TW200 Forum banner

1 - 20 of 41 Posts

·
Registered
Joined
·
81 Posts
Discussion Starter #1
When I purchased my '93 TW a month ago, the previous owner mentioned he recently did some carb work. He was having some issues getting the carb dialed and was drilled a small side hole in the airbox so he could shoot starter fluid into the air intake. He mentioned something about a paper clip and I told him I wasn't too concerned, I've rebuilt carbs before...



After replacing the old gas that was in the tank and putting running some 91 octane gas/seafoam mix through the carb, it seemed to run better. I still had a flat spot down low and a hanging idle. Coming off throttle through a turn for instance, the idle would stay high and I'd have to throttle on then quickly dethrottle to break the hang.



Some pictures of the carb when I opened it up today:



Notice something unusual?





Yup, a Paper Clip in my main jet!





Here are the jets, they checked out clean:







I figured I had to throw some pictures of the bike into this thread!





The water is the Pacific Ocean. The left half of the distant land is Mexico, the other half USA











Carb Stats:

Idle Jet - 40

Main Jet - 114 (was plugged by paper clip)

Fuel Screw - 1.25 turns out



The baseline for the fuel screw on most four strokes is 2-2.5 turns out. I have a 116 and 118 jet and some washers from Ayers Garage. I ride in Southern California 0-4,000ft. I'm thinking Idle Jet 40, Main Jet 116, Fuel Screw 2.5 turns and 1 washer for the needle.



Any thoughts on my mystery hanging idle? Thank you for reading and I appreciate your thoughts/tips!
 

·
Registered
Joined
·
70 Posts
I've seen that done before, usually after somebody drills the jet way too much. Just because it says 114 on the side doesn't mean it hasn't been drilled larger. Compare it to your other main jets. If you want to get fancy, you can do the calculations and figure out roughly how much area there was for fuel to flow through, if you can accurately measure the hole and the paper clip.
 

·
Registered
Joined
·
81 Posts
Discussion Starter #3
I've seen that done before, usually after somebody drills the jet way too much. Just because it says 114 on the side doesn't mean it hasn't been drilled larger. Compare it to your other main jets. If you want to get fancy, you can do the calculations and figure out roughly how much area there was for fuel to flow through, if you can accurately measure the hole and the paper clip.


Woa thanks for the input. I would have never guessed its a common thing ha. I think the main jets were $5 or something at my local dealership.



I'll be interested to see if my "new setup" will cure the idle hang. I don't think there was any air leak.

idle jet - 40

main jet - 116

needle - 1 shim

fuel screw - 2.5 turns out





On bikes like the DRZ and DR650 they speak of a 3x3 airbox mod where you cut the top of the airbox to improve flow into the intake. I haven't found a definitive answer for an airbox mod (besides the hollow frame mod) on the TW. Is it common to cut off the snorkel on TWs?



Thanks!
 

·
Registered
Joined
·
7,369 Posts
There's no magic bullet when it comes to the idle mixture screw, no matter what you've heard.



I recomend you remove the shim and put a legit, known 114 or (at most) 116 in there while sorting this out, but that's just me. That takes main jet leakage out of the equation. But the proper procedure for adjusting idle mixture is as follows:



Warm your bike up. Adjust the idle for a couple hundred rpm or so above what you normally run.



First, frontseat (close) the idle mixture screw 1/2 turn at a time and make sure the engine COMPLETELY dies when it's fully closed or just slightly beforehand. If it doesn't, your idle jet is too big. Maybe someone drilled it er sumpin'. Conversely, if your engine dies somewhere nearer to 1 turn out than it does to zero turns, your idle jet is either too small or is partially clogged.



Now backseat (open) the screw to 2 turns. Start the bike and again begin to frontseat (close) the mixture screw with engine at high idle 1/2 turn at a time. Allow it to settle down each 1/2 turn. Once the idle begins to slobber or become uneven, count the turns out at which it occurs.



Then do the same procedure in reverse. Open the screw 1/2 turn at a time, allow it to settle, then when the idle begins to slobber again, count the turns out at which it occurs.



Now split the difference. If for exmple the idle craps at 1 turn closed then again at 2 turns open, your starting point is very close to the vicinity of 1 1/2 turns.



