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Farmall & IHC Tractors Discussion Forum
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Way off subject backfireing ?

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Paul Shuler

11-24-2004 15:03:29




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I have a similar problem as the post below about blowin the muffler apart on the Super M. The problem I have is on my truck though. It is a 400 small block chevy. With an Edelbrock 4 barrel carb. It is backfireing back through the carb though. I have triple checked my timeing. Tried two different dist. I'm not sure where to go from here. It has LOTs of power and runs very good with no miss. When it does it is when I'm running along about 50 or 60 mph and have to slow down like for a car pulling out, and when I go to accelerate there is a loss of power followed by a loud pop through the carb. Sometimes two or three pops then it takes right off like there is no problem. It has been doing this for a year and I have had a bunch of people look at it but no one can has any ideas. I can't ever reproduce it in the garage just working the throttle. It seems to have to be under load. Sorry this is off subject but it is my tractor hauler.

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Allan in NE

11-24-2004 15:15:52




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 Re: Way off subject backfireing ? in reply to Paul Shuler, 11-24-2004 15:03:29  
Paul,

It is the accelerator pump in the carburetor and/or the power valve (99% of the time it is the accelerator pump or a missing check ball).

You might want to check and make sure that the secondaries aren't hanging open too (they should be fighting against spring and vacuum resistance when set correctly).

Also, that engine will run better with the static timing pulled up to around 8 or 10 degrees.

I time 'em by ear by advancing the timing until the engine just barely "pings" under a hard pull, then just back it off until the pinging is gone.

If it cranks good at this location when hot, this is where they run the best.

Hope this helps,

Allan

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Paul Shuler

11-24-2004 15:51:27




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 Re: Way off subject backfireing ? in reply to Allan in NE, 11-24-2004 15:15:52  
Right know it is timed around 8 or 9. I could advance to around 13 and it would still start good but needed 89 octane to not ping and I hate to buy the high dollar gas. The thing realy runs good is what confused me. From a dead stop it will flat lay your ears back. But slowing down then and then taking off or accelerating out of a turn will make her pop off about everytime.



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Allan in NE

11-24-2004 16:03:15




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 Re: Way off subject backfireing ? in reply to Paul Shuler, 11-24-2004 15:51:27  
Paul,

It is definitely your accelerator pump causing your woes. Even tho it may even look like it is working okay. You are just not getting a good enough fuel charge under acceleration.

It doesn't do a 'machine gun' series of pops back thru the carb does it? (this is a different problem). Just the one or two loud "poof" sounds and she falls on her face? That is classic accelerator pump trouble.

If you take the air cleaner off and snap a picture of the top of that carb, I can tell you exactly where that part lives and how to change it out. (There are lots and lots of different Eldebrock carbs out there).

Allan

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Paul Shuler

11-24-2004 16:28:56




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 Re: Way off subject backfireing ? in reply to Allan in NE, 11-24-2004 16:03:15  
It will loose power and if I get my foot out of it sometimes it wont pop but If I keep my foot in it, it will forsure pop. Usualy once but if I keep on it two or three times. I still have the book with the carb and all of that stuff. It is only a year old. I can snap a few photos of it tommorow for you also. I'm at work right now.



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Allan in NE

11-24-2004 16:33:37




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 Re: Way off subject backfireing ? in reply to Paul Shuler, 11-24-2004 16:28:56  
Okay, that works and yes that sounds just like a pump problem.

We also had a lot of trouble with fellas putting on one of those "Econimizer" type carbs. That 400 is a hungry engine and these "starvation" type carbs just weren't throwin' enough fuel on acceleration.

Allan



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old

11-24-2004 15:13:40




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 Re: Way off subject backfireing ? in reply to Paul Shuler, 11-24-2004 15:03:29  
This may sound strange but your problem is that it is running to lean. You need to adjust your carb to give it more gas. When you hammer it to get back up to speed it isn't getting enough gas so it pops back out the carb. Also running lean like that can burn valves.



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ChadS

11-24-2004 16:14:03




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 Re: Way off subject backfireing ? in reply to old, 11-24-2004 15:13:40  
Check your electric connections to the distributor as well. HEI ignitions love their voltage. Spark plugs will tell the story, check em out immediately after it happens. ChadS



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