I was dealing with some cooling issues yesterday, so I was letting my camaro idle for little while while watching the temperature gauge. Well after flushing the radiator and adding a smaller water pump pulley, I drove the car and was way down on power. I couldn't figure on what was going on so I pulled a plug and it was BLACK. I put a new set in and after a short cruise and idling for about 20 minutes and watching the temp gauge, I pulled a plug and was shocked at how black it was. The car ran great but still almost fouled the plugs. The car runs 12.05's and idles great.

The carb is a 750 DP with a 6.5 power valve and 72 and 80 jets I believe. I know the jets don't affect idle so that shouldn't matter. The 4 corner idle screws are out 1 1/4 turns and they are very effective if I turn them all in even 1/8 turn the car wont start. So I know they should be close. Also the car idles at 1100 in park and around 750-800 in gear. If I lower the idle the car wont idle in gear. The fuel bowls are set at the bottom of the sights on the sides while running.

What could be causing this rich mixture? I assume if the car is running to hot the engine would run leaner anyways.

Thanks, Erik

Are your bowl screws tight, as in really firm? Power valve OK? They're easy to check.

What is the vacuum at idle?

The bowl screws are tight and the vacumm at idle is 12. Like I said the car runs great and it doesn't smell overly rich at idle. Maybe a tad but not to much. Does turing the 4 corner idle screws in or out lean the condition. I just adjusted for highest vacumm. Somebody told me that maybe the floats were to high or the carb gets to hot and it percolates the fuel and they drip into the cylinders. That doesn';t make sense to me since I can hold the carb because its nice and cool.

Thanks, Erik

Are the plugs too cold ??? What #'s you running ??? With MSD ignition that shouldnt be happening . I had a similar problem with my 81 Z/28. Turned out to be a weak Mallory HEI coil. Put a stock GM coil in..... problem cured.



bob

I am running the AR3933 Autolites. The car runs agreat and idles great just cant figure out which way to tune the idle to get it alittle leaner. I assume it is at idle or just off idle rich.

Thanks, Erik

Two different copmpanies told me two different fixes this morning and I don't like either one of them. One said to drill out 3/32 holes in my primary throttle blades and that I shouldn't have the secondaries crack open at all. If you do a search here so many people have to crack open the secondaries to get there cars to idle. The other company told me to replace the power valve. They said it sounds like there is some fuel leaking somehwere and the power valve would be the biggest factor. They did tell me that 1100 rpms in park and 800 rpms in drive is not loose enough, they said my convertor is too tight.

How do I get my rpms down in Park but not too low in drive? I do know alittle about tuning a carb and this tells me to open the secondaries some, is this true? I really want to avoid drilling on the carb at all costs. This isn't radical of a motor.

Thanks, Erik

Eric, the 4 corner idle screws lean the mixture when turned in. You could be rich on the idle curcuit, I have found that running the primary and secondary blades open the same amount, keep the idle mixture screws the same all around but adjusted for highest idle but to the leaner side help. Make sure the primary and secondary blades only expose about .020 of the transfer slot. Here is a link to BG Demon carb adjusting that shows a good picture of the idle transfer slot and how much of it should be exposed. The more this transfer slot is exposed the more fuel it will dump in at idle no matter where the 4 corner idle screws are set, you will need to remove the carb to check this. http://www.barrygrant.com/fromBarryGrant/Demon%20Instruction%20Manuals/Idle-Eze-Addendum.pdf

If your idle is still to low you can advance the idle timing to bring idle up but remember to take some of the total timing back out. This has worked really good for me and at idle and cruising speeds I am no longer running rich.

Hope this helps.

You need to quit calling the two companies that you talked to ;) DO NOT drill any holes in your carb unless you feel like buying a new base plate!

The first thing you need to do is set the air/fuel mixture at idle with a vacuum gauge. Set it as lean as you can and still make max vacuum. That should be very close to 13:1 which your plugs and engine will like.

I do not understand why the engine will not start if the idle screws are leaner then they are set now -- that should not be because you can always tap the gas pedal to squirt a little extra fuel in there with the accelerator pump to get it started. The hard starting may be due to fouled plugs.

You may also want to consider what heat range plug you have in it. Plugs that are too cold will not get hot enough to self clean and as a result will look rich and foul quickly. Take a plug out and post a close up picture of the ground strap if you can -- we should be able to tell you if the heat range is in the ball park by looking at the position of the anneal mark on the strap. The anneal mark should be close to the bend in the strap -- closer to the base is too hot, closer to the tip is too cold.

Hope that helps. If you try these two things and still do not have any luck there are a bunch more things we can try.

I have never had to much success with calling Holley Tech Support, I never like what they have to say. I called QuickFuel and Sean Murphy Induction (which I like) and they told me I might want to get a heat shield. The cam I have doesn't really like to idle for long periods of time and I had it idling for 20 mintues or so. Since Goodguys is this weekend, I should get one for cruising around the fairgrounds. Basically he said after I park the car after running it, I am boiling the fuel in the bowls and probably dripping into the venturies, thus causing a rich condition. Sounds reasonable since its a little hard to start after I shut it down for 5 mintues or so.

