Carb issues or what????

[whatever01]

:bang: I have had issues with my bike from day one. It always had a back fire back through the carb on occasion from the begging , everyone said it was lean so I bought a GIII from Zippers w/ the thunder jet and paid a guy to put it on an air fuel meter and tune it in. Well it was popping from the big radius so bad when you let off of the throttle that I couldnt take it. Took it to another guy for tuning under load on the dyno helped some but was spitting and sputtering @ low throttle @ a steady cruise, until it warmed up, it also had black smoke when I hit the throttle. So I had the bike checked @ the dealer for intake leaks and I re-checked for intake leaks and exhaust leaks, nothing. Re- jetted the carb and tuned it in. Took care of the black smoke and bike pulls strong when accelerating, but still has popping back through the carb and a steady issue @ low steady speed where it blips and spits as well as occasional pop through the carb. I am at a loss and have no clue what the hell is going on but I am very frustrated @ this point and time. I have a 600 cam GIII dialed in with the air fuel mix screw out 1.25-1.35 from seat 78 main and a 31 int. It has had a .295 and 33 int. the 33 was to much and caused smoke the .295 was to small. I have also had a 74 and 76 in the carb as well as some larger mains. Does anyone have any ideas on what this could be? I am tired of paying people for me to have to turn around and make the corrections, I always felt that they were the professionals and let them handle it, but obviously I havent found the correct mix. I have also changed the plugs etc. I forgot to mention I even tried a PSI @ one time and I couldnt get it to work for S--T. Could there be an issue with the timing, air bleeds or what? I just want to get this right. Like I said it runs grat when you are getting on it but @ a slight throttle and steady speed its sneezing. blipping and popping etc on a regular not constant basis. HELP!!!!!:angry:

 

[Gas Man]

295 is way too low....

poping out the exhaust is common on the BR pipes.

Coughing out the carb around 2500rpm while cruising indicates a lean condition.

sounds like you need to first... adjust the carb and replace the plugs... try it out.

But you said you have a thunderjet... so I believe I was told that usually allows you to have a smaller main so I'm not sure what's up with that then...

 

[Vegas]

If you haven't tried a .032 intermediate that may be the key. You should look for Vaccum leaks around the intake seals. One thing I have noticed with my bike is if I set the idle mixture screw at the highest and best idle, it pops more and does surge at just off idle cruising. If you turn your idle mixture screw just a .25 turn out it helps the surge and the pop somewhat. You problem has nothing to do with your main jet so concentrate on your intermediate, accel pump, and idle tuning. If you have a spike it may be contributing as well. Highly recommend the S&S extended filter. It really woke my bike up above 4k.

 

[whatever01]

Sul I am running the S/S extra wide filter w/ a desperado cover.

 

[whatever01]

Thanks for the tip @ this point I am willing to try about anything.

 

[05chop]

you have done a shit load of carbs.Could try something with the ignition coil,timing,plug wires this too can cause intermittent misfire.

 

[delly2]

so some of you guys say the backfiring on decel is normal?? i cant see that, whatever01 do you have your baffels in your pipes?? try driving it and then pulling your plugs to read them see what color they are? they will determine a lean or rich condition..

 

[05chop]

When you are riding in decel the throttle plate is where? Closed so you are running on the low speed jet with high vacuum. My first mod was gut the stock pipe. I got back fire on decel and back fire on startup loud too.Tryed jetting with gut then went to martin bros exhaust. Never looked back from there no more backfire.

 

[sun_bill1974]

Whatever01,
I had the exact same syptoms...my bike was sputtering in low gears, and a cloud of gas would emit. I have a D&M filter, and anytime you have a high performance breather, you should remove bowl vent screw. That fixed the problem. If your looking at your carb, the screw is at 7pm, and underneath the carb...its an alan screw underneath.

would think when the first guy tuned it with an a/f meter that should have been good. the exhaust pop was most likely an exhaust leak at the flange.

not knowing what filter your running and since you've tried so much i'd say pull the bowl vent screw to see if that helps.

 

[P8RIOT]

...so some of you guys say the backfiring on decel is normal?

Mine never backfires on decel, and I have V&H Big Radius pipes - that would not be normal.

 

[whatever01]

After hours of research and trial and error the problems seem to be solved. Sgt Fury and I worked on the carb and switched the jets out. I now have a 32 int 76 main and a thunder jet. I switched out the external air bleed, externally installed on the zippers G3 carb, makes it easy to change. we then changed the jets . I proceeded to dial it in by S&S standards and still had popping etc. I rode the bike w/ one hand on the air/fuel mix and one on the throttle and kept making low speed passes. I was able to tune out the popping and sputtering. I ended up @ 2.5 turns out on the air fuel mix, went up from a 31 to a 32 on the int and started over, I was shooting for the 1.25-1.75 turns out, this never worked I ended up @ 2 1/8 with the 32 and no popping etc. 100% better. I am assuming that S&S gives you those guidlines for set up on a stock carb, this has been bored out and smoothed circuit etc. so I guess more air flow needs a little more on the air fuel mix. seems to be working well at this time.

 

[barhopper]

Seems like a small main. I have a 84. How does it run full throttle?

 

[Raywood]

After hours of research and trial and error the problems seem to be solved. Sgt Fury and I worked on the carb and switched the jets out. I now have a 32 int 76 main and a thunder jet. I switched out the external air bleed, externally installed on the zippers G3 carb, makes it easy to change. we then changed the jets . I proceeded to dial it in by S&S standards and still had popping etc. I rode the bike w/ one hand on the air/fuel mix and one on the throttle and kept making low speed passes. I was able to tune out the popping and sputtering. I ended up @ 2.5 turns out on the air fuel mix, went up from a 31 to a 32 on the int and started over, I was shooting for the 1.25-1.75 turns out, this never worked I ended up @ 2 1/8 with the 32 and no popping etc. 100% better. I am assuming that S&S gives you those guidlines for set up on a stock carb, this has been bored out and smoothed circuit etc. so I guess more air flow needs a little more on the air fuel mix. seems to be working well at this time.

You shouldn't be using S&S guidelines for tuning the carb. You need to use Zippers which differ due to the three jets and an airbleed vice only two.
Download them from Zippers. They advise upping the intermdeiate even though it means the air/fuel screw will only be turned out 1/2 turn. Then dropping the main 2 sizes cause at 4500 rpm the thunderjet comes in.
There is a long thread on it here somewhere.

Good luck,
Ray

 

[Raywood]

I see that Zippers website is being upgraded where you download the tech notes. If you pm me your email I will send you the .pdf file although it is almost 9mb so if your server can handle it I can send.

Let me know,
Ray

 

[whatever01]

Barhopper do you have the zippers g carb with a thunde jet? the thunderjet is a third circuit that works w/ the main.

 

[Raywood]

Here, I print screened an image for you. Read carefull the things to do with the Intermediate, air bleed, main and thunderjet. Totally different than with a stock S&S. Yes, I had a thunderjet on my 03 Mastiff!!!

Good luck,

 

[whatever01]

thanks.