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General Category >> Rubber Side Down! >> high end stumbling - fix now or wait?
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Message started by Thumpin on 06/06/07 at 10:27:12

Title: high end stumbling - fix now or wait?
Post by Thumpin on 06/06/07 at 10:27:12

After the discussion last week from various people about max speed, high end stumbling, and back firing I got to thinking. My bike (2000 LS650) does indeed like to backfire (not always the loud cracking type) between gears if you are slow on the shift. SO I was suspecting that I am running lean (the carb srew has never been drilled out). On the way home I had a situation where while going about 55 I needed to pass. When I rolled on the accel (in 5th) it started stumbling at about 65. I let off (I didn't need to go any faster to get around the guy anyway) and the problem went away. This left me w/ a huh??? whas up in my mind. So when I got to a long staight away I decided to see either what the max speed of the bike was or where the stumbling begins. At a little above 70 the stumbling starts no mater how gently I apply accell.
Also note that the muffler that I have is the stock muffler but it is blown (a little better than a strait pipe).

What I need to know is: Am I just running lean and if so is this a problem that I can leave to fix the next time I tear the bike down. I put roughly 100 miles every day on my bike but it is all below 60 mph. I want to wait due to cash flow. I need a new muffler but i want to put a supertrapp on and that will lead likely to rejetting and such. I do not have a crap load of cash to blow but will due what is necessary to keep the bike healthy.

And could someone out there take a photo of thir carb so I can see exactly where the proper spot is to drill access to the adjustment screw.

Title: Re: high end stumbling - fix now or wait?
Post by Savage_Rob on 06/06/07 at 10:38:54

So far as backfiring at throttle snap-back, that can be a lean condition or an exhaust leak but it doesn't sound like that symptom is very bad. I'm not sure what you mean by "stumbling" but if it were just a lean top end (main jet too small), I would think it would just run out of oomph, not stumble. I wonder if the opposite condition might be happening, like maxing out your airflow and becoming too rich. I'll let some of the gurus here debate whether that might be the case. What is your airflow setup (i.e. air filter type, exhaust type, etc.)?

Title: Re: high end stumbling - fix now or wait?
Post by tuxedo on 06/06/07 at 10:42:49

sounds like the centrifugal force of acceleration caused your float to stick a little and the bike leaned out. Stock it should be capable of doing that without a stumble...I think?

Title: Re: high end stumbling - fix now or wait?
Post by Thumpin on 06/06/07 at 10:48:32

Everything is still stock. And I had not thought of the exhoust leack possibility. When I bought the bike 2 months ago the fool I bought it from had a 4 inch auto exhaust tip screwed in place instead of the muffler. I reinstalled the original muffler. Also If you look in the end of this muffler the entire end (last baffle) is gone.

I am going to check for black soot at the junction of the header and muffler.

Title: Re: high end stumbling - fix now or wait?
Post by Dynobob on 06/06/07 at 14:35:21

If your stock muffler has baffles removed, you're probably running way too lean now. If your jetting is stock, you need to rejet.

Title: Re: high end stumbling - fix now or wait?
Post by Polar_Pilot on 06/06/07 at 18:25:14

That back fire issue sure has been a problem for a lot of riders for a long time.

I overcame the backfire in the following manner.

When decelerating I always shut the throtte completely - this prevents the engine from pumping unburned gasses into the muffler where they finally hit a spot of hot carbon and blam!

Same thing when shifting - slow the process down a touch make sure the throttle is completely closed and then do your shifts - no banging and popping

Finally if you are not already doing it - run the bike on the highway at a steady speed every now and then - take it up to 100kmph and hold it there for 5 miles - that will clean out a lot of the carbon that is in the exhaust pipe and muffler and decrease the chances of a hot spot to ignite the fumes on the overrun.

Ride safe

Title: Re: high end stumbling - fix now or wait?
Post by Rockin_John on 06/06/07 at 22:24:38

If you like the sound of the exhaust as it is set up, you need to jet (tune) to it. Otherwise go ahead and get a muffler or whole exhaust system that you DO like the sound of and tune to it. There is no sense in tuning to a pipe if you don't like it.

Personally, I find the Stock H-D Dyna I put on my 87 to be too wimpy sounding. I don't know how the baffles were modified in the Dyna muffler on my 99, but it sounds much deeper, and a bit louder without being obnoxiously loud. I do wonder why it has turned blue in only one spot about 2/3 the way down the muffler's length.

However, since the 99 is chopped, I'm considering putting on a really loud turnout style muffler I've got. People kind of expect "obnoxious" loud from a chopper, and I wouldn't want to disappoint anyone! After all, somebody has to live up to that "menace to society" reputation. ;-)

Title: Re: high end stumbling - fix now or wait?
Post by skatnbnc on 06/07/07 at 05:33:52

I happen to like the sound I can get out of my bike from the backfire, but after reading this thread I have a related question.

I commute 5-6 days a week about 6 miles (one way) and almost never get out of second gear.

A couple times a week I also do errands in the afternoon on Suzi (i use any excuse to get out, especially if the day is fine), and that is when I might get up to third gear.

Unless I plan in advance to do so, I never get on the highway, just use the more scenic, quiet (less cage issue) backroads.

Do I need to hop on the highway once a week or so and get her up to a speed to clean out the carbon?

Title: Re: high end stumbling - fix now or wait?
Post by azjay on 06/07/07 at 07:24:39

skatnbnc wrote:

Do I need to hop on the highway once a week or so and get her up to a speed to clean out the carbon?

i dont think carbon build up is big issue with these bikes, because they are running so lean(as a rule). HOWEVER, in your case, you should take the bike out and give it a good warm high speed run, to warm the oil up and heat the moisture out of it, to prevent sludging and corrosing from aluminum/water. perhaps once a week, or what ever is convenient. jmo

Title: Re: high end stumbling - fix now or wait?
Post by Thumpin on 06/07/07 at 08:28:31

Alright my check for making this work related move finally came in. So now I am ready. I hear alot about Supertrapp and have also heard about a jardine. Not being a long time moder of bikes I am a bit ingnanat here. What are the plus- minuses of the variouse say most popular 4 mufflers for our bikes. Note: The last baffle in my stock muffler is missing (removed??) and you bet you it is currently quite loud. I dont really want to quiet it down (maybe a little deeper but still loud). I do want to take advantage of any HP that can be reclaimed (I am thinking superstrapp here) yet I do not want to turn my bike into a high gas consumer. I drive 45 miles to work one way each day on this bike and one fill up a day is enough.

Anyone got any info to help make this choice?

Title: Re: high end stumbling - fix now or wait?
Post by verslagen1 on 06/07/07 at 09:05:28

I just put on a supertrapp, 6 disks, no tuning required.

In fact, I'd say it's a little more restrictive than stock, yet louder. The sound reminds me of the Gold star my dad raced. Good rich tones, only not as loud.

After having this for a few weeks my opinion of loud pipes has changed... I still beleave loud pipes don't save lives, but quiet pipes are a liability. If you are hard to be seen, it's good to be heard. ;D

Title: Re: high end stumbling - fix now or wait?
Post by skatnbnc on 06/07/07 at 14:43:24

verslagen1 wrote:

I still beleave loud pipes don't save lives, but quiet pipes are a liability. If you are hard to be seen, it's good to be heard. ;D

Yeah, I intentionally backfire Suzi if I need to make a cage wake up and share the road. Otherwise, the HD pipe on mine can let out a good strong BBRRRACCCKK to keep em on their toes. 8)