Another good observation by the Erbman. Link to original RSR post HERE
My observation's after a yr + reading on this forum and
reading, and reading, and retaining, and seeing the same questions. and answers
on starting carb set-up. Mind you this
is a compilation from various members with tons of knowledge, and like I said,
"my observations".
I would say a good 87.4% (fictitious
number, but I hope you get my point)
of the time there are usually 1 of 2 main jets used, 1 of 2 needle settings, 1
of 2 jet kits, 1 of 3 manifolds (2 of which are ported) a number of air kits and
pipes. But still for the most part, carb
set-up is the same for most
combinations of aftermarket air
filter/pipe and manifold. Also for elevations under 1000ft. And no air leaks!
Mileage as a self test for correct carb set-up, can be a subjective subject tho,
but try this, and make the commitment
to do it this way, fill-up near a hwy where you
know for sure that you can do a minimum of
55mph to no more than 75mph for at least 100 miles, fill up, check
mileage, do it twice, the same day or
whenever. For the most part this seems to be around the speeds people are
seeing their best mileage. Majority I read are getting between 45 to 50mpg,
yes, I have seen higher, and lower. I guess it boils down to where you feel
satisfied with the mileage and performance, and of course how much time you want
to play with it. like I said "subjective". Let me just add this, what do new
cars have on their window sticker?
....................................................figure it out yet? an
approximate on city and highway mileage that the car gets, and they get that by
testing under controlled conditions. Should a bike be any different? Hence,
that is why I asked you to do a test run under certain conditions, may not be as
accurate as the auto manufacturers do, but you do get the point?
Popping on decel as a sign of being lean,
I think another one of those subjective subjects. Yes, it can be lean, or an
air leak, the pipe's, and a number of other reasons. So I ain't going there.
And besides, this is for those that wanted a start point when they are doing the
basic mods, in laymen's terms, I hope.
These following combination as I have observed will work on both 1600 and 1700
engines.
Main jet:
Mikuni 167.5, 170 (DJ180 would fall in between the 2 sizes of mikuni)
your choice, pick one....eeny, meeny, miny, moe
Pilot jet;
stock
Barons Needle:
counting from blunt end. c-clip on 3rd groove, spacer, 2 washers
c-clip on 4th groove, spacer, 1 washer
These are the 2 most widely used needle set-up's. Pick your poison , ya gotta'
start somewhere. On top of the c-clip is a washer too, for that small spring to
sit on. You'll see it when you take the carb apart. Also, if you need the
extra washer for the 3rd groove set-up, you can use the washer on top, and get
something to replace it, basically, it's just for the spring to have a totally
flat surface for the spring to seat instead of on the c-clip.
DJ Needle:
counting from blunt end. c-clip 3rd groove, spacer, 1 washer
c-clip 3rd groove, spacer, 2 washers
Hmmm, did ya notice, both sets here have the clip on the 3rd groove. Well, it
recently came to my attention that the DJ needle is just a washer's thickness
shorter then the Barons needle, unless I was lied to about the information. If
that's the case, oh well, life still goes on. Deal with it.! lol.
Pilot Main Screw (PMS):
2 turns out from a light seat, + - 1/4 turn. well, another thing that you have
to start somewhere, I just like 2, easy to remember. Hey!! It's a "starting
point"
Accel duration screw:
1600 engine, most have turned this all the way in, with nut on back side
1700 engine, most have this at 1 to 2 turns out, nut in stock position.
I think that's about it, they're a start point when you're going to add an air
kit and pipes, and ported manifold or not ported manifold. But I suggest you do
the porting and lapping of the manifold, or an aftermarket one, you'll get a
nice boost from that.
Any way, like I said, "my observations" of where most are starting their
re-jetting at. Then we tweak from there, where necessary.
And one more note that I will add, which is my observations on my bike. I
highly suggest to get a dyno run with a air/fuel reading after you think you got
the jetting down to where you think it is correct. Myself, I don't care about
the dyno numbers, but I do care what my the air/fuel ratios are. On both carbs
that I have used (stock & 42mikuni) what I thought to be the correct main jet,
on both carbs, ended up to be too lean, air/fuel ratio's showed lean about 15:
1, and as high as 16;1. When I upped the main, wow, what a performance
difference when I get on it. My cruising mileage was not changed by going to
the larger main since keeping at a cruising pace you are somewhere around a 1/4
throttle, main jet takes over at 3/4 throttle.
BTW, if anyone see's where I screwed up, let me know, so to make corrections.
Anyway, hope this helps.
Here's some info on my bike, and some of my
observations as of late. But here is the important thing I am using a Mikuni
42HSR. I did use the Mikuni manual to tune it. I leaned out from stock
configuration the pilot jet, accel pump nozzle, and the needle. On this carb,
Mikuni makes 4 needles (you only use 1 tho), one they consider standard size
which is the #97. #'s 96 & 95 are richer accordingly, and the #98 is leaner
compared to the standard. Accel pump nozzles come in 3 sizes, this controls the
amount of squirt. I had a 160 main jet in there too, which is the stock size
jet. My cruising mileage was approximately 50mpg. Getting on it, acceleration
seemed okay, but had nothing to compare it to. Well, had an opportunity to use
a air/gas analyzer last week, at
cruising it gave a good reading, but at wide open throttle (WOT) was too lean.
I don't ride like that anyway, but decided, due to a very lean reading to up my
main by 3 sizes and put in a 167.5 main jet. Then went and did my cruise test.
My cruise mileage is still the same. However, my acceleration, no comparison,
it's fantastic. Overall, average fuel city/hwy went down a little, why? Hmmm,
I'm enjoying my new found power and developed a lead wrist. lol. Keep in mind
that the carb circuits overlap one another, so even tho the main jet does not
come into play till 3/4 throttle, I guess when I git on the throttle, I'm close
enough in the overlap area to draw some fuel from a larger main jet, and of
course mileage goes down, but the grin gets wider and wider. Anyway, this is my
observations and opinion, take it or leave it, use what you can, toss the rest.
Take me back to Roadstar Documents
Last edit:
02/02/2008
Joe Friday