Stage 1 or 2

Hi group, I own a 1997 flht with a v-thunder 3010 cam, free flowing mufflers, se air cleaner. Thinking about putting in either a stage 1 or 2 carb. kit.The previous owner put in a dyno kit with the plastic slide which gave me terrible mid range performance. I just acquired a new cv carb and think about butting in a kit before I install it on the bike. Any thought appreciated. Thanks, Dayrider

Do not waste your $$$ on a Dynojet kit, Thunderslide kit, Yost Power Tube, etc. The only place you'll find that stuff @ the best tuners' shops is in the trash can. All you need are a few jets & perhaps a different needle. You can get a CV carb to work fine on engines making up to 100 HP with about $15 worth of factory parts.

I don't know the baseline for your engine, but I do for a 1200 Sportster thru 2003 so I'll give you that as a guideline - 42 slow jet, 175 main, N65C needle & 2.5 turns out on the idle mixture screw. Your engine will probably want a 45 slow & a main in the 185-195 range - maybe more, but jets are cheap & readily available.

And I can tell you why you had such poor performance with the plastic slide - it galls on the carb body & it also "hunts" - always trying to find the right spot, but it never does. And do not drill the stock slide to make it raise quicker - it will, but then it'll overcorrect & "hunt" too.

Dyno kit

Art?..thanks for the reply, I put the new cv on the bile with 45/175 jets and a Sportster needle, but the only thing I like about the Dyno kit is that it seemed to have better pull out power. Any thoughts on how to get better low end/pull out power without putting in some type of kit. I agree the stock cv is a much better performer...thanks again, Dayrider

I'm not familar with the V-Thunder cam you're running & if I knew the lift/duration/timing specs I could be more helpful, but what it boils down to is when going to a "hotter" cam, you always give away low-end torque for top-end HP & tuning in the low rpm range is difficult.

Also, do you know which Sportster needle the carb you're working with has? They have been changed over the years, the N65C I mentioned is for a 1988 XL1200 & is the most popular replacement, but the stock ones '91-'03 were awful. Can't remember right off what comes in '04-'06 Sportsters (NE4Y?), but those work just fine & are nearly identical to the old N65C.

- Art

cv carb

Thanks Art....The V-thunder cam is equivalent to the Andrews ev-27, it has .2340 duration/.0960 lift. It's just funny that the Dyno carb had much better pull out power, also I used the N8EA needle which looks to be very close to the N65E needle.....thanks again, Dayrider

OK, I went to the Andrews site to see the specs on the EV-27 cam: .495" lift, .236 duration intake, .240 exhaust & the timing is 20/36 intake, 46/14 exhaust. Add the 1st & last timing numbers & you get the amount of "overlap" - 34 degrees. BINGO - now we know what we're dealing with - "reversion".

I will try not to get into a long engineering dissertation here, but what "overlap" refers to is how many degrees of flywheel rotation there is between the intake valve starting to open & the exhaust valve closing down - both valves are open @ the same time for a while & in this case, 34 degrees.

In other words & using the timing specs, as the piston is going up on the exhaust stroke, the intake valve starts to open 20 degrees before the piston hits Top-Dead-Center but the exhaust hasn't closed down until 14 degrees after TDC. And the 2 other numbers tell us that the "intake closing event" (crucial) is 36 degrees after the piston hits Bottom-Dead-Center & is starting back up on the compression stroke & the exhaust valve starts to open 46 degrees before BDC as the piston is on the way down during the power stroke.

OK - back to overlap - and add the exhaust pipes to the mix - what goes back up the pipes is even more important than what goes down. During the overlap period, sound & pressure waves that travel back up the pipe can go in thru the exhaust port, thru the combustion chamber & out the intake port, right into the intake manifold. And since we're dealing with an "odd-fire" engine (firing order =315-405), what comes up the front pipe & back pipe arrive @ the intake manifold & irregular intervals.

