It sounds like the transition from slow speed jet to needle. So to find out if your slow speed is correct set your air/fuel mixture screw at highest idle. I usually run it clockwise till the motor slows or stumbles then back it out a 1/2 turn. You can go it till it slows then out till it slows and split the difference. Either way will get you close. Now count how many turns it takes to bottom out the screw. If it's between 1-1/2 and 3 turns your slow speed jet is good. If it's less than 1-1/2 then your jet is too rich. Over 3 and your too lean. Get this dialed in first. If you still have your stumble then switch to the 88 needle. With the needle all the way closed you are still getting fuel from around the untapered diameter of the needle. The 88 needle has a smaller diameter on the straight part allowing more fuel at the transition point. You may or may not need a washer. I would try it without first and then tune from there. This is the hardest part of tuning the CV so don't feel bad. It's driven me crazy in the past!!

 

OP says it coughs when entering 3rd pulling hard, but then says it doesn't when shifting, only leveling off to cruising speed. So it sounds to me he's coming off full throttle to mid or low range.

 

When he's going to mid or low range which sounds like the same spot. My guess is the needle either way but you shouldn't deal with the needle till your slow jet is correct. It's in that overlap that causes problems and those cooler temps definitely don't help the situation. Also an intake leak could still be happening if he's getting the cough after letting off the throttle. When you're at high rpm's and let off the vacuum increases a lot more than at idle where it was tested. This can cause a lean spot and when you reopen the throttle you create a lean spot for a split second till the fuel starts to move and since you're already lean from a vacuum leak you will get a cough.

 

I think a 52 for the low is about right for that. He also says his plugs are whiter than he likes them. Lots of variables here. What kind of tuner, what do the plugs really look like, where's the line on the strap, is the base black, can you get soot on your finger from the end of the exhaust? Sometimes an exhaust leak will do the same thing. Was the slide modified or changed? What about the spring? Stock or shortened? Lots of unknowns. I chased an intake leak for days once and swore I couldn't find any, and then did.

 

to clarify: throttle open maybe 3/4 in 2nd, shift to 3rd throttle now 5/8ths gaining revs more slowly is when it occasionally will cough

this cough was horrible and present everywhere on #45 pilot / going to a 48 removed 80% / going to a 50 took out all but the current symptom

rev limiter set at 4900 and I`m not hitting it so I`m not twisting it that hard ( no tach )
default ign curves set as suggested for break in / testing by Twin-Tec
Carb is stock except #50 pilot jet
Will dbl chk for vac. leaks and test in warmer temps before looking into the idle screw.
Thank you all for your input !

 

I'd seriously look at the needle and the slide and spring. You can go larger on the main to 190. But I'd really like to know what the plugs look like. You have to have some back pressure but I don't know what kind of pressure you have now with your setup. Again, review Nightrider's CV suggestions if you can. And triple check for leaks. Set the idle about 1000rpm and take your time. Listen closely because without a tach it will be difficult to notice a slight drop.

 

The additional info is very helpful.

I can't disagree with any posts so far, and symptom does sound a bit like a sticky slide. At the same time, I do disagree with many tuning tips and tricks found on may websites - particularity, cutting springs, drilling slides, etc. All that's fine for tuning to a specific rpm/load range that's constant (racing) but for "all conditions riding," not so much.

The biggest issue I have with tuner info websites is that most say the main jet only affects WOT and the needle does everything from 1/4 throttle up to that point, but think about it - would you have the same fuel delivery at 1/2 - 3/4 throttle with a 160 main as you would with a 205? No.

You've improved the efficiency with heads so obviously it's pulling a lot more air, and with better combustion efficiency you can run a lot leaner but still need the mixture right. Especially without an O2 monitor, I've found it's best to tune from the top down. That is, get the high speed circuit right first and work back to mid-range then finally low speed. (but that's just me) Most stock TC engines use a 190 main and you're well past that with your current setup. With your good start/run/idle I'd be tempted to leave the low circuit alone for now and go up a main jet size or two before doing anything else. ...

 

I thought OP said he's only running a 185 main. Since it's a new build I am hesitant to add that a lot of builders will torque the heads with the intake manifold in place eliminating any possibility of fractional slippage and creating intake leaks. So, another unknown.

 

Yeah, he said 185... Most 80 inch bikes use that size with an exhaust or cam upgrade.

He needs a good bit more than that for sure. I'd go at least 195...

 

You ever thought about installing a wideband sensor to see what actually is the problem?