prop and back fire

philbullet

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A 4.3 v6 Lx, could a prop that is pitch to high make it back fire some what?
I switched from a 21' 4 blade to a 17 p 3 blade and it stop the back firing but it fan faster with the 4 bkade.
sent it off to pitch down to a 19p.
 

wrench 3

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It sounds like you have a tune up problem. Lower pitch prop, less load on the engine, doesn't stress it to the point where it misfires.
Personally I'd start by looking at the distributor cap and wires..
 

alldodge

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A 4.3 v6 Lx, could a prop that is pitch to high make it back fire some what?
I switched from a 21' 4 blade to a 17 p 3 blade and it stop the back firing but it fan faster with the 4 bkade.
sent it off to pitch down to a 19p.

Agree with wrench you need to check timing and fuel supply. Backfiring in most cases is timing, but if your running lean this could also cause similar symptoms.
 

Bondo

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A 4.3 v6 Lx, could a prop that is pitch to high make it back fire some what?
I switched from a 21' 4 blade to a 17 p 3 blade and it stop the back firing but it fan faster with the 4 bkade.
sent it off to pitch down to a 19p.

Ayuh,..... At what rpms is this all happenin',.??
 

philbullet

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Ayuh,..... At what rpms is this all happenin',.??

Well before we adjusted the valve springs I couldn't get on plane because of backfiring, fixed that Problem , was running a 19 P. Prop.
tryed a 4 blade 21 p., faster all around but kinda backfiring when giving it gas.
Put the 17 p back and it runs fine.
thinking it's just to much pitch.
ops around 2000 or so getting on plane.
 
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Bondo

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Ayuh,.... to much pitch ain't what induces skippin',.... to much pitch causes the motor's rpms at Wot to drop due to runnin' outa horsepower,...

At what rpms would it run, 'n at what rpms did it skip with each prop,..??

I'm thinkin' yer valves are still screwed up, or it's runnin' lean,.... or the timin',.... or the valve timin',.... or,....
 

wrench 3

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I'm curious as to why it needed a valve adjustment. Did it have major engine work recently?
 

philbullet

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Yes, rebuild,valves lift was .430 and needed .500
this heads was not original , came for a truck motor.
IT wouldn't even get on plan before backfiring reel bad.
 

philbullet

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Ayuh,.... to much pitch ain't what induces skippin',.... to much pitch causes the motor's rpms at Wot to drop due to runnin' outa horsepower,...

At what rpms would it run, 'n at what rpms did it skip with each prop,..??

I'm thinkin' yer valves are still screwed up, or it's runnin' lean,.... or the timin',.... or the valve timin',.... or,....

Yes Bondo, I think I may still have some timing isue and maybe carb. Adjustment needed.
 

wrench 3

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I'm still curios about the valves. The only way of changing the valve lift is to replace the cam shaft with a different model. How exactly are you adjusting?
 

philbullet

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I'm still curios about the valves. The only way of changing the valve lift is to replace the cam shaft with a different model. How exactly are you adjusting?
Different valve keepers and spacers Under spring s.
 

sub2010ss

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All that should do is change spring performance. Lift can only be carried by camshaft or rocker ratio.
 

wrench 3

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Did you put old style heads and intake on a vortec engine? How are you adjusting the rocker arms?
 
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