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 Post Posted: Thu Mar 08, 2012 10:07 pm 
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seems to me that the afr readings are null and void considering how bad car was running. maybe i should have not posted the numbers considering i was in and out on the throttle.
well anyway think i figured out what the problem is.
i will however not disclose [-( my findings until next Wednesday.


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 Post Posted: Thu Mar 08, 2012 11:01 pm 
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Slowpoke wrote:
I think it will show lean if it's missing because of the unburned oxygen.


You might be right about this as sometimes I forget that we're measuring oxygen not fuel, but, I'm having a problem getting my head around thos AFRs he's getting if this is indeed an ignition miss? According to those readings there's not much oxygen left, which says rich?? Unless, the s**t is burning in the pipe before it gets to the sensor? :-k

Either way nothing will be near correct until the miss is fixed!

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 Post Posted: Thu Mar 08, 2012 11:24 pm 
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There needs to be distinction between a Miss fire and a partial burn. Partial burns are very common, total missfires are not. Partial burns produce CO because the pressure is low. When the pressure is low the temperature is low and it doesnt reach the required temp to make CO2.
Also the easiest AFR to ignite is 10.5. It takes the least ignition energy to ignite that mixture so an ignition problem may be overcome by going excessively rich. the engine may even make more power but what your chasing is the wrong thing. Everybody must aspire to the best ignition energy system possible, only then do you start to fix the carburetion. Its not the other way around.


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 Post Posted: Fri Mar 09, 2012 8:21 am 
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since my problem is a lack of fuel to motor, is that really consider a misfire? :-k i think of misfire as an issue contributed to the ignition system not functioning correctly. because in my mind
i am still receiving fire in each cylinder, even though there is no fuel to fire. think i might have answered my own question. O:)


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 Post Posted: Fri Mar 09, 2012 8:32 am 
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I'm a little late to the party here.
What is the engine combo?

If I'm reading correctly this is a 1050 with non oxygenated fuel. It should be pretty darn fat with a 93 jet and you have 96's correct?
I run 98s on Q16 and 92s on regular fuel.


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 Post Posted: Fri Mar 09, 2012 4:23 pm 
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themadreefer wrote:
since my problem is a lack of fuel to motor, is that really consider a misfire? :-k i think of misfire as an issue contributed to the ignition system not functioning correctly. because in my mind
i am still receiving fire in each cylinder, even though there is no fuel to fire. think i might have answered my own question. O:)

This is how it goes, the ignition system puts an electric charge into each cylinders spark plug every time, it never fails, it's the fuel around the sparkplug that fails. Provided you have the basics of the electrical system in good condition it will always put a charge to the plug. However it may not arc correctly. In order for the electricity to ignite the fuel the electricity has to pass through enough fuel molecules. It only takes a tiny bit of electricity in the order of 6 millijoules to ignite fuel. Now the basic MSD has around (well its supposed to) 180 millijoules so you may think there is plenty of electricity to do the job, Well there is but it doesn't matter how much electricity you pass through the gap if there is not enough fuel molecules for it to work on. The electricity that is used to heat fuel from liquid to gas state is wasted electricity, if you use the wrong fuel the vaporization level may be lower than optimum and then you need the electricity to do the work for you. That creates whats called flame kernel retardation. The cylinder burns like the ignition was retarded because the arc took too long to get the fire going.

The main reason why cylinders experience partial burns is because the AFR varies a lot per induction event and the exhaust contamination and the homogenization vary. The inducted AFR can vary absolutely heaps, it may be 11:1 then 17:1 the next time. The exhaust contamination depends on what the exhaust gas species are. If the previous burn was really good there will be high CO2 present, CO2 is a fire extinguisher gas, its obvious what that's going to do. If the previous burn was a poor one there will be high CO levels and minimal exhaust scavenging because there was a low exhaust energy on the previous burn. So now you get a change in AFR (because the CO is a burnable fuel gas). Also the poor scavenging creates higher cylinder pressure during the exhaust stroke, which makes the possibility of intake runner reversion more likely.
The homogenization of the charge at ignition time is highly variable in some engines, intake reversion from a previous poor burn goes up the intake runner on intake valve opening, heats parts of the intake charge and alters the vaporization of part of the charge. So was it CO or CO that did that? How many hot free radical HC's were there involved in that reversion?
These things and lots of others make engines random and not very well controlled.
The larger the cylinder the more difficult it is to control.


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 Post Posted: Fri Mar 09, 2012 4:45 pm 
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Scott Smith wrote:
I'm a little late to the party here.
What is the engine combo?

If I'm reading correctly this is a 1050 with non oxygenated fuel. It should be pretty darn fat with a 93 jet and you have 96's correct?
I run 98s on Q16 and 92s on regular fuel.



