Need advice on engine stalling reasons

[HiTech]

2006 Mastiff 117 motor & Super G carb. Bike always ran great until this year when it started shutting down only when throttle is opened close to full. I noticed for awhile that with a full fuel tank it would stutter & sometimes die & loosening the cap made it run again. However now the problem is more consistent and loosening the fuel cap has no effect. Engine always ran too rich & never needed enrichment activated. Often backfired on startup & guys complained the exhaust too smelly to ride behind. So I rebuilt the carb w/ S&S Master kit, rejetted to next smaller size: main to .070 & intermediate to .033 & it now requires me to engage the enrichment on cold starts only just for a few seconds, and accelerates smooth, no hiccups no backfires, smooth consistent idle too..... until I reach speeds of 55+ & higher where the engine just dies and acts like it's fuel starved. Pull in clutch, let rpms go back to idle and it restarts & runs fine until risking full throttle again. Sometimes climbing a hill & giving it more throttle will cause it to die unless I keep it at lower to medium rpms. Gas cap is the aftermarket ratcheting type and I disassembled it twice & it looks fine & passes airflow. Should I decrease that main jet to .068 or .066? I don't suspect a faulty handlebar RUN/START switch (checked it as well), Air filter is very clean, fuel strainer & petcock clean & good flow. Spark plugs are burning a dry medium to dark gray color but far better than the black they were before the carb rebuild & rejetting. Electrical connections to ignition coil & ECM module are good & tight. Running ethanol free 89-91 octane depending on the vendor. Any ideas on what's going on?

 

[Rottweiler]

I would be checking the fuel shut off valve. Could be getting clogged.

 

[mleach72]

A .070 is unusually small for a 117. Most guys are running a .078 main jet. Your intermediate was probably too big. That's why it smelled bad. The main jet doesn't come in until 3k rpms or so. The most common jet combination is a .031 intermediate and .078 main. Minor adjustments may be needed, but you should be in that area.

 

[Mikeinjersey]

2006 Mastiff 117 motor & Super G carb. Bike always ran great until this year when it started shutting down only when throttle is opened close to full. I noticed for awhile that with a full fuel tank it would stutter & sometimes die & loosening the cap made it run again. However now the problem is more consistent and loosening the fuel cap has no effect. Engine always ran too rich & never needed enrichment activated. Often backfired on startup & guys complained the exhaust too smelly to ride behind. So I rebuilt the carb w/ S&S Master kit, rejetted to next smaller size: main to .070 & intermediate to .033 & it now requires me to engage the enrichment on cold starts only just for a few seconds, and accelerates smooth, no hiccups no backfires, smooth consistent idle too..... until I reach speeds of 55+ & higher where the engine just dies and acts like it's fuel starved. Pull in clutch, let rpms go back to idle and it restarts & runs fine until risking full throttle again. Sometimes climbing a hill & giving it more throttle will cause it to die unless I keep it at lower to medium rpms. Gas cap is the aftermarket ratcheting type and I disassembled it twice & it looks fine & passes airflow. Should I decrease that main jet to .068 or .066? I don't suspect a faulty handlebar RUN/START switch (checked it as well), Air filter is very clean, fuel strainer & petcock clean & good flow. Spark plugs are burning a dry medium to dark gray color but far better than the black they were before the carb rebuild & rejetting. Electrical connections to ignition coil & ECM module are good & tight. Running ethanol free 89-91 octane depending on the vendor. Any ideas on what's going on?

mleach72 is on the money! The jets you chose are not conducive to the engine running well. Look inside the carb while you hit the throttle and look to see if your acceleration pump is producing a squirt. Then pull the carb apart and put in the recommended jets from this file and follow the directions closely. After your done the idle mixture screw will not be to far off of the 1 1/4 turns if the carb is set up correctly with the correct jets.
When you drop the bowl be sure to replace the small blue ejector nozzle O-ring when you put it back together.

 

[HiTech]

I did follow the S&S carb tuning page as you posted. Idle mix screw is 1.5 turns out from seated, Accelerator pump appears to be set at its best performing setting. The .070 jet was what the bike came with when bought and the engine never skipped a beat for years other than running too rich and producing carbon rich exhaust & dry black spark plugs. But I agree from reading other posts the .070 main jet seems a bit too small according to S&S jetting recommendations, so I will change that too & experiment more are needed. In the past I never touched the throttle to start the bike as that would flood it easily, hence wrong jet size. Previous owner may have altered things from original factory jets. Perhaps because of the TP rocker boxes somehow changing the need to alter carburation(?) or maybe some guys just like stinky exhaust to keep others further behind them! LOL
Oh the joys of carbureted engines! My buddy keeps teasing me about his reliable Victory EFI & worry-free riding. His day will come when something fails during a ride. Meantime he still monkeys around with his Polaris 106ci trying to reproduce the exhaust sound of the S&S with no success. He just can't eliminate that Singer sewing machine whine!