That's a far cry from the recomended 2 1/2-to-3 turns, no? Whatever that number turns out to be, yer about done. Bring the idle speed back down to normal RPM, makes sure you still have a smooth, crisp idle. Only then are you ready to procede with the main jet and lifting the needle.



Any pat formula for jets and shims are crap, as well. Main jet first til it's right, THEN lifting the needle. When you cease to realize gains or are running rich it's time to stop or even reverse the change. It's really difficult to avoid placebo effect, so take the time to read your plug.



Same thing with airbox and exhaust mods. Perfect one thing before moving on to the next so you have a baseline and things don't become a mishmash of issues on top of previously unresolved issues. It's pretty hard to UNCUT a hole in your airbox. Removing the snorkel is relatively harmless but even that should only be done AFTER you've got the jetting right with it in place. Removing the snorkel introduces intake noise which can also contribute to placebo effect. That sudden audible rush of air can give the sensation of more power just as can the racket of an aftermarket exhaust. Make sure you actually gained something from it before moving on.



If you want to you can refine things even further by using 1/4 turn increments during the idle jet adjustment but seldom is it ever gunna be anywhere near a pat number for every bike.



I suggest you not mess with airbox mods until you get your idle issue and main jet selection squared away. Opening up the airbox will neither cure nor improve your idle issues.
 

·
Registered
Joined
·
81 Posts
Discussion Starter #5
There's no magic bullet when it comes to the idle mixture screw, no matter what you've heard.



I recomend you remove the shim and put a legit, known 114 or (at most) 116 in there while sorting this out, but that's just me. That takes main jet leakage out of the equation. But the proper procedure for adjusting idle mixture is as follows:



Warm your bike up. Adjust the idle for a couple hundred rpm or so above what you normally run.



First, frontseat (close) the idle mixture screw 1/2 turn at a time and make sure the engine COMPLETELY dies when it's fully closed or just slightly beforehand. If it doesn't, your idle jet is too big. Maybe someone drilled it er sumpin'. Conversely, if your engine dies somewhere nearer to 1 turn out than it does to zero turns, your idle jet is either too small or is partially clogged.



Now backseat (open) the screw to 2 turns. Start the bike and again begin to frontseat (close) the mixture screw with engine at high idle 1/2 turn at a time. Allow it to settle down each 1/2 turn. Once the idle begins to slobber or become uneven, count the turns out at which it occurs.



Then do the same procedure in reverse. Open the screw 1/2 turn at a time, allow it to settle, then when the idle begins to slobber again, count the turns out at which it occurs.



Now split the difference. If for exmple the idle craps at 1 turn closed then again at 2 turns open, your starting point is very close to the vicinity of 1 1/2 turns.



That's a far cry from the recomended 2 1/2-to-3 turns, no? Whatever that number turns out to be, yer about done. Bring the idle speed back down to normal RPM, makes sure you still have a smooth, crisp idle. Only then are you ready to procede with the main jet and lifting the needle.



Any pat formula for jets and shims are crap, as well. Main jet first til it's right, THEN lifting the needle. When you cease to realize gains or are running rich it's time to stop or even reverse the change. It's really difficult to avoid placebo effect, so take the time to read your plug.



Same thing with airbox and exhaust mods. Perfect one thing before moving on to the next so you have a baseline and things don't become a mishmash of issues on top of previously unresolved issues. It's pretty hard to UNCUT a hole in your airbox. Removing the snorkel is relatively harmless but even that should only be done AFTER you've got the jetting right with it in place. Removing the snorkel introduces intake noise which can also contribute to placebo effect. That sudden audible rush of air can give the sensation of more power just as can the racket of an aftermarket exhaust. Make sure you actually gained something from it before moving on.



If you want to you can refine things even further by using 1/4 turn increments during the idle jet adjustment but seldom is it ever gunna be anywhere near a pat number for every bike.



I suggest you not mess with airbox mods until you get your idle issue and main jet selection squared away. Opening up the airbox will neither cure nor improve your idle issues.


I set the fuel screw at 2.25 and played around with it. I felt at 2.25-2.5 was fine. I put the 116 main in and at full throttle the bike started cutting, eerrr, eerr, eerr, eerr and wasn't running clean. I should have read that as too rich but I was thinking too lean.