One thing you see with drag pipes is one cylinder running rich while the other is running lean & that's because the exhaust "reversion" from the front pipe is affecting the intake differently than the reversion from the rear pipe. It gets really tricky with 2-1 exhaust systems. And another thing you see on the dyno is "standoff" - take the air-cleaner off & you'll see a fog of air/fuel mixture standing outside the carb throat - "reversion" is literally blowing mixture out of the carb !!

That doesn't happen idle to redline & most commonly around the 4500 rpm range, but when will vary a great deal depending on exhaust system & cam timing. The A/F mix gets sucked back in & blown back out so fast all you see is the fog - best not be smoking a cigarrette on the dyno ;-)}

H-D knows all this stuff & that's why the bikes come with such mild cam timing - for example, Sportster D cams have only 4 degrees of overlap, not 34. That's also why there's a crossover pipe in the exhaust on numerous bikes (including all Sportsters) - to equalize the uneven sound & positive/negative pressure waves in the exhaust system. End result is the reversion effect is eliminated because there's not enough time for what reversion is left after passing the crossover to go all the way thru the cylinders.

But put a different exhaust with no crossover on & put in a different cam setup with a lot more overlap & the reversion monster rears it's ugly head !! Oh, you can put a "Band-Aid" on the lower rpm tuning problem with a Dynojet kit & just drown it out by running too rich in the problem range - the "seat of the pants dyno" may tell you the bike runs great.

But pull the top end of the engine off after 10,000 miles & you'll see the engine doesn't like that one little bit. And if you go to a dyno with an air/fuel "sniffer" you'll see the problem show up real quick on the charts - even if you don't feel it while riding.

In racing, you can actually use "reversion" to your advantage, but only in a narrow rpm range & you can't do it on a street bike. So what to do in your situation? Get the slow jet & the idle mixture set right 1st - probably a 45 slow & definitely 2.5 turns out on the idle mixture screw.

May have to adjust the screw a little bit either way once the engine's warmed up, but if you have to go more than 1/4 turn either way to hit that "sweet spot", something's wrong - intake manifold leak, ignition timing off - wrong size slow jet - find the problem & fix it. Then you can do some trial & error to find the right size main jet.

The "carb farts" should be gone & the throttle response good from idle to redline. If not, look @ the needle - that's what controls the transition phase onto main jet. And when you see (very typical) a spike in the A/F ratio on the dyno charts in the 2500 rpm range, lights should start flashing NEEDLE-NEEDLE-NEEDLE - 'cause that's what the problem is.

I've seen it more times than I can count - the A/F ratio shoots to over 16:1 & even as high as 17.5:1, then it comes back down. The "stochiometric" (theroretically ideal) ratio is 14.7:1, but that doesn't work in the real world - a bike like yours is going to want in the 13.5:1 range & max power @ full throttle is made @ 12.5:1.

Throw a Dynojet kit in the carb & you can turn that spike into a bump - but - it makes the low end way too rich & causes all sorts of problems, including fouled plugs & gas in the oil. You'll never get a flat line on the A/F charts, but you can get pretty darn close - been there, done that, got the T-shirt ;-)}

You don't need to be a "rocket scientist" either, just take your time & only address one issue @ a time - if you change more than one thing @ a time you won't know what did what.

With the cam you've got, I would expect your powerband to be 3000-5200 rpm - the bike ought to pull like a freight train. But because of the valvetrain design, revving higher does not make sense (& will cost you). And the idle to 3000 rpm range will not be easy to tune - but it can be done & you don't need any fancy gizmos to do it - just slow jet, needle & idle mixture screw.

