Stumbling

[Auggie_1970]

Hi Guys, was hoping to get some carb tuning advice for I'm stumped.

I'm getting some pretty good stubmling around 5500-6000 rpms when I whack the trottle from about 5500. Its not consistant though, does it about 80% of the time (seems to have gotten worse with change in mains).

I just got my smaller mains last night and installed them , synced the bike and took it for a ride. I went from 155 mains to 147.5's and seems like the sputtering/stumbling got worse..I have stage one needles in there and I didnt touch them, so I'm not sure if the increased hesitation/stumbling means I need to tweek the needle height. After the bike gets past 6200 it seems to pull great then, better than it did with the 155's

Also seem to have a little bit of an issue now at around 2,200 that clears up quickly but its there.

Here's my current set up:

2004
K&N
2-3/4 turns on air/fuel
Stage one needles with clip thrid from blunt end.
147.5 mains
Y from airbox removed
4-2 Holeshots



So does this seem to be a rich or lean issue. I'm not sure what else to check...Seems to me changing the mains increased the issue in this rpm range but bike now seems to respond much better at the highter rpms 6k+...

Not sure if this is the correct way of thinking but since I reduced the mains, from my understanding the mains play a role with the needle , thefore maybe I need to fatten up the needle a bit to compensate for the change in mains??

Also where's everyone gettnig their shims from..I've seen some post using radio shack ones but was curious if there's a more precise set of shims..Was thinking about going back to stock needles

On a positive note, I've managed to reduce the time it takes to pull the carbs Including changing the mains and syncing the carbsl, I think I've gotten it down to a little under 1.5 hours from start to finish give or take a few minutes for trips to the fridge for beer

 

[Thevmaxrider]

Since you went down a few sizes with the main jets you can rightly assume you leaned out in each of the 3 phases of the carb's operation.

Phase 1: idle to 4k rpm you are on the idle circuit which you change by adjusting your A/F screws.

Phase 2: 4k-6.5k rpm you are on the needles. You do not need shims as yours are adjustable. As this is where your stumble is I would advise you go 1 notch at a time closer to the "pointy end" of the needle and see how it runs.

Phase 3: 6.5k rpm and up you are running on the mains. No need to talk about those as you seem to have a handle on them:biglaugh:.

My advice is to adjust the needles and only make ONE change at a time. Test run the bike and see how it reacts. If it gets better you know you are on the right track, gets worse well you already know about that.

 

[Auggie_1970]

OK great, sounds like a good plan. Whats your take on the Y, put it back on first or leave it off? I'm sure with it being off its contributing to leaning out the mixture a bit...

I was thinking about possibly going back to stock needles and if I did I'm sure I'll end up having to shim it so I wasnt sure where to go for those..Thanks for you help

Although this takes a bit of patience, this **** if fun...

 

[Rhoy Carter]

I had my Y removed and could not get the low end right, I put the Y back on and shimmed it with 3 washers and that cleared up the low end.

 

[Auggie_1970]

Rhoy, for the airbox shimming are you talking about your average home depot type washers?

 

[Rhoy Carter]

Yes, just small washers that fit the screws, I used 3 washers per screw

 

[Rhoy Carter]

If you are under 500 feet the 147.5 mains may be a tad lean also, im at sea level and 150 mains put me right on 13.5 o2 reading

 

[Auggie_1970]

Yeah I'm at 250 ft...Damm, I'm going to be an expert at tearing these carbs off

 

[Rhoy Carter]

Put it on a dyno and find out before you change the jets

 

[Thevmaxrider]

Put it on a dyno and find out before you change the jets

Good advice! Each bike has it's own individual likes/dislikes when it comes to tuning. Otherwise who would ever need a dyno:confused2:. Your best bet is to get it running well by the "seat of the pants" tuning method and THEN if you feel the need to tune it to a gnat's ass you can put it on a dyno for that. If you do that though you will find yourself changing PAJ's, Main jets, AND needle settings to get it at the "perfect" tune. Unless you are racing the bike regularly you won't need to go that far.

As for the Y, never noticed a difference with it on or off except the amount of induction noise.

 

[Auggie_1970]

Yeah I think seat of the pants tuning is good enough for me..Besides, I'd be worried about someone putting it on the dyno and f'n it up somehow....

 

[one2dmax]

The "Y" on is usually preferred though you can shim it up. The ideal A/F ratio is 13:1 and I think your 147.5's will be fine. Adjust the needles since you have that capability (stock does not). 1 shim or 1 clip move. Add the shim and try it. Then you can take off the shim and move the clip. Try it. Then add the shim and repeat again.

Sean

 

[twistedmax]

ok guys same problem bout 5000 5500.only change is its about 15 degrees cooler and dryier air.and just a reminder.I dont have any carburators to adjust. I thought the colder air would require More fuel,this thing seems to be rich..................I wonder?...........Im gonna try the volocity stacks friday.

 

[Auggie_1970]

Thanks for all the advice guys, very much appreciated. Since I didnt have any shims tonight, I went ahead and raised the needle height or lowered the clip on the needle one notch. I ran much much better, not sputtering like last night. I took a ride for about 40 minutes and I only got a very small hint of a stutter on one occasion but not bad at all..Pulls very nice throughout the rpm range I was having problems with.

I think next thing I'll check out is putting the Y back on and shimming that a bit and see how that impacts things.

While i was messing around with the needles I did happen to take notice of the paj2 and it was a 170, cant remember what was stock but I'm going to look that up after this post and see if thats a stage 1 add on or stock..Anyone have a picture of the markings on one of them...Looks very simillar to a main jet...hopefully its stock

Whats interesting is that I have what I'll refer to as a very stong exhaust smell when its running..kinda like when you get behind and old beater once in a while...I would assume thats my air fuel mixture screws?

Also dumped a few ounces of seafoam in there tonight just to clean up anything that may be gumed up..

I'll keep posting the changes I end up making while daiilng this in so that anyone else with similar issues can learn from my mistakes


Ohhh almost forgot, for the first time since I owned this bike, I had the front wheel up tonight, that was f'n awesome..I must be getting the tune close.. Considering I have the crappy stock tires, I cant wait to see how she'll hook up with the Metzlers I have coming on Monday of next week...This **** is addicting.