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Discussion in 'Thumpers' started by sleepywombat, May 1, 2006.
Ain't that the truth!!
I've also learned a valuable lesson about why I need to get that god damned extended fuel screw. So I backed the fuel screw out about 1/2-1/4 of a turn. The bike fired up, with choke, but when I gave it throttle, the engine would sputter and die. Assuming that I had the mixture too rich, I screwed it in about 1/4 turn, put everything back in place, and fired it up again. It's about the same. The idle is still very "chuggy" and dies after about 10 seconds, and now, when I open the throttle any more than 1/3 or 1/2, the engine sputters and dies. I'm assuming that I'm running too rich, but I also know next to nothing about carburetors, so I might be a bad judge here. Does it sound like I'm running too rich?
The pilot screw should only be used to tune the idle mixture. Anything that is not idle is the responsibility of other components. Correspondences on CV carbs:
Low rpm all throttle positions: float height, needle base diameter, emulsion tube outlet size
WOT operation overall: main jet
WOT operation between HP peak and red line: main air corrector
WOT operation below red line: jet needle shape
1/4 throttle opening: jet needle clip position
1/8 throttle opening: pilot jet size
1/16 throttle opening: pilot jet size
idle: mixture screw adjustment
Realistically, the float needle condition should be verified and the float height set before the idle mixture is adjusted.
Hold the carb in one hand and hold the base of the float cage tightly against the carb body with the index finger of the same hand. Rotate the carb so that the float tang just contacts the float needle's spring loaded plunger, but does not depress it. With the float height setting tool set to the desired height, use the other hand to drop it down over the float so the tool's posts contact the bowl gasket surface and the posts are square to the body (front to back - the tool takes care of side to side). Flip the tool to check both sides (as the float may have some twist in it). Bend the float tang until the tang on the float height setting tool just contacts the highest point on the float, but does not depress it.
Procedure for setting idle mixture:
Start the engine and warm it up. Lower the idle speed below the factory spec. Starting from a setting that is known to be lean (1-1/2 turns is likely but not guaranteed to be), adjust the fuel screw to obtain the highest idle speed. Adjust to 1/8 - 1/4 turn richer than that. Then, adjust the idle speed back to 1500 rpm.
Once you have the correct fuel screw setting, there should not be too many reasons to have to revisit very often. I'm therefore not a big proponent of extended fuel screws. If you intend to own carbureted motorcycles in the future, I recommend procuring an angle-drive screwdriver, which will be universally applicable.
Screw it in snug, back it out 1-1/2 turns, ride. Some time ago (39,000 miles or so), I was browsing the internet and I kept seeing 1-1/2 turns. Sounded good to me. I've since bought the extended fuel screw and messed with it. I'm still at 1-1/2 turns, give or take. At my altitude (6000 +), I'm satisfied; although I've heard that riding a TM-40 or FCR will ruin me forever (or until I convert).
Yesterday, my baby turned 40. :eek1
205'd by motolab
Thumb screws...made all the difference
got my single track setup. 18" rear wheel with 90/90-18 and drive hub with off road gearing.
I have a street tire for the 17" rear with another drive hub and highway gearing.
I've also made a different dog bone plus the larger wheel gives me about an extra inch of ground clearance.
1/4 Throttle opening sounds about right for where it starts dying, and if I remember my names correctly, that's where the clip is missing from the spring. So if that clip isn't there, I'm guessing that's letting the jet needle move around incorrectly. If that was jacking with my fuel flow, then maybe that's causing it to die out? I don't get why this didn't happen before, and I'm damn near positive that I didn't see that clip when I pulled out the spring, but I've been checking around my work area just in case it fell out when I was pulling it out.
I'll give 1 1/2 a try tomorrow when I'm ready to get dirty again. I'm right at the same altitude as you, so it's at least a starting point. I've been wanting to snag a TM-40 after the first review I read for one. Considering all the stupid stuff I spend money on, $450 really isn't all that much.
Woah. That's a crazy skinny rear tire. Does it still have enough traction with that narrower profile?
should be ass-loads of traction on the single track.
probably not so good on the paved canyon twisties, but that's what the 17" wheel is for. This is my single track only setup.
I don't know how old many of you are :huh but WAYYY back in the day, I recall my old YZ 125 A to date myself. You know BEFORE the days of one shock suspension . It had aircraft DZUS (sp?) quick connects to hold the side panels on. To refresh old dusty memories, it was like a bolt with a single slot with a quarter turn and and a notch. On the other side there was a heavy gauge wire that would hold it together . Its along the lines of an interrupted screw.
For the gas tank you can use more of these OR there is the alternative of having a stud welded in with a hole drilled in the top of it so you can pass a cotter pin /' a linchpin with an integral sprung retainer through it(connect these to the frame with a small wire so you dont lose them). Add a washer then pin the tank down the tank into location . That along with the seat being held down holding the tank in position should seem secure.I may not be smarter then the average bear but I am almost as old as dirt. Now who's gonna send me a royalty check.
