Gas mileage question

[dolt]

I have the mikuni on my 2 big twins as the suffered a lot from carb icing with the CV however 883 sportster ran well on the CV with no hint of carb icing. Carb icing has more to do with the amount of moisture in the air and can occur between 3 and 15 degreese centigrade below 3 the airborn moisture is already frozen. Big bikes run much better with a mikuni in my environment. Brian

No disrespect intended but so far, the discussion has been focused on performance as it relates to the CV carb, i.e., poor mileage and partial throttle response with no mention of carb icing which may be an issue in your environment but has nothing to do with the OPs issue. However, I will file the carb icing information away for future reference should I relocate to an environment similar to yours but I doubt that I will relocated from south Texas.

JMHO but I don't believe the OP has systematically approached the problem by investigating other reasons for the poor mileage and partial throttle hesitation; AFAIK at this point, the A/F idle adjustment has never been adjusted from the factory settings which is a necessary part of a Stage I upgrade. Carb tuning requires time and patience, only one change can be made at a time between test rides and the motor must be up to operating temperature before the effect of the most recent "tweak" can be evaluated. Tuning any carb by the seat of the pants is tough; much easier if the "tuner" has an A/F meter to check readings at idle, partial throttle positions and WOT before making the next "tweak".

 

[SavageShy]

Hey fellas. Yes, i understand that the cv can be a good carb, and yes i know how to tune carbs. I messed with the CV for a week or so and got the bike to run pretty good, but you are correct Dolt, I didnt really dig too deep with troubleshooting the carb. There were other issues at play i i found out later, one of my slip ons was some how missing a baffle, and i dont trust anything rubber on the bike after 20 years as far as intake leaks go. So im sure thats most of the issues. But the point is, i would rather just put in new vaccum lines, intake seals, and a brand new carb to be sure. I plan to have the bike a while and rack up miles on it, besides i bought a sportster to customize so I dont mind spending the money. Besides, ive never had a carb on anything that was less than 20-45 years old, so i figured id treat myself to a new one and just skip the troubleshooting phase completely.

But its all a moot point anyway, last snow I decided to swap cams and wound up buckling down for a whole top end rebuild instead. Once parts come in I will have an engine with enough power to justify the new carb anyway.

 

[dolt]

so i figured id treat myself to a new one and just skip the troubleshooting phase completely.

But its all a moot point anyway, last snow I decided to swap cams and wound up buckling down for a whole top end rebuild instead. Once parts come in I will have an engine with enough power to justify the new carb anyway.

If you think you won't have to tune the new carb with the cam upgrade and top end rebuild, you are most likely wrong. If you think the CV was a tuning challenge, the Mik will be a handful for you.

 

[SavageShy]

Words do have meaning. If you read my post carefully, you will see that i made the distinction in no unclear terms between tuning and troubleshooting. I never once mentioned or even hinted or gave any indication whatsoever that i think i wont have to tune a mikuni, or that i can slap it on and it will magically solve everything. I also never said anything about the CVs "difficulty" to tune. If I am rebuilding the engine, replacing exhaust, ignition, tuneup parts, intake, and anything else that attaches to the engine then why would it not also make sense to have a shight and briny new mikuni? They have greater tuning flexibility, in fact the CV doesnt even come close in my opinion. For example, the mikuni has adjustable needle jets and accelerator pump, both of which are sorely missed on the CV. Have you ever looked at the cost of a new needle for the CV? Secondly I have tons of experience tuning round slide mikunis, why would a flat slide be any different?
But again, its a moot point. The carb is already on order and im knees deep in the engine rebuild, so i guess if i cant tune my carb properly i will just have a poor running and potentially damaged bike. Which luckily affects nobody but me.

My laziness with the CV is directly related to the fact i think its a stupid carb design and very quickly decided Id rather have a Mikuni.

Im gonna cut out now because i dont think this conversation is headed a positive direction, but I will post back when everything is tuned and done, i dont like leaving threads unfinished, pet peeve of mine when im looking for info and OP doesnt follow through.
G'day yall

 

[dolt]

[QUOTE="SavageShy]Im gonna cut out now because i dont think this conversation is headed a positive direction, but I will post back when everything is tuned and done, i dont like leaving threads unfinished, pet peeve of mine when im looking for info and OP doesnt follow through. G'day yall[/QUOTE]

Awwwwww, come on, sorry to see you leave so soon and we were just starting to have some fun.

