Motor Stumbles when accelarating

[Bigbass]

Guy's bare with me. I am brand new to owning a Big Dog. I have wanted one from the first time I seen them and my wife bought me a 2006 mastiff with less then 3000 miles on it. Thing runs great and has plenty of power.

I changed out the stock pipes with V&H big radius and also purchased and installed the jet kit from Big Dog for the radius pipes. Here is the problem I adjusted the carb per the information on the forum but can not get it to stop stumbling when I do the quick throttle check. It backfires and dies no matter how far our I turn the accel pump screw. If I get into it slowly it is fine but if I do a quick throttle twist at idle it will backfire and die.

It also started backfiring when I first hit the starter tonight. It seems to als backfire alot when i am down shifting or just decelerating.What do I need to do to fix this, It has stock filter on it at this time.

I talso does not seem to keep my idle rpm's where I set it at. if I drive it for 50 miles or more the idle rpms seem to drop to where it blinks all the lights on the tach.

 

[Little-Boo]

Guy's bare with me. I am brand new to owning a Big Dog. I have wanted one from the first time I seen them and my wife bought me a 2006 mastiff with less then 3000 miles on it. Thing runs great and has plenty of power.

I changed out the stock pipes with V&H big radius and also purchased and installed the jet kit from Big Dog for the radius pipes. Here is the problem I adjusted the carb per the information on the forum but can not get it to stop stumbling when I do the quick throttle check. It backfires and dies no matter how far our I turn the accel pump screw. If I get into it slowly it is fine but if I do a quick throttle twist at idle it will backfire and die.

It also started backfiring when I first hit the starter tonight. It seems to als backfire alot when i am down shifting or just decelerating.What do I need to do to fix this, It has stock filter on it at this time.

I talso does not seem to keep my idle rpm's where I set it at. if I drive it for 50 miles or more the idle rpms seem to drop to where it blinks all the lights on the tach.

You mention that you have played with the Accel Pump screw and that is continues to stumble. Well have you tried adjusting the A/F screw on the left side of the carb below the idle screw. You need to set the idle (after its warmed up) to at least 1000 RPM's. Now go and turn you A/F screw in until the motor stumbles. Then back it out 1/4 turn at a time until you reach the highest RPM or until it runs smooth then back in about 1/4 turn. If that A/F is out more than 3 full turns you need to change out your Intermediate Jet. Lets say you are running the .0295 you need to go up to the .031, if you have the .031 you need to go up to the 33. Your main jet should be at least 74. Now only change the intermediate if the A/F is out more than three full turn. Now you can play with the Accel pump 1/4 turn at a time until you are able to hit it without any hesitation. Try that and see how it works for you. Good Luck

Carlos

 

[Bigbass]

Carlos, thank you so much for the speedy response. The carb I have is the G series. Here is what I do to set it thus far.

I set the idle mixture screw 1 1/4 turns out from lightly seated.
Idle speed screw high turn in after it touches
Then set Accelerator pump screw out 2 turns from seated.

I then start the bike and hold my hand on the jugs until it is too warm to comfortably hold it there. I have to set the idle up at that point so it will idle at the 1000 rpms.

I then adjust the idle fuel mixture by turning it in until it starts to stumble I then back it out to where it stumbles again and try to find the center between those two points.

I then quickly twist the throttle and it back fires and dies. I restart it and back out the fuel mixture screw a 1/4 to a 1/2 turn at a time and it seems to get a little better because it does not kill it the further out I go but it hesitates and you can hear the carb gasp like sucking air hard through the breather then back fires, stumbles and then I let off the throttle because it is not gaining rpms.

It was doing this when I had the stock pipes on it and the factory jets. If I roll on the throttle like leaving a stop sign or something. I can be running down the road let's say 65 and quickly twist the throttle and it takes off with no hesitation. Runs great at any speed with any twist of the throttle on the road just not when sitting at idle.

I appreciate any help and sorry for bugging you. I just want to fix it so I don't foul plugs.

This is my very first S&S motor and love the bike and good with wrenches when I know where to go to fix it.

 

[Moespeeds]

From what he just wrote I think he's got the gist of it. I'm not sure about the accelerator pump setting, I think you should turn it off completely until you track down the stalling problem, then set it 1/2 turn at a time till you get a good throttle response. Make sure you don't have an intake leak.