Westley's Bleache White (tire/whitewall cleaner from Walmart) worked very well on a white tank I had. I soaked paper towels in the Westley's and left them draped on the tank overnight. Soak them again the next morning if you need to.
When you break into the carb, be sure to check the condition of the two o-rings on the float assembly. They'll deteriorate with age and allow gas to leak thru. This might not be such an issue with a stock vacuum-operated tank but it'll get you in trouble in a hurry with a gravity-fed system like an IMS. Congrats on the bike!
Want to run Sta-Bil to keep things runnin good but I see they have this Marine Sta-Bil for 2 and 4 cycle motors....has any one had good luck with this newer stuff?:huh
Typically, as the contact patch decreases the contact pressure increases. As you lose floatation you often increase bite, or traction due to the smaller contact patch. I have more experience in offroad truck tires, but if you want to increase traction, you often need a narrower tire. There are trade offs and conditions can dictate what works in a given situation, but riding desert sand might favor a wider tire, where you need more floatation, and forest single track might favor a narrower tire, where the narrower tire has more traction.
There are a myriad of opinions about additives, since you asked, this is mine. Reports a few years back were that the higher percentage of alcohol in fuel (and the water it attracted and held) was causing good old red Stabil to be less effective. I don't know what it's 'failings' were but I changed over to the green (Marine Formula) about 5 years ago and haven't had any problems. That said, it is entirely possible that had I not used anything the results 'could' have been the same. I put it in my boat whenever it will not be used for a while, I usually add it to my bikes when the weather gets cool (due right about now). I try not to mix additives since I have no idea if they will 'play nice together', I generally keep a can of SeaFoam near my gas can and add some of that every time I fill the can so my small engines never see 'untreated gas'. Probably either, both or none of them wouldn't change much but this works well for me and I am happy (maybe just because I 'think' that I am doing something for my engines). Despite all of that, I am leaning toward replacing both with Startron, based on reports from others who have done well. YMMV!
Sound advice, except a distinction should be made between the two o-rings. The smaller one of the two is the cold start enrichment feed pipe o-ring, and the larger one is the float seat o-ring. Of course they're both important, but it's the latter of the two that pertains to the concern you raise. Also, it's just as much of an issue with a vacuum operated petcock. Sure, the vacuum operated petcock theoretically shuts the fuel off when the engine is not running. However, whether it's being opened via vacuum or manually, the petcock has to be open when the engine is running, and the bowl only overflowing when the engine is running is really no better than overflowing all the time.
With some practice and a few tricks you should be able to remove panels, tank and seat in less than 3 minutes, easy.
I have an IMS tank ... so only two bolts for that. I use my electric drill with socket to whip out the two bolts, rubber bumpers are glued in place, so they don't fall, get lost or waste time.
Removing stock tank may take more time ... dunno, been years since I had a DR with stock tank on.
I only ever have ONE bolt holding my Corbin seat. No need for two. Side panels out in less than a minute.
Pulling fuel hose just takes a second ... have a plug ready to avoid drips.
I've also re-routed my crankcase vent hose to allow easier access to Carb.
More direct flow, no smog systems in line, less crap in the way.
So far, so good!
One correction, I would NOT screw the fuel mixture screw in "Snug". It has a very sharp point on the tip which can be damaged from over tightening. Just screw in till it bottoms ... never force it, it will last a LOT longer this way and be more effective when fine tuning.
1.5 turns out works for me too at most altitudes. (I'm at sea level but ride frequently at altitude). When I'm up high I LEAN out the mix and go in a half turn or so on the Fuel mixture screw. Works a treat. At 12,000 PLUS ft. I got the DR idle to smooth out and starting recovered to normal ... and leaner settings save fuel!
Excellent as usual Derek!
But I do this just a bit different ...
For me, the extended fuel screw is invaluable if you ride at mixed altitudes. I ride the Sierra a lot and have ridden the high passes in CO a couple times, Mexican Sierra Tarahumaru and more.
The convenience of the extended screw has saved me every time. If your bike is jetted Super Lean, then perhaps the Fuel Screw may not need much fiddling. But at 12,000 ft. my DR was rough idling, running at too low RPM and was hard to start.
A quick tweak to the fuel screw fixed all that. I went in from around 1.5 turns out, IN (lean) to about 1 turn or less. Smoothed right out, idle came up, but I raised it manually another few RPM's faster to where it felt right.
All this done on the trail. Only a minute or so to correct it. Without the extended screw getting to that inset stock screw can be tricky.
At Sea Level I run my mixture quite lean ... and actually go IN past fast idle peak, until bike begins to idle just a bit rough. That's where I leave it.
In super hot weather, riding in traffic, I richen it a bit. (turn OUT) In my experience running it a bit on the lean side helps my Fuel economy as well.
That makes a lot of sense! In the future I'll say that it shouldn't require much fiddling unless you will be riding in conditions where there are large changes in altitude.
I do have one more concern, and that is that the material an extended fuel screw is made of seems to be important. On other carbs I've seen galling and seizures when the extended fuel screw is made out of aluminum (that is a similar material as the body). I would therefore specifically look for one made out of stainless steel or brass, and I would put a dab of grease on the threads before installing.