was running rich... why? - Team Camaro Tech
Troubleshooting Diagnosing problems done here.

 
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post #1 of 9 (permalink) Old May 31st, 02, 06:44 PM Thread Starter
 
Join Date: May 2002
Posts: 23
Well, I fixed the rich problem, but still curious as to what's up. Here's the story...

I've got a '68 w/ a 327... headers, moderate perf cam (but plenty of vacuum).

Always smelled a little gas, and ran rich... some rare plug fouling problems... occasional backfire through the exhaust. Had a qjet, R43 plugs, points, 8 degrees init (ported) advance.

This winter, car was apart for some unrelated restorations and I decided to replace a few engine parts too. Went to a Road Demon, Performer intake, and Accel Billetproof distributor.

Guess what? Same problem... only worse. So, installed R45s, upped the timing to 15, took the jets down by 2, lowered the floats (to the bottom line). Things got better, no longer smelled gas, but, still eventually fouled plugs! Note: secondaries are closed at idle.

So, I bought a set of Demon's idle feed restrictor (IFR) inserts, drilled them to 0.029" (stock IFR is 0.031"). Finally the problems are gone. Car runs great.

My question to you all - what would make an engine want a more leaned out condition like this? Even now, the best vacuum (about 17") is found with the idle screws 3/4 out. Demon recommends no less than one turn, so I have them at 7/8. Tempted to take the IFRs even smaller.
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post #2 of 9 (permalink) Old Jun 1st, 02, 02:07 AM
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Join Date: Apr 2001
Location: Out here
Posts: 111
My Demon does the same thing. I had to go way smaller on the idle feed restrictor and even went as far as drilling a small hole in the butterflys to lean it out a bit at idle.

I believe that those guys are proponents of having things on the rich side for one big reason. Its hard to break parts when you are running rich. I have yet to hear of a demon that came out of the box a little to the lean side. Scott
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post #3 of 9 (permalink) Old Jun 1st, 02, 05:15 AM
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David
 
Join Date: May 1999
Location: Jefferson City, MO.
Posts: 621
i have been fighting the same problem, only i have a high compression, long duration cam 377 with a speed demon 750 double pumper. the best vaccum is less than one turn out on the idle screws, maybe i need to do the same thing you guys did. did you get you're ifr's directly from demon? andis this an easy modification? David

------------------
67 RS marina blue
SUPER T10 4 SPD
377, demon carb
91 formula 350 firebird (wifes car)
01 siverado 2500HD
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post #4 of 9 (permalink) Old Jun 1st, 02, 05:43 AM Thread Starter
 
Join Date: May 2002
Posts: 23
Barry Grant calls them "Dominator Press-In Air Bleeds". Apparently they work both to modify the air bleeds or the IFR (same outside diameter). They are part number 120081. They come in a 10-pack, predrilled at 0.020". Cost about $10. You'll need four of the ten... leaves 6 for mistakes

I used a 'pin vice' and 0.0292" drill bit. Drilling them was very easy - do it manually.

Trick is - inserting them in place of the IFR. I had to freeze them to get them in, and now, am unsure how to get them out (if I want to go smaller). Maybe someone else has had this issue?

By the way, pick up a copy of "How to Tune and Win With Demon Carburetion". Outstanding book.

Thanks for the interesting responses. Back to my original question - this is more than a Demon issue, since the qjet did the same thing... right? I will say though, the qjet was looking pretty bleak - top warped enough to be a cereal bowl.

------------------
1968 Camaro 327
12BPosi
Power Disc
4 Speed
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post #5 of 9 (permalink) Old Jun 1st, 02, 06:59 AM
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Mark
 
Join Date: Feb 2002
Location: LR AR
Posts: 2,372
I was able to cure my Holley by playing with the secondary butterfly stop adjustment. It is on the bottom of the baseplate so the best way to get at it is with the carb off the engine. I found 1/2 turn in past closed worked well enough to get the idle mixture screws to work and the richness went away. I would have drilled the holes in the butterflies if that did not work.

-Mark.
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post #6 of 9 (permalink) Old Jun 1st, 02, 10:42 AM
 
Join Date: Nov 2001
Posts: 138
Hey guys the next time you have your carb off take the secondary stop screw out and install it from the top.--easy adjustment.
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post #7 of 9 (permalink) Old Jun 1st, 02, 03:40 PM
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David
 
Join Date: May 1999
Location: Jefferson City, MO.
Posts: 621
ok, my demon came with two of those air bleeds in a package in the box, so i guess if i need four to use them as ifr's then i'll have to spend the ten bucks. David

------------------
67 RS marina blue
SUPER T10 4 SPD
377, demon carb
91 formula 350 firebird (wifes car)
01 siverado 2500HD
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post #8 of 9 (permalink) Old Jun 2nd, 02, 06:06 AM Thread Starter
 
Join Date: May 2002
Posts: 23
psalm69, I am curious... did you use the same approach I did to reduce the idle feed restrictor? If so, were the inserts really tight?

Sometimes people use a thin piece of wire inserted in the IFR, if they need it smaller.
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post #9 of 9 (permalink) Old Jun 29th, 02, 10:26 AM Thread Starter
 
Join Date: May 2002
Posts: 23
What else is wierd about this engine.... I have the manifold vacuum advance on the carb pluggled (I'm using ported advance). When I pull the plastic plug off of the port on the carb (engine not running), it always has a little puddle of fuel in it. Anyone else seen this with their engine?

The engine does ok, but it is still definitely rich. I'll work on it in the fall/winter. For now, doesn't hurt much except mileage.
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