I got greedy and went for a home run, installing a 118 and 2 needle shims. Ive read that multiple guys run that set up with positive results. 0 throttle to 1/4 throttle felt great but everything else was horrible. It wouldn't rev out and was jumpy.



Back to the basics... bone stock settings (without the paper clip that is). Any tips on how to adjust the fuel screw while the bike is running?



I appreciate the input
 

·
Registered
Joined
·
7,369 Posts
Some guys use a bit from a 4-way screwdriver, shorten the handle on a stubby screwdriver, etc.



Your pilot circuit is open 24/7, so ta speak, so it's a component of your total fuel volume at w.o.t.



That's why it's so important. If your pilot circuit is lean or rich the cumulative effect of whatever main jet you install will be leaner or richer accordingly. Hope that makes sense.
 

·
Registered
Joined
·
3,517 Posts
Boy, I can't imagine that the O.D. of a paper clip small enough to represent the orifice diameter of any small displacement (carburetor jet) engine. Perhaps I have found a new 'tool'. Gerry



Per Lizrdbrth above:



 

·
Registered
Joined
·
81 Posts
Discussion Starter #8
Some guys use a bit from a 4-way screwdriver, shorten the handle on a stubby screwdriver, etc.



Your pilot circuit is open 24/7, so ta speak, so it's a component of your total fuel volume at w.o.t.



That's why it's so important. If your pilot circuit is lean or rich the cumulative effect of whatever main jet you install will be leaner or richer accordingly. Hope that makes sense.


That makes sense. In an effort to do things incrementally, I took out the 2 shims and rode the 118 around. It was still rich but ran better without the shims than with the shims. I'm going to work my way down (leaner) slowly. On my ride around the neighborhood, I saw a TW parked. I'm going to leave a note for the owner to check out tw200forum.com



Lizrdbrth, out of curiosity, how many turns is your fuel screw set at?
 

·
Registered
Joined
·
7,369 Posts

·
Registered
Joined
·
7,369 Posts
Aight. I found this on the internet:



http://www.iwt.com.au/mikunicarb.htm



Srictly speaking most of it pertains to two strokes. We don't have idle air screws on our carbs, the pilot mixture screw covers that task. We don't have the option of different slides and our needles don't have clip grooves so we gotta use the washer method, but most of the info is valid with any carb you're trying to tune.



I selected it for the graph of how the various systems overlap. If you get nothing else out of it try to make sense of the graph. Start thinking of your carb as 3 seperate carbs and it'll go a long way not only helping you get your jetting right but in diagnosing problems when they crop up, as well.



This guy does the pilot circuit last. That's fine, but most of our crowd breaks out in hives at the prospect of doing plug readings. If you're not gunna be bothered with plug readings at various throttle openings you can still get your carb tuned properly, but it'll take longer. Do the pilot circuit FIRST because as you can see from the graph it will remain a constant. Do the main next, then any needle lifting to cover midrange gaps. No harm in trying things like shimming the needle, etc. to see if it effects a significant change, but don't just put 3 shims in there because it worked on Ernie's bike.



So, the next time you hear someone suggest lifting the needle or installing a bigger main jet either will cure (or has cured) a starting or idling problem and gave him 5 more mph you can just smile knowingly.
 

·
Registered
Joined
·
3,477 Posts
Your pilot circuit is open 24/7, so ta speak, so it's a component of your total fuel volume at w.o.t.



That's why it's so important. If your pilot circuit is lean or rich the cumulative effect of whatever main jet you install will be leaner or richer accordingly. Hope that makes sense.


My my, in all these wrenching years (50) no-one ever explained that to me....I always thought the idle mix wasn't important above about 1/3 throttle.




No wonder I've never been able to tune carbs well! I'll do your procedure as outlined, although my bike is running more or less OK. Perhaps the idle mix does have something to do with my ocassional WOT bog I posted about a few months ago.




Lzrdbrth, you are a gold mine!
 