Art, Thanks for the schooling, always wondered what overlap was & how it affected performance. I am running a stock duels header pipe with the crossover which makes sense now as for what the crossover does. I agree with you the dyno kits run rich, for no matter how I jetted itIt was always rich. If I leaned the slow jet down to a 42 it would pop & bang & run like crap & the plugs were still pretty carboned up on the base of the plug. Since my bike had better bottom end performance with the dyno. kit in it do you think a needle change or shim under the needle would help at all. I think you just answered this question in the previous post but I'm not sure. Thanks again & have a great day....Dayrider

If it was me, I'd get slow jets 44-48 & start with a 45. And the infamous N65C needle for a 1988 XL1200. And main jets 180-195, starting with a 185. Then run the idle mixture screw in *gently* & back out 2.5 turns. That ought to put you pretty darn close & will give you some extra jets to fine-tune with.

But as I said, get the low end right 1st - don't mess with the main until the bike runs great from start-up thru idle & warm-up, to around-town speeds. You may need a shim (get a few .010" brass washers @ the hardware store - about 10 cents ea.) or even 2 on the needle, but I'd start with none.

Start with the baseline & just change one thing @ a time until you've got the low end sorted out. Take good notes too, so you'll always be able to go back to a known good setup in case future changes don't work.

Then you can go play & see if the main needs to be changed. Know what a "plug chop" is? The NASCAR boys do it in practice & qualifying all the time - wide open throttle, cross the finish line, then hit the kill switch & push the clutch in @ the same instant - coast back around to the pits where the engine builder & a spark-plug guy are waiting for you. Pop the hood, pull the plugs & have a look @ 'em with one of those lighted magnifying glass deals.

They can tell on the spot if this cyl. is too lean, that one's too rich, the timing's too far advanced or not advanced enough, etc. Go back to the garage & change whatever. Then go do it again. And again. Qualifying you only get to do once, but you still want to see if you got it right after all those practice runs.

OK, so you don't have a million dollar semi with a machine shop in it & a whole crew @ your beck & call - not a problem. Get a couple new plugs, a plug wrench & go for a ride on your favorite stretch of road where it's safe to pull off somewhere. Pick a couple points on the road & do a full-throttle "roll-on test", preferably in high gear - how long did it take to get from point A to point B, or how fast were you going when you got to point B? Go do it again.

Then do a "plug chop" after crossing point B & coast off to a safe spot. Pull the plugs - what do they tell you? Too rich, too lean? Did you get any "spark knock" (pinging) or have any hesitation? Make whatever change you think is necessary & go do it again. And again. And again.

It's time-consuming but fun & will actually tell you more than the dyno does because the dyno can't factor in road conditions & wind resistance. Don't get me wrong, I love to go to the dyno & I learn a lot there - but you will always find a bit more with real world testing. Just as long as you've got a place to do it that doesn't invite the whole Sheriff's Dept. ;-)}

This is quite true & reading plugs today is a lot harder than it used to be. But you can still do it & even NASCAR has gone to unleaded gasoline.

You'd be surprised how little a lot of the guys in the shop are paid & anybody can buy a lighted magnifying-glass plug-reading tool. I ought to get one myself 'cause they're not all that expensive, but I know what I'm looking for & I also hand the plugs off to others for their read.

The big salaries go to guys like crew chiefs, but they started out sweeping the garage floor like everbody else. You can walk into a NASCAR shop with a Master's Degree in Mechanical Engineering & you'll start out sweeping floors too - might get to be a team engineer in a few years if you're willing to work 12-16 hours/day, 6-7 days/week for low pay until you earn the respect of the team.

I know that 'cause I live in the heart of NASCAR country - about 80% of the teams are within 25 miles of where I live & with the windows open, I can hear the sweet sound of engines running on the dyno right up the road. And there are some fab shops not 5 minutes away. One I use myself & made things there like the extended swingarm for a LSR bike.

But as I've said before, there are really good little shops all over this country & the best guys will not only show you what they're doing, they'll explain why they're doing it. Hand 'em a spark-plug & they'll tell you what they see, explain why it looks the way it does & what you need to do to get the engine to run better. H-D dealership ain't going to do that, but a little indy shop will.