Carb jetting, looking for recommendations

[Meatball]

Hey guys, new here. I’m building a rather unique Sporty Bagger out of an 05 XL883C. I have V&H straight shots on it now, it was like that when I bought it, and the stock air cleaner. The bike never ran right, though it ran well enough to get me back and forth to work. Well, the rear brake went out and I took it off the road. Been down for months. I finally got my Heritage back on the road so I am just about ready to jump back on this Sporty project. I bought the screaming eagle air cleaner kit, screaming eagle plug wires and new plugs. Next I want to buy jets and a carb rebuild kit. I’m still a bit of a novice when it comes to carbs, so I was wondering what jets I should get for this combination of parts and what carb kits you guys recommend. Thanks!

[JBinNC]

In my opinion and experience, the Keihin jet kits are the only way to go. They are sold by various distributors and are model specific. I do not like the Dynojet kits, and have removed those parts from a few "jetted" carbs, much to the improvement of the carb and the overall tune-up. You don't really need a carb rebuild kit to work on a CV carb, and you definitely want to keep and use the original float needle, if it's any good, because the aftermarket float needles suck, and the H-D replacement needle is expensive.

Jim

[Skjoll]

I'm a fan of the Velocity needle (the N65 needle can also be a good choice depending on the situation) which has helped cure lean stumbling in the 1/4-1/2 throttle range on my '98-2006 Sporties yet it's taper didn't have any ill effects on the wider throttle openings.

Here are a few diagrams that may help in understanding the relationship of the carb's various circuits and how changing one circuit such as either the needle or the main jet can affect the other circuits and why it's best to systematically target a specific throttle opening for rejetting rather than just running the bike around town, reading the plugs and then making changes at random. IMO set low circuit first after the bike has been warmed up, then determine the size of the main jet by running WOT exclusively, running around town after doing a WOT run will skew plug readings. Once the lowest and highest throttle settings have been dialed in you can begin targeting 1/4, 1/2 and 3/4 throttle openings and finding a balance between all three by adjusting the needle or trying out needles with different tapers.

[Meatball]

I'm a fan of the Velocity needle (the N65 needle can also be a good choice depending on the situation) which has helped cure lean stumbling in the 1/4-1/2 throttle range on my '98-2006 Sporties yet it's taper didn't have any ill effects on the wider throttle openings.

Here are a few diagrams that may help in understanding the relationship of the carb's various circuits and how changing one circuit such as either the needle or the main jet can affect the other circuits and why it's best to systematically target a specific throttle opening for rejetting rather than just running the bike around town, reading the plugs and then making changes at random. IMO set low circuit first after the bike has been warmed up, then determine the size of the main jet by running WOT exclusively, running around town after doing a WOT run will skew plug readings. Once the lowest and highest throttle settings have been dialed in you can begin targeting 1/4, 1/2 and 3/4 throttle openings and finding a balance between all three by adjusting the needle or trying out needles with different tapers.

I'm a fan of the Velocity needle (the [="https://cv-performance.com/cvp-n65-needle"]N65 needle[/URL] can also be a good choice depending on the situation) which has helped cure lean stumbling in the 1/4-1/2 throttle range on my '98-2006 Sporties yet it's taper didn't have any ill effects on the wider throttle openings.

Here are a few diagrams that may help in understanding the relationship of the carb's various circuits and how changing one circuit such as either the needle or the main jet can affect the other circuits and why it's best to systematically target a specific throttle opening for rejetting rather than just running the bike around town, reading the plugs and then making changes at random. IMO set low circuit first after the bike has been warmed up, then determine the size of the main jet by running WOT exclusively, running around town after doing a WOT run will skew plug readings. Once the lowest and highest throttle settings have been dialed in you can begin targeting 1/4, 1/2 and 3/4 throttle openings and finding a balance between all three by adjusting the needle or trying out needles with different tapers.

Right, that sounds amazing... a few questions... what is WOT? How am I taking these readings? I’m doing this in my garage, so I’m kind of doing this by ear, so to speak...

