FUEL SYSTEM PROBLEM, CARB. SPUTTERS AT HIGHWAY CRUISING SPEED. NEW STAGE 1 INTAKE. V&H EXHAUST. REJET OR OTHER PROBLEM?

[QMChief]

08 MASTIFF NEED HELP!!!
While riding she sputters at highway cruising speed (FRUSTRATING). Give it gass and she goes great. Startoff, low gears, all good, maybe excess backfire but it has V&H pipes and stage 1 air intake. I sprayed the carb throat externally with carb cleaner while running and it didn't stall so I assume no leaks. I have never rejetted so I assume it has stock jets but I'm not original owner.
Does it need to be rejetted or do I have a carb issue?
I don't remember it doing that but could have been a problem when I bought it. Big question is would a rejet fix a highway cruising speed sputter? Runs like a bat from hell when giving gas. PUT NEW OEM PLUGS IN AND THEY ARE DARK. Could too much fuel cause a sputter at highway speed? Do I need to reduce fuel jet regardless of air/exhaust upgrades?
Thank you my Dog riding friends!!!

 

[mleach72]

08 MASTIFF NEED HELP!!!
While riding she sputters at highway cruising speed (FRUSTRATING). Give it gass and she goes great. Startoff, low gears, all good, maybe excess backfire but it has V&H pipes and stage 1 air intake. I sprayed the carb throat externally with carb cleaner while running and it didn't stall so I assume no leaks. I have never rejetted so I assume it has stock jets but I'm not original owner.
Does it need to be rejetted or do I have a carb issue?
I don't remember it doing that but could have been a problem when I bought it. Big question is would a rejet fix a highway cruising speed sputter? Runs like a bat from hell when giving gas. PUT NEW OEM PLUGS IN AND THEY ARE DARK. Could too much fuel cause a sputter at highway speed? Do I need to reduce fuel jet regardless of air/exhaust upgrades?
Thank you my Dog riding friends!!!

If your plugs are dark, you are running rich. Your intermediate jet might be too big. Drop your bowl and see what jets are installed. Follow the tuning manual. Also, make sure your enrichner is completely closed.

 

[Mr. Wright]

I agree with Matt. I'll drop another link for the manuals. Run through the carb adjustments also.

Dropbox

www.dropbox.com

 

[QMChief]

Is changing the jets as simple as unscrewing the jet and screwing the next size in or is there a technical aspect of adjusting the jet once it's in?

 

[mleach72]

Is changing the jets as simple as unscrewing the jet and screwing the next size in or is there a technical aspect of adjusting the jet once it's in?

Yep, just unscrew the old jet and screw the new jet in. Adjust your idle mixture screw after changing jets.

 

[QMChief]

YOU GUYS ARE AWESOME! I'll keep you posted how it goes!

By the way, would the jet/dark plugs issue cause the sputtering at highway speeds? I'm hoping it is. I've got some jets and will be smelling like gas tomorrow!

 

[QMChief]

The S&S Tuning Guide says "Low rpm operation is controlled by the intermediate jet (#11)". My sputtering happens at 60-70mph so that would mean I'm rich in the MAIN jet correct? Or should I decrease both because my plugs are dark?

 

[QMChief]

I just realized how crazy this is. I bought the bike used with OEM exhaust and filter. I upgraded to V&H exhaust and stage 1 Velociraptor and my plugs are showing too rich. It should be too lean with the upgrades! It is used though, so no idea what the previous owners did to it.
I'm going to start with downsizing the intermediate jet and going through the S&S tuning guide and reset the settings. If you guys think I should downsize the main jet while I have it cracked open please let me know!

 

[QMChief]

Yep, just unscrew the old jet and screw the new jet in. Adjust your idle mixture screw after changing jets.

Are all jet kits the same? I have a kit I bought for $17 with the same and more jets than another kit for $69 both on Amazon!

 

[Rottweiler]

Let us know what size jets are currently in it. They have a number on them. Then we can make a better suggestion.

 

[mleach72]

I just realized how crazy this is. I bought the bike used with OEM exhaust and filter. I upgraded to V&H exhaust and stage 1 Velociraptor and my plugs are showing too rich. It should be too lean with the upgrades! It is used though, so no idea what the previous owners did to it.
I'm going to start with downsizing the intermediate jet and going through the S&S tuning guide and reset the settings. If you guys think I should downsize the main jet while I have it cracked open please let me know!

The main jet comes in at about 3k rpms. Generally, while cruising, you are running on the intermediate jet.

 

[mleach72]

Also, make sure the auxiliary vent plug is removed from the carb.

 

[HMAN]

Also, make sure the auxiliary vent plug is removed from the carb.

I bet you nailed it Matt.....?

 

[Mr. Wright]

I was about to say that too. Take that plug out, it will fix your problem.

 

[Mr. Wright]

Number 114. Remove it and don't put it back.
Hold on, I don't have enough internet to upload a picture this morning.

 

[mleach72]

Number 114. Remove it and don't put it back.
Hold on, I don't have enough internet to upload a picture this morning.

I got ya Shannon.

 

[Mr. Wright]

I got ya Shannon.
View attachment 125371

Thanks,

 

[Mikeinjersey]

The S&S Tuning Guide says "Low rpm operation is controlled by the intermediate jet (#11)". My sputtering happens at 60-70mph so that would mean I'm rich in the MAIN jet correct? Or should I decrease both because my plugs are dark?

If you follow all the instructions on the tuning guide you will get to the best adjustments/jets for your setup. Go in order but pay special attention to steps 8 and 9. Double check for vacuum leaks where the carb connects to the intake manifold and where the manifold connects to each cylinder. Spray while at idle and listen for change in idle speed or stall. There is a small rubber cap on top of the carb that sometimes cracks. Check for tight exhaust flanges and no leaks. If you have removed the baffles from your exhaust pipes the adjustments will be affected because of lack of back pressure.
When you drop the bowl to clean or check/change your intermediate jet be sure not to loose the small blue o-ring on the top of the ejector nozzle.

 

[41bigdawg]

Newer model G-carbs don't have the plug they actually have a bleed jet in them, if that is the case put a #60 bleed jet in it and that will solve your stumbling problem. Then you can play with the main jet to get it tuned the way you want.

 

[mleach72]

Newer model G-carbs don't have the plug they actually have a bleed jet in them, if that is the case put a #60 bleed jet in it and that will solve your stumbling problem. Then you can play with the main jet to get it tuned the way you want.

All S&S carbs have the plug. Some aftermarket air cleaners block the main vent. You have to remove the auxiliary plug so air can move in and out of the bowl as the fuel level rises and falls. It is on the outside of the carb. The air bleed jet is inside the bowl. It controls the main jet. It functions like a straw with a hole in it. The bigger the hole, the more vacuum you have to produce to get the drink through the straw. The auxiliary vent plug and the air bleed jet are completely different.