| Author | Message | ||
     Notsofastblast |
Hey guys, i could use some of your infinite wisdom on how to properly tune my carb. Im new to bikes and carbs are definitely not my specialty. Ive read a bunch of other threads on tuning and tried tuning it a bunch of ways but it really mind boggling how no matter what i do it always struggles somewhere. Obviously everyones bike is different so it wont be the same for everyone, id really appreciate some guidance on what to try. Heres what i have done to the bike so you can get a better idea what might work for my situation - Filterwears pre-filter - 4” velocity stack - 6sigma Carb jets (48-175) *do not recommend kit* - Needle shimmed to .045 - Dans Allen head bolt kit - Air fuel EZ-mix screw - Dans Superboot - Carb brace (carb springs) - NGK Iridium spark plug - Vance and hines exhaust (packing blew out) Last night i went on a group ride with some friends and i know its got to be running lean in the mid range because my carb blew itself off 3 times. Under heavy load it bogs down like its flooding the cylinder, and at high speeds i can barely hit 80 mph and then it will start bucking like its flooding and then all combusting at once. I want to order the yost kit to dial it in properly but have to wait until i get paid to order it this week. Obviously i know it needs to be re-jetted but i dont know what ones id be looking at changing to cure the problems. I have 42, 48, 162, 175, 180, 190 jets right now. Do you think adjusting timing could help at all? If so, could you share a link to that thread please? Thank you all for any suggestions and advice! Heres a pic of my velocity stack  | ||
| Gearheaderiko |
More than likely it’s your V stack and filter. Run without the filter and see what happens. Also, it’s VERY easy to block the intake with your knee, that will also cause issues. | ||
| Gearheaderiko |
PS it’s not going to be lean with that jetting, unless you mixed up stock and an aftermarket/needle kit. | ||
| Missionbolts |
Check the ignition timing just to make sure it's not contributing to the problems The velocity stack could potentially increase surging sort of feedback issues, by increasing the ramming effect of airflow going into the venturi underneath the throttle slide, when it needs to close due to the engines airflow slowing down in between air intake periods (when intake valve is open The only time the airflow will act like a constant flow situation is when the engine is well up into it's higher rpm range I would run a normal intake until the carb is dialed-in to the point that the engine runs smoothly at all speeds and all throttle positions. Only then would I add the velocity stack & fine-tune the jet selection yet again - if the stack actually does what it looks like it might be attempting, it'll throw the tuning off A CV carb needs airflow that is smooth & consistent at all points across the carb opening, specially around the small openings where air is siphoned off to feed the jets and the slides diaphragm I would suspect the velocity stack might increase the air pressure at those holes when the slide dips closed momentarily in between intake valve cycles, thus throwing off the finely tuned balance designed into the carb at the factory (ie - it'll tend to pop the slide open sooner than it ought to & lean out the mixture by not having a matching airflow on the downstream side of the carb But all that's just my intuition and I could be wrong about all that I don't know the parts you threw at it, so I couldn't say what all, but I would have to think judging by your pic that there's either no air filter, or your running something inside the velocity stack that will choke off the airflow The original airfilter might be a bit goofy because it runs the dirt to it's inside where you can't see how bad it's getting, but it does have just enough surface area to get the job done without creating a major flow restriction. You might try running without the pre-filter just to see what effect it might be having at higher rpm's. If the pre-filter is an insert that fits inside that velocity stack, then that'll answer why you might run too rich at slow speeds and lean out at cruise A basic carb tuning guide is this simple diagram, which I always use to refer back to what any expert or manual might be telling you:  Clip position, Needle Straight Diameter & Taper are much more important anything less than full throttle, as the needle is mostly blocking off the mixture flow through the main jet Throttle Slide cutaway isn't something you want to play around with unless you have plenty of spare slides to begin over with That Air Bleed adjustment sure can have some impact right at the beginning. The HD carb that comes on the Blast doesn't have a dedicated slow air bleed adjusting screw, but the cold start auto enrichener may take the place of that by adjusting how far in or out it's screwed into the side of the carb. It controls the amount of bleed air when fully warmed up. If I understand the carb design well enough, that's both the slide position and slow speed jet circuit combined into a single adjustment. The enrichener was designed to open the slide more than normal, for a faster idle when it's first beginning to warm up. On a well running Blast, you can see this happening the first time you start the bike in the morning. My usual routine is to leave the throttle untouched, just simple crank the engine until it fires and leave it alone. It'll run fast at first, during which time I'll begin to put my helmet & gloves on. I'll know the engine is ready to go when the idle drops down, which usually takes less than a minute Any performace muffler which uses a packing & that's blown out will lose power on the the bottom end up into the mid-range. That'll hurt the most on street riding and whenever you need to slow down then speed up quickly, like on tracks with tight corners mixed up with long straights Repacking that muffler will improve the throttle response in the low to middle range, and sound better Take a look for something like this: https://thermalzero.com/product/power-pack-1-inch- ceramic-muffler-packing-kit-2-sqft/ | ||
| Gearheaderiko |
All that aside, it’s probably just the filter you’re using on the stack. If you don’t use the right one, it will cause issues. I’ll spare you the long explanation. Just try running without it first before you go willynilly into everything else. | ||
| Notsofastblast |
