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Lean idle mixture=Higher idle?
- Thread starter Vloukole
- Start date
I don't either. (have an ultrasonic cleaner) The older style caustic dip would work, but the real deal is to disassemble, pull the mixture screw at the top front ( count how many turns out from lightly seated so you can put it back to where you started from) don't forget the spring, washer and o ring if it has them down the hole. Also pull the jets. They are all no doubt crudded up. Be sure no rubber parts get carb cleaner of any kind on them. Then blow it out with compressed air. With suitable ventilation. If you let it sit for a month, you'll be doing it again unless you put ethanol specific fuel stabilizer in the fuel.
The pilot jet and passages clog from the ethanol. The little holes in the throttle bore at the top of the bore by the butterfly is where it gets to the engine. All have to flow. Avoid putting objects into the passages and jets to clean them. Soak and then use compressor to clean it out. After cleaning, reassemble. Download the manual from the top of the garage page.
The pilot jet and passages clog from the ethanol. The little holes in the throttle bore at the top of the bore by the butterfly is where it gets to the engine. All have to flow. Avoid putting objects into the passages and jets to clean them. Soak and then use compressor to clean it out. After cleaning, reassemble. Download the manual from the top of the garage page.
You didn't say what throttle opening. RPM is nice, but throttle opening is useful.
closed-1/8 open: pilot jet
1/8-1/4: slide cutaway if it has one. We don't.
1/4-3/4: needle and needle jet
3/4-fully open: main jet.
They all overlap, and with CV carbs, just because you have the throttle pegged doesn't mean the slide is all the way open. It opens as the engine vacuum and slide diaphragm dictate.
Bogging usually means lean. However, it could be lean because the fuel can't get into the carb fast enough, rather than small jets. It could also be vacuum leaks, which show up as lean. Look at the carb mounts and vacuum hose to the petcock, plus rubber block off on right side carb mount, all know culprits.
Last: the needle jets in the carbs have to be clean as well. They are emulsion tubes, meaning the little holes on the sides need to be cleaned out as well. As fuel and airflow demand go up, the fuel level around the outside of the needle jets lowers, and adds more air from the air jet through those holes to mix with the fuel coming up from the main jet. It all has to be clean to work correctly. A partially clogged gas cap vent could slow fuel flow enough to act like a lean condition.
Be careful not to correct symptoms instead of problems: bigger jets can correct for vacuum leaks, but are not an ideal solution.
closed-1/8 open: pilot jet
1/8-1/4: slide cutaway if it has one. We don't.
1/4-3/4: needle and needle jet
3/4-fully open: main jet.
They all overlap, and with CV carbs, just because you have the throttle pegged doesn't mean the slide is all the way open. It opens as the engine vacuum and slide diaphragm dictate.
Bogging usually means lean. However, it could be lean because the fuel can't get into the carb fast enough, rather than small jets. It could also be vacuum leaks, which show up as lean. Look at the carb mounts and vacuum hose to the petcock, plus rubber block off on right side carb mount, all know culprits.
Last: the needle jets in the carbs have to be clean as well. They are emulsion tubes, meaning the little holes on the sides need to be cleaned out as well. As fuel and airflow demand go up, the fuel level around the outside of the needle jets lowers, and adds more air from the air jet through those holes to mix with the fuel coming up from the main jet. It all has to be clean to work correctly. A partially clogged gas cap vent could slow fuel flow enough to act like a lean condition.
Be careful not to correct symptoms instead of problems: bigger jets can correct for vacuum leaks, but are not an ideal solution.
Best advice ever!And the hardest lesson to learn...
I learned it the hard way. Painful lessons.
Being a deaf old goat, I can't say I hear any air entering the gas tank over the intake, exhaust or mechanical noise of any engine.
Missing at WOT is often ignition related: crappy points, bad plug wires, sick plugs, etc.
Missing at WOT is often ignition related: crappy points, bad plug wires, sick plugs, etc.
That's somewhat normal when you shake any can with gas in it.
But back to WOT: full load misses are usually as I sated earlier: ignition related. Plugs, wires, coils, points, circuit connections, etc. Start with plugs: if they aren't light tan and dry, find out why before you do anything else. You could be oil fouling them, or any of a number of things.
Put some anti-sieze on the plug threads so you don't kill off the threads in the cyl head. 14mm plugs are somewhat easy on aluminum threads, but properly lubed threads are always a plus. I use moly assembly lube or anti-sieze compound, since I have a lot of both.
But back to WOT: full load misses are usually as I sated earlier: ignition related. Plugs, wires, coils, points, circuit connections, etc. Start with plugs: if they aren't light tan and dry, find out why before you do anything else. You could be oil fouling them, or any of a number of things.
Put some anti-sieze on the plug threads so you don't kill off the threads in the cyl head. 14mm plugs are somewhat easy on aluminum threads, but properly lubed threads are always a plus. I use moly assembly lube or anti-sieze compound, since I have a lot of both.
