Carb

I am changing my motor from turbocharged to non-turbocharged, and I am looking to purchase a new carb for my 107 ci Evo before bringing it in for a Dyno Tune. Out of all the carbs, which is the easiest to dyno tune for a correct fuel mixture thru all the throttle / rpm spots (CV, S&S, Mikuni)? The bike is a FLHT touring bike. And which size would you recommend?
And would there be an advantage of getting a modifed carb from Zippers or Woods Performance, as compared to just dyno tunning it? And what is your thoughts on adding a Thunderjet? Is that going to make it more difficult to tune? OR less?

1997 FLHT
107 ci S&S Evo
8.5:1 compression
S&S .600 lift cam
Heads modified by Baisley

[Mike]

All of the carbs you mentioned would work fine. The S&S tends to be the easiest to tune since it has the least number of circuits. Installing a thunder jet adds two more circuits (T jet fuel and air bleed) and more tuning time. The Mikuni has the most circuits but we rarely have to change more than the main jet, pilot fuel jet and adjust the accelerator pump (sometimes the needle may be changed for part throttle). The CV carbs are the most forgiving as far as altitude changes and are similar to the Mikuni as far as what we change (main jet and needle position-shims) but when you get into slide, spring and needle changes the dyno time gets lengthy. Tuning for all throttle/rpm spots is more problematic with fewer circuits. This is also strongly enfluenced by the type of exhaust. Carbs can not be perfectly tuned for all possible throttle, load and rpm situations (that is why we have fuel injection). Zippers offers modified S&S carbs, with thunder jets installed. The Woods carbs work very well but are a bit pricey, the H-D Screaming Eagle 51CV seems to be working just as well and can be tuned very well with it's Race Tuner jet kit. We've tuned all of these.
I would recomend the Zippers G3 carb kit for the S&S, the H-D 51CV (easiest to install and most user friendly) or the Mikuni HSR 45 or 48 (kits available from Zippers and Rivera).
Leg clearance, use of the bike, fuel milage, HP/TQ expectations and the type of exhaust used all need to be considered as part of the final decision.

The bike is used for everything. Work, touring, travel, going fast. As far as milage. I would hope to get at least 30-35 mpg on the highway. And the exhaust! I am putting back on the original bagger exhaust with some free flowing mufflers like the Screamin Eagles slip ons or a set of Python Slip ons.

Is there a manifold for the SE 51mm for the S&S Super Sidewinder 113? The motor is 107, but I am running 113 cylinders with custom pistons.

S&S claims I need to run a big carb that is around 54mm, Woods says the 44mm would run great. From my past experience with cars, I think the big carb would work better on the top end, but the smaller carb would give better throttle response in town. Would you agree?

Also in the mean time I want to run the bike with the stock carb until I decide on which carb and get it. It has a 230 main in it now from the Turbo application. I have no idea of about what size of main I need for a small carb 107 inch motor. I am sure that the 230 is going to be too big. Does like a 180-190 sound OK to start with?

Thanks for your input.

[Mike]

The SE slip-ons or S&S' new slip-ons would work the best with the 8.5 compression. Open exhaust's may develope a torque dip between 2.5-3.5k rpm when not supported by compression/cylinder pressure. The cam also plays a big part in this, but I suspect the .600 cam used for the turbo application would be very narrow on the timing with little overlap and this would help (without the timing specs I'm guessing). Be sure to modify "Y" pipe to remove the restriction where the rear pipe intrudes into the front inlet.

You are using Baisley heads. Are these H-D castings or S&S? Are they 1.630 or 1.800 intake ports? Was the cylinder lenght changed for the pistons/compression? Were the heads decked for compression? The H-D manifold, included in the carb kit, would work with stock head castings (the 44cv requires seperate purchase of the manifold and air cleaner kit). S&S makes spigot style manifolds for the 44 and 51cv's when used on their Superstock 1.800 heads. In either case, the manifold may have to be fitted to the heads to correct for the spread between the intake ports (easily done on a belt sander).

Your compression, cam and exhaust may not support a 54mm carb. Our testing on a 103 (125hp) motor confirms your experience on carb size. We saw a slight increase in low to mid torque and a 4 hp loss on top, with the 44cv vs. the 51cv. This test was done with and without air cleaners. The 51 uses a larger/wider AC, causing a leg clearance issue with the owner. The 44 AC was more restrictive at this HP level. We did not test the 51 with a 44 AC but suspect the majority of the HP loss would be a function of the AC restriction.

The Wood carbs work really great but typically also use a larger/wider AC (leg clearance). They are also quite expensive when the Air Package is included. I know Bob Wood and use a lot of his products, but to be honest, we have been getting similar results with the SE 44 and 51 cv kits for less expense. The best size for your combo would be 48cv (they do not make one) but I supsect the 44 may be the better choice for all around drivability, user friendlyness and fuel milage ( see our "fuel Milage" notes in the Dyno section of our web site). You'll need the "Tuners Kit" with either and I would recommend a dyno tune.
Mike

The .600 lift cam is just the stock out of the box S&S 600 Cam. It has a pretty late intake closing (55 degrees ABDC), which is got me worried a little having only 8.5:1 compression. The overlap is a modest 40 degrees. I did a compression check and I am getting around 152 psi on the front, and 138 psi on the rear. This is cold testing with the throttle open. I don't know why the back is so much less. but the good thing is it will be easy on my starter. :D
The Heads are S&S Supersidewinder that are used on the 107 & 113 4"bore motors. They have been fitted with bigger 1.700 Exhaust valves with some special seats. Some mild port blending, and no decking.
I went with the 113 cylinders for the 107 because they are 1/8 longer, which allowed me to have some forged dished pistons made with a 1.325 compression height, compared to S&S 1.200 compression height. This allowed me to move the rings down futher away from the combustion, and also strengthen the top ring land.
I already have the S&S Spigot style manifold that will accept the 40 or 44mm CV carb. I think I am talked into the 44CV . My only question now is should I get the Zippers HPCV 44mm and you guys dyno tune from it, or should I just buy one from Harley and have you guys tune it? Zippers says they can jet it pretty darn close which may save some dyno time. But then you probably already have a good idea where to start from. I had a 44mm a while back and sold it, but I may still have the tuners kit. Do you think the K3 needle from Bob Wood would be a worthy item to install? He claims to get a incredible fuel milage out of his carbs! I would think it would be from the needle he uses.

[Mike]

I like the Zippers HPCV with the thunder jet. We often find ourselves in the position of wanting to reduce the main jet size due to rich conditions from 2-4k rpm but then it goes lean on up (the more cam overlap the worse this becomes). The T-jet allows us to reduce the main and then supplement it on the top end. I do not know if this carb has an adjustable air bleed to control when the main becomes active but this would help if it did. Yes, they do get them pretty darn close (so does Bob Wood).

You are right about Bob's carbs and fuel mlg. What few people realize is that he recalibrates the air side of the carb in addition to the fuel side (that's why his low speed jets are so big). His needles are designed for his carbs and I would hesitate to use them in others, the needles that are in the Tuners kit would be OK. You are also correct in that fuel mlg is mostly a function of the needle and this sometimes involves experimenting (the dyno is not always good at getting this optimized for a particular riding style).

Your compression numbers seem a little low, but we have to be careful because many gauges read low. I could only be sure if we were to use the same gauge we use here. The difference may be carbon buildup on the valves, a warm check (hot checks can melt the shrader valve in the gauge, giving false reads) may show less diff.