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Old 09-20-2013, 07:32 AM   #1426
erohver
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I just brought home a 2002 640 with 7500 miles on it, the previous owner de-snorkled, upped the main jet to 157.5, 4th clip down, stock pipe is opened up and it detonates under heavy load in high gear even running 93 octane. At least I think that's what I'm hearing, it's a high-pitched rattle only when I go WOT at speed. I put the snorkle back on and it stopped doing it...but now it's not as snappy. I'm going to try a 160 main with the snorkle back out. Is there anything else I should be looking at?
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Old 09-20-2013, 10:34 AM   #1427
motolab
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Quote:
Originally Posted by erohver View Post
I just brought home a 2002 640 with 7500 miles on it, the previous owner de-snorkled, upped the main jet to 157.5, 4th clip down, stock pipe is opened up and it detonates under heavy load in high gear even running 93 octane. At least I think that's what I'm hearing, it's a high-pitched rattle only when I go WOT at speed. I put the snorkle back on and it stopped doing it...but now it's not as snappy. I'm going to try a 160 main with the snorkle back out. Is there anything else I should be looking at?
Since the pre high-flow head models are severely prone to detonation in stock form, I would not take any measures (including removing the snorkel) whatsoever to increase cylinder filling (and therefore dynamic compression) without first having taken significant measures to get the engine out of the danger zone. One of the things it absolutely needs in efforts to curb detonation is much more exhaust flow. The stock pre-muffler and Supertrapp muffler are horrible for flow (come to think of it, so is the header). While anything to increase flow is good, a good slip-on muffler and elimination of the pre-muffler won't be enough to safely allow snorkel removal. Therefore modifications to the stock muffler certainly won't.

A 160 main jet will be way too rich for your combination.

Regards,

Derek
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Old 09-20-2013, 08:38 PM   #1428
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Quote:
Originally Posted by meat popsicle View Post
Remember a engineer likely specified a plastic part for a reason; why would they?
Unfortunately due to commercial realities you cannot be sure of that. The engineers may have specified metal but the accountants may have said plastic. To be fair to KTM, the engineers seem to have more say than for the Japanese manufacturers, up until recently. (An example being the expensive but arguably better angular contact bearing in the rear sprocket carrier where other manufacturers and lately KTM use deep groove roller balls.)

As far as the thread corrosion issue goes, if you read the Loctite thread, dirty suggests using blue (or low strength purple if appropriate) threadlocker on any threads to stop corrosion and galling.
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Old 10-31-2013, 06:51 AM   #1429
meat popsicle
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Originally Posted by warewolf View Post
...

As far as the thread corrosion issue goes, if you read the Loctite thread, dirty suggests using blue (or low strength purple if appropriate) threadlocker on any threads to stop corrosion and galling.
I use a marine grade anti-sieze (so not a thread locker) on fasteners that look vulnerable, after paying a couple hundred bucks to have a stuck bolt disintegrated via wire-EDM.

But now onto my issue: what makes bikes not want to stay running when cold, even with the enrichner?

I recently got a new Staintune muffler, installed on stock pipes (can't have it all they say, where would you put it?), and rebuilt the BST. Got the parts from Motolab - thanks for being there Derek - and didn't seem to have much trouble with the job. Upon first start (with enrichner) the bike roared to life and did the centerstand shuffle I had heard so much about.

That made me think the air-fuel mixture was better than before but I still thought it wise to run through Creeper's fine-tuning routine with the idle screw. This time the process was not as fulfilling as last, there was no "that's good" moment, even after starting over a few times, so I got to ok and tried a ride. The bike seemed to run fine and I thought I was good.

Nope... I found the next time I went to start the bike (details might be important here) it would start easy with enrichner (note: with previous "race core" exhaust it never seemed to need the enrichner) but then it would simply die. I could restart easily and it might run for a second, or a few seconds, but then die again. I would struggle with this, scratching my head, until the bike warmed up and then it would run ok - no more dying suddenly.

