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midrange popping/backfire

  • Thread starter Thread starter robotkillerbees
  • Start date Start date
R

robotkillerbees

Guest
well after reading alot of other posts and threads, i couldent find any thing about exactly what my bike is doing. i found some simalar simptoms and used there ideas but to no avail.
my bike is a 78gs1000 4cyl/8 valve , vmcarbs, kerker exhaust, 125 main jets, pod filters, i just made three trips to the suzuki dealer for valve shims. rebuilt the carbs new coils,points/condensors
it should run tip top but i have a bit of midrange popping and everyonce in a while back fire between grear, it doesent really affect the performance she still screams, but its still anoying

any help would be great
charlie

also if theres a thread/post that i missed.. let me know and i will check it out
 
robotkillerbees said:
well after reading alot of other posts and threads, i couldent find any thing about exactly what my bike is doing. i found some simalar simptoms and used there ideas but to no avail.
my bike is a 78gs1000 4cyl/8 valve , vmcarbs, kerker exhaust, 125 main jets, pod filters, i just made three trips to the suzuki dealer for valve shims. rebuilt the carbs new coils,points/condensors
it should run tip top but i have a bit of midrange popping and everyonce in a while back fire between grear, it doesent really affect the performance she still screams, but its still anoying

any help would be great
charlie

also if theres a thread/post that i missed.. let me know and i will check it out
Click to expand...
ok what size are the carbs stock 26 or 29 smoothies ??
what size is the pilot jet
how many turns out are the pilot fuel mixture screws (if they are the stock 26mm carbs)
what position is the clip in for your jet needle

a lean condition in your carbs is not related to RPM or speed
it is related to throttle position and the throttle position that the popping and back firing occurred usually means a lean condition
but in order to get rid of it you need to know the throttle position so that you can then adjust the correct circuit in the carbs to get rid of it
 
Try putting the needle clip one notch down. This will rasie (richen) the needle circuit.
 
SEE wahe happens thanks

SEE wahe happens thanks

the fuel jets are set 2 turns out and the main jet size is 125 . the clip is in the fourth position from the top, i am going to try puting it on the last one and leaveing the air 1 1/2 turns out and the fuel 2 turns out
and i will see what happens

charlie
thank guys

1978 gs1000e (current)
1980 xs400 (current)
07 dyna superglide(current)
previous bikes
1980 gs1000
sportster
1979 xs750 tripple
 
Last edited:
monster

monster

cheff1366

dude your bike sounds like a monster. where on earth do you find face shields/goggles that dont blow off your head while you are rideing

charlie
 
sometimes you can get rid of it by enrichening the pilot circuit just a bit.

if you have a exhaust without baffle it is nearly impossible


honda bikes have a separate fuel circuit in the carbs to cure this event.

it is annoying but harmless.
 
no dice

no dice

well no dice on the fith position. it made it run like it was under water. so i tryed putting them in the third position as a control. and it looks like 4 is where it needs to be. so i will go from there tomorrow. it was running pretty good befor i messed with it. one thought is to leave it alone, but i just cant its got to be tiptop or or nothing . also i think i will change out the clutch and springs next week . it seems slipping a bit so that cant be helping either.
another note. i have never changed out a cam chain, now i am able to build a jig to feed a new one in while pulling out the old one ,as to not missalign the cam sprokets. the question is where or can you find a cam chain with a masterlink

and right on , nakid rider that is why america rocks!
 
this happend twice today

this happend twice today

picture.php
 
square one, almost

square one, almost

well i put the clips back in the forth position , pulled off the carbs sealed up any possible leak(because of sputs coming from the carbs)
noticed a small oil weepage went to tighten the bolt it was closest too cracked the valve cover and snaped off the bolt. so she is on hold untill i get a new valve cover, then i will pick up where i left off. , im in to deep now to just give up, i know when i get it dialed in just right . it will fly
 
geting closer

geting closer

well even wih the crack in he valve cover i coulden resist playing with it. and im getting closer, just so happens i didint really know anyhing about these carbs, i scowerd this sight and found ou some really good suff, so i sarted off with the mains took out the 125's and put in 120'sseems to be running great after 5k. so tomorrow im on to the needle jets. and from what i have read and been told thats where the problem with the midrange popping should be

also iv been told the pod filters are a bad idea. do to turbulance causeing lean/rich/lean/rich conditions
either way the stock air box is not going back on. butt does any one know if there is a cfm rateing for the sock air box im thinking about at least makeing a custom one and kicking he pods to the kurb
 
got skinny

got skinny

on a good note. when i was doing a shake down ride last week. i took my bike to the transfer station(the dump). and the lady there let me put it on the scale, it weighed in at 460lbs (+/- 5lbs scale sensitivty) the original bike weight was 562 i think
so it lost 20% of its original weight

when i get thses carbs figured out its going to be a death trap
 
Last edited:
new clutch

new clutch

just got my new barnett clutch and heavy duty springs. going to put them in tomorrow night. decided to take a break from the carbs and get back to enjoying working on the bike.
also someone asked for photos of how i made this bike . sorry couldent find the message but i put them in my album for viewing
 
Sounds like a cool ride -- we look forward to a full report with lots of photos...

Also, how are your exhaust gaskets? These can cause popping if they're old.
 
Go up a size on your pilot jet

How old are your carb boots?

Pods are okay, just a PITA to get dialed in, as you've discovered

Start working out with your left hand, that Barnett is stiff (ask me how I know)

Also, you'll probably never find neutral with the motor running, ever

Are you coming to Shasta??
 
i think you are right on about the pilot jets i will pick them up tomorrow as my clutch springs came but not my disks. i think new pilots will do the trick. the carb boots are in great shape with no leaks i used starter fluid squirts to check. good news no leaks bad news starter fluid on the motor if you act quick its also a degreeser:D
the barnett's that bad huh?
the exhaust gaskets are new . it was a bit tricky getting the 30yo ones out. but i was more stubborn
as for shasta i will be on my honeymoon in cabo. but i wish you guys safe rideing.and great weather
 
Yeah, the Barnett is pretty much a race clutch

Some put 1/2 Barnett fiber plates, 1/2 Suzuki plus 3 Barnett springs, 3 Suzuki as a upgrade
 
Big T said:
Yeah, the Barnett is pretty much a race clutch

Some put 1/2 Barnett fiber plates, 1/2 Suzuki plus 3 Barnett springs, 3 Suzuki as a upgrade
Click to expand...
I've heard of splitting the springs but doesn't the Barnett use the extra fiber and steel?
 
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