Carbed guys come on in.

[samuraichamploo]

I have just recently finished my project stang, And I am having a strange problem(s) with it. The first would be that after 5 minutes or so of driving, the car will kill if you take a corner to fast, or stop too quickly. Now I know what your thinking, The carb float. But I adjusted it, Perfectly you might say (On a brand new 4150 holley 650 carb) And I still have the same problem..
The car is also sputtering above 4500 rpms, Not accelerating as it should.
Now, I have asked some other people this question, and the only good explanation I have gotten is that the coil is bad, and when it heats up, its unable to produce enough spark, causing it to die when I turn / brake.
I dont know if I neccesarily agree with that assumption, but Its the best I have heard, seeing as I am out of ideas for whats causing this.
BTW, In case I didnt mention this, both problems dont happen untill the car is warmed up, or around 5 minutes of idling. Also, the Fuel Pressure is at a constant 8.25 PSI

See sig for combo im using ATM

 

[samuraichamploo]

ttt

 

[Jameasun]

yep my first guess would have been the fuel floats. Do you have any vaccum leaks? You can use carb cleaner to test. Just spray it around the base of the carb, the intake, and vaccum connections under the hood.

My next guess would be that the fuel is boiling.

Is your fuel pressure regulated? Do you have a mech or elec. fuel pump?

 

[samuraichamploo]

electric FP, a holley blue, and yeah its regulated.

 

[Jameasun]

just an idea. you might try to post your question over at www.carbdford.com
I visit there often and they have some really smart carbed folks over there.

 

[1985MustangGt]

Do you have a carb spacer? Sounds like it may be boiling the gas out. How many volts you putting out to the coil? Is it the stock coil?

 

[crazypete]

It _is_ a vacuum leak. I went through this _exact_ problem and it went away when I tossed the gaskets and went RTV (a sin, yes, but an effective one). When you corner, the carb leans a tiny bit and some vacuum gets in and stalls the motor.

The AFR changes dramatically even on an unchoked motor as the temp rises. Did you keep your stock O2's? Hook up one of those light show AFR guages. They'll give you an idea of how the AFR is changing as you drive. Invaluable.

A vacuum guage is also invaluable for selecting the right PV.

Sputtering above 4500 you say? I dont think this is the carb. Sounds like the ignition system to me too. The 2 systems to be suspect are the secondaries which open with load and the power valves, which open with load. Are you running some crazy 3.5 or 4.5 hg power valve? I always run the 8.5 or 9.5 PV. Starts giving it gas right at the onset of acceleration.

Vacuum or mechanical secondaries?

Honestly, you need to get the AFR guage and vacuum guage and watch what it's doing while you drive. Otherwise it's educated guaesswork.

 

[Boss 351]

Over 8lbs of fuel pressure? That's too much bring it down to 6.5 or 7lbs MAX. If it still happens, check the coil.

 

[samuraichamploo]

ok, Im getting a blaster coil today, and taking the FP down to 7.
Whats a RTV? sorry im new to carbs...
Its vaccum secondaries, and the stock coil.

 

[1985MustangGt]

RTV is a silicone that dries similar to a gasket. The make all types, red, blue, orange, brown, black.... See which is best for your application

 

[fly4spd]

i didn't see if your carb had an electric choke or not, but if it does make sure that it is opening ALL THE WAY, and make sure that it's not being stopped from opening by mangled linkage or your air cleaner. you should be able to look into the float sight windows and see the level of fuel in the float, adjust it so that it is right about halfway in that window. if all that is fine then like someone else said check other problems. two of my cylinders aren't firing at the moment and i was told that it could possible the the motorcraft ignition modules, and was told that they tend to go bad. to check the ignition system check the spark off the coil if it looks like a thick blue spark, then your in business. Good luck
-aj
edit: sorry didn't see that you checked your float level, but i'll leave it in for someone else if they need it.

 

[Hissing Cobra]

Your fuel pressure is set way too high. It should be set at the aforementioned 7psi MAX. Anything more than this will result in needle/seat problems. At wide open throttle, you never want less than 4psi.

I've got two 4 barrel carbs on my 306 and I've got it set at 7 psi at idle and 4-5 psi under wide open throttle. That's plenty, especially for two carburetors.

 

[hllon4whls]

The sputtering problem above 4500 could be countless ignition problems. I also want to mention that it could be valve springs. Does it free rev past 4500 and run like crap under load?

That is what mine did with 70lbs of seat pressure. Cam specs called for 110 lbs of seat pressure. What a difference that made!

