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Old 05-08-2013, 03:38 PM
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SBF 347 with rich smelling exhaust

New member but been lurking around for a while.
I have a 347 in my 65 Mustang that runs pretty good except for this heavy, rich exhaust smell. At this point I'm kind of grasping for a solution.
347 w/ AFR heads, Pertronix distributer, Air Gap manifold, roller cam 625 AFB carb and headers. I'm not very good with tuning carbs but I had 3 different carbs to try. I tried an AED 650, mech sec, 600 vac sec Holley and the new Edelbrock 625. No difference in the smell, none. I have played around with float levels and idle mixtures with no change in smell. Plugs look a little black but not horrible. I have about 9 in of vacuum at idle. Timing is 18 at idle. Runs and drives pretty good but this smell is pretty bad; wife wont even ride in the car. ANY suggestions are most welcome. Looking forward to hearing from some people that know this stuff alot bettr than I do.

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Old 05-08-2013, 03:57 PM
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Quote:
Originally Posted by Cpartridge View Post
New member but been lurking around for a while.
I have a 347 in my 65 Mustang that runs pretty good except for this heavy, rich exhaust smell. At this point I'm kind of grasping for a solution.
347 w/ AFR heads, Pertronix distributer, Air Gap manifold, roller cam 625 AFB carb and headers. I'm not very good with tuning carbs but I had 3 different carbs to try. I tried an AED 650, mech sec, 600 vac sec Holley and the new Edelbrock 625. No difference in the smell, none. I have played around with float levels and idle mixtures with no change in smell. Plugs look a little black but not horrible. I have about 9 in of vacuum at idle. Timing is 18 at idle. Runs and drives pretty good but this smell is pretty bad; wife wont even ride in the car. ANY suggestions are most welcome. Looking forward to hearing from some people that know this stuff alot bettr than I do.
Carburetors are not like EFI, more fuel pressure will not make more horsepower. What it will do is to overpower the needle and seat in the carburetor bowl and allow the pump to blow raw fuel into the intake manifold, creating a tuning nightmare. Carters, Edelbrocks and Rochesters will tolerate about 5 psi at the carburetor inlet before the needle unloads. Holleys will stand a little more, about 6 psi.

Tee off at the carb inlet using short pieces of rubber fuel line hose to connect and run a small copper line or dedicated fuel hose back to the firewall, then up past the hood lip to the cowl in front of the windshield. Temporarily mount a 0-15 psi, liquid-filled, mechanical fuel pressure gauge on the cowl so that you can monitor it through the windshield while you drive. It can be mounted with duct tape, tie wraps or whatever, since it's only temporary until you get the fuel pressure sorted out. Never bring liquid fuel lines or mechanical fuel gauge into the driver's compartment.

Mechanical, cam-driven pumps are available in the 5-6 psi range if you shop around. Forget about those trick-of-the-day, double-throwdown super pumps that are marketed for carburetors. They don't work, as you have discovered. Also, trying to control the flow of a mechanical pump with a pressure regulator is an exercise in futility, because of the surging of the pump, which is unlike the steady flow produced from an electric pump, which can easily be controlled at 5-6 psi with a quality pressure regulator.
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Old 05-09-2013, 05:29 AM
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Awesome info! As far as fuel pressure; i am running a mech regulator but will only get it down to around 6 psi and its a crappy gauge and regulator. Without the regulator I had 8 or 9 psi. I'll get a different fuel pump and see what happens.

