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Regarding the CVP emulsion tube and jet fitment, per CV Performance (quoted and copied from CVP website):
"Special Note: Unlike other aftermarket tubes, the CVP Velocity Tube will accept both CVP brand jets, OEM, Keihin and Harley-DavidsonŽ original main jets. Will not accept DynoJetŽ main jets or various import jets using non-standard thread sizes".
Regarding the CVP emulsion tube and jet fitment, per CV Performance (quoted and copied from CVP website):
"Special Note: Unlike other aftermarket tubes, the CVP Velocity Tube will accept both CVP brand jets, OEM, Keihin and Harley-DavidsonŽ original main jets. Will not accept DynoJetŽ main jets or various import jets using non-standard thread sizes".
The CVP emulsion tube is either OEM or an exact copy.
The DynoJet kits sold as "Screamin Eagle" kits would accept stock jets. The kit from DynoJet would not accept stock jets. I don't know about the Yost tube.
All I know is that whenever I get a CV40 and there is aftermarket parts in it, SE or otherwise, I replace everything with OEM and just work like their supposed to. The CVP tube, you cannot tell the difference... or I can't.
OK, I will be the outlier. I ran an all bore 107 with a CV44, tossed the OEM parts for a Yost kit and put the bike on the dyno. Mike Lozano, one of the best tuners in the country and we could not get everything right and by that I mean smooth from idle to WOT, no hesitation, no decel pop, etc. At cruise, every 25 miles or so, the carb would "burp", no loss of power but annoying and not suppose to happen and mileage sucked. Tossed the Yost kit and went back together with OEM parts. Back to the dyno; took about three sessions to get the right needle and needle position, slow and main jet right. Big difference; smooth from idle to WOT, no carb farts, and picked up some HP/TQ; final figures were, IIRC, 124TQ/110HP. I built that motor when I was afraid of compression, I think CCP was about 185psi. If I was building that motor today, I would set CCP somewhere between 195-200psi and watch the number jump. I did drill the vacuum port and install the lighter spring which did improve throttle response; not as quick as a cable operated Mik but better than stock.
I like to post this comparison between a CV40 and Mik 42 whenever this question comes up. I have nothing against Mikuni carbs but don't see spending $250, or whatever they are going for these days to replace a CV; can't justify it but that's JMHO.
Two quite unrelated comments:
The lighter springs that are used to improve throttle response on the CV carbs come with a negative side effect. The plastic throttle will be able to vibrate more up and down during running, and this will result in the throttle getting worn and not sealing properly. So if you experience rough running or other issues it can be a good idea to check the state of the throttle and replace it if necessary.
Secondly, when I upgraded my TC88 to 95" I also replaced the CV40 with a Mikuni HSR42. I think it will allow for a few more hp of top end power that might or might not be noticeable on my particular engine. But the thing that strikes me is how small the difference is in the running characteristics, I read a lot about the CV being smoother but the HSR having much better throttle response.
I might be stupid but to me there is basically no difference at all, the bike ran perfectly smooth with the CV and it runs equally smooth with the Mikuni. Of course more power now but that is mainly due to bigger bore and different heads and cams.
I have a suspicion I could just have stayed with the CV and been equally happy. And avoided the annoying rattle of the Mikuni slide
I ordered all of the upgrade and maintenance parts from CV Performance. I'd rather have the parts on hand and do it once.
Reviewing the service documents I see what happened, I think.
The bike gets jetted with a 48 and a few other maintenance parts. The guy went back to HD and complained of it burning rich.
HD replaces the 48 with a 45. The guy goes back and complains of carb coughs and tech is getting pissed.
I'm still waiting for parts but the mixture screw is all the way out at 4 turns. Definitely a 46 maybe a 48, I'll see what's there when I disassemble it.
Just going off the service docs - it has an intake leak either at the carb/mainfold seal or the o-rings on the heads.
A 45 is plenty for most EVOs. If you need more than 2 rounds on the idle screw, something is wrong. Probably an intake leak.
NOTE: very few intake leaks ever get found by spraying fluid all around the manifold. Don't waste your time, replace all the manifold seals and be done with it.
Two quite unrelated comments:
The lighter springs that are used to improve throttle response on the CV carbs come with a negative side effect. The plastic throttle will be able to vibrate more up and down during running, and this will result in the throttle getting worn and not sealing properly. So if you experience rough running or other issues it can be a good idea to check the state of the throttle and replace it if necessary.
Not in my experience with the CV44. Maybe over a longer period of time, more miles , etc. but in the 25K-30K miles before selling the bike, not an issue.
Originally Posted by SwedishMeatball
Secondly, when I upgraded my TC88 to 95" I also replaced the CV40 with a Mikuni HSR42. I think it will allow for a few more hp of top end power that might or might not be noticeable on my particular engine. But the thing that strikes me is how small the difference is in the running characteristics, I read a lot about the CV being smoother but the HSR having much better throttle response.
I might be stupid but to me there is basically no difference at all, the bike ran perfectly smooth with the CV and it runs equally smooth with the Mikuni. Of course more power now but that is mainly due to bigger bore and different heads and cams.
I have a suspicion I could just have stayed with the CV and been equally happy. And avoided the annoying rattle of the Mikuni slide
I am not sure how you can attribute more power to the Mik after the performance mods; maybe you weren't suggesting that. Whenever this issue comes up, I like to post the attached comparison that speaks for itself. The difference between the two would never register on the butt dyno and certainly not enough to justify the cost of the Mik.
Had the dyno jet kit, and the Yost power tube with a cam for over 10 years. I also tried the turbulator. Ran drag pipes with baffles for over 10 years with no complaints, except from the neighbors. Never dyno'd it, but eventually the carb needed work, and I brought it back to stock except for the jets and CV slide spring. Starts right up and runs well at different sea levels/altitude which is where the CV excels. I had another Evo that came with a Mikuni. I had nothing but problems, and when it started leaking, I put a CV back on. Sold the Mikuni for 75 bucks. Keep your gas fresh, change your intake seals every now and then and the CV will always get you home.
Last edited by SirHarley; Aug 7, 2024 at 03:41 PM.
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