 

[mleach72]

I did follow the S&S carb tuning page as you posted. Idle mix screw is 1.5 turns out from seated, Accelerator pump appears to be set at its best performing setting. The .070 jet was what the bike came with when bought and the engine never skipped a beat for years other than running too rich and producing carbon rich exhaust & dry black spark plugs. But I agree from reading other posts the .070 main jet seems a bit too small according to S&S jetting recommendations, so I will change that too & experiment more are needed. In the past I never touched the throttle to start the bike as that would flood it easily, hence wrong jet size. Previous owner may have altered things from original factory jets. Perhaps because of the TP rocker boxes somehow changing the need to alter carburation(?) or maybe some guys just like stinky exhaust to keep others further behind them! LOL
Oh the joys of carbureted engines! My buddy keeps teasing me about his reliable Victory EFI & worry-free riding. His day will come when something fails during a ride. Meantime he still monkeys around with his Polaris 106ci trying to reproduce the exhaust sound of the S&S with no success. He just can't eliminate that Singer sewing machine whine!

The intermediate jet is still flowing when the main jet comes in, so you had an intermediate jet that was too big and a main jet that was too small. The resulting air/fuel ratio was probably close enough that the bike ran ok at higher rpms. At lower rpms, it was way too rich. That's why the exhaust was stinky. Your fuel mileage probably sucked too.

 

[Mikeinjersey]

I did follow the S&S carb tuning page as you posted. Idle mix screw is 1.5 turns out from seated, Accelerator pump appears to be set at its best performing setting. The .070 jet was what the bike came with when bought and the engine never skipped a beat for years other than running too rich and producing carbon rich exhaust & dry black spark plugs. But I agree from reading other posts the .070 main jet seems a bit too small according to S&S jetting recommendations, so I will change that too & experiment more are needed. In the past I never touched the throttle to start the bike as that would flood it easily, hence wrong jet size. Previous owner may have altered things from original factory jets. Perhaps because of the TP rocker boxes somehow changing the need to alter carburation(?) or maybe some guys just like stinky exhaust to keep others further behind them! LOL
Oh the joys of carbureted engines! My buddy keeps teasing me about his reliable Victory EFI & worry-free riding. His day will come when something fails during a ride. Meantime he still monkeys around with his Polaris 106ci trying to reproduce the exhaust sound of the S&S with no success. He just can't eliminate that Singer sewing machine whine!

Your jets are just the opposite of what the recommended is. Get the .078 for your main and the .031 for the intermediate as recommended. Then adj accordingly and change only if you need to.
Keep in mind above 3000 rpm the bike uses the main jet and .070 isn't enough for a 117. Also below 3000 rpm the intermediate jet is used and your .033 is too large.

 

[Snuffy]

I agree EFI is good yet it will never sound as good as a carb bike. Carb bikes are just as reliable with the right set up and occasional maintenance.

 

[mleach72]

Also, check the air bleed jet. The PO may have messed with that as well. It should be a .040

 

[Sven]

Have to disagree with the main coming on later in rpm. There is no door/gate/anything to close off a suck out of an open jet so all 3 circuits feed from the first suck to redline.

The feed is more linear in throttle openings. Falls on its face at higher rpm means less fuel being sucked out of the jet(s). Being the main is the largest hole so concentrate on the main jet.

 

[creakyfalcon03]

2006 Mastiff 117 motor & Super G carb. Bike always ran great until this year when it started shutting down only when throttle is opened close to full. I noticed for awhile that with a full fuel tank it would stutter & sometimes die & loosening the cap made it run again. However now the problem is more consistent and loosening the fuel cap has no effect. Engine always ran too rich & never needed enrichment activated. Often backfired on startup & guys complained the exhaust too smelly to ride behind. So I rebuilt the carb w/ S&S Master kit, rejetted to next smaller size: main to .070 & intermediate to .033 & it now requires me to engage the enrichment on cold starts only just for a few seconds, and accelerates smooth, no hiccups no backfires, smooth consistent idle too..... until I reach speeds of 55+ & higher where the engine just dies and acts like it's fuel starved. Pull in clutch, let rpms go back to idle and it restarts & runs fine until risking full throttle again. Sometimes climbing a hill & giving it more throttle will cause it to die unless I keep it at lower to medium rpms. Gas cap is the aftermarket ratcheting type and I disassembled it twice & it looks fine & passes airflow. Should I decrease that main jet to .068 or .066? I don't suspect a faulty handlebar RUN/START switch (checked it as well), Air filter is very clean, fuel strainer & petcock clean & good flow. Spark plugs are burning a dry medium to dark gray color but far better than the black they were before the carb rebuild & rejetting. Electrical connections to ignition coil & ECM module are good & tight. Running ethanol free 89-91 octane depending on the vendor. Any ideas on what's going on?
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Sounds more like the fuel level in the bowl can't keep up at sustained throttle than a main jet being a hair off. A smaller main could just make the high-rpm cutout worse.

