Remember the Intelajet install article intended for last month? Well… here it is… sorta. Only it’s done on a S&S Super E, rather than the CV Keihin or HSR Mikuni. Why pick the carb H-D never sold, rather than the two they have? To paraphrase what flow guru Jerry Branch once said, “Butterfly carburetors are like having a five-speed transmission but only first and fifth are working.” What he was getting at is that these carbs (notably early ’76–’87 Keihin and S&S) have only three real adjustments as delivered: idle mixture screw, idle jet and main jet and regardless of air bleeds, air jets, etc.… very little overlap in function. Use a big one for peak power and transitions are a bitch… the carb stumbles or hesitates as it goes from pilot to main all at once. Credit where credit is due, nobody argues much with the results in “fifth” on an S&S! Still, it’s all this fuss in the range most ridden in that prompted Mr. Branch’s remark. It also doesn’t help one bit that butterfly carbs “leak” air from both the top and the bottom of the butterfly thus adding turbulence to the already leisurely flow velocity, oozing along in the neighborhood of 25–26 feet per second (about 10 percent as fast as a flat slide carb flowing the same CFM). Not much has changed… until now.
Giving the butterfly wings
The Intelajet works well on all types of carbs, but gives the butterfly carb, in particular, a huge boost in mid-range behavior and performance. So, without much further ado and many thanks to the boys at California Harley (Eric and Allan) who donated their time, talent and a Shovelhead FXRT as “Lab Rat,” here’s what happened.
1-Mark cable adjustments with a Sharpie, or be prepared to do ’em from scratch when reassembled. Use the adjusters to add slack. Remove the air cleaner, undo the carb mounting bolts and the cables from the carb. It’s all prep for Thunder Products’ so-called “pro install” method.
2-Trickiest part of the whole thing. We wound up using a plywood scrap and a big C-clamp to hold the carb in proper position in the drill press. You can improvise or take the carb to any good machine shop if this intimidates. In the end… the critical deal is to ensure the Intelajet nozzle is installed in a way that its 1/2″ body clears the air cleaner backing plate and its brass tube is perpendicular to the bore of the carb.
3-Allan drilled the pilot hole on the bottom line of the cast-in “Shorty” rectangle and above the “Made in USA” stamping. Could have been done further out; some even put the hole right over the Shorty mark. Slow, straight and steady are the watch words for this operation.
4-Next…drill to size with a #21-size “numbered” bit. A rag in the carb bore helps catch any errant swarf… as does a greasy bit.
5-Off the press and in the vise… to be tapped with 10/32″ threads. The alloy is soft, so go easy and keep the tap straight and slippery with a drop of oil or dab of grease.
6-Drill the bowl drain plug from the inside out… much easier!
7-Tap… from the outside in.
8-Install the hose nipple… just tight enough to avoid leaks… finger tight and half a turn is usually plenty. Don’t overdo it! Now, before you do much of anything else, clean, clean, clean everything you’ve just exposed to metal shavings and grit! It’s also a good time to check the general condition of the carb, O-rings, gaskets, needle and seat, float… on and on.
9-Screw the nozzle assembly into the carb body… gently! No need for force here… ’tain’t goin’ anywhere. The nipples should wind up facing more or less as you see them here and with clearance for the air cleaner backing plate. There are two sizes of nipple… the smaller for fuel, the larger for air. Very hard to get that wrong, so the objective is accessibility in order to fit the appropriate tubing as easily as possible.
10-Critical task #2… and a confession. We did not know for sure what size the main jet would be in this carb, in advance. Online homework implied the odds were best for either a 72 or 74. So we had both a 66 and a 68 on hand for the swap. Oops… the main turned out to be a 70! Using the 66 was our only option, but knowing very well the Intelajet would work better with an even smaller main there’s a swap to a 62 in the future. By the time you read this it should be a done deal. The point being, a drop of two sizes gets the Intelajet’s attention, but it will really come alive with a reduction of three or even four main jet sizes.
11-OK, we also removed the actuation rod from the accelerator pump. Not the heretical move you might think. The whole point is to achieve precise, atomized carburetion, and having random shots of raw fuel mess that up is not in the cards. The fact is, when it comes to the “butterfly bog” the Intelajet cures it, and an accelerator pump just tries to hide it… but fails.
12-On the bench, no hoses routed yet. Some, in the name of a slightly more sanitary finished installation, might want to go with the optional 90-degree nipple for the drain bowl… helps make hose routing “cleaner.” Allan was fine with what came in the kit (#IJ-210-AO), so next…
13-Install the IJ controller, complete with tiny air filter. Since the Lab Rat is an FXR, locating it on the coil bracket was pretty much a no-brainer. Other applications on other models might require a little more creativity but any place is better than one place, the handlebars. It might be tempting to put the controller up there where you can easily play with it but it’s a bad idea for two reasons. One, you don’t want the hoses to chafe, kink or tear as the bars turn side to side. Two, you shouldn’t play with it! The purpose of the controller is to allow easy adjustment when needed… and you won’t need it very often. The IJ balances mixture on its own, within quite a range of conditions. The only time you might need to interfere is when things get to extremes. By that I mean major changes in altitude and/or temperature during the course of a ride or road trip. If you live in Denver and go to see the ocean. If you live at the sea level and go to the top of a mountain, like Pike’s Peak. If you start your trip in warm weather and get caught in a blizzard. Stuff like that. In other words, unless the bike starts to run notably worse than usual, because conditions are notably worse, don’t mess with success. Even if the occasion arises, a little adjustment goes along way… be judicious. They don’t call this thing an “Intelajet” for nothing, so let it do most of the thinking and enjoy the ride.
14-On bike… no air cleaner yet…you can see the hose routing. Clear tubing across to the controller on the left and smaller blue (optionally black) tubing from the smaller bottom nipple on the IJ to the mating one, on the bowl drain plug.
15-Yeah, the air cleaner hides a lot. Hook up the cables, the choke mechanism, filter, cover, etc., adjust as required, double check everything; you know the drill. Lastly, make sure the IJ controller is set in the middle of its three-turn adjustment range. Fire it up, warm it up and get ready for “OMG… didn’t know this thing could work this well!”
16-Lord knows there are plenty of other “improvements” for S&S carbs to be had from the aftermarket. IMHO… none compare to the Intelajet, but the real question might come when you try to install one in addition to bits and mods you might already have on your S&S! The one in this pic has a “fix” referred to as a “booster.” An idea borrowed from hot rod four-barrel car carbs, it works to improve air speed. But there’s a catch; it only makes a big difference in S&S carbs that have had the body bored out. (Seems to me the presence of the IJ’s brass tube in the throat of a stock S&S would have as much positive influence in air speed as the add-on booster “doughnut.”) I doubt the wisdom but, fact is, you could do both… the IJ won’t mind.
17-And… as mentioned before… adding a thick spacer like the one Harley used to include in the Screamin’ Eagle butterfly carb kits (#3 seen here), is a known and proven way to accomplish the same end. Yup… simple mods that address real-world conditions (like air velocity and a self-correcting atomized mid-range circuit) are the best for getting all five speeds in a butterfly carb… in gear!