Daddyflip offers good advice. Check float level. Higher the float level, the richer the mix, lower level is leaner. Also consider fine tuning with the needle: The higher the needle, the sooner the fuel (mid range circuit) comes in, and the lower the needle, it comes in later. Make sure the O-ring in your new adjusting screw is in good shape and didn't fall out when switching it out.
I checked the float last night on the 15 degree slope and it was pushed away from the carb (lower?). I called the HD parts guy to see if he could verify the carb year by part number so I could be certain on how to adjust it. He confirmed its a '92. Dude also tells me that when the float is pushed away from the carb on its 15 degree slant, it is creating a rich condition. I think what you're saying and what I understand about the carb, is that it actually is creating a lean condition. This would be lower (leaner) when upright, correct? I adjusted it up (towards the carb) to 0.430 in. (spec: 0.413-0.453 in). So confusing... anyway, it was out of spec and now it is in. Problem is that it should have been running lean from that not rich.
Originally Posted by Yankee Dog
Assuming you carb is clean, and your intake seals are making a good seal, It sounds like you had the idle circuit dialed in pretty close with the 44 (maybe split the difference and try a 45), and the black soot is probably caused by the mid range circuit. If it is the midrange, then besides the main jet, the needle thickness, needle taper, and needle height come into play. Any shims on the needle? If so, remove them and see if it helps.
I've got a 46 on my bench so I'll drop that in today and check the needle jet for shims. If not I'll lower it a notch if possible. If its not adjustable, I'll look at fatter needle.
Originally Posted by Yankee Dog
I am kind of playing with the same issue as you right now, but am a touch lean. So I plan on checking float level and adjusting to max height spec, then if need be, switching to a thinner needle to let more fuel in. My main is a 185, and my slow is a 46. I had a 48 slow but adjusting it did nothing, so I changed to the 46 and am at two turns out. I am using a NOK M needle with two washers under the needle. Bike runs great but it seems a little lean. No blisters or specks on the plugs, no engine ping, just very little color to the plugs. I might go to a N65c needle or the CVP velocity needle next. If I do, then I need to consider that I will probably have to start over with the tuning. Might even need to switch out the main jet because I will be getting more fuel into the mix with the thinner and shorter needle.
When I pulled the plug there wasn't much color and a little blistering (see pic). Does that look like its too lean to you?
I agree with DaddyFlip and don't think your plug looks bad either. Especially with the short amount of time on that plug. I usually look for blisters or melting of the porcelain, the ground strap looks like just deposits on it. I see some color to base ring of the plug and that is good. I don't see any specks on the porcelain either (another indicator of lean). Hard to get a good look at the plug but I think your pretty close. Take a look at the pics below and see how your plugs measure up. Question is, how does it run? Does it ping? If so when?
It's kind of hard to get a good tuning of the idle mix screw if your idle is set a level where the transfer ports are exposed by the throttle plate. The transfer ports are that group of 4 holes in the back part of the carb throat near the idle port at the throttle plate. They help the transition from just past idle till the needle starts coming in. If the transfer ports are exposed because the throttle plate is elevated due to idle speed adjustment, they will feed fuel into the engine in addition to the idle port feeding fuel during idle. The slow jet feeds fuel/air to the idle port AND the transfer ports.
I keep my idle speed at about 800 to 900 (evos need better than 700 for oil flow purposes) and at 800 rpms the transfer ports are exposed by the throttle plate (at least on my carb). Try adjusting the idle temporarily low and then adjust mix screw for best idle speed, then when that is dialed in, adjust idle back up to 800 or 900 rpm's. This method might help you adjust your idle mix screw a little more accurately.
And not to beat a dead horse, but you can read post after post about what size main jets people use, but often they don't tell what needle they use or if it is shimmed. If you have a 180 jet and you use a stock needle, it gives a certain amount of fuel. Now change to a thinner needle, and the same jet will let in more fuel. Shim it and the fuel curve ramps up sooner. Ad another shim and it comes in even sooner.
Determine which circuit you want to dial in first (usually slow) and do a plug chop for that circuit only. Then once that is good, move up the circuits taking into consideration that fuel circuit chart and reading your plugs. Mark you throttle and housing with tape to indicate 1/4, 1/2 and 3/4 throttle so you know where you are at in each circuit and do what Daddyflip suggests for tuning.
Finally, when adjusting the float, make sure your not compressing the little plunger on the needle when measuring. The needle should be seated, and the tiny plunger/spring loaded tip should NOT compressed when measuring. BTW, there is a line molded on the side of the float that should run perfectly parallel with the carb housing gasket/seal surface when it is adjusted properly. That is why MOCO tells you to use the 15 to 20 degree angle, to prevent compressing the plunger, but I hold the carb a little bit differently when adjusting and measuring so I can get the float to pivot, not compress the tiney plunger, but am sure the needle is seated. Sorry hard to describe.
