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  #1  
Old 05-19-2006, 12:38 PM
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FSJ-Earl FSJ-Earl is offline
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BACKFIRING / EXHAUST ISSUES

My 83 J10 w/ 258 and stock carb, has been backfiring like crazy lately. What causes backfiring? I also noted that the very END of my tailpipe is REALLY hot, enough to blister skin, ask me how I know. My 89 GW tailpipe NEVER gets that hot, nor does my wifes 90 GW. I have a manual choke and I need to keep it at least 1/2 choked to keep it from stalling at stop signs and red lights. Any ideas? THANKS!

EARL!
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Old 05-19-2006, 12:40 PM
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Lindel Lindel is offline
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Sounds like a very bad vacuum leak to me.
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Old 05-19-2006, 01:09 PM
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Backfiring tends to do with too much unburned fuel being dumped into the exhaust, then igniting. That can be due to running very rich (not as likely) or timing being off (more than likely). When the timing is off, unburned fuel is dumped into the exhaust, and the valves aren't completely shut, allowing part of the combustion flames to go through the exhaust, thus igniting it and causing backfires / incredible heat in the exhaust system.

Just a few suggestions: check timing & check mixture.
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Old 05-19-2006, 01:42 PM
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rustywagoneers_com rustywagoneers_com is offline
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possible timing chain also, but that is down the list a little... also look for liquid fuel running out of the booster venturis as the engine is running..

peace
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Old 05-19-2006, 03:10 PM
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Timing is fine, Zack and I just put in an HEI a few weeks ago so the timing is good. I would most likley lean towards the carb problems. I hate the carb on the 258, I need to repair / replace this thing in the near future.
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  #6  
Old 05-19-2006, 05:18 PM
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When I mentioned timing, I was also thinking that it might have jumped timing. But, when you installed the HEI, are you sure you weren't a tooth or two off? I'm guessing that since Zack was helping, that wouldn't be the issue, but worth asking to be sure.

For carb mixture, you can do what lots of folks are starting to do: buy or build your own AFR (Air-Fuel-Ratio) meter with LED's. Most have a 5 LED display, and you typically want 3 bars for perfect mixture. You install an O2 sensor in your exhaust, and connect the wires to the little meter (you can build one for around $50), and that way you can always be 100% sure that you have a good mixture on the carb.
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Old 05-19-2006, 05:26 PM
Ristow Ristow is offline
 
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are you backfiring through the pipe or the carb?
i think you're lean,and it's popping through the carb,if you were rich,choking it at the stop signs would make it worse.

being a couple teeth off on the distributor install would only mean you would have to rotate the housing a little more to correct the timing-15 degrees btc is 15 degrees btc,regardless of distributor orientation.
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Old 05-19-2006, 06:20 PM
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Backfire/exhaust is like a virus. You live with it intermittently, it's always dormant, you can't kill it, and when the engine is cherry and running prime it comes out of nowhere like a cold sore.
Like that? I didnt think so. Grades were posted today and I got an A in my grad-level poetry workshop. The high should wear off any minute now.
Only posting because the symptoms you described happened to me in an isolated incident and the $759 K&N air filter was so plugged I couldn't see daylight holding it against the sun. Re-adjusted carb screws ever so slightly after dousing the $879 K&N air filter in gasoline and dish soap. Things were back to normal. Absence of air, in other words.
Quite often with me its the 1% of the chances and that's not a good thing. Good luck Earl, I know you've put a lot of dough in your beasts.
Brent
PS--If I lived as close to Zack and his gadgets as you do, Zack would have my picture with a red stripe thru it on the shop wall with the words "86 on sight unless carrying cash"...
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  #9  
Old 05-19-2006, 07:21 PM
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I am backfiring through the exhaust - 2 - 3 foot flames last night, it was pretty cool! I am pretty sure that it is all carb. I need to get rid of or do some work on the stock carb. I am too cheap to spring for a Weber!

Quote:
Originally Posted by Ristow
are you backfiring through the pipe or the carb?
i think you're lean,and it's popping through the carb,if you were rich,choking it at the stop signs would make it worse.

being a couple teeth off on the distributor install would only mean you would have to rotate the housing a little more to correct the timing-15 degrees btc is 15 degrees btc,regardless of distributor orientation.
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  #10  
Old 05-19-2006, 07:36 PM
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are you still running the air pump? Maybe the diverter valve aint functioning. Vacuum hose loose in that system or something?
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Old 05-19-2006, 07:47 PM
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the coke thing and the REALLY hot tailpipe tells me that your running WAY lean. change the fuel filter now and see what that does then check some other things that would couse that
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Old 05-19-2006, 08:12 PM
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The War Wagon did this when I first got it. 3 foot flame out the tailpipe
I rebuilt the carb and that fixed the problem. That sure pissed off my son that it would not do it any more.


Jim
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Old 05-19-2006, 08:22 PM
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If you still have the stock carb, you might have a blown power valve and be running very rich. Is it hard to start in the mornings (ie, 10-15 pumps of the go-pedal to get it to fire)?
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  #14  
Old 05-20-2006, 04:23 AM
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oh yea, every AM it takes 10 - 15 pumps of the accelerator to get er to fire up.

Quote:
Originally Posted by billyrb
If you still have the stock carb, you might have a blown power valve and be running very rich. Is it hard to start in the mornings (ie, 10-15 pumps of the go-pedal to get it to fire)?
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Old 05-20-2006, 06:20 AM
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91G-Dub 91G-Dub is offline
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I had a similar problem with my GW and it was a combination of things:

1. Dizzy roter was chewed up
2. Couple of vacum leaks
3. Carb way out and needed to be adjusted

I didn't have the flames (man oh man that would be b@#$hing at night) but the 10-15 pumps and backfiring, burping and farting like at drunken sailor when it was cold.
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Old 05-20-2006, 08:04 AM
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First things first........you most likely have a blown power valve on the front of the carb. You can buy them for around $20. Replacement takes about 15 minutes. When you blow the power valve, you basically leak fuel on to the top of the manifold, and your float bowls go dry, dumping the raw fuel either on to the manifold or into the engine. Then, when you go to start it, you have no fuel in reserve, thus the 15+ pumps to bring fuel into the carb, enough to fire. Also, your mileage should be around 8-9mpg when you blow your power valve. Once replaced, you'll get around 12 or so, possibly more with an HEI & proper tuning. It'll also fix your cold-start issues, so that you only pump it once to engage the choke, then it'll fire.
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  #17  
Old 05-20-2006, 11:57 AM
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If you're having to keep the choke on to keep it from stalling, you're almost certainly running very lean. The extremely hot exhaust would support this theory.
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  #18  
Old 05-22-2006, 03:52 AM
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Well, I did not have time to work on this thing this weekend, but I did notice that the backfirning only happens when the engine and exhaust are REALLY warm. If I drive to work (1 mile), I don't have the problem, If I go to the autoparts store (4 miles) it backfires when I turn it off or downshift from 4 to 3.
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1983 - J15 - J10 body + J20 running gear = J15 Trail rig
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