My fumes on a cold start are so bad, I cant even stay in the garage with the door open.. The rest of the circuit runs great. From a dead idle (1000rpm), I can mash the pedal and get a great response and the car pulls good throughout, its just the idle thats killing me.. I have all "external" adjustments fine tuned but its still eye burning rich.. The motor is fresh and the carb is new. I have been working with BG on this issue and they are now telling me to change the IFR's from the stock .036 to .034, which doesnt seem dramatic enough for this rich of a condition. I went to the strip this past weekend, pushed my car in the stageing lanes and only ran it for 3 passes and my plugs were already fouled just from the little ideling I did in the pits and the plugs were brand new.. After 3 cold starts with a fresh set of plugs they are already toast and wont clean up unless I put a few miles on it at 3000+rpm... I have the secodaries open .020, which allowed me to bring the curb idle down so I know I'm not drawing from the main idle circuit.. The idle eaze has no effect.. Float bowl levels are perfect, fuel pressure is perfect, idle screw adjustments are optimized for highest vacuum reading (3/4 out on all 4 corners), etc, etc, etc..

Motor
355 SBC
10-1 Comp
Cam dur- .250 @ .050 (.555 lift)
Aluminum heads
Timing- Locked out at 38 degrees
Ignition- Mallory high output dizzy and coil with a hyfire multi spark system..

Should I go lower on the IFR's or should I also change the Idle Air Bleeds too? I'm just tired of having to buy new plugs every week and want to get this resolved..

Thanks for any help
Cuz

 

I have a 750 Mighty Demon also (with annular boosters). I have messed with it quite a bit this last year to get it running well from idle to WOT. First thing I would suggest is find more timing advance at idle and low speed. With that cam and compression, 38 is not optimal. You should be around 50. The only way to do that is with vacuum advance. What is your vacuum reading at idle? I am guessing it is pretty low (maybe only 9" or so). More advance will bump up the vacuum and allow you to close up the idle screws (you are using the primary and secondary?) some.

Lastly, I would look to the IFR's. .002" change is moderate. Initially, I would close them up .004 to .006 just to see if it has a possitive affect. You can fine tune from there if you have a pin vice and drill bits.

Lastly...what intake? If it is a single plane, I would be looking into a dual plane. Air Gap seems to work real well on mine. I have a 236@.050" hydraulic roller, AFR 190's and 10.8:1 compression. Put down an 11.89 two weeks ago and it was HOT and HUMID. The Air Gap has a lot more torque down low than the miniram I took off. Seems to pull just as hard up top.

 

Thanks!!
I didnt realize I could run that much timing.. In my old drag car (73 camaro) I ran 41 degrees and thought that was high
I'm running a dual plane Performer intake.. My vacuum reading at idle is 8.5hg and I already installed a 4.5 power valve (as suggested by BG).. Yes, I adjusted all 4 idle screws and they are all 4 set at 3/4 turn out, which gave me the highest vacuum reading and smoothest idle. I'll order some .032 IFR's, which is .004 smaller, instead of the .002 they suggested because your right, I should go a little extreme to see if it has a positive effect..

I ran 12.10's and then shot it with 100hp and it ran 11.30's..

Edit: I just think its odd that some racers will stick a .017 staple or speaker wire in it, which reduces the IFR by about 50% but when they suggest reducing the actual IFR size, they only suggest going a few thousand's smaller.

 

I should have explained the timing better...50* only at idle and part throttle. 38* is about perfect for WOT. In a drag only car, locked out timing works well, but plug fouling is always a possibility. If you drive it at all on the street, you could lock it out and keep vacuum advance (if the distributor is equipped with it).

PV sounds right. My idle mixture screws are right around 1 turn out each. What I was asking is, do you use the idle screw that opens the primary throttle and also the one that opens the secondary? If you have one opened only at .020", you could have two opened at .010" (approximatley). This may help some with the rich idle.

Glad to see you are using a dual plane. Too many guys with street 350's running a single plane. 12.10 is stout...11.30 is really stout!

 

I did play around alot with the primary and secondary buttlerfly openings.. I first started out at .020 on both and then had to back down the primary to get the idle down but that did solve my off-idle stumble. I have since found that .015 on the secondary works best..

Here is a picture of me in the stagng lanes this past weekend (the corvette)..

 

Try opening the idle-eeze all the way and slowly turning both idle scews back in. On my car, this made the mixture too lean (car overheated). I decided to not mess with the idle-eeze at all and just use the IFR's and LSAB's to get idle mixture correct. Mine is still a little too rich, but much better than it was.

Nice looking car. I like the corvettes when they still had the thin, chrome bumper.

 

Ok 50 degrees of timing on a carbed engine is just crazy! What exact heads are you running? What gas are you running? Your idle air bleeds is what you need to change first, you will see a change I promise. If everything else is correct as you say then this will fix all of your problems. Your street engine needs a timing CURVE. How is your Mallory dizzy set up, springs and weights? One more thing to check, make sure your boosters are tight in the main body and are not loose otherwise they may drip excess fuel in thus affecting idle and your fuel curve, usually see this on older carbs but if you have been wrenching long you know new means nothing lol!

 

Right now I'm not even running it on the street and Like I said, after only 3 passes at the track, the plugs were shot just from the little idleing I did in the pits and staging lanes.. My dizzy doesnt have springs or weights, its locked out at 38 degrees and I have an ignition cut-off switch for starting.. I had the same set-up on my last drag car and never had fouling issues this bad.. BG is telling me to change the IFR's but I have read other places where they say to change the Air Bleeds.. What size Air Bleeds do you recommned? The stock ones are .070

I just ordered new IFRs and Air Bleeds
Stock IFR's are .036 and stock Air Bleeds are .070... I ordered .032 and .034 IFR's and .071 Air Bleeds..

 

Motor
355 SBC
10-1 Comp
Cam dur- .250 @ .050 (.555 lift)
Edelbrock RPM aluminum heads (64cc)
Edelbrock RPM intake
Timing- Locked out at 38 degrees
Ignition- Mallory high output dizzy and coil with a hyfire multi spark system..

I was running 93 octain but ran 100 for this weekends race because I planned on shooting it with 100hp NOS.. As for the 50 degrees of timming, thats not what I said, thats what pancherj suggested.. I'm running 38 total (lockout).

 

I too have a 357, 10.5?:1 compression, canfield 195 heads, solid roller, 650 mighty demon, yada yada and run a total of 50 degrees timing on the street with no problems. The motor runs much better now than when I only ran 35 degrees. You have to remember, its not 50 at WOT, its 50 under part throttle. 15 of it is vacuum advance.

 

Vacuum advance on locked out timing works well on drag cars. Bigger spark plug gaps (.045-.050) works good too...if you have enough coil to jump it. This may be a race car, but it still idles. Try it and see what happens.

You could also lean out the idle/transition circuits a ton to limit fuel flow at idle, or slow the response of those circuits with the IAB's. This could cause a lean stumble when you floor it. You could cover that up with a giant pump shot. That's not the route I would go.

Are you launching from a foot brake at near idle? The extra timing advance could give you a boost off the line in this situation too. Not sure it would help with a trans brake.