As for the timing; i didnt know you could lock out the distributer and run that much timing at idle. I'll mess with it this weekend and let you all know how it goes. Thanks
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Old 05-09-2013, 02:30 PM
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If you get the ignition timing squared away, you'll think someone swapped in a BBF while you slept. With locked out timing, the motor will probably want to kick back against the starter, so you will want to introduce some manner of killing ingition altogether while you spin the crank. A momentary on-off push button switch mounted where you can get to it with your left hand while you're spinning the crank with your right hand will work fine. Just include the switch into the ignition/coil feed line. Hold the momentary-off, normally-on button down, get the crank spinning, then release the push button, providing fire to the plugs. Aftermarket ignition products manufacturers such as MSD make dedicated electronic devices to do the same thing.
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Old 05-10-2013, 10:35 AM
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Bought a new mech fuel pump, hopefully get to put it in tomorrow. Will advise results.
About the timing thing, after reading a little about locking out the dist. I'm a little apprehensive just because this is just a street car. Would changing springs and weights be something to try before doing the whole lock ot thing? Just curious.
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Old 05-10-2013, 03:51 PM
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Quote:
Originally Posted by Cpartridge View Post
Bought a new mech fuel pump, hopefully get to put it in tomorrow. Will advise results.
About the timing thing, after reading a little about locking out the dist. I'm a little apprehensive just because this is just a street car. Would changing springs and weights be something to try before doing the whole lock ot thing? Just curious.
What rpm does the motor stall to against the converter, generally speaking, stoplight to stoplight, right off the mark?

Here's a wiki article that I started years ago about how to syncronize the #1 piston position in the bore and its relationship to the inertia ring of the harmonic damper......
http://www.crankshaftcoalition.com/w...op_dead_center
If you zero the damper and lock out the distributor, you will be waaaaaaay ahead of the game.

And while it may seem unrelated now, replace all the grounds with new braided cables and "down to bare metal" connections. Replace the hot and ground cables at the battery. Scrape off, sand off all surfaces that touch each other, make certain there is no corrosion in the connection, then spread clear RTV over the connection to prevent corrosion from moisture. If you drill through the firewall to make a new firewall connection (very strongly recommended), go inside the car and install a locking nut on the bolt, then apply RTV, inside and out. I usually try to mount this one pretty high on the passenger's side, out of reach of the passenger's shoe. It is not possible to have too many grounds on a car.

Last edited by techinspector1; 05-10-2013 at 04:16 PM.
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Old 05-11-2013, 12:04 PM
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I have a 5 speed in the car so no converter. Will check out grounds as mentioned. New fuel pump is in but havent tested yet. Will let you know how it goes.
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Old 05-12-2013, 07:06 AM
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The front throttle blades are open too far at idle, putting the blades past the idle circuit. Do a web search "how to tune a holley the scientific way".

The solution is to add more timing which increases the idle speed, then can turn down the idle screw which closes the front blades. And you can also crack the secondaries open a little more using the screw under the carb (need to pull the carb off to see it). You can also drill a 0.090" hole in each front blade. These adjustments allow more air into the carb which allows the front blades to be closed more.

I would put a 750 holley 3310 on that engine.
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Old 05-12-2013, 12:09 PM
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Trying to find cam specs. A little ignorant of the distributor mods but I'll read up on it an give it a shot. Thanks for all the great info. Will keep you posted.
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Old 05-14-2013, 09:19 AM
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So, I'm going to get some advance limiters from Pertronix, come in 12, 16, and 20. You would recomend limiting the mech advance to 12 and setting initial timing to 24 ish? Sound like a plan?
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Old 05-29-2013, 01:39 PM
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Ok, initial timing set to 22, limited to 34, all in by about 3000 rpm. New mech fuel pump installed, fuel pressure around 6 psi ( need a better gauge) with the Edelbrock 600. No change in smell but holy crap! I thought it was quick before! Havent really adjusted anything else other than the idle speed down some. Runs awesome but smell still there. Would you try advancing a little more? The limiters I have in are 12 deg. Thanks again for all the grwat info; learning a lot.
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Old 05-29-2013, 04:01 PM
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The Carter 625 and Edelbrock Carbs work best at 5 psi max of 5.5 psi,just to make the wife happy Speedway has your back: Manhattan Oil 19769-19 Fuel Fragrance Additive, Cherry Bomb, 4 Oz. - Speedway Motors, America's Oldest Speed Shop other scents available too Save this guide lots of good info:http://www.mymopar.com/downloads/carterafbtuning.pdf You may want to post a link to the cam you are running,check out the section on metering rod springs and how a camshaft affects them.

Last edited by JeffB; 05-29-2013 at 04:11 PM.
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