By dying, I mean no auto decomp - no clacking as the engine tries to keep running - it would just die with a "clank". The only noise is a soft, popping sound from the exhaust (quieter than the auto decomp), just before dying.

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Old 10-31-2013, 09:58 AM   #1430
motolab
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Quote:
Originally Posted by meat popsicle View Post
That made me think the air-fuel mixture was better than before but I still thought it wise to run through Creeper's fine-tuning routine with the idle screw. This time the process was not as fulfilling as last, there was no "that's good" moment, even after starting over a few times, so I got to ok and tried a ride. The bike seemed to run fine and I thought I was good.
I don't know what Creeper's routine is, but I recommend:

If exhaust gas analysis is not available, adjust the fuel screw to a known lean setting and lower the idle speed a little bit (this increases sensitivity). As you open the fuel screw you will notice the quality of the idle improve, until at some point there will be a threshold where opening the screw further does not improve matters (but doesn't hurt it either). Open the screw 1/8 to 1/4 from this threshold, then adjust the idle speed back up to normal.

For diagnostic purposes it is helpful to note:

1) At how many turns is the aforementioned threshold?
2) At how many turns can you kill the engine on the lean side?
3) Is it possible to make it idle poorly on the rich side? If so, at how many turns.
4) Is it possible to kill the engine on the rich side? If so, at how many turns.
Quote:
Nope... I found the next time I went to start the bike (details might be important here) it would start easy with enrichner (note: with previous "race core" exhaust it never seemed to need the enrichner) but then it would simply die. I could restart easily and it might run for a second, or a few seconds, but then die again. I would struggle with this, scratching my head, until the bike warmed up and then it would run ok - no more dying suddenly.
How long and how much are you leaving the enrichener on?

Regards,

Derek
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Old 10-31-2013, 12:43 PM   #1431
meat popsicle
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Quote:
Originally Posted by motolab View Post
I don't know what Creeper's routine is, but I recommend:

If exhaust gas analysis is not available, adjust the fuel screw to a known lean setting and lower the idle speed a little bit (this increases sensitivity). As you open the fuel screw you will notice the quality of the idle improve, until at some point there will be a threshold where opening the screw further does not improve matters (but doesn't hurt it either). Open the screw 1/8 to 1/4 from this threshold, then adjust the idle speed back up to normal.

For diagnostic purposes it is helpful to note:

1) At how many turns is the aforementioned threshold?
2) At how many turns can you kill the engine on the lean side?
3) Is it possible to make it idle poorly on the rich side? If so, at how many turns.
4) Is it possible to kill the engine on the rich side? If so, at how many turns.

How long and how much are you leaving the enrichener on?

Regards,

Derek
I'll try your routine this weekend.

I don't get to turn the enrichener off, the bike just starts dying and continues to do that until warm. I've tried turning the enrichener off, as well as varying the amount, but that only makes the bike not start at all (so enrichener still required at some setting). Use enrichener enough and the bike starts easily but then suddenly dies after a few seconds, again until warm.
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Old 10-31-2013, 02:15 PM   #1432
Boon Booni
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Does it fast idle on the enrichener?
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Old 10-31-2013, 03:01 PM   #1433
Sparrowhawk
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Quote:
Originally Posted by meat popsicle View Post
... rebuilt the BST. Upon first start (with enrichner) the bike roared to life ...

That made me think the air-fuel mixture was better than before but I still thought it wise to run through Creeper's fine-tuning routine with the idle screw. This time the process was not as fulfilling as last, there was no "that's good" moment, even after starting over a few times, so I got to ok and tried a ride. The bike seemed to run fine and I thought I was good.

Nope...
These potential issues come to my mind. Did you change the idle jet? That would change how it responds to air screw adjustments. Is the air screw adjustment sweet spot in the proper range of turns out? Could you have cross-threaded the crappy plastic end of the enrichment cable? Float level adjusted properly? Leaks in the rubber intake boot?