Eric68 - I hoped you would chime in here!! I have the air/fuel mixture screws set with a vacuum gauge and am getting the most vacuum I think I can with it. But thats where it seems rich. So if I turn the screws in even an 1/8 of turn to lean it out it will start to die. Which what those screws are suppose to do correct? Once you turn them in the engine should want to die correct? Maybe I need to turn them in just little and bump the over all engine rpms with the idle screw.

What is a good heat range plug to use. Quickfuel did say that could be an issue, maybe to try a little hotter plug. I am using the AR3933's right now, what would be a hotter plug to use in Dart Pro 1 aluminum heads? I will get a picture tinight of the plugs.

I also asked about 1100rpms in park and 800rpms in gear and they all thought my convertor was too tight. Isn't there a way to get it to idle at 900-1000 in park and 750rpms in drive by opening the secondaries some or anything like that? I was under the impression that its o.k. to have the secondaries cracked open but both said I shouldn't have to with this setup, as its not that aggressive. They said close them and them botton the screw out and turn 1/4 to 1/2 a turn.


Thanks again, Erik

It's not uncommon for plugs to be black after idling. You really need to drive the motor and get it good and hot before reading the plugs. There may be issues there, but a plug that hasn't gotten hot enough will give you misleading results.

That is not right if the engine dies when you lean them a little past best vacuum. Could you have a vacuum leak? The RPM change between park and drive is pretty big which seems to fit with a vac leak. Also, try turning the idle speed screw up a little until you get it dialed in.

For plugs I have had good luck with the Autolite 3924. They seem to run pretty clean for a while in my car.

Erik - if you have a 4 corner idle you already have your sec's open some or should. Both throttle blades should be set the same and all 4 mixture screws should be the same.

Some things I see are you could be idling on the advance curve. Check your timing to see what rpm the curve starts. Excessive rpm drop can be from a converter with a low stall speed, if you are using vacuum advance you can counter this by putting your vacuum advance on a manifold source which will increase your idle advance.

As for your plugs stick with the same brand but get one step hotter and see from there. Typically you go one step colder for every 75-100 hp you increase over stock.

Depends Dennis -- I know BG recommends .020 front and back, but they specify idle speeds when they say that. As I recall BG recommends closing up the secondary when idling under 1000 RPM. But BG carbs now have "idle eeze" which allows you to control idle air without touching blade angle.

The big reason you may need to deviate from the "balanced all the way around concept" is that the blade angle relative to the transfer slot position on the front is very important. Too much or too little t slot exposure can cause tip in problems or a lack of response from the idle mix screws.

The idle fuel comes from the idle port anyway (well below the blades) so blade angle difference front to back does not really effect the idle mixture as long as the total amount of air remains the same. The difference will however change the tip in characteristics.

Not trying to debate with you Dennis -- I just have been playing with this A LOT as I converted to E85. I think I've changed every hole in the carb a half dozen times figuring it out!

Sure Eric, be a trouble maker! ;) LOL I'm sure all input is welcome by the guy having problems...

I didn't see anywhere that this was a BG carb but do tune 4 corner about the same BG or Holley. I have found the BG recomended "uncover .020" of the transfer slot on both sides" very workable and tried it on a holley with good results. Never read or heard 4 corner only if idle is above 1000 rpm though.

If killing half the carb's idle circuit works that's what is important. I'll be the first to say you are far more into all this than I am, I've just found the quickest way that has worked for me and kinda stuck with it. I have never played with a BG with idle ease so can't even comment on a carb with the feature...

LOL . . . there is more then one way to skin a cat for sure. Just hoping that a little tweak of an idle screw is all this gentleman needs to cure his ill.

WOW - thanks for all the feedback on this post!! I really appreciate it. I am pretty confident that I do not have a vacuum leak unless it is under the manifold somewhere. I checked everything there seems to be no leaks from above. I tried the starter fluid method. How much of this can really just be blamed on a really hot day and my water temps going up to 210 degrees over and over again while idling, while I was trying to figure out the cooling and the radiator. It has been extremly hot and humid here in Ohio.

I am sure we cracked open the secondaries just a 1/2 turn or soo to get the car to run 2 years ago. And I haven't had any trouble since until this week. As far as turning the screws in an 1/8 of a trun, that is if all the screws turned in 1/8 turn. The idle goes down but it still idles real rough and unacceptable. Like I asked, if I turn them all in some to 1 1/8 turn instead of the 1 1/4 turns I have now, can I just turn the main idle screw in some to get the idle back up? I have a feeling I don't have anymore room to turn the idle down anymore with the idle screw because it has no affect when I turn it out anymore.