There's the miss. Too rich = black plugs. The sooty residue is shunting off some of the spark voltage, causing the miss. Fresh plugs will be ok until they get sooty too.
So, correct the fuel problem, and the miss should go away as the plugs clean up.
- be sure O ring on float seat is good.
- be sure float needle is good. Viton (rubber) tip should be smooth, not cracked, and have no visible bad spots. If suspect, replace as a set.
- check float level.
- be sure all pilot/idle mixture passages are truly clean.
- be sure the jets are clean and properly installed.
- be sure carb mounts are good, not cracked, etc. same for any other rubber parts such as vacuum lines, plug that blocks off right side brass fitting, etc.
- be sure diaphragms and carb tops are fitted properly. Slides that are controlled by diaphragms need to move smoothly in carb bores.
- after assembling all proven good carbs and things, be sure valve adj is in spec. Cold engine.
- if you have points, be sure they are clean and properly set. If electronic ignition, be sure plug wires are good. This applies to points as well.
- start engine and warm up. After warmed up, adjust mixture screws at top front of each carb. Both should be set the same. In 1/4 turn increments, turn in until engine runs worse, then out until better, back in to exactly the point it is just short of running poorly again. Sync carbs and repeat idle mix screw adj. set timing if it has points, then one more sync/mix check. Now it is fully tuned up and runs great.
So, correct the fuel problem, and the miss should go away as the plugs clean up.
- be sure O ring on float seat is good.
- be sure float needle is good. Viton (rubber) tip should be smooth, not cracked, and have no visible bad spots. If suspect, replace as a set.
- check float level.
- be sure all pilot/idle mixture passages are truly clean.
- be sure the jets are clean and properly installed.
- be sure carb mounts are good, not cracked, etc. same for any other rubber parts such as vacuum lines, plug that blocks off right side brass fitting, etc.
- be sure diaphragms and carb tops are fitted properly. Slides that are controlled by diaphragms need to move smoothly in carb bores.
- after assembling all proven good carbs and things, be sure valve adj is in spec. Cold engine.
- if you have points, be sure they are clean and properly set. If electronic ignition, be sure plug wires are good. This applies to points as well.
- start engine and warm up. After warmed up, adjust mixture screws at top front of each carb. Both should be set the same. In 1/4 turn increments, turn in until engine runs worse, then out until better, back in to exactly the point it is just short of running poorly again. Sync carbs and repeat idle mix screw adj. set timing if it has points, then one more sync/mix check. Now it is fully tuned up and runs great.
Guys
I have the same old problem again.
The bike wont idle. It starts off great then it start to fall en then dies.
I can either keep it idling at +-1700rpm (with the idle screw) or try to set it to 1200rpm and die after 5sec.
I have cleaned the carbs many times. How do you guys clean the idle circuit and that 3 little holes on top of the butterflies?
I have the same old problem again.
The bike wont idle. It starts off great then it start to fall en then dies.
I can either keep it idling at +-1700rpm (with the idle screw) or try to set it to 1200rpm and die after 5sec.
I have cleaned the carbs many times. How do you guys clean the idle circuit and that 3 little holes on top of the butterflies?
Sesty
H.E. Pennypacker
useful guide:
http://www.amckayltd.com/carbguide.pdf
http://www.amckayltd.com/carbguide.pdf
And a big thanx to Bentwrench with his insight to the 650 carb cleaning guide, the three hole mystery is solved!
In the forward end of the carburetor bore, you'll find a number of holes (see Appendix,
item 11). In front of the throttle plate (butterfly), you'll find either one or two large holes
and one small hole. One of the large holes draws mixture from the enricher, and the
other will either be blind or open into the synchronizer attachment port if the carb is so
equipped. Do not apply solvent without removing the choke plunger (see enricher
section). The small hole draws mixture from the fuel screw. Blow aerosol carb cleaner
into the hole until it flows freely from the fuel screw area. Then block the hole with a rag,
insert the tube from a can of carb cleaner in the fuel screw seat area, sealing with a rag,
and blow cleaner in until it flows freely from the hole in the carb body that sits above the
pilot jet (BS38) or the pilot jet casting (BS34). Follow with compressed air.
Behind the throttle plate are more small holes, 2 in BS38's, a cluster of 3 in BS34's (see
Appendix, item 11). In early BS38 carbs these are fed by the bypass pipe, a brass tube
between the slide and the throttle plate in the middle of the bore. Find its source in the
carburetor body and shoot with carb cleaner and air until clear.
In later BS38 carbs and all BS34's, the bypass nozzles are fed from the fuel screw
passage, and no tube is present. Seal the tube on a can of carb cleaner in the fuel
screw hole with a rag or drilled plug, cover the small nozzle in front of the throttle plate
with another rag and hold it in place with your thumb, hold the throttle plate open, and
spray until cleaner emerges from the nozzles. Follow up with compressed air.
Making a modification is not the best way to correct a problem and may lead to more problems. You would be better off finding the cause of the problem. If your bike is stock, and running rich, check the o-rings on the starter plungers. If they are leaking, this will cause a rich condition.
