Polecat

I put this 750cfm machanical secondaries on my 383, and with the old setup it was fine. But then I went new 383,wilder and having carb problems.
First, with the Comp XE284 cam, it only pulls 7-8hg of vacuum at idle(800rpms). So I took out the stock 6-5 powervalve and put in the Demon recommended 4-5. Then took the jets from stock 76/83's to 74/80's due to WOT rich black smoke. Now, it still puffs a big black cloud when I romp it hard.
By changing all those, I was hoping to cure that.
Any ideas?

thanks in advance.

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350 4 bolt main, Speed-O-Motive 383 stroker kit, re-sized rods ground for clearance,TRW Forged pistons,10.7:1 compression,HPC Coated RPM intake, Speed Demon 750 cfm carb,World Products Sportsman II heads,2.02/1.60 valves, Comp Cam 1.6 roller rockers, Comp Xtreme 284 cam,240/246@.050 with .540 lift,Crane pushrods,ATI damper,Proform HEI and MSD6A box,HPC coated 1 5/8 headers, 2.5" exhaust with 40 series mufflers,TH350 with Hughes 3000 stall, Powertrax NoSlip Locker, 4.11 gears.

[This message has been edited by Polecat (edited April 16, 2001).]

bottledpower

try changing your secondary accelerator pump profile. it may be dumping to fast. you might want to step down the secondary squirter also. look for a vacuum leak. thats quite a bit lower than you want.

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85 IROC 350 11:1keith blacks,.555lift erson roller cam,1.5 crane roller rockers,edelbrock intake,holley 4150 750dbl pumper, nitrous oxide,full length heddman headers,true dual exhaust, 11"stall converter, 700R4, 3.73 locker

greearhr

I'm running the 750 vac sec on a 400ci engine. I have reduced the jets by about 6 numbers and still need to go lower. They are supposed to be much more efficient at metering the fuel. I also had trouble with the idle. I drilled out the outer bleeds in the air horn to .070 and installed restricted bleeds in the metering block (.031 I think). Still don't get the idle mixture screws out very far. I'm going down some more on the jets and then will work on the accelerator pump circuit next time. Keep us posted. We can share info.

Bear Tracks

Jester

That idle vacuum sounds pretty low to me too, I'd look for a leak. Could be right tho..depends on the LS of that cam. I'd definatly alsoset the idle with a vacuum gauge if ou havn;t already.

As far as your problem, bottled power hit on it. Try a smaller pump cam in the secondaries, and a smaller squirter if you have to.

C h r i s

Ok this may seem obvious but on my Road Demon Carb I was having similar problems. I finally traced it to the floats being too high. In the video that came with the carb it said to center the fuel level in the sight window. I ran my car (daily driver) this way for months trying to figure out why it was running so rich, had low vacuum and put out a MAJOR smokesceen when the secondaries opened. I lowered the fuel level to even with the bottom of the sight glass and it cleared up. It may be simple but try lowering your floats - it's an easy thing to rule out.

HTH
Chris Lindh

greearhr

After reducing the facory jets about 6 numbers I checked my plugs (see previous reply) and they were white. I still had black smoke off the line so I replaced the green squirter cam with an orange unit in the number 2 hole. It's better but still needs a little less squirt. I think I'll try lowering the floats to help with that and cold warm up being too rich. By the way I also cut off 3/8th inch of the choke plate due to extreme richness when the choke is on. It helped.

Bear Tracks

C h r i s

We Demon owners need to share data somewhere. Maybe a Yahoo Group? My Road Demon causes black smoke when I go to WOT. My thoughts are that it is accelerator pump related and that a smaller squirter could help. Possibly a different pump cam? I think Demons are good carbs they just calibrate them way rich for racers who aren't concerned about idle, low rpms, etc. My mpg went from ~14 to ~10 since I swapped from an old worn out Holley 1850 to the Demon - I know with tuning I can improve this.

More info on my car here:
http://personal.atl.bellsouth.net/at...dh/webpage.htm


'78 Malibu 350/TH700R4
'68 Chevelle SS396

greearhr

I have reduced the squirter size to a 25 and used a smaller pump cam (don't remember which off hand). The float level definitely has an effect. Also the fast idle screw doesn't go in far enough. I think i'll cut down the spring.
Beartracks

C h r i s

Wow, that's coincidental - I just robbed the 25 squirter from that old 1850 I had AND a few months ago I installed a longer fast idle screw. I've also jetted mine to 66/76's down from 70/80's. If the way smaller squirter (down from a 31!) doesn't cure the smoking at WOT I'll look at the pump cam - can you use regular Holley pump cams?

Chris

-Someone else on this board mentioned their Road Demon throttle linkage was bound up when they got it - mine was too - the choke mechanism was hanging. The Demons IMO are a better carb - but the minor details (small parts, etc) are a bit inferior.

greearhr

Regular pumps and squiters work fine. I think I'm about 71/79 on the jets now. I'd have to check my records. Plugs have mostly white porcelan's now.
I'm running a 400ci F... in my cowboy coupe (pickup). It has a Crane roller cam and everything else you could think of. Getting 10.25 mpg (5,000" elevation). I think B. Grant could use some carburator people help. Where did you get the longer screw? Out of a Holley?

Bear Tracks

C h r i s

The times I've called B. Grant the tech guys have been relatively helpful, but I haven't called them lately - and they never suggested lowering my floats which fixed about 90% of my problem. The squirter seems to have gotten rid of my WOT smoke but a night drive with headlights behind me will have to be done to be sure. The longer screw came from a random screw/bolt jar I have.

Chris
'78 Malibu 350/TH700R4
'68 Chevelle SS396