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ktmnate 12-09-2004 02:04 PM

LC4 Adventure Carb problems?
 
I recently did the "Flanny" carb fix which fixed everything except the top speed. My bike runs great starts right up but won't go over 85mph. Yea, yea, I know it's a dirt bike and shouldn't be going that fast. But it did before I tinkered with the carb. Here is what I have:

Drilled out the exhaust with 12 plates
carb needle moved down one position (raising needle)
162.5 main (I also tried 152.5 and 157.5)
2.5 coils cut off the slide spring
drilled out the slide
KTM hard parts air box cover
1.1 air jet


I have checked the slide and everything looks like it's working. The slide goes up and down without any binding. I checked the carb vent and breather. Looking at the parts diagram, I am missing a "throttle stop". If I remember correctly, the throttle stop just keeps the power down by keeping the slide from comming all the way up. Would anyone have any sugestions/Ideas. I am at a loss.

Thanks

meat popsicle 12-09-2004 03:20 PM

Quote:

Originally Posted by ktmnate
I recently did the "Flanny" carb fix which fixed everything except the top speed. My bike runs great starts right up but won't go over 85mph. Yea, yea, I know it's a dirt bike and shouldn't be going that fast. But it did before I tinkered with the carb. Here is what I have:

Drilled out the exhaust with 12 plates
carb needle moved down one position (raising needle)
162.5 main (I also tried 152.5 and 157.5)
2.5 coils cut off the slide spring
drilled out the slide
KTM hard parts air box cover
1.1 air jet


I have checked the slide and everything looks like it's working. The slide goes up and down without any binding. I checked the carb vent and breather. Looking at the parts diagram, I am missing a "throttle stop". If I remember correctly, the throttle stop just keeps the power down by keeping the slide from comming all the way up. Would anyone have any sugestions/Ideas. I am at a loss.

Thanks

Put your IMO back to 21" :thumb

:lol3 ok, just kidding, might want to state what you drilled the slide holes out to - creeper said that more is not better (:cry) they thought that .110" was groovy, maybe a bit more. Also, you should state how many miles and any other info that might be relevant (you are a leadwrist, streetlight dragracer, never change the oil, 50,000 miles on the clock - :lol3 stuff like that).

My 03 shows over 85 and that speed is fine with me on the street; haven't tried those speeds off road :eek1. Staying at those speeds might have other consequences... If Jerome is right, keeping the revs above 6K for extended periods is what puts your valves out of spec (he said that he didnt see them vary unless he had done lots of speed runs :evil).

ktmnate 12-09-2004 03:35 PM

the bike just broke 15k with 17/42 gears. I drilled the slide out to 1/8". wasn't really that much bigger than they were. I do change the oil frequently between 500 and 3000 miles depending on what kind of riding. Valves were adjusted 1500 miles ago and weren't that really off. I do all kinds of riding. I don't usually ride over 75mph, I was just passing someone and noticed that my little girl didn't want to go.


PS -I am using the GPS for speed reading, not the IMO. I find that the IMO isn't very accurate regardless of wheel size setting.

meat popsicle 12-09-2004 04:14 PM

Quote:

Originally Posted by ktmnate
the bike just broke 15k with 17/42 gears. I drilled the slide out to 1/8". wasn't really that much bigger than they were. I do change the oil frequently between 500 and 3000 miles depending on what kind of riding. Valves were adjusted 1500 miles ago and weren't that really off. I do all kinds of riding. I don't usually ride over 75mph, I was just passing someone and noticed that my little girl didn't want to go.


PS -I am using the GPS for speed reading, not the IMO. I find that the IMO isn't very accurate regardless of wheel size setting.

That should do it. The .125" drilling was the top end of the suggestions so its probably fine. I don't know the gearing changes but I guess you would know if those are geared too low for top speed... :dunno

The IMO crack was from a thread a bit back when there was a "Taste's Great/Less Filling" debate about 19" vs. 21" - the 19" gives better speed estimates while the 21" gives better odometer estimates. Something about EU rules requiring the speedo to read lower - which makes no sense to me (if everyone knows what's the point? :lol3)

creeper 12-09-2004 04:42 PM

Hey Nate...

