[silverhead]

I made myself familiar with the bike tonight for the first time. I bought a new NGK plug and gapped it at 0.65mm. Valve lash was inspected at TDC and was found to be intake: 0.004mm, exhaust: 0.006mm. The timing chain lines up with T and TDC and has tension. My bike has 3800 miles indicated on the odometer and seems to be about right. My carburetor boot was found to be chipping off that rubber material from the metal part. I pulled the carburetor and completely cleaned it. I pulled all the jets and choke parts and cleaned all passages with piano wire and carb spray. The carburetor looks great. 40 pilot and 114 main jet. Pilot screw is turned out 1.75 turns from bottomed.

OK, so my problem is that the bike doesn't like to idle. It starts right up on choke, but the engine runs way too fast. When you turn off the choke, the engine runs poorly. Giving throttle makes the engine race. This leads me to believe there's an air leak. I coated the intake boot with clear nail polish to seal it up. I also sprayed carb cleaner around the intake boot while the bike was running and it had no effect on how the bike ran. I used a timing light to check the ignition to make sure it was firing every time, and it is.



So, I'm a bit stumped, but how likely is it that my intake boot is shot? It seems solid, but the cracking bothers me.



I made a video of the bike running and am looking for any opinions about what to do next.



http://www.youtube.com/watch?v=Nwb7eOzxesY





I wanted to shim my needle, but I couldn't figure out a safe way to remove the slide. This video ( youtube video shows the same type of carb as mine (pre 2001) but mine is not identical inside where the slide exists. Mine has a metal linkage and springs and crap in there. Is there a simple way to free the slide so I can get at the main jet needle to shim it?

 

[B-dub]

Take another look at the valve clearance specifications. My manual says .05mm to .09 mm or .002 to .004 inches on the intake, and .11mm to .15mm or .004 to .006 inches on the exhaust. I think you're confusing the mm and inch specifications.

 

[silverhead]

You're correct. I meant inches.



Anyway, the old 'carb spray' around the intake boot didn't yield any difference in the way it ran.. Meanwhile the pilot circuit is clean and clear and the screw is set right (has the spring and everything.)



I'm stumped.



I need to find an adapter so I can pull a compression test on the engine. The plug is white, so it's definitely lean. The plug I removed was black, however...



The mission continues.. It's nice out today.



Even though the part numbers differ due to the tube that sticks out of it, can you run a 2001+ carb joint (intake manifold, boot, what have you) on the older bikes or did the size of the carb change?



The newer part is much cheaper.

 

[mhomadness]

Don't mess with that old boot. Replace it. If the rubber is in that kind of condition, you may not have a good seal where the throat of the carb clamps inside the boot. This can cause lean run conditions that are difficult to detect. I would recommend replacing the intake boot, Check the valves again (per B-dub) check your air filter if you have not done so already. The important thing is to eliminate the questionable intake boot, and then you can go from there. m.

 

[mhomadness]

I don't know if you can use the newer intake boot...



That 114 jet makes me wonder too. First though, you must take the boot out of the picture. Then you will have a better place from which to go. m.

 

[silverhead]

My dealer discounted me on the boot.. 55 bucks, so I ordered one.

 

[mhomadness]

Lot's-O-Munny, but well worth it! m.

 

[silverhead]

I did a lot of little things today. I'll start by saying the bike still runs exactly the same (badly, really lean.)



I'm pretty sure my intake boot is sealed, but I can't be certain. I can't believe it leaks enough air to cause the problems I'm having.



Things I did:



1) Set cam chain tension by the book (0.5mm on the adjuster rod)



2) Set float height to 27mm (it was set at 24mm)



3) Reassured myself the pilot circuit was clear



4) Made shims for the needle (three, or about 1 click higher on a Mikuni needle)



5) Pulled a compression test (160 psi which is higher than max specification??)



The bike runs exactly the same with surging on throttle, running very hot (I could tell the exhaust header was way too hot way too fast)



Here's how it started after I did all of this stuff:



http://www.youtube.com/watch?v=HB7PVXrfzIo





Photos from today:





Clean carburetor

Float height setting (I set my floats at an angle like this to engage the needle spring about half way)

Pilot jet re-examined and cleaned

Slide and needle look fine. No scratches to let air past the slide. Needle isn't bent.

Shims I made out of pop tabs for the needle

I cut a rubberized gasket just for good measure at the intake joint/cylinder mounting point.

Compression when hot.. What could cause it to be higher than 150psi? I checked it with two different gauges, both registered 160psi (throttle open, using the starter)

This is what the plug looks like after what little riding around I have done. I don't want to cook the exhaust valve. The tip is white and crusty.

I'm trying to cover all my bases. Can you actually set ignition timing on the bike? I haven't looked at that yet. I probably will check it to make sure it's not too advanced.

 

[mhomadness]

OK, if you have not read this thread yet, go here: http://tw200forum.com/index.php?/topic/647-carb-tuning/



I am suspecting the main jet. The 114 is the stock jet, and you would think that stock should be good / correct. However, my engine is stock, low miles, and when I got the bike (used) I replaced the carb, as the original was beyond reasonable repair. I was having similar problems as you are having, I did shim my needle, and went to a larger main jet, a 118 if I remember correctly, & that fixed it. Don't let it get you too crazy until you get the new boot. And you may want to try a lager main jet, IMHO. m.

 

[silverhead]

Typically the main jet doesn't set in until you're at 1/2 - 3/4 throttle, correct?