[Skjoll]

Right, that sounds amazing... a few questions... what is WOT? How am I taking these readings? I’m doing this in my garage, so I’m kind of doing this by ear, so to speak...

WOT = Wide Open Throttle.

Adjusting the idle circuit can be done in the garage but to target a specific throttle opening you need to take the bike out to a secluded area where you can run it under load, preferably in top gear but the highest you can manage should suffice, and maintain that specific throttle opening for as long as you can and then immediately shut the ignition off so that your plug reading reflects the air/fuel mix at that particular opening... also clean the plugs with a wire brush between readings. Jetting a carb to it's optimal efficiency is time consuming and can be very frustrating which is why most people just settle for 'good enough' but a spot on carb is a joy to ride around on because throttle response is smooth, the motor runs cooler than a bike with a maladjusted carb and it's easier to start.

An easier and more accurate way to dial in a carb in lieu of reading plugs is to use a wide band air/fuel ratio (AFR) gauge... it displays the ratio on the fly as you're riding the bike (in a safe low-traffic area).


BTW, do the V&H Short Shots have a baffle in them or are they straight through? If they're straight through do they at least step up to a larger diameter near the end where the baffles would fit in? Straight pipes, by nature, will cause what is known as 'drag pipe sag', a dip in the powerband usually at the lower end of the midrange that is caused by 'harmonic reversion'. The only real fix for that is installing a tuned exhaust because inserting a restrictive baffle into a stright pipe may help quel harmonic reversion to an extent (what a lot people mistake as 'necessary backpressure') but any exhaust restriction will hamper performance at larger throttle openings.

[Meatball]

Well, I think it’s important to mention that I am not trying to eek every last drop of performance out the bike. I’m building the bike out to crush miles. I am going stage 1 with it, but I’m not doing cams or big bore kits, etc. I bought an 883 for the fuel economy. I got a rubber mounted engine for the reduced vibrations. I wanted to get a little more pep out of it, hence the stage 1, because I wanted to compensate for when the bags and trunk are loaded down. That said, since I’m worried about fuel economy and ‘highway performance’ I do want a well tuned carb, better than good enough, but perfection is not really required.

[JBinNC]

The stock CV carb is very easy to work with. A good first step in tuning is to remove the plug over the idle mixture screw so that you can adjust it. (Although on the XL carbs that screw is well out toward the rich side from the factory.) Next would be to go up on the intermediate jet for better driveability. Next would be a slightly richer needle. And last, and maybe not needed, would be a larger main jet.

I will say again, the Keihin performance jet kit for your specific bike is the way to go. All the jets you need, a needle better suited to non-stock pipes and air cleaner, and at a very reasonable cost.

Jim

[Skjoll]

... That said, since I’m worried about fuel economy and ‘highway performance’ I do want a well tuned carb, better than good enough, but perfection is not really required.

I know exactly what you mean. Getting the carb jetted properly also applies to stock bikes that owners just want to 'crush miles' on. I brought my '98 XL1200C back to stock condition and got her dialed in and she performs better than when fitted with the Stage 1 Screamin' Eagle crap the previous owner slapped onto the bike (and I do mean crap, the SE slip-ons were highly restrictive, about as much as the stock mufflers and all they did was make the bike louder). She'll return ~54 mpg when bombing down the interstates and adhering to speed limits (70-75 mph) and ~59 mpg when on secondary roads (55-60 mph), which helps when you have only a 3.3 gal king peanut tank to rely on. She's taken me from thick pine forests at sea level through open mountain passes at +14K feet and back down... from early morning snow covered mountain tops with temps in the teens (fahrenheit) to desert gravel roads with temps above 100°F all in the same day without skipping a beat. To me that's a definition of 'performance'.

Incidentally, the info and observations/experiences I post isn't an attempt to convert anyone and insinuate they've been doing anything the wrong way, just sharing info that some people may be interested in yet won't be exposed to in a typical forum. Ultimately it makes no difference to me what anyone does with their bike.