You know me, I always ask the stupidest, most obvious questions first to get them out of the way... so, the most stupid and obvious is.........................




Did it go over 85 before you modified everything? :D







Obviousman

creeper 12-09-2004 05:13 PM

Here is another one.... have you recently cleaned and re-oiled the air filter?

And... one more... are your throttle cables adjusted correctly, to open the throttle all the way to the stop?


Ooh ooh... one more... :D Kidding :smooch

ktmnate 12-09-2004 05:16 PM

Quote:

Originally Posted by creeper
Hey Nate...

You know me, I always ask the stupidest, most obvious questions first to get them out of the way... so, the most stupid and obvious is.........................




Did it go over 85 before you modified everything? :D







Obviousman

It sure did. I even have an award from the Kalifornia Highway Patrol! I tried to explain that I was doing some testing and it's only a one cylinder but he didn't bite. He actually called it a Beemer! I almost slaped him but then remembered he had a gun and a badge :hide

creeper 12-09-2004 05:22 PM

Quote:

Originally Posted by ktmnate
He actually called it a Beemer! I almost slaped him but then remembered he had a gun and a badge :hide

BMW? Apparently... he did not realize that to exceed the speed limit, you must first actually ride the motorcycle. :wink:

ktmnate 12-09-2004 06:51 PM

I'm gona finish playing with it on Saturday. I decided to go snow skiing tommorow. I will keep you updated.

Flanny 12-09-2004 07:30 PM

Quote:

Originally Posted by ktmnate
I'm gona finish playing with it on Saturday. I decided to go snow skiing tommorow. I will keep you updated.


You should experiment with the main jet. For top speed and WFO, that is the circuit in question. By definition, the right main jet is the one that gets you the best speed for a given section of road....

You are probably too rich on the main jet. I think with my stock exhaust, I never needed more than 157.5 at sea level on the BST40. So, go back and re-try the 157.5 as a starting point, and then try each interval of 2.5 until you get to 165. (my guess is that a 160 is probably the one you need for best top speed).

Another approach would be to put 3 disks back in to your exhaust to lean out your mixture, essentially "simulating" a move toward a 160 MJ...that will give you an idea of which way your jetting needs to go. If adding three disks back in to your exhaust improves top speed, then you were too rich...

Good luck...remember jetting is pretty much always a work in progress....and you just have to keep trying different jects until you get it right.

markjenn 12-09-2004 08:22 PM

What was the top speed before? Most will do around 100 indicated on the IMO, so if this is the case, and it s down to 85 under the same conditions, you're looking at 25%+ drop in power. And engine power in a four-stroke doesn't change drastically with minor adjustments in jetting - if you plot hp vs. a/f ratio, the curve is very flat for anything near the optimal ratio, so you're not going to get a 25% hp decrease with sub-optimal jetting unless the current jetting is WAY off. I don't think the main jet is the culprit.

I suspect something happened in the mods where you're not getting the throttle all the way open or where the slide is getting hung up. Or some other restriction on the intake side - I've seen bikes run terribly where the only problem was over-oiling of the filter or oiling the filter while it was still wet from cleaning. This just doesn't sound like jetting tweaking issue.

FWIIW, I've never "drilled my slide" and have never felt the need to. The bike runs great with tweaks in the main jet (155), raising the needle one clip, and a slight richening of the idle mixture. YMMV.

- Mark

Esteban 12-09-2004 08:59 PM

It could be like Flanny suggested - the main jet. And it could be something else. Maybe it is...

I have also found that very subtle obstructions in any of the atmospheric vents - float bowl, slide diaphragm, or fuel tank can affect high speed running. Make sure all vents flow air well with little restriction. These vents must be able to equalize pressure adequately. The diaphragm on top of the slide must be installed correctly also. Check for cracks in slide diaphragm cover which I have seen happen once before on a CV carb (KLR) from over tightening.