I remember a long time ago when I got this motor together, I had to adjust something on the carb to get the car to idle higher in gear. It was dropping down alot from park to drive and wouldn't stay idling. 300rpms doesn't seem to excessive right now but what do you think? If its the torque convertor then I will just have to live with it. I know once the car has been driven and heated up for a little while the rpms in park seem to hover around 1100 to 1150. I would love for it to idle around 900 and 700-750 in drive, but if this cam or torque convertor won't let me then so be it.

Thanks, Erik

Erik, where is you idle timing set at?

I have my timing set at 18 degrees intial and 36 total all in by 3000rpms. I draw a bout 11-12" of vacuum at idle in park. I never checked it in gear.

Erik

I am sure we cracked open the secondaries just a 1/2 turn or soo to get the car to run 2 years ago. And I haven't had any trouble since until this week.

you might try putting it back to where it was from Holley. Sometimes extreme weather will effect the engine enough that something borderline in the tuneup is enough to cause a problem. From what you are telling me I think that LESS idle air on the secondary side (and more on the primary) would help your situation.

As far as turning the screws in an 1/8 of a trun, that is if all the screws turned in 1/8 turn. The idle goes down but it still idles real rough and unacceptable. Like I asked, if I turn them all in some to 1 1/8 turn instead of the 1 1/4 turns I have now, can I just turn the main idle screw in some to get the idle back up? I have a feeling I don't have anymore room to turn the idle down anymore with the idle screw because it has no affect when I turn it out anymore.

Yes, increase the idle speed screw in front. If you cannot get it to idle correctly, I think you need to take the carb off and flip it over to see how much transfer slot is exposed both front and back.

I remember a long time ago when I got this motor together, I had to adjust something on the carb to get the car to idle higher in gear. It was dropping down alot from park to drive and wouldn't stay idling. 300rpms doesn't seem to excessive right now but what do you think?

300 RPM is probably OK, but a little much IMO. A 300 rpm drop alone is not a problem, but if you are having other issues it may be a clue that something is not setup correctly with the idle speed or idle mixture (if not a vacuum leak)


If its the torque convertor then I will just have to live with it. I know once the car has been driven and heated up for a little while the rpms in park seem to hover around 1100 to 1150. I would love for it to idle around 900 and 700-750 in drive, but if this cam or torque convertor won't let me then so be it.

the looser the TQ converter the less RPM drop between neutral and drive you will typically have. As for idle speed, I think when you get this problem figured out you will be able to lower it down a bit

Thanks, Erik

Have you gone through the rest of your ignition? Are the cap, rotor and wires all in good condition? What about he mechanical advance? Anything loose or sticky in there? Sometimes the carb gets blamed for "ignition deficiencies"

Also, are you running vacuum advance? If so, are you running a manifold or ported vacuum source? If manifold, try switching to ported.

No, I haven't gone through the rest of the ignition at all. I assume since it runs real good while dcruising that the ignition would be fine. If a MSD box goes then it would run, correct? The only thing that might need changed is the Blaster 2 coil. I was tld if they heat up alot they will go bad. I really think its the carb and some small tuning on it. The car runs great except for a little rich at idle while idling for a longer time then it should. I do think I need to get to bottom of the problem why my idle screw won't lower my idle down anymore.

Thanks, Erik

Don't assume that the ignition is all good if it will cruise fine. I agree on the coil -- maybe you could borrow one from a friend to test? At least pull the cap and rotor and clean it up -- while its apart check for loose or sticking hardware in the mechanical advance.

If the idle screw does not have any physical effect on the idle speed check to make sure the throttle cable isn't holding the throttle open a hair. Try pushing the throttle closed with the engine running and see if this makes a difference.

Eric you may be idling on the curve. I was in the same boat as you as far as how high my car ldied. I turned back the idle to under 900 in park/neutral and 650 or so in gear. I run 15 initial and 36 all in by 3000. It really shouldn't drop that many RPM's when you put it in gear. It's puting a lot of strain on drivetrane components. At least that's what I was told by TC. I could never get my car to idle in gear unless the park idle was above 1000.

I had a similar issue with a new motor. I kept trying things to keep the plugs from turning black. What helped a little were some hotter plugs but that was just masking the real problem which was not enough vacuum advance at idle in gear. (Automatic)

I found that the vacuum can on my HEI was not deploying until about 9 but I was only getting 6-7 in gear at 700-800 rpms. Swapping out the can for one that deployed at 5 and adds 12 fixed the problem. It would then idle cleaner and smoother. I haven't had a fouled plug since. I wound up with 16 initial, 20 in the distributor and 12 in vacuum advance. Getting 28 degrees at idle really cleaned/smoothed things out. Before I would get that 28 at idle in neutral or park, but dropping it in gear caused a big RPM drop caused by the timing getting pulled out of the vacuum advance. Now I have a solid 12-13 of vacuum at idle IN GEAR.

Oh I should note that the plugs stopped fouling because of the vacuum increase at idle. The power valve was opening at 6.5 while I was idleing before the can change.. causing more fuel to add to the mix.