500 RPM's, then settled down to around 1200-1000 RPM's!! WOOOO HOOOO!!!:hurray:
So now its just getting her dialed in, and she should be ready to roll!
The RPM's still drop to about 500 when in gear though...I would really like to have them at around 700-800, but thats another day.
Thanks guys for ALL your help! I guess I am buying a new carb! ;)
 
#24 ·
Coool getting better I think everett touched on whaty could be wrong
you have gone from a 2 B to 4 B, this will also change the nature of the engine idle vac.

The HEI was designed for later models that used ported vac rather than manifold vac
I suspect with the change in engine vac the HEI VA could be out of range....it is not all in at idle on manifold vac.
Simply changing an early engine with A HEI to ported may work as a patch fix....but essentually the cam etc is also a little different in later models.
 
Discussion starter · #25 ·
Steptoe said:
Coool getting better I think everett touched on whaty could be wrong
you have gone from a 2 B to 4 B, this will also change the nature of the engine idle vac.

The HEI was designed for later models that used ported vac rather than manifold vac
I suspect with the change in engine vac the HEI VA could be out of range....it is not all in at idle on manifold vac.
Simply changing an early engine with A HEI to ported may work as a patch fix....but essentually the cam etc is also a little different in later models.
Click to expand...
So changing the carb to a 4bbl affected the vacuum? I dont understand why? Is there something I need to do to counter the change? Is this why my RPM's are dropping so much when in gear?
 
#26 ·
If it's a stock HEI or MSD StreetFire, it's got over 20 degrees of advance built into the vac can and needs around 19" to fully deploy. The Streetfire now comes with a limiter plate.

Steps, since you know ignitions, how would putting the transmission load on one running too much advance at idle react?
 
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#29 ·
Brew, there may be a little screw on the back of the gauge that will adjust the needle (zero it). Mine has two... one of which zeros the needle. Of course there may be one on the front instead. Won't hurt to try them. If the screw doesn't turn (clock-wise) easily, don't force it.... if it's an adjustment screw it'll turn pretty easily.
 
#30 ·
Okay, 15 inches of vacuum, good for a stock 327, due to short stroke - longer stroke, larger volume to create vacuum.

Gauge needle needs reset, I imagine Joe's suggestion would work some, but maybe not for 15 inches. It reads like the guts should come out, pull away the Bourdon tube, the part having a curl in it, has gear teeth to mesh with the needle teeth, and reset/zero the needle the best you can mechanically, then use the adjustment screw to finalize zero setting.

Or, for less tan $10 dollars, buy a new gauge or use your hand vacuum pump.
 
#31 ·
Hand vac pump....you can check the specs on the VA,( start inch finish inch and how many degs in it.) bleed brakes etc...handy little tool.
You can adjust the inches , top and bottom ..also changes the degrees my making an adjustable tag like this...either end or just 1 end as needed
Image
 
Discussion starter · #32 ·
Steptoe said:
Hand vac pump....you can check the specs on the VA,( start inch finish inch and how many degs in it.) bleed brakes etc...handy little tool.
You can adjust the inches , top and bottom ..also changes the degrees my making an adjustable tag like this...either end or just 1 end as needed
Image
Click to expand...
Cool...thanks!
So what about the drop in RPM's when put in gear? Any idea's?
I triple checked everything, and I do not have a vacuum leak. Is the HEI set up wrong?
 
Discussion starter · #33 ·
HwyStarJoe said:
Brew, there may be a little screw on the back of the gauge that will adjust the needle (zero it). Mine has two... one of which zeros the needle. Of course there may be one on the front instead. Won't hurt to try them. If the screw doesn't turn (clock-wise) easily, don't force it.... if it's an adjustment screw it'll turn pretty easily.
Click to expand...
Thanks Joe! :beers:
I'll see if I have this on my gauge...if not, its off to advance auto for a new one, and I'll retest it and let you know.
 
#34 ·
Taking a 'normal' car idles at say 800 when droping into gear there is a little load on the engine and it drops around 100 rpms. Because of the load and the lower rpms the engine vac may drop from 20 to 16.
If the VA is not all in at 16 it will tend to drop the intail advance (manfold vac) which will also drop the rpms more than it should, maybe even cut out.

A similar issue can be found with dizzy spring (s) too light...they are partly activated at idle speed increase in advance, idle speeds up, runs out of 'idle' fuel supply, rpms drop, counter weight drops, spring let cent force drag up it up and repeats.

I do recommend having an incar vac gauge...perminent.
It cam mount here without harming anything...uses the screw that holds the lens on...well not that screw...get a longer one, uses the same mounting piont as the lens cover.
Image
 
#35 ·
I'm having a similar problem. I have a 67 camaro with a 350 and T350 trans. The problem I'm having is the car will be idling at a intersection and somestime it will idle up and want to lunge forward. I have to put the car in neutral and it will idle down. This only happens when the engine has been running for a while. Any ideas?
 
#36 ·
You Va unit is in the wrong Vaccum range for the vac charactorists of your engine
And/or the weight springs on the dizzy weights are too light...increasing the weight of the lightest 1 maybe enought to stop it.
and/or you have worn plastic bushes on the counter weights.
And/or Your sec butterfly maybe a smiggen to far open.
Asuming everything is in good conition, no vac leaks etc
 
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Steptoe
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