 

[Bigbass]

Sorry I posted it before I proof read it. Never claimed to be any good at typing. It would probably help if you could read my mind instead of reading what I type. LOl

I turn the idle screw in which is on the far left side beside the throttle cables in a 1/4 turn after it touches the arm. I do not know why I posted it as high turn. Sorry about that. would help to type correctly if I want help HUH ?

The accelerator pump screw I am refering to on my G carb would be located on the far right hand side when looking at it from the air filter.

If I am correct the idle adjust screw is the far left one beside throttle cable. The idle mixture screw in roughly in the center top closer to the air filter and the accelerator pump screw would be the far right one down a little on the side of the card closer to the mounting side of the card.

I am sorry for pestering you with this. Once I get this whole thing fixed I will be back on the bike and out of your hair.LOL

 

[Bigbass]

That helps tremendously thank you sir.

 

[barhopper]

I am sorry for pestering you with this. Once I get this whole thing fixed I will be back on the bike and out of your hair.LOL

You ain't going nowhere till you buy a round of beers for all the info you get from these guys.

 

[Bigbass]

Okay I will buy this round because he deserves it but I did find another thing that bothers me with this.

I pulled off the air filter which I just installed it less than 200 miles ago and the bottom portion is wet and has small gas odor but the liguid in the breather cover feels and smeels like fresh oil. What would cause my air filter to have oil and fule on it. Filter is fairly wet on the bottom.

The reason I got in there was cleaning the bike I noticed a stream of liguid dripping off the cover . It is not l;eaking setting just when I ride.

 

[Bigbass]

Damn you guy's are quick. I owe you a case instead of a beer. Thanks. The bike is an 06 but only had 2,300 miles and with it sitting as long as it did I knew there was going to be some minor here and there things and love working ot it just want to make sure thaat I work on it properly. I am not a big fan of taking anything to a dealer when I can fix it if driected properly. Thanks again.

 

[Bigbass]

okay here I am again. Sorry to keep bugging you guy's but I finally broke down and changed the jet from the .031 to a .033 and the stumb;e seem to get less but now I have a carburetor back fire. Sorry I keep pestering you guy's just nobody around me has any good knowledge of a S&S 117 or a big dog.

Did seem to be faster throught the gears but would hesitate a split second when I hit the throttle and a lot more exhaust back fire when decelerating. Where did I go wrong here.

I must add that I have a Spike air filter on it now too.

 

[Little-Boo]

okay here I am again. Sorry to keep bugging you guy's but I finally broke down and changed the jet from the .031 to a .033 and the stumb;e seem to get less but now I have a carburetor back fire. Sorry I keep pestering you guy's just nobody around me has any good knowledge of a S&S 117 or a big dog.

Did seem to be faster throught the gears but would hesitate a split second when I hit the throttle and a lot more exhaust back fire when decelerating. Where did I go wrong here.

I must add that I have a Spike air filter on it now too.

What about your main jet what do you have in there. If you have a spike air cleaner and other than stock pipes you should be running at least a 74. Also check for exhaust and intake leaks like Dead suggested. One good way to check for an intake leak is to spray W-D 40 on the intake ports and see if the the motor changes speed (as in RPM) if not you are OK. If it does than you need to fix that and start all over with the carb adjustment. :bang::bang:

Don't worry about being a pain in the ass :lol::lol::lol:, just keep us posted on what you are doing and what works best for you. Before long we will nip it in the butt.

Don't give up I have a 06 mastiff myself and went Thru the same shit until I finally got it deal in to where I wanted it to be. I now have much more than what the dog came with, 650 woods Cam, Ported & polished head with bigger valves, programmable Thunder heart Ignition, Hydro solid lifters and the good Ole Big Air PSI Carb which you can easily adjust, no jets to change :2thumbs: Hope that help, good luck

Carlos

 

[Bigbass]

I have a 76 main jet. I appreciate you guy's allowing me to pick your brain. I am confident I will get it jsut need a little guidance in the right direction.


With the new .033 jet it did not take as much turn one way or the other on the idle mixture screw to get it to stumble. If I turn the idle mixture screw a 1/2 turn in it stumbles and if I turn it a 1/2 turn out it stumbles so I set it in the middle.