Last edited by Yankee Dog; 08-21-2018 at 05:47 PM.
I checked the float last night on the 15 degree slope and it was pushed away from the carb (lower?). I called the HD parts guy to see if he could verify the carb year by part number so I could be certain on how to adjust it. He confirmed its a '92. Dude also tells me that when the float is pushed away from the carb on its 15 degree slant, it is creating a rich condition. I think what you're saying and what I understand about the carb, is that it actually is creating a lean condition. This would be lower (leaner) when upright, correct? I adjusted it up (towards the carb) to 0.430 in. (spec: 0.413-0.453 in). So confusing... anyway, it was out of spec and now it is in. Problem is that it should have been running lean from that not rich.
I think that is backwards. If the float is "out" at 15 degrees, then it will be "deeper" in the bowl and will open the valve sooner (at a lower level of fuel) and never close because vacuum wants the bowl to be filled to a certain level. If it is "in", then the float will be above the bowl will never fill enough to open the valve. I could be wrong on this, but I'm saying out is rich and in is lean. Also, make sure to check the condition of the valve itself; it might not be seating properly.
Ah, that makes sense. Thanks for helping clarify that.
I found a couple shims on my needle so pulled them. The #46 was too big, affording no adjustment from the mixture screw. I picked up a #45 last night so I’ll drop that in today. The float adjustment and shim removal should improve things. Getting closer!
Thank you both for your posts. Lots a great info!!
I may have gotten it backwards myself; I been studying it or thinking about it all day. As the float rises it pushes the fuel valve up to close; as it falls, the fuel valve opens. The fuel valve is on the float side of the pivot pin. The logic is if you need to reduce the measurement to spec (float out), then you bend the tab away from the carb which increases the fuel level (or makes the fuel valve close later). So I think out=lean is right, but if your fuel valve is making a bad seat, then fuel can still get by even with the float set right or out. Good luck!
Picture the carb as it is installed on your bike. We will use that as a reference. If the float tang is adjusted (bent down) so the tang is lower (tang is the metal tab you bend to adjust the level and is what supports the float needle with the little clip on it), the carb bowl will fill to a higher level before the needle is pushed up to it's seat shutting off the fuel flow from the tank. So a higher level of fuel sitting in the bowl will make your carb run richer. Of course it's the opposite if you bend the tang up, it will push the float needle up into it's seat sooner and shut the flow off sooner making the level in the bowl lower, thus making the carb run leaner. It's just like a toilet tank and the the float in that toilet tank. Bend the rod so the float sits lower and it shuts the water off at a lower level when refilling.
Kind of hard to put that concept in your mind when the carb is sitting sideways on a 15 to 20 degree wedge making adjustments to that tang, as well as paying attention to not compressing the little spring loaded plunger (shock absorber) while paying attention to when the float needle is also properly seated in it's seat and measuring it all at the same time. That is why I suggest you adjust so that the raised line on the plastic float runs parallel with the carb gasket surface. That will put you right on the money. You can see that line in the diagram/pic figure 4-20 letters A, B, C.
A) is leaner if your float looks like that when the float needle is seated in it's seat. (lower fuel level in the carb)
C) is Richer (a higher fuel level in the carb)
B) is just right as the embossed line in the float is level (parallel) with the gasket surface
Im on the page. Thanks to both you guys again for helping.
I dropped the #45 in and couldn’t get it to stumble with the mixture screw so I dropped the #44 back in, rechecked the float, and pulled the two spacers from the needle. I can get the engine to stumble at 1-1/2 turns so leaving it at 2. Plugs look good and seeing much less smoke. I did get some small backfires from the exhaust at about 1/8 throttle in second as I putted home. Maybe turn it to 1-3/4?
Wont hurt a thing to adjust the idle mix screw in or out to see what works best. Anywhere from 1 to 3 turns out is an acceptable range. Anything less or more and it's time to change jets.
So what is the final data? What is your main jet size? What needle are you using and any shims? Curious what your mileage will work out to be, etc. Please keep us informed. Glad your getting it dialed in. YD
I kept the needle which appears to be stock non-adjustable. I didn’t notice if there was anything stamped into it. I pulled off the two shims and put it back in. I left the main at #180. I went from #44 to #42, then #46, then #45, landing back to the #44. After all that, the only real change was an adjustment to the float and pulling needle shims. performance is good, so I’ll keep an eye on the smoke. If it sill seems too rich, I think a new fatter needle and new float needle just to make sure that’s sealing.
Or a 175 main and keep the needle you have. Usually a factory needle will have some letters and a few numbers stamped on them at the nail head like N72S or N86E, etc.
My bike liked the 175 main and 46 slow with CVP velocity needle when it was in stock form, now...not sure yet. Still working on it. Currently at 185 main with a 46 slow, and a CVP velocity needle. Two turns out on the idle mix screw. Just need to give it a test run to see where I am at. YD
08-21-2018 | 09:42 AM