 

[mleach72]

Have to disagree with the main coming on later in rpm. There is no door/gate/anything to close off a suck out of an open jet so all 3 circuits feed from the first suck to redline.

The feed is more linear in throttle openings. Falls on its face at higher rpm means less fuel being sucked out of the jet(s). Being the main is the largest hole so concentrate on the main jet.

No, that's not right at all. The emulsion tube, which the main jet screws into, has a bunch of holes in it. Air is able to get into the tube and displace the vacuum at lower rpms. It's like trying to drink a soda through a straw with a bunch of holes in it. If you lightly suck on the straw, all you are going to get is air. You have to suck really hard to pull soda up through the straw. The air bleed jet controls how much air gets into the tube. A smaller air bleed allows less air into the tube. The motor doesn't have to produce as much vacuum to pull fuel through the tube. The main jet will come in earlier. A bigger air bleed allows more air in the tube. The motor has to produce more vacuum to overcome the air bleed jet. The main jet will come in later. Personally, this convergence of three variables at roughly 3k rpms is the reason I got rid of the S&S carb. It can make you want to pull your hair out trying to figure out what adjustment isn't right. There is no circuit overlap in a Mikuni. Problems are much easier to diagnose.

 

[Rottweiler]

Good information Mleach72

 

[Sven]

Hands on here... Warrantee new bike comes to the dealership, falls in my lap. Workorder says, 'hard starting, no/poor idle.'

So it's a brand new bike. Pull the main jet out and there is what I guess is a factory worker's eyelash stuck in the main jet like this [ / ].

Blew it out and the bike lit right off, revved, etc. Being empirical, you can't convince me it's anything but linear where it takes all 3 circuits to start and WOT to the top.

Signed,
NOLTT (no one listens to turtle)

 

[Snuffy]

No, that's not right at all. The emulsion tube, which the main jet screws into, has a bunch of holes in it. Air is able to get into the tube and displace the vacuum at lower rpms. It's like trying to drink a soda through a straw with a bunch of holes in it. If you lightly suck on the straw, all you are going to get is air. You have to suck really hard to pull soda up through the straw. The air bleed jet controls how much air gets into the tube. A smaller air bleed allows less air into the tube. The motor doesn't have to produce as much vacuum to pull fuel through the tube. The main jet will come in earlier. A bigger air bleed allows more air in the tube. The motor has to produce more vacuum to overcome the air bleed jet. The main jet will come in later. Personally, this convergence of three variables at roughly 3k rpms is the reason I got rid of the S&S carb. It can make you want to pull your hair out trying to figure out what adjustment isn't right. There is no circuit overlap in a Mikuni. Problems are much easier to diagnose.

I don’t care what anyone says this dude knows his stuff @ carbs. Good advice

 

[mleach72]

I don’t care what anyone says this dude knows his stuff @ carbs. Good advice

Thank you Snuffy! That means a lot! I am constantly looking for a better tune. Everyone loves more horsepower, but I like my bikes to run at peak efficiency. I'm not an expert. I'll admit that. If you want electrical advice, you need to go to someone like knothead. I do like to learn about the fuel system. It's a constant search.

 

[Sven]

The motor has to produce more vacuum to overcome the air bleed jet.

I believe the suck is a constant so there is no 'more air' to be had. Thus the constant 14.7 psi on the close of the valve. Ever notice the AFR remains constant short of a pull for passing, meaning, it's either the plunger opening shooting more gas in there or with FI, it's programmed in.

Top gauge is a medical vacuum in mmHg so it more zeros out to 760mmHg showing at the end of the video. Press full screen.

Signed,
NOLTT

 

[Sven]

Don't have that video, but if I WOT the throttle, it goes to zero as if the engine is off, or 14.7 psi aka, one atmosphere = 14.7.

Plus, the only way to exceed 14.7 is to turbo it or supercharge it past atmosphere.