Rochester carb with blower
Hi all iŽam new to this forum i got a tip that this is a good place to ask about blower engines.
So heres my problem at the higher rpm my car feels like its not getting out all the power it wants, but in the low rpm it haves lots of power.
So iŽam wondering could it be the carburetor that donŽt work correctly?
Its a JET Streetmaster Quadrajet Stage 2 Carburetor
What rods and hanger should i use in the carb?
And if you look at this picture
Behind the carb you see a port what should go in there or can i just plug it?
Its a csb 350 engine with weiand 144 blower.
I use 95 and 98 octane gas "live in sweden"
if you wonder anything just ask and ill try to answer.
It sounds like you are going lean at higher RPMs, which is a very bad thing. That's a sure way to kill a blower motor. Check your plugs for signs of detonation... little specks of metal stuck on the electrode and/or the ceramic, or chunks missing. Compare your plug colors to this chart...
spark plug color chart
There should be no open ports at the base of the carb. An open port is a giant vacuum leak, which will cause a lean mixture. The ports either need to be connected properly to the PCV, distributor (if you have vacuum advance) and your transmission if it has a vacuum modulator. If the port is not needed for the above, it should be capped.
I would not drive your car until you sort out the mixture issue. It may be as simple as capping that port.
Oh, and welcome to the forums. Lots of knowledgeable people here!
Hi, i checked the spark plugs they looked normal.
And i plugged the vacuum port on the carb.
And i made the return line from the regulator smaller.
So now the engine feels a bit stronger true all the gears, but it still lacks the last push if u can say so...
And one more thing i have a auto meter Boost/Vacuum gauge and i hooked it to the intake but it only shows vacuum???
If the port you were referring to is the port at the top towards the right side on the rear of the carb, this is a port that is used to draw air into the choke heater on a factory set-up. It relies on the volume of air being drawn through the carb. Plugging it will not richen it up enough on a blown application. As far as Boost, you will not see any revving it up parked, only driving it down the road under load.
Hope this helps.
Look at this picture it shows what port i mean, its at the top middle rear.
And the gauge don't show any boost when i drive it down the road under load neither :confused:
That is the port I was referring to. I am finally enjoying my first day off in the last 30 days, and my memory is a little foggy, but getting better. Hopefully one of the Rochester Carb guys will chime in on this post, on how best to set it up for a blower. I have always used Holley and Edlebrock carbs pre-referenced for boost, when installing a blower.
Also, do you know what your static compression ratio is?
Here is a thorough discussion of technical info on Weiand supercharges.
You need to get a Edelbrock Qjet calibration kit #1992
Jet as follows #75 primary jet .048 primary metering rod
use the yellow power piston spring under the primary power piston.
Install the big .049" hi flow needle and seat from the kit.
Your fuel pump must be capable of feeding the carb and keeping the fuel bowl full at WOT high rpm.
secondary metering. Start pig rich "CC" secondary rod and "B" hanger from the kit.
Install the hi perf accelerator pump .
recurve the distributor for 24deg at idle and 28 to 32 deg max timing.
(shorten the advance curve) vacuum advacne should be limited to about 10deg and be connected to the manifold below the blower.
A good super charger cam for the 144 is the Crane #113801 HMV278-2
Another good one is Crane #113821 H-288-2
You want a 2.08 to 2.38:1 pulley drive ratio.
I recomend a water injection system for high boost.
use cooler than stock heat range spark plugs with a non projected tip and .035" gap.
Hi and thanks for all the input.
I have this cam Crane #113801 HMV278-2
And i use the stock pulleys that came with the blower.
And i use a piston style 170 gph fuel pump.
Heres the pulleys thats on the blower
Crank pulley is 6 inch
Upper is 3.07 inch
On my 78 GMC jimmy with a 350 and a quadrajet that port goes up to my air cleaner
Once your carb jetting/spark timing is dialed in correctly, you can step up the blower boost a bit to maximise power. (may require more spark retard or higher octane fuel)
A 2.38:1 pulley ratio is about tops for these blowers. (blower air discharge temp and belt slip/belt life gets excessive beyond this point)
More critical detail. At WOT hi boost, the blower can and will pull so hard on the carb that a vaccuum can/will be created just under the carb at high rpm max load.
The power piston and step up spring that controls the primary metering rods ( cruise/power circuit) reacts to any vacuum under the carb. On a N/A motor it does what it is supposed to do. But on draw thru supercharger system like yours the power piston can get fooled into going lean at the wrong time High rpm WOT max boost. So, you must install a vacuum guage and read the vacuum at the carb base at full throttle max rpm. If the power step up spring gets pulled down in its bore (lean) bad things will happen. Select a power step up spring with enough tension to prevent it from being pulled down (lean) at WOT max rpm.
There are various edelbrock QJET power piston springs of various vacuum ratings to select from. If say you get 4" of vacuum under the carb at WOT high rpm then use a spring rated higher 6" 7" or 8" or so.
Usually on these blowers once the power piston spring is propely selected a boost referenced power piston is not nessessary.
This is a critical must do calibration modification when using a QJet with a blower.
Thanks to all the help i got it running great :thumbup:
But for a week ago evertyhing went awfully bad, one "arm" in the carb got loose and went inside the blower so no more blower this summer :(
But atleast i have something to do in the winter now :rolleyes:
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