454, 12.5 cr, brodix 320cc heads, mechanical roller 732 lift.

yes 1050 with non oxygenated fuel.

yes ran 96's this past wednesday for the first time. they were actually a partial band-aid to my fuel problem that i discovered last night in my work shop


Last edited by themadreefer on Sat Mar 10, 2012 4:56 am, edited 1 time in total.

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 Post Posted: Fri Mar 09, 2012 4:46 pm 
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shrinker wrote:
themadreefer wrote:
since my problem is a lack of fuel to motor, is that really consider a misfire? :-k i think of misfire as an issue contributed to the ignition system not functioning correctly. because in my mind
i am still receiving fire in each cylinder, even though there is no fuel to fire. think i might have answered my own question. O:)

This is how it goes, the ignition system puts an electric charge into each cylinders spark plug every time, it never fails, it's the fuel around the sparkplug that fails. Provided you have the basics of the electrical system in good condition it will always put a charge to the plug. However it may not arc correctly. In order for the electricity to ignite the fuel the electricity has to pass through enough fuel molecules. It only takes a tiny bit of electricity in the order of 6 millijoules to ignite fuel. Now the basic MSD has around (well its supposed to) 180 millijoules so you may think there is plenty of electricity to do the job, Well there is but it doesn't matter how much electricity you pass through the gap if there is not enough fuel molecules for it to work on. The electricity that is used to heat fuel from liquid to gas state is wasted electricity, if you use the wrong fuel the vaporization level may be lower than optimum and then you need the electricity to do the work for you. That creates whats called flame kernel retardation. The cylinder burns like the ignition was retarded because the arc took too long to get the fire going.

The main reason why cylinders experience partial burns is because the AFR varies a lot per induction event and the exhaust contamination and the homogenization vary. The inducted AFR can vary absolutely heaps, it may be 11:1 then 17:1 the next time. The exhaust contamination depends on what the exhaust gas species are. If the previous burn was really good there will be high CO2 present, CO2 is a fire extinguisher gas, its obvious what that's going to do. If the previous burn was a poor one there will be high CO levels and minimal exhaust scavenging because there was a low exhaust energy on the previous burn. So now you get a change in AFR (because the CO is a burnable fuel gas). Also the poor scavenging creates higher cylinder pressure during the exhaust stroke, which makes the possibility of intake runner reversion more likely.
The homogenization of the charge at ignition time is highly variable in some engines, intake reversion from a previous poor burn goes up the intake runner on intake valve opening, heats parts of the intake charge and alters the vaporization of part of the charge. So was it CO or CO that did that? How many hot free radical HC's were there involved in that reversion?
These things and lots of others make engines random and not very well controlled.
The larger the cylinder the more difficult it is to control.


i see said the blind man.


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 Post Posted: Thu Mar 15, 2012 7:33 am 
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well went back to the track last night. seems my ignition system is starting to fail. after having to replace my crank pickup pick up last week and now my 3-step rev limiter.

first pass last night, car breaking up. second pass removed chip on "race" side of rev limiter and bam, finally made a full pass. should have
by passed the 3-step all together as i am still having a slight breakup as soon as i get into throttle. which i think might be an issue with idle circuit on carb.

so back to subject matter. nowing that my previous jet sizes were probably causing car to be fat. i started jetting down. mph stayed pretty consistent but was dropping about .1 per pass. wanted to jet down one more time, but redlight in first round of eliminations.

ar readings are little better than last week, getting a little closer to 12.

good new is that i have set a new et for car. finallly made a 9.93 pass at 134 on motor only \:D/ . once i get carb dialed in better, will start spraying the good stuff again. and based on my et gain with the nos on previous carb, pretty confident car should run a low 9, possibly a high 8 :-$


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 Post Posted: Thu Mar 15, 2012 9:37 am 
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If you're too lean at the hit then the AFR should show that? But glad you're getting it sorted out.

On the 2 circuit swap, there's been a "few" Dominators that didn't suffer lean top end because of the idle tubes in the mainwells. And I mean damn "few". Maley stated at one time that he figured about one in ten would get rich enough to slow it down. On those carbs and even some others a performance GAIN is not always seen so if you're faster now, that means yours was likely too lean up top before the conversion. And even if the conversion doesn't make it faster, the lean and clean bottom end is worth the trouble and expense of doing it.

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 Post Posted: Thu Mar 15, 2012 2:11 pm 
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yes afr are showing way lean at the hit off the line when foot braking car.
my plan next week is to jet down a few number and see how car runs. once i find the sweet spot with jets, i will play with air bleeds.
yes right now the car is about .15 faster with the conversion. i am sure she will be faster once i get the tune better.

giving last nights weater condition, heavy dense fog, sure she would have run faster


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