I am alomst completely backed out with the Accelerator pump screw just like I was with the .031 jet.

When I say snap the throttle I mean quickly twist like stepping on a car accelerator real fast. Is it possible I am just twisting the throttle too fast to check?

The set up is a stock 117 a spike air filter with K&N filter with 2 into 2 Big radius pipes with a 76 main jet and a .033 intermidiate jet.

The thing seemed to be a whole lot stronger power wise when going through the gears but hesitated between shifts. BAckfired through the exhaust on deceleration and back fired through the carb on acceleration.

 

[BadBrad]

Do you still have the stock filter? Just curious if all this is related to your spike or if it's still in the jetting.

 

[Bigbass]

The Spike air filter looks identical to the D&M but it is a Volar Motorsport Product: IK003. I just put it on last night before going to bed. The vent hose that goes from the head that was hooked to the back of the original mounting plate has no place to hook up on the new air filter so I just ran the hose down between the jugs for now until I figure out what I am going to do with it. It is not hooked to anything on this new Air cleaner.

I made sure that all the boltss for the carb and y intake pipe behind the carb were good and tight last night but will check the WD40 trick out here in a little while. Here is the air filter parts and all.

 

[Moespeeds]

Make bold jet changes and see what it gets you, one jet at a time. Go up to a 36 and try it, then go up to an 80 on the main and try that. This will give you a clear indication of which jet is causing your issue. No harm in going too far either way, if it's not going to run right you will know in the first 100 feet. If this stumble you are getting gets worse, then you know to go leaner. Close the accelerator pump screw until it lightly seats, and leave it off until you get everything else straight. The last thing you adjust should be that accel pump. If you leave it on while jetting it can mask problems. Check for an intake leak with WD40 or Brake Cleaner as someone else told you. The backfiring and stalling from full throttle are both symtoms of an intake leak.

 

[TEXASDOG]

First of all throw the Spike air filter in the trash. I tried running one of those POS on my 2001 Harley 95 Cu inch and it ran terrible. The Spikes are real pretty but a total waste of $169.

 

[Bigbass]

Here is what I found. I can spray carb cleaner all around the intake gaskets both at the jugs and the base of the carb and nothing changes but when I spray carb cleaner around the throttle linkeage shaft or directly across from it on the fuel pump side the motor stumbles. Nothing else causes it too stumble. Is it normal too pull air through that shaft?

 

[Bigbass]

Awesome guy's I took the air filter off and nothing changed with how the bike was performing so I started all over again with the settings this time I went ever so slowly on the Accelerator pump turns and I seemed to ahve got a grip on it. There is a very slight hesitation when I quick twist the throttle but so minut hard to tell it.

I then rode it and there is some loud back fire when I decelerate but it occasional instead of the whole time decelerating . Which way would you suggest Ihead for this fix? The air filter was not causing me any problems cause bike acted the same either way on or off. I know there will be some backfire but this seemed a bit loud. No carburetor backfire though.

 

[Staffy]

Poping from the carb often indicates a lean condition.

Let's start with the INT - a 33, when you turn the air/fuel screw all the way in does the engine stumble and stall - if yes we can work with that, if not time to go down a notch.

If the ABOVE is good, how many turns out do you have the air/fuel screw (at optimal setting) - any more than two turns?

Are you stumbling around the 2500-300 RPM mark?
Also, pull your air/fuel screww out and check for damage.
Keep it coming, will get there eventualy.

 

[Bigbass]

The Dead One, you are correct. When I went home at lunch I got on it and twisted the throttle twice and it backfired and did not start. I then hit the starter again and it firred up.

Staffy, if I turn in very far on my fuel/air mixture screw it will stumble bad and I assume it would die if I kept going. I will put out the screw tonight and check it for damage.

I truly thank you guy's again. To have a forum where I can go to ask questions from owners that have been down this road and get answers without feeling like an idiot or being treated like a dumbass is priceless.

I love my bike and you guy's truly make me proud I own one. I am glad the filter did not change when I removed it. I posted the wrong picture. Here is the one am running same filter just different mounting bracket. I paid $ 235.00 for it.