 

[samuraichamploo]

revs fine, under load it bogs.
BTW, if your ever in nola and feel like giving me a hand, il provide the lunch and beers. I am trying to do most of this myself, but Im somewhat clueless when it comes to carbs

 

[samuraichamploo]

Also, when you say that it should be a certain FP at idle and a certain FP at WOT.
I know how to set the FP via the regulator, Is there a second measurement for WOT, or is that just the outcome for FP considering the bigger drain of the fuel at WOT?

 

[Hissing Cobra]

That's usually the outcome of the initial throttle opening and the draining of the fuel bowl in the carb. If it's set at 7psi while idling, you probably won't have a problem, especially since you have the infamous "Blue" pump.

To check the psi under wide open throttle, you need to have a fuel pressure guage hooked up so that you can view it while driving. Mine is mounted on my cowl vent, while other's mount their's inside the cockpit (an isolator is required.) If it drops below the 4psi mark, that'll indicate that your fuel pump isn't producing enough volume under wide open throttle. Again, I don't think you'll have a problem here, as you have the Blue pump.

I also don't think that you're boiling the gas. I realize that this problem starts about 5 minutes after startup, not nearly enough time to boil the gas. Most cars don't even come up to the full operating temperature in five minutes.

When a car is cold, it requires more gas and less air to run correctly (hence a choke, which limits incoming air.) As it warms up, more air is needed to even out the mixture (choke opens, allowing more airflow.) If your car is running right when cold, but running rough when warm, it could be an indication of too much fuel (8.5 psi?) If the choke is open all the way, then you've got the required amount of air, but could have too much fuel. This may not be a problem at a cold startup because you need to run it rich to keep it going. Make any sense?

I would definitely start at the fuel pressure and continue to ask questions before buying parts (possibly needlessly.) It gets expensive taking shots in the dark.

Does it feel like it's misfiring when warm? If so, you may have some fouled out plugs from the higher fuel pressure. Check your spark plug wires and distributor cap to make sure that they're in good working condition, with no cuts or cracks. I noticed that you have the MSD distributor, did you have to cut/splice wires to hook it up? If so, make sure that they are not loose.

There are many things that could be causing this, keep trying and good luck! Don't be afraid to ask for help, and definitely do so, before spending money.

 

[crazypete]

Obvious one I missed but...

if you have the vacuum advance hooked up.....toss it and go for another drive. I realize that there should be zero vacuum advance above 3000 and all mechanical BUT...

I've had so many problems with vacuum advance and my holley avenger that I finally tossed and capped the vacuum advance system. I was getting spikes at idle and stumbling until I unhooked it.

Attach a timing light and rev the engine. Should be 10-16 degrees at idle and then hand rev the motor and see where it ends up (32-38 degrees). See if the timing does anything funky at 4500+. It might free rev ok but mis-timing will make a dog under load. Stock balancers are marked -10 to +40 so you can see the whole range of timing motion.

Obvious stuff: check under the cap. If you see any signs of wear then this is your problem. I had a crazy misfiring mustang that barely ran. Turns out my fat coil had blasted the cap terminals to charred stumps. Quick fix and I was back on the road. My old saab ran like crap under acceleration and I switched cap+rotor and she ran like a champ under the gun. Try it. Cheap stuff. Cant hurt.

FP-wise

I might recommend the FMS kit for mechanical FP with the timing chain cover, eccentric for the cam and lever type pump. Perfect FP across the board. Pumps harder as you rev. I have never gotten (despite 3 attempts and dual FP regulators) to get good FP with electric pumps (not sure if a "blue" pump is electric or not). A lot of others would say else but this was my experience.

Hope this helps!

Setting up a carb conversion is a pain but once you figured out it's settings, it's a breeze to maintain and very accessible so hang in there. Took me about 2 months to get my carb conversion acting right but I have never looked back.

 

[bluevenom867]

What with all the high FP?I got a holley black pump and my pressure stays at
5.5-6psi at any throttle.I have run it at 7-8psi it made no differance, but at 5.5-6psi my nitrous kit works better.Also check what heat range and gap on your plugs, I had the wrong plugs in one time (4 ranges to cold) with a gap of like 35 and it would do the same thing.

 

[Hissing Cobra]

Bluevenom867,

The Holley "Blue" Pump will flow 14psi at Max pressure and flow 88 gph (gallons per hour) @ 9 psi. This is way too much fuel for a carburetor, which generally can't operate correctly with anything over 7 psi. Needle and seat problems will surely occur. This is why an adjustable fuel pressure regulator is needed.

If your running at 5.5-6 psi, you're in the correct range.