Thank you guys for all the suggestions!! Its just weird because with the needle shimmed further it ran much better in low to mid, but still surges at high speeds. Ill try taking off the prefilter and see how it does. I just didnt want to run it open for dirt and dust to fly into my engine and cause problems. I have a stock needle now, but i got the jets from jets-r-us. I plan on getting the yost this week to swap everything over in hopes itll help. Gearhead - im 6’5” and the stack comes out behind my leg. Im definitely not blocking the filter😂 but i definitely understand why that would be a concern. Thats Also why ill only ride with tight pants. Ill update tomorrow after i get a chance to take it out and test it. | ||
| Gearheaderiko |
Don’t make anymore changes until you get this sorted out! | ||
| Notsofastblast |
UPDATE I took off the pre filter today and Reset my air fuel mixture screw. its definitely A LOT better, but now it surges at low speeds. Ive seen ez and jet talk about the yost spring making a big difference on velocity stacks because its stiffer. My prefilter is almost a fine mesh that sits tightly on the top of my stack. Ill add a pic of it so you can see what im talking about.    | ||
| Gearheaderiko |
If you’re not using the right pre-filter you will have problems. Just think about how much air flow you’ve actually cut down. You've gone from a giant air box to a 3-4”? (appx). hole that you made even smaller by putting mesh over. We went through this years ago. If you’re following EZ and Jetlee, then they should know the right filter-I don’t remember what it is-it’s been a long time-but I did the research. Stacks aren’t really meant to run with a filter like that. If you’ve actually tuned to the filter you’re using, then you’ll have to re-tune. If you’ve just replaced jets and shimmed, then you’ll need to find the right pre-filter and follow EZs recommendations. (Message edited by Gearheaderiko on September 01, 2020) | ||
| Missionbolts |
That pre-filter was doing a couple different things. Restricting airflow and damping the response of the velocity stack so it was only working well at higher rpm's Now that you mention this Yost spring as helping a velocity stack by being stiffer, then I'm more convinced the stack is creating a higher pressure spike than normal You really ought to try riding the bike without the velocity stack And repack your muffler | ||
| Notsofastblast |
I went on a couple test rides without the Pre filter and it seemed to help so obviously ill have to find the one EZ recommends and get that. I still feel like the jets are off (lean at low speed and rich at high speed) and need to be changed again, so i went ahead and ordered the yost rev1 master kit. With what i have done to the bike (stack and exhaust) should i use the red or blue needle? Clip location? Shims? Im really not to knowledgeable on carbs and thats why im asking. Figured its better to ask and maybe get an answer by the time the kit comes and save me a few times of ripping the carb apart lol. Thanks for the tips guys! | ||
| Gearheaderiko |
Once you get away from using stock jets and needles, you’re on your own; unless you find someone who is using your exact same engine/carb set up or who is knowledgeable on how to set those particular jets, etc. up. At this point it’s best to read up on carb tuning, so you learn how to read plugs, exhaust note, acceleration tendencies, etc. Installing an oxygen sensor can really help. Or find someone with a dyno-that’s the best way-but you’d better have all the needles, jets and springs available, because chances are they won’t. | ||
| Missionbolts |
My Blast has the same jets it left the factory with, same airbox and a new OEM filter. All I did was delete the hose that blows engine oil down the carb, plugged off that hole in the airbox and royally chopped up my stock muffler so it's as loud as a Supertrapp So now my Blast zips through gears faster than I can shift, and I'm getting up to 96, which takes less than half a mile of road Didn't do a thing with the ignition timing. Just tightened up the valve clearances My tires help, as they have a lot less rolling resistance than the original sport bike tires, and I run them at their higher pressure range. Putting skinny tires front & rear really helped both acceleration & handling. It's only 30 HP, I don't need 150 HP tires on my bike When I start the bike, I don't touch the throttle at all. I just crank the engine a bit, it fires up instantly & idles perfectly fine. By the time I get my helmet & gloves on, the RPM's have dropped down to normal and it just gets up & goes | ||
| Ezblast |
an Outer Wears Stack filter outerwears.com - the new part number is - " 12-1267-01 Black"Call to order. EZ | ||
| Gearheaderiko |
There you have it!  | ||
| Notsofastblast |
Thanks guys. Ill order that tomorrow, I just installed the yost kit, with no drilling. Im running 48-175 jets, the blue needle 3rd clip from the top(flat) and im curious to know if your supposed to used the spacers included... they’re practically the same size as if you just moved the clip down one more so i just used a .01 washer instead. Please elaborate if im missing something here. | ||
| Gearheaderiko |
Are the needles compatible with the jets? | ||
| Notsofastblast |
Yes. The kit is special for cv40 carbs. People have been using them for years. Doing more reading last night i saw i should use one of the shims from the kit. So ill try swapping that today | ||
| Notsofastblast |
UPDATE: i decided im going to get a wideband to tune and dial in everything properly. i orderd the aem wideband kit and the glowshift clamp on 1-3/4" bung so i dont have to try to weld a bung on my vance and hines exhaust. (ive seen people say it was really difficult because the metal is so thin) when i install the o2 sensor do i need to try to have it close to the head or will anywhere be fine? | ||
| Notsofastblast |
i have a serious problem with leaving anything stock lol  | ||
| Notsofastblast |
Ok. Second update today 😂 So i moved the clip to the 4th from top and it didnt go to well. Was definitely running way to rich. I came back home and moved it to the 2nd from top position and used the included shim, DEFINITELY getting a lot better now. When im just cruising through the town it seems to be sluggish at low throttle, but really improved mid range. Im thinking if i drop the jet to a 46 instead of the 48 i have in it now it would help. Right? Wideband will be here tomorrow. But unfortunately the bung wont be for at least a week or so. Ill keep updating on here. | ||
| Ezblast |
Yes - 48 too rich. EZ | ||
| Notsofastblast |
Thank you EZ!  i will order a 46 tomorrow! Do you think a 175 will be good? Or should that be changed? I have a ton of different sizes for that one. |