·
Registered
Joined
·
81 Posts
Discussion Starter #14
Boy, I can't imagine that the O.D. of a paper clip small enough to represent the orifice diameter of any small displacement (carburetor jet) engine. Perhaps I have found a new 'tool'. Gerry



Per Lizrdbrth above:





Your picture got me thinking...



I found these at Rocky Mountain ATV



Dubach Racing

http://www.rockymountainatvmc.com/p/44/-/256/731/-/4395/Dubach-Racing-Pilot-Fuel-Screw-Tool





Motion Pro

http://www.rockymountainatvmc.com/p/43/-/171/989/-/1472/Motion-Pro-Carb-Tool-Kit/carb+tool

 

·
Registered
Joined
·
7,369 Posts
My my, in all these wrenching years (50) no-one ever explained that to me....I always thought the idle mix wasn't important above about 1/3 throttle.




No wonder I've never been able to tune carbs well! I'll do your procedure as outlined, although my bike is running more or less OK. Perhaps the idle mix does have something to do with my ocassional WOT bog I posted about a few months ago.




Lzrdbrth, you are a gold mine!


We're here to help one another. I'm glad you got something you could use out of it.
 

·
Registered
Joined
·
7,369 Posts
Seems some are a little displeased with my saying you should do the pilot first.




Normally, they'd be correct. Just to clear things up, note that what I said was that if you're NOT gunna do plug chops do the pilot first.



If you've blindly followed someone else's settings for the pilot screw, odds are your pilot isn't right, has never been right and will never be right. If you do the pilot first you'll at least have one thing nearly right and won't be as likely to under- or over-compensate for it or mask the problem with jetting.



"Jetting a carb" is a very different matter from "messing with jetting a carb". If you want to get it right the first time sooner or later you're going to have to man up and learn the black art of plug chops. An hour later you'll KNOW it's right.
 

·
Registered
Joined
·
81 Posts
Discussion Starter #17
Well I put in the 116 and started messing with the Fuel Screw. I did find a good usable range for the fuel screw (it died as I closed it as lizrdbrth said it would). The bike was puffing white smoke out the exhaust and cutting out at high RPM (signs of a rich mixture) so I pulled the plug and its black as an old bbq grill... Time to buy a few fresh plugs and start from the beginning again.







btw I did pick up that Dubach Racing Fuel Screw - it works well. I've burnt my hand on the exhaust a couple times now... gotta put my gloves on!
 

·
Registered
Joined
·
81 Posts
Discussion Starter #18
I spent the afternoon working on the TW with minimal forward progress. I installed the stock 114 and it seemed no matter what setting the fuel screw was at, it was still rich. I put a fresh plug in and it was black and sooty within 20 minutes. I tried running the bike with the air filter and then again without it. At high rpm the bike was spewing rich black smoke.



I feel high off the exhaust fumes. My buddy came over to help and he couldn't diagnose it either. He thought it may be the intake valve that could be giving us trouble?



Considering the bike came to me with a 114 AND a paperclip in the jet... I'm now even more confused.



Any help or thoughts would be appreciated. I think the idle jet might be off but its stock settings... Could the valves be an issue?
 

·
Registered
Joined
·
7,369 Posts
Have you had the needle out? I do have one other potential explanation for your paperclip. Wrong needle. It's pretty remote, but if the P.O. istalled a too-short needle or one with the wrong taper, or if the stock needle were overshimmed it would be rich across the board.
 

·
Registered
Joined
·
81 Posts
Discussion Starter #20
Have you had the needle out? I do have one other potential explanation for your paperclip. Wrong needle. It's pretty remote, but if the P.O. istalled a too-short needle or one with the wrong taper, or if the stock needle were overshimmed it would be rich across the board.


I pulled the needle when I tried shimming it when I went for the homerun hit during my 118 main install - it didn't work. I "assumed" it was stock, it didn't have any needle clips nor shims.



I posted my issues on my local San Diego riding forum and they suggested I run a compression test and check the valve guides. I don't even know what type of valves the TW has but its not a bad idea to baseline the motor. 1993 with 1,400 miles - it sat for a long time before I got it and there could be a bad gasket somewhere.



I appreciate all the thoughts and help!



This was the new spark plug 10 minutes after installing the 114 main jet. Eeek!

 
1 - 20 of 41 Posts
Top