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firing order ..Int. 345 truck motor,backfire probl

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markmark

01-12-2006 18:41:44




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backfire problems when I throttle up..I rebult the carb? did not help.....Could it be a bad dist. diaphram ,losing vacuum because I can't get it to idla low without keep om trottling it up or it stalls ...




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fastcattle

01-13-2006 06:49:19




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 Re: firing order ..Int. 345 truck motor,backfire p in reply to markmark , 01-12-2006 18:41:44  
Had a 392 4-barrel that acted very similar.Rebuilt the carb with a Holley kit and new power valve.Still not much better.Did it again,no change.Had a carb man older and wiser than me look at it,he said carb not the problem.Bought a brand new(not rebuilt) Holley just for grins(and about $200)runs like a brand new truck.My point-sometimes rebuilding just wont work.PS That was 5 years ago,have not touched it since best running engine I own-boy do I wish they were still in business.

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Buzzman72

01-13-2006 07:58:32




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 Re: firing order ..Int. 345 truck motor,backfire p in reply to fastcattle, 01-13-2006 06:49:19  
You make another good point about these engines and the Holley carburetors. They'd usually only rebuild once. The last time Dad had a problem with one on his '67 1200 with 304, he finally gave up and sent the carb to a shop in town...the fellow there said the metering plate had warped, and it was about as cheap to buy a fresh rebuilt carb. Instead, Dad robbed the metering plate out of an abandoned Holley 4-barrel, and it worked just fine.

Dad's experience was: rebuild the Holley at 50,000 miles, and replace it at 100,000 miles...so his '62 Travelall was on its 3rd carburetor when Dad quit driving it at 240,000 miles [head and pan had never been off the engine].

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Earl in KY

01-13-2006 05:25:44




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 Re: firing order ..Int. 345 truck motor,backfire p in reply to markmark , 01-12-2006 18:41:44  
Gents,
Some IH V-8 gasers time off of #8



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Buzzman72

01-13-2006 05:31:50




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 Re: firing order ..Int. 345 truck motor,backfire p in reply to Earl in KY, 01-13-2006 05:25:44  
Yes, the International SV-series engines, which include the 266, 304, 345, and 392, all time on #8 cylinder...so that's where to hook up your timing light.

And about the initial question...the firing order is just like Chevrolet...1-8-4-3-6-5-7-2.



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markmark

01-12-2006 20:59:53




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 what is the firing order?345 Int... in reply to markmark , 01-12-2006 18:41:44  
yes ii backfires thru carb..only when you try to advance the throttle..it won't idle under 1000 rpm it will stall out ..black sotty plugs ..it rev's to good and has smooth top end so I don't think it is timing chain..maybe bad coil or wires or advance not working in dist..with a chevy you can see plate move theu inspection hole in cap..



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Allan in NE

01-13-2006 05:26:37




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 Re: what is the firing order?345 Int... in reply to markmark, 01-12-2006 20:59:53  
Mark,

I think you have a vacuum leak if you've already rebuilt the carb and it belches at throttle-up along with it's not idleing down. Is the accelerator pump working okay?

The governor and the vacuum advance work backwards to what you would think on those things.

Under acceleration, the advance should be moving back toward base timing, not away from it, therefore will not really have much of an effect on drivability; just fuel economy.

The first order of business is to find out why that thing will not idle down. After you cure that little problem, I think the belchin' will subside.

Allan

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mno

01-12-2006 21:19:22




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 Re: what is the firing order?345 Int... in reply to markmark, 01-12-2006 20:59:53  
it would idle and not pop out carb.if you took vac.advance off and put it in your seat,sounds like carb. wires,points together,timing.



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Bluto

01-12-2006 20:21:41




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 Re: firing order ..Int. 345 truck motor,backfire p in reply to markmark , 01-12-2006 18:41:44  
Backfiring out of the carb or exhaust?

If it's popping out the carb look for bad intake valve or manifold to head gaskets.

If it's popping out the pipe like a big old bang during deceleration, and equipped with an air injection (smog) pump, look at the gulp (diverter) valve.

Weak ignition can make it pop and sputter.



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mno

01-12-2006 19:49:32




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 Re: firing order ..Int. 345 truck motor,backfire p in reply to markmark , 01-12-2006 18:41:44  
Mark don"t think vac. advance would have anything to do with it not idling,it should not do any thing until you give it gas,how long has it done this? before carb. rebuild? did it start all at once? if it"s got vac.leak you can put your hand over carb. part way or close choke part way and it will smooth out,sounds like carb. bad igi.wire out of time.



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RustyFarmall

01-12-2006 19:05:49




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 Re: firing order ..Int. 345 truck motor,backfire p in reply to markmark , 01-12-2006 18:41:44  
The vaccuum advance on the distributor could be at fault, but I would investigate the possibility of an extremely weak ignition coil, or could be as simple as a defective primary coil wire. Might be the ignition timing is slow, could be the timing chain has jumped a tooth. Check out the coil wire first.



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Buzzman72

01-13-2006 05:28:29




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 Re: Int. 345 truck motor,backfire in reply to RustyFarmall, 01-12-2006 19:05:49  
Does this truck have the Holley 2-barrel carb?

When you rebuilt the carb, did you replace the power valve?

In all my years of working with International V8's, the most consistently troublesome thing was a bad power valve on the Holley carb. And if you're not using a genuine Holley carb kit, you're probably not getting a genuine Holley power valve...and those from SOME suppliers are just plain inferior, if not defective from the get-go.

Backfire thru the carb can blow out a power valve in an instant...so you might pick up a spare--or two.

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