d50guy
Need a Spot
Reged: 05/23/12
Posts: 16
Loc: utah
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I know there are lots of threads on this topic. but none seam to be able to help with my problem. I recently rebuilt my motor. now running 135 lbs compression across the board. i am running a carter bbd 2 barrel carb a pace setter header. ngk v power plugs. one step hotter than stock. (the burn on the plugs looks pretty good if any thing a little on the lean side) right now the timing is advanced as far as the distributor will allow. and i have managed to minimize the dieseling. but still on occasion it will diesel. I am currently running the distributor that has 2 stages of advance. but only have one stage hooked up. (the bottom stage) to a port on the upper side of the carb that has vacuum when above idle but nothing at idle. i do not know what rpm my idle is at but i know its pretty low. ( ac pump all but kills the motor at idle) I have tried to retard the timing and that only made it worse. also i have eliminated all vacuum except the advance. and running an electric fuel pump with about 4 psi pressure. with no return on the carb to the tank. I am currently getting about 22-25.75 mpg and thats running 75-80 on the freeway. and 35 around town about a 50-50 split on a tank of highway and city driving.
so my questions are
1. any suggestions on the dieseling issue?
2. what mpg does every one get?
3. if i were to add a return to the carb (drill and tap a port) would i want to regulate on the return side, or the inlet side and does the 2.5 psi every one has posted really work?
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fasteddy
Web Wheeler
Reged: 01/30/01
Posts: 12747
Loc: Flat Creek, GA
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Does the carb have provision for a fuel cut solenoid?
I think you are running too lean. Plugs are harder to read with gasohol, and tend to be darker than on gas, so you can get fooled with the color.
The mileage you show is quite high, further proof of too lean, as is the need for tons of advance and weak idle torque.
You need a regulator with 3 ports - inlet from the pump, regulated delivery to carb, and excess pressure return to tank. Don't know carters very well, but I think your pressure is too high.
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"If you can't be a good influence, don't worry, you can still be a horrid example."
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d50guy
Need a Spot
Reged: 05/23/12
Posts: 16
Loc: utah
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no fuel cut solenoid.
this is an all mechanical carburetor.
it runs fine retarded as well. its just the dieseling is worse when retarded. and its slightly under powered. when retarded.
I do know i can take the top of the carb off and watch the float and with the pump on the float does shut the fuel off. and it doesn't flood it out as far as over powering the needle valve.
and the ac may be not quite right because it acts a little funny at times. so thats probably not the best judge to go off of. and once again what mileage are people getting so i have something to compare to.
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fasteddy
Web Wheeler
Reged: 01/30/01
Posts: 12747
Loc: Flat Creek, GA
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mileage is quite high. I used to see about 18 mixed
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"If you can't be a good influence, don't worry, you can still be a horrid example."
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d50guy
Need a Spot
Reged: 05/23/12
Posts: 16
Loc: utah
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i could get 20-22 with the stock carb when the truck had 190k miles on it and it was so rich then that at times you would have to rev it up with a big cloud of smoke to get it to clean out...... I went to the bbd carter carb so i could have some adaptability. so with the new gas what should i be looking for on the plug? or if i put a pyrometer in what temperature should my exhaust be. Is that the best way to tell if its to lean?
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fasteddy
Web Wheeler
Reged: 01/30/01
Posts: 12747
Loc: Flat Creek, GA
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You'll have to google for egt ranges.
I use an edjicated nose. Gassy smell (unburnt fuel) at the tailpipe is rich, acrid burny (increased NOx) smell is lean.
Gasohol means the deposits look a little different. I've read that the proper range is a hair darker than you were used to before, but real white is too lean, sooty black is too rich, and the proper range is a clean grayish tan, just a tad darker than the good old all gasoline days.
The dizzy vac advance you describe is the high altitude version, I think. What kind of shape is the centrif advance in? Use a timing light and someone watching the tach, with the vac advance removed and plugged, and chart the centrifugal advance curve. Increase the engine rpms from idle slowly, looking for any jumpiness or hang up. You should see a smooth advance from idle setting to the max the centrif allows. Chart the numbers at 500rpm intervals. I don't remember the numbers offhand, but I think the fsm has them in the distributor section of the ignition chapter.
Then use a hand vac pump and apply varying amounts of vac to the vac advance pot at idle to test that section. The range of interest is from idle (that dizzy should use ported vacuum, i.e., the vac advance should not operate at idle rpms, only when the throttle is opened up - the port is uses is above the throttle plate until it opens up some) up to around 22" ov vacuum. The specs for this are also in the fsm.
Having to use as much static advance as you describe is a sign that you have a very slow buring mixture. This could be a very lean mixture (probably) or some other problem. This is why I think it's running lean. You have to use a lot of advance to burn a lean mixture and get the max cylinder pressure at the most advantageous crank angle. It's like shooting birds on the wing. The speed of the projectile is analagous to the speed of the burn. The slower the burn, the more advance you need so the burn is complete in time, or the projectile gets to the bird in the case of a slow moving shot pattern.
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"If you can't be a good influence, don't worry, you can still be a horrid example."
Edited by fasteddy (05/24/12 12:58 PM)
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JohnnyBfromPeoria
Trail Leader
Reged: 06/10/02
Posts: 5096
Loc: Phoenix, AZ
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I had a dieseling problem with my first Raider that I never did solve completely. I got into the habit of engaging the a/c compressor just before I keyed the ignition off. I got the idea from my '72 Impala that automagically did it every time you shut down.
My solutions often don't fix the root cause of the problems, just make them somewhat bearable.
John B.
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d50guy
Need a Spot
Reged: 05/23/12
Posts: 16
Loc: utah
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I have not charted how my advance is working, but I do know as i watch with out the vacuum advance hooked up that the centrifugal advance is working smoothly, Just not charted. And as for the vacuum advance I don't have a hand vacuum pump but if i suck on the hose and watch the advance I do know it is working as well. as for my burn it is on the lighter side of gray, and there is little to no deposits on the plug. if you follow the electrode on the plug around it is past the bend before there is much of a deposit, chocolate milk in color for about .050 and then a line about .010 of clean, then more of a deposit, that looks about like chocolate milk
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TOASTY
Trail Leader
Reged: 01/17/02
Posts: 5058
Loc: Gilbert AZ, US.
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Maybe it just wants some diesel?
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Az Crew, full fledged member!
"Strange things are afoot at the Circle-K." -Ted.
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fasteddy
Web Wheeler
Reged: 01/30/01
Posts: 12747
Loc: Flat Creek, GA
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I'd try decoking the combustion chambers. Running at an idle of around 2000, spray water into the carb throat with a spray bottle. This will "steam clean" the combustion chambers and remove any deposits that are running white hot and providing a dieseling ignition source.
Make sure you are using ported vac for the dizzy. There should be no vac at idle, and plenty just off idle.
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"If you can't be a good influence, don't worry, you can still be a horrid example."
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