Anything else you did at the same time? I recently replaced the large cam bearing and when I put it back together I mounted the cam chain one link off from where it should have been, changing the cam timing. It surprisingly ran well but was a bitch to start when cold.
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Old 10-31-2013, 07:05 PM   #1434
bmwktmbill
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Quote:
Originally Posted by erohver View Post
I just brought home a 2002 640 with 7500 miles on it, the previous owner de-snorkled, upped the main jet to 157.5, 4th clip down, stock pipe is opened up and it detonates under heavy load in high gear even running 93 octane. At least I think that's what I'm hearing, it's a high-pitched rattle only when I go WOT at speed. I put the snorkle back on and it stopped doing it...but now it's not as snappy. I'm going to try a 160 main with the snorkle back out. Is there anything else I should be looking at?
Ero,
I have an '02 Adventure with the factory Comp pipe and the pre muff replaced with the now not available free flow replacement pipe, my exhaust pipes are stock. My snorkle is removed and the hole was enlarged 1 inch by the length of the opening the long way, my jets are stock the needle is raised one notch from stock. I have about 50+ K miles.
I broke a top piston ring and replaced the piston and rings with the OEM parts.

All that said I had a habit of lugging the machine and running regular octane fuel.

Now I run premium and run the snot out of the engine.

I feel like it has plenty of snap, wll pull over 100mph with stock gearing and the vibration is not excessive.

You might try that?

And listen to Derek!!!


bill
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Old 10-31-2013, 07:24 PM   #1435
motolab
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Quote:
Originally Posted by Sparrowhawk View Post
These potential issues come to my mind. Did you change the idle jet? That would change how it responds to air screw adjustments. Is the air screw adjustment sweet spot in the proper range of turns out?
The idle mixture screw on a BST40 carb is a fuel screw. Distinction: A fuel screw richens the mixture when you unscrew it. An air screw leans the mixture when you unscrew it.
Quote:
Float level adjusted properly?
I would like to request that you use the terms "float height", or "fuel level", but not "float level". If you use the term "float level", it is possible to get confused between float height and fuel level, which is undesirable because when you increase the float height, you decease the fuel level (and vise versa).

Regards,

Derek
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Old 10-31-2013, 11:22 PM   #1436
meat popsicle
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Originally Posted by Boon Booni View Post
Does it fast idle on the enrichener?
yes, but then dies suddenly w/out any decomp activity.
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Old 10-31-2013, 11:26 PM   #1437
meat popsicle
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Quote:
Originally Posted by Sparrowhawk View Post
These potential issues come to my mind. Did you change the idle jet? That would change how it responds to air screw adjustments. Is the air screw adjustment sweet spot in the proper range of turns out? Could you have cross-threaded the crappy plastic end of the enrichment cable? Float level adjusted properly? Leaks in the rubber intake boot?

Anything else you did at the same time? I recently replaced the large cam bearing and when I put it back together I mounted the cam chain one link off from where it should have been, changing the cam timing. It surprisingly ran well but was a bitch to start when cold.
no idle jet change, yes the (strangely vague) sweet spot is about 2+ turns out, I don't think so, I think so, and I don't think so...

just the new Staintune can; nothing as cool as cam work.
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Old 10-31-2013, 11:36 PM   #1438
Sparrowhawk
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Quote:
Originally Posted by motolab View Post
The idle mixture screw on a BST40 carb is a fuel screw. ...

I would like to request that you use the terms "float height", or "fuel level", but not "float level".
My bad on both counts. Typing in a hurry during a break at work and thinking about the basics of what might cause the symptoms without remembering the specifics of the idle circuit or considering proper vocabulary.

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Old 10-31-2013, 11:52 PM   #1439
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Meat, is it possible that you have some schmutz in your idle jet or circuit causing it to be a little lean and unresponsive to adjustment?

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Old 11-01-2013, 01:35 AM   #1440
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Meat, look for an air leak in the carb boot. Try if you fastened the screws holding the carburetor to the engine intake.
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