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  #31 (permalink)  
Old 05-22-2013, 03:04 PM
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Something is telling me it's not the carb but ignition system. I would check everything. Bad plug or wires, make sure the voltage are correct.

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  #32 (permalink)  
Old 05-22-2013, 04:52 PM
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Its not ignition related the distributor has its power straight from the battery through a toggle switch and I have a volt meter hooked up and its 13.5 to 14 volts and I also put all new plug wires and spark plugs in just a month ago and did not have any backfiring till I put this new carb on. Previous one did not have this problems like this. Distributor is all new as well with everything top to bottom so there is nothing else to check. I have already looked over everything and I also checked each wire with a ohm meter before I even hooked them up and they all were spot on and very close to one another. Timing has been checked and verified and tested with different settings and no difference in how this just happens. This thing is going to make me pull my hair out soon. High speed rpms are nice and good with no missing or anything. If I had money to buy a better carb and chuck this one I would but can't right now. I just paid over 1500 bucks for my heads just last month so can't afford stuff right now but I just don't know why this tiny but problem issue keeps rising its ugly head and no amount of carb tuning is changing it. Something is bad somewhere but its not constant only at certain times does it do it. I will have to see if I dig in some more but for now I don't know what else to check as have been through everything.
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  #33 (permalink)  
Old 05-22-2013, 05:09 PM
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One suggestion I did not try yet is using a different metering block. I got a new one and will take this one off and install the new one and see how that does. If it does the trick then problem solved. I will have to wait till next week for that as this weekend taking truck to have timing cover replaced cause I have a seal leak and installing a high volume water pump.
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  #34 (permalink)  
Old 05-22-2013, 08:01 PM
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If you're using manifold vacuum for the vacuum advance, swap it over to ported. There are cases where the sudden loss of advance at the hit of the throttle (caused by a manifold vacuum-equipped vacuum advance) will cause a *pop* through the carb, similar to a lean condition.

If this is the problem, it can be dealt with so you can still use manifold vacuum if you wanted. But trying it will at least rule out or verify it as the core issue.
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  #35 (permalink)  
Old 05-22-2013, 08:59 PM
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if your going to chase gremlins in the ignition system take your dizzy cap off inspect the inside and make sure all the contacts are clean and not chewed up or arcing, make sure spark plug wires are not laying ontop of each other. if you have ability to run the vehicle in a completely dark space for a min with the hood open you chould look for arcing from the wires to virtually anywhere
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Old 05-23-2013, 07:53 AM
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Already done that. Putting it on ported makes no difference and I have already checked my wires and the distributor is brand new from top to bottom and has less then a hundred miles on it. Old carb when it was on did not do this issue at all.

Soon as I put this new one on then it started and that was the only thing I changed. I wanted the electric choke setup of the 80457 so I used the main body and base plate and used my old metering blocks from my 1850 to put on the 80457.

Thing should not have any problems but I have gotten duds out of the box. I bought a brand new holley 670 street avenger almost 5 years ago and the engine would run fine then all of a sudden it would almost die and you would have to keep giving it big shots of gas to keep it running.

Spent countless man hours checking ignition and everything else and ruled out the carb cause it was new. Well after sometime we said it had to be the carb and put my dad's old 80457 carb on he just got rebuilt and it ran just fine.

Replaced my holley 670 with another one and it did the exact same thing like this one cant get rid of an off idle backfire. I sent it back and got a third one and it would not even shot gas out the shooter and taking it apart it looked fine but got fed up with it. Shipped it back then got the 1850 carb and it ran just fine with no issues.

I am going to try a new metering block I got and if that does not get rid of it. I would have kept old carb but I already sold it to help pay for my 80457 carb so to late for that.

I got a spare quick fuel 600 tower to use and if the changing the block does not cure it then I am taking it off and checking it out and if looks anything bad its gone and replaced with the quick fuel one.
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Old 05-28-2013, 06:57 PM
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Hey guys the mystery has been solved. Turns out it was a combo of initial timing and vacuum advance conflicting each other. Was running 14-16 initial with the 14 degrees of vacuum advance on full manifold. Putting vacuum advance on ported did not help at first but adding more initial with full manifold vacuum advance did not help. But initial was put to 17-18 and vacuum advance was then put to ported and wow what a difference. It runs like fuel injection and no more backfire. For some reason just that little difference made all the difference. Tried the different settings of timing before and could not cure it. But I did not figure this combo of just a few degrees and hooking vacuum advance to ported would make a world of difference. Something what works for one does not work for the other. Hard to read timing with new power steering bracket in road and was off about 4 degrees of timing. Thanks guys for your tips.
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  #38 (permalink)  
Old 05-28-2013, 07:30 PM
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You can go to 10 degrees of vacuum advance if need be. 10-12 degrees is about all we usually use.
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  #39 (permalink)  
Old 05-29-2013, 07:53 AM
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So, It was the ignition system that was giving you problem.
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  #40 (permalink)  
Old 06-01-2013, 08:52 AM
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Sure Was lg1969. I tried original initial setting with vacuum advance hooked up to full manifold and with ported and it did not make any difference either way and added some extra timing and tried both ways and it still did not work right. It was up at my dad's house over the weekend and he thought it must be close and maybe I tried too much but not enough so he adjusted the initial a hair at a time till he got it just perfect and it only needed just a few more degrees but any more then that and it caused its own problems but he tried with full manifold vacuum and it for some reason was too much so put on timed and walla it works perfect and has real nice throttle response and responds nice and quick. I was only off about 4 degrees give or take. I tried adding more then that and it did not help as it was too much and caused other issues. Hard to believe just a few degrees too much or too little can make that much of a difference but this was a learning lesson for me that's for sure. Thanks guys
Eric
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  #41 (permalink)  
Old 06-01-2013, 10:00 PM
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I'm glad it's working great. Good luck and have fun.
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  #42 (permalink)  
Old 06-01-2013, 11:07 PM
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Quote:
Originally Posted by eric32 View Post
Sure Was lg1969. I tried original initial setting with vacuum advance hooked up to full manifold and with ported and it did not make any difference either way and added some extra timing and tried both ways and it still did not work right. It was up at my dad's house over the weekend and he thought it must be close and maybe I tried too much but not enough so he adjusted the initial a hair at a time till he got it just perfect and it only needed just a few more degrees but any more then that and it caused its own problems but he tried with full manifold vacuum and it for some reason was too much so put on timed and walla it works perfect and has real nice throttle response and responds nice and quick. I was only off about 4 degrees give or take. I tried adding more then that and it did not help as it was too much and caused other issues. Hard to believe just a few degrees too much or too little can make that much of a difference but this was a learning lesson for me that's for sure. Thanks guys
Eric
Your experience is exactly why I keep preaching that even w/similar combinations there is NO ONE TIMING SETTING that can be given over the 'net that will be perfect in all cases! And yes- just a few degrees one way or the other DOES matter!!

From here:
Quote:
A word on giving exact timing recommendations

It is all but impossible to give exact timing numbers because of the variations in engine builds and conditions in which these engines run. It is always preferred to work up to the optimum timing a step at a time. This is the safest way to go about it. What has to be avoided is too much timing under load; too much timing under load can cause engine-damaging detonation.

*SNIP*

But any way you slice it, it's still trial and retrial to get the curve dialed in. No matter what we do (short of digital control), the timing curve is always somewhat of a compromise, being as how all engines and vehicles (and all the other considerations) are different from case to case. So don't be surprised or alarmed if you end up with a curve that is different from what is presented in this article.
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