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"popping" on decel

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E. Murray

Farmall Cub
Joined
Sep 13, 2002
Messages
97
Points
0
Location
Springfield, MO
Hey,
All seems to be well mechanically except that there's a popping noise through the exhaust when I let off the gas when under way. It is a repetitive "pop pop poppoppop pop" sound like a small backfire (but more of a dull thud). I just replaced most of the ignition stuff, so what does it sound like? New to the carb thing, so I tend to blame it for everything... might as well get all the info first this time:D .
 

E. Murray

Farmall Cub
Joined
Sep 13, 2002
Messages
97
Points
0
Location
Springfield, MO
Exhaust leak where (at the header?)? I would think the gasses would be burnt enough to not be able to react with straight air. Am I running too rich maybe and expelling unburnt fuel? It sometimes diesels after it's been running...bad valve or something?
 

Robert Mann

Farmall Cub
Joined
Mar 5, 2001
Messages
334
Points
0
Location
Stockton Ca
Have air injection???
Disconnect it and it should stop. Just remove the supply hose for the right side and put it on the left side, then remove the belt from the pump.
 

E. Murray

Farmall Cub
Joined
Sep 13, 2002
Messages
97
Points
0
Location
Springfield, MO
No air injection... Why would it do it only on deceleration in gear (i.e. engine braking)? If I push the clutch it quits. :confused:
 

Baradium

Lives in an IH Dealership
Joined
Nov 11, 2001
Messages
6,090
Points
36
Location
Fairbanks, AK
Dieseling can be caused by a number of things, engine hot spots, timing too advanced, plug too hot a number, too low of a grade of gasoline, etc. Is the noise like the you get from the big tips on the exhaust? Maybe an exhaust leak like previously mentioned?
 

E. Murray

Farmall Cub
Joined
Sep 13, 2002
Messages
97
Points
0
Location
Springfield, MO
So it sounds like the two problems aren't necessarily connected. I think my timing is too far advanced so that may be the dieseling problem. The exhaust was new behind the manifold when I bought the vehicle last year; that's why I was asking about the mechanism in an exhaust leak that can cause the problem. Maybe I need to go over the exhaust more closely... I didn't mean to question Mr. Tabor's diagnosis; I'm just curious how it works. Thanks for all the help.
 

Baradium

Lives in an IH Dealership
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Nov 11, 2001
Messages
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Location
Fairbanks, AK
Some exhaust systems just pop. Varies with muffler etc, but some of them always pop on decel.
 

Jay Tabor

Banned
Joined
Jan 2, 2002
Messages
4,716
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Location
Pahrump, Nevada
static ignition timing has nothing to do with 'dieseling' when ignition is turned off. or any other time either.
what element is needed for combustion to take place?
Oxygen!!
when you decelerate the engine in gear, the engine is sucking in fuel, understand?
the engine's cyls dont burn all that fuel completely, because the throttle is closed. so- little/no air gets in, got it?
so- that means all that fuel gets pumped into the exhaust pipe unburned.
some were, somehow [ one of lifes mysterys] air [ OXYGEN] gets into the exhaust pipe, and mixes with the hot fuel laden exhaust gasses and goes -BOOM! got it?
when you coast to a stop, out of gear, the engine isnt sucking fuel, so you dont get gas reigniting in the exhaust pipe.
write this down and memorize it, there will be a test!
 
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75SII

Farmall Cub
Joined
Dec 10, 2002
Messages
20
Points
0
Location
AZ
vacuum leaks?

Mine popped real bad on decel 'til I fixed a few vacuum leaks and it hasn't popped since. I had leaky diaphragms in the vacuum advance, throttle pull-off and egr valve.
 

David Banner

High Wheeler
Joined
Apr 19, 2003
Messages
1,475
Points
83
Location
Galloway, OH
Execellent explaination John. Your explaination also explains WHY the airpump was added to lower emissions! A pox on anyone who removes their emissions equipment (with the possible exception of those switching to EFI) PRETENDING to make their vechicle run better.
Point in fact I recently reinstalled all the cut and plugged vaccum lines (done by the PO) on a recently acquired '75 S11 345--it runs noticably smoother at idle and I certainly don't notice any loss of power on the highway!

Sorry if I've hijacked the thread...

Moderators feel free (I'm sure you do:p ) to move this post...
 

Jay Tabor

Banned
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Jan 2, 2002
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Pahrump, Nevada
David yes the A.I.R. pumps were/are great emissions reducers for free! injecting air into the exhaust pipes to afterburn fuel! heck yeah leave em on to fool the smog machines into thinking the engine isnt polluting much. my only gripe is the pumps and manifolds were in the way of changing plugs on IHV8 s.
except of course the defective'gulp' valves would cause the mufflers to explode!!!!!!!!!!!!
 

pandorasboxg

Farmall Cub
Joined
Apr 2, 2003
Messages
133
Points
0
Location
branson mo
mine deisles when turned of i think (that is when it keeps turning over after you "turn it off"?) what does cuase this and how do i fix this? i have never seen a car do this before i started driving my scout but this is also the first car with a carb i have driven are these related the few people i have talked to havn't said much but " your timing must be off" but im with you john how does this happen with the ignition off? mine also pops sometimes on decel but its pretty quiet so i just ignore it i just don't like how it turns over sometimes when i turn it off
 
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pandorasboxg

Farmall Cub
Joined
Apr 2, 2003
Messages
133
Points
0
Location
branson mo
another symptom is if i coast down hill for a long time in gear but no throttle as soon as i get back on the pavment or what ever i have no power at all....the only way to accel is to pump the gas....i don't know if the two are realated
 

Jay Tabor

Banned
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Jan 2, 2002
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lower the idle speed that usually stops/eliminates the 'run on', or dieseling. if the carb is leaking fuel internally that also will make it 'run on'
why you have to pump the throttle several times after long decel is caused by accelerater pump not working. why? I dont know could only guess
 

Paul "Misterfixit" Schulz

Super Mod from Downunder
Staff member
Administrator
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Dec 8, 2002
Messages
4,662
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Yarrawonga Victoria Australia
at least yours is only popping - my ol c1200 international with the 281 - 6 cyl had a cracked exhaust manifold and on a down hill stretch with the foot off the gas it would easily blow a 5 foot flame out of the top of the 4 inch exhast stack, i could see it in my mirror as it was happening! the first time i saw it on me and my laundry man knew how scared i was.
 
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