One time on my Ducati 900 SS I was having a similar problem (at 115 mph + speeds) , and found that it was being caused by high wind speed pressurizing the float bowl vent tubes on the FCR carbs. I had removed the small plastic triangular plenum chambers that the vent tubes went into. I did this while stripping all "unecessary" items off the bike. However I did not realize that this small useless looking item was very necessary to keep wind pressure from acting on the floatbowls at high speeds.

BTW, my 640 LC4e will pull 110 mph indicated with the 17:42 gearing
(it has: FCR 41 with a 138 main in Denver, internally altered SXC pipe)

1)Diaphragm vent/seal problem and the slide will not go all the way up
2)fuel tank vent problem and the fuel won't come out of the tank
3)floatbowl vent problem and the fuel will not meter properly.

So check the vents, that might be it.

Steve

creeper 12-09-2004 11:13 PM

There you go Nate. Lots of things to look at. :D



An open comment directed at no one, but intended for everyone…

We make all these modifications, usually (incorrectly) all at once, in a kind of shotgun approach, based on what others have tried and/or what we know about tuning.
It's funny... I've had people PM me because their bike wasn't running right.
They’ve used jetting info for an '00, on their '03 and visa versa. They confused 4" Supertrapps with 3"... IDS2 data with stock (and modified stock) muffler data. Thought that a larger jet always would make more power than a smaller one... never factored elevation into the equation, made assumptions based on… more assumptions... and so it goes, and always will.

I based my tuning on the data acquired nearly 2 years ago by Flanny… who I know spent a good deal of time tuning and tweaking his bike. (How many of the current crop of 640 owners are aware of this?)
I knew that his 640 (an ’01 wasn’t it Flanny?) was not my ’03 640, and that the info that he had obtained was although very useful, was only a baseline for me to work from. Some of the information was near perfect verbatim, and some required further “tune and test” on my part.
What I’ve posted, repeatedly, was what I found to work on my bike, not every year of every 640 with a BST, ever made.

I hope I’ve made it clear, and I’m sure Flanny and most everyone else that has provided tuning information would agree, that the data is pretty much empirical… that everything we know is based on subjective data and not chiseled in stone.

It’s not rocket science… but it is science… and experimentation… and trial and error… and effort.
The people who benefit, should keep that in mind.

And before I close, I’d like to offer to Flanny a public “Thank You” for the work and time and thought that he put in a few years ago with his 640.
His efforts, and willingness to share, provided me with the raw material and a direction to develop the state of tune on my bike… and in that spirit, the willingness to share what I have learned as well.

We all have someone to thank... someone that came before and was willing to share... but we also must be mindful that information is not just what it is but, how it is used.

Thats it...
Chris

Reformed DucFlogger 12-10-2004 05:54 AM

Well...
 
...said.

I was also a grateful recipient of some Flanny tuning material/wisdom for my wife's 640 Adv (now referred to as "the other man").

It is for this type of Creeper & Flannyesque (no nefarious insinuations there y'all) assistance and idea-sharing that AdvRider really shows it's value.

(soapbox start) Far too often we (myself included - bad RDF :whip ) members allow ourselves get tempted into ego-laden (and !@#$ lengthy) hissy-fits on 'bestbikeitis', personal spats, bloody TV programs, etc. :war -- instead of helping riders navigate crappy repair manuals, lousy dealers, legions of mechanics with conflicting 'expert' opinions, manufacturers who blissfully choose to ignore problems with their bikes, simple head-scratching and the ever-infuriating, hide the firearms, "!@#$, WTF do I do now..?!" :baldy problems (end of soapbox)

GT-STMC 12-10-2004 10:46 AM

I'm one of the "new crop" of 640 owners.
Refering back to this post:
Quote:

Here is another one.... have you recently cleaned and re-oiled the air filter?
Is there a schedule or process for this here ?
I've searched (but have trouble with the Search engine) and couldn't find one.


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