At least that's how a Mikuni (which I'm much more familiar with) works.



ie: pilot jet is the only one working at idle unless RPMs are high enough (like in this case) to suck up some gas from the main circuit. The boot should be here by the end of next week. I stuck it on a rubber block and pulled vacuum on it and it was holding pretty steady. I still think it's sealed.



If the main jet and the boot are fine, what other things can cause this in terms of mechanical problems with the engine? I'm trying to figure out if someone else screwed the bike up and dumped it to the previous owner, and then to me ;-)



I just get impatient when dealing with something as simple as a lawn mower and I can't figure it out, haha. I sprayed carb cleaner around the boot, the plastic cap over the slide, and around the head, looking for a change in the way the bike runs to find the leak and didn't turn anything up.



114 is the factory OEM main jet and 40 is the factory pilot jet. I live at 1000 feet and typically bikes 'run OK' at factory settings here.

 

[mhomadness]

Ok, I watched your video & listened to how your bike ran. The simple stuff first, & I apologise if you have already done this. Did you make sure that the throttle cables are adjusted correctly, allowing the slide actuator to come to a full rest on the idle speed screw? Turning the idle speed screw changed nothing?



Did it idle this fast before the needle was shimmed?



If you eliminated those things, it still seems like a vacuum leak, or way too lean main?



Ok, beer now, think more later... m.

 

[mhomadness]

This is a quote from qwerty's post.



"There are three adjustments in fuel metering in nearly all carbs. Some carbs have more. We will be working with 1) the pilot jet and screw, 2) the needle, and 3) the main jet. All three have an effect at all engine speeds/throttle settings. Adjustments to the pilot jet and screw have the most effect at low throttle settings. Needle adjustments have the most effect at mid throttle settings. Main jet adjustments have the most affect at high throttle settings. However, the main jet does affect part-throttle operation, but not much. The pilot jet and screw do affect operation at high throttle, but not very much."



My idle did change a bit with different main jets. I know it seems unlikely, but it could be the case.



Good idea checking the boot for holding a vacuum, the boot may not be it... I just don't trust cracked aged rubber parts, but you've done your homework, & it did pass the carb spray test...



I apologise if I've added to your pain. m.

 

[silverhead]

I turned the idle down so low that the slide bottomed and I started the bike with choke. This is more like it.. The bike is behaving better.



That said, I either still have an air leak or the pilot circuit needs more fuel flow. Where can you even buy TK pilot jets? Yamaha doesn't list an alternative to the 40. I'm 1.75 turns out on the pilot adjustment screw. I guess I can go out past 2 turns and see what happens. But, I got way closer to normal with the throttle screw backed out.



http://www.youtube.com/watch?v=QpamNdk7xrE

 

[silverhead]

Reading further, I think I'm running my pilot screw way too far in. I'm at 1.75 turns out and I'm going to try 3 and work my way in tomorrow. The goal is to be able to start the bike without choke when it's 70F or warmer. It looks like everyone is getting along with a 40 pilot jet regardless of altitude. I get confused with pilot screws because depending on what bike I'm working on, screwing it out lets either air or gas enter the circuit. And I presume that on the TK carb backing the screw out lets in more gas.

 

[mhomadness]

Your bike sounds much better! The fact that you can roll on the throttle that fast without it stopping, or stuttering, seems to indicate that the pilot / low end circuit is working well. As far as starting at 70 degrees f, if you are going for your first start of the day, & the bike is at 70f +/- it is not uncommon to have to use the choke a little to get that first go. I think it helps pull up a bit of fuel to prime the carb. Adjusting the pilot screw out a bit more, is a good experiment. You will have to find a happy balance, as doing so will affect the running between cold start, & warm engine. I think you have a good hold on your situation, you seem to have a good mechanical ability, and your bike looks pretty nice. m.

 

[mhomadness]

I remember using this thread from the old TW forum: http://tw200forum.com/forums/2/88964/ShowPost.aspx#88964



You'll have to sift thru it a bit, but I think it's worth reading through. m.

 

[mhomadness]

Ok, Silverhead, I drug myself off the couch & out to the shop today. Found some info from my carb exploits. I have my pilot screw turned out to 3 turns, although I think I have ran it back closer to 2.5 turns. My main jet is a #116, pt.# 288-14343-58. I can not remember what the replacement carb came with, but I think it was a #118, as that is the only jet I have that does not have a factory package. My elevation is pretty close to sea level.



My impression is most folks feel that the stock 114 jet is lean, allowing the bike to pass smog / EPA.



Remember, this is what worked for my bike. Every bike is different. m.

 

[silverhead]

Thanks for relaying your numbers. I'm at 1000 feet here. I'm thiking a 116 mainjet may be in order as well. The handoff from needle to main jet feels weird when coasting down into that range and trying to accelerate out of it.



Here's a video from this morning. I think I figured it all out.



http://www.youtube.com/watch?v=KqhM-0KW_iQ



The carb boot breeched on me almost immediately after the bike warmed up. So I had to use calking silicone to make it seal up. My new intake boot won't get here until next week, but the bike is running now. I rode it over 25 miles today.

 

[mhomadness]

That's great!! Your bike is running / sounding like it should. Next weekend you'll have it dialed in with the new boot.



Then you need to give it a good ride, 'cause it's way too clean looking! m.

 

[small's]

The idle air mixture screw being out 2.5-3 should fix it. If not i would agree you have a leak. The 114 jet shouldnt be a problem especially at your elevation. It might like a 116 but im lower in elevation than you are and i had a older style tw and my buddy has a 96 and both run fine on the 114 once we opened up the idle/air screw and shimmed the needle.