I have not suggested that the Mik was a poor choice; lots of guys run them. What is tuning if not trouble shooting? Semantics.

To counter your assertion that the CV is a "stupid" carb design, I have attached a HP comparison between a CV40mm and a Mik HSR42; same motor, tuned on the same dyno on the same day AFAIK. Not an apples to apples comparo since the Mik has a 42mm throttle bore but yet, the CV runs right with the larger Mik. Don't know about you but for the ease of tuning and the marginal difference in performance, I would never spend $275 for the Mik; I would spend that money on something that would actually improve performance, like head work but that's just me.

Last I looked at the SE44mm on my all bore 107" motor (124TQ/110HP), it had an accelerator pump. True that one of the early OEM CV needles is getting hard to find but a complete "deluxe" CV rebuild kit including a hand full of jets, needle and all the other bits to rebuild a CV carb can be had for about $65. Individual needles go for about $15 and they are easily shimmed for adjustment. There are aftermarket adjustable needles but I have proven, on a dyno, that the CV carb performs best with OEM parts.

BTW, those flat slide Miks also rattle; I know guys that have returned to the CV because of the annoying Mik slide rattle.

I wish you well with your project; please come back and post a dyno sheet or let us know how it goes.

 

[Tileman]

When driving half sane....2002 carbed Sporty stage 1, 51-53 and 2006 Dyna efi stage 1, 44-46 mpg

 

[SavageShy]

Hey, just to follow up on this forum, everything is back together, I ended up going with a 1275 kit, stage 1 headwork, n4 cams, cycle shack slip-ons, and a daytona twintec. Corrected compression ratio bumped up just about 1 whole point (IIRC it ended up just over 9:1 corrected). In the tuning department, I went with a 48 pilot, stock needle, and a 185 main. In this case I truly got lucky with jetting on the first try, it seems to be nearly spot on aside from being ever so slightly lean at the bottom of the needle, around 1/8th throttle. For my efforts I was rewarded with much better throttle response and better power everywhere. down below 3500 it feels like stock but a bit stronger, then pulls like a freight train from 3500 clear til it signs off at 7k. Gas mileage during breakin was a whopping 48 mpg every tank!!! Since break in is finished, I consistently get 35 mpg while beating on it like a redheaded step child. In addition, carb farts are almost non-existent, Ive only noticed it once or twice, and nowhere near as severe as before. (Before rebuild carb farts were nearly constant). I initially thought it would be too much power, but i couldnt be more satisfied with how it runs. Im still going the mikuni route at some point, the CV works much better with this setup, but it still leaves some to be desired. I ride 2 strokes on the weekends, so the difference in throttle response is almost alarming when I get back on the sporty and have to wait for the vacuum slide to mosey its way up everytime i crack the throttle. If I ever actually find the funds to do it, Ill report back again with my findings and whether its worth the $250

And to Dolt, maybe i had a few too many last time I posted, but it does look like I overreacted to your comments a bit. Sorry I was being a (EDIT) about it.

On a side note, I love how many perfectly good used parts are available for these things for cheap. I saved hundreds buying cams, ignition, pipes, bars, shocks, etc used. Currently have a bead on a mikuni I should be able to pick up for $150 or so.

 

[dolt]

CV throttle response can be improved by drilling the vacuum hole to 1/8" and installing the lighter spring. The previous chart I posted should inform as to whether the swap to the Mik is a waste or money. Not my call but the $$ spent on a Mik would be better spent on a couple of dyno polls to fine tune, or an AFR meter. Without either, timing and AFR are not optimized and performance is suffering. I would question the consistent 35mpg though as I get 38mpg out an all bore 107" motor, SECV44 carbed, DTT ignition, .600" lift cams and big flowing heads in a heavy FLHT but I tuned the carb and dialed in the DTT on a dyno and I don't baby the motor.

BTW, my posts are always grounded in fact and personal experience so I pay little attention to disagreeing posts. You are happy with the outcome and that is what counts.

 

[Jeff Klarich]

BTW, my posts are always grounded in fact and personal experience so I pay little attention to disagreeing posts.

Pretty bold statement, you didn't leave yourself any wiggle room just in case your not 100% correct.

 

[dolt]

Pretty bold statement, you didn't leave yourself any wiggle room just in case your not 100% correct.

It is a bold statement but, when sticking to facts and personal experience, I don't need the wiggle room; it is what it is. However, when expressing an opinion, I will so state and while my opinion might be different from others, it is just an opinion and you know what "they" say about opinions and the reader can take it or leave it.