new motor help?

teton

teton

tetongravity.com
Location
Washington DC
I have a problem, and i need to solve it before daytona,

i have a fresh built 701 61x topend 82.5 bore and exhuast porting (just widening to 70% of bore), the cases are 6m6 and it has after market reeds (i think boysen, they are clear yellowish material) i recently built this engine and it rips compared to stock, im running a factory b mod pipe, stock electronics and rev limiter, ada head with 37 cc domes, the cylinder has been decked .008" and the compression is about 190psi, the squish is .045, the carb is stock. im running 40:1 93 octane with yamalube.

i asked advice on the carb tuning and got a response from supertune (thanks by the way i really appreciate it) the carb settings im running are

130 H, 120 low, 1.5 needle valve (stock) and a 95 gram spring. low speed screw out 2-1/4 turns,high screw 1 turn out

my question is that all the signs show that its running rich, the piston wash (no carbon build up) and the spark plugs are black, the only time i have noticed brown on the plugs is after a 3/4 throttle run for about 2-3 minutes and cutting the motor before letting off the throttle and checking the plugs immediately after.
it is running extremely rough on idle, and when i start it out of the water it sometimes sounds as though its backfiring? so im worried about the idle, also when running the motor at idle and messing with the low speed adjuster, it does not seem to effect the idle speed (like it says it should in the mikuni manual).

i am new to all this and tried my best to read up on carb tuning, however im a little worried that i might mess up my new engine, does anyone have any advice on what to do next, like i said the motor is extremely fast as is however it seems like it needs to be leaned out a bit (dont know) and it could be faster.........but im worried about the idle
 
teton

teton

tetongravity.com
Location
Washington DC
ive gotten one feedback on jetting anyone else have any recommendations, im hoping to put in a big order of jets,springs, etc......so i need a couple of different options
 
SUPERTUNE

SUPERTUNE

Race Gas Rules
Location
Clearwater Fl.
Yes, I did say 2 1/4 to start with as he stated to me that he is running the stock 44mm carb. That means to me a stock 44mm mikuni from a 6m6/61x cased superjet. These carbs are manufactured with Stainless steel low speed screws and have a very fine thread pitch and would equal about what an aftermarket carb set at 1 1/4 because of the course thread pitch on the aftermarket Mikuni. This is the reason I stated that... Yes you can lean the idle mixture with turning the low adjuster in more but no less than 1 1/2 on an OEM carb. So you do have about 1 turn you could possibly do to help the rich idle.
Look in the carb throat when idling and see if the bombsite is dribbling fuel, if so try a stock 115 gram spring and leave the same jets.
 
teton

teton

tetongravity.com
Location
Washington DC
is there a way i can tell if the carb is a stock 6m6? is there a difference between the 6m6 carb and the 61x carb?


....as usual thanks for the help chuck and everyone else
 
SUPERTUNE

SUPERTUNE

Race Gas Rules
Location
Clearwater Fl.
As far as I can remember 6m6 and 61x 44mm carbs are the same with maybe only a jet change between 650 & 701cc's. The 61x 701 waverunner models are a different carb than the superjet. (internal)
 
teton

teton

tetongravity.com
Location
Washington DC
ok so i went out riding today, and the ski did not run well, it had absolutely no low end hit like it seemed to when i first fired the motor. checked the compression....it was fine 190psi both cylinders

im still running the same jets, and when i looked into the carb at idle there was in fact gas dripping out of the bombsite. so i changed the spring to the stock 115 gram, the dripping continued and it seemed to hesitate off idle, and would barely run at all past idle. put the 95 gram spring back, still dripping.

the water temperature was colder and was about 50, however adams ski, ran just as good as it did in the same water.

any ideas?
 
Mike W

Mike W

Infidel
Location
North Florida
Take your needle and seat out and check for wear near the needle tip. If its worn you will see a wear mark (ring) just before the tip of the needle. Also check the condition of the O ring.
The biggest thing you can do is check popoff. If it does not pop cleanly or dribbles any than it is bad.
 
teton

teton

tetongravity.com
Location
Washington DC
the needle and seat is brand new, i have inspected it and it looks great, i can always try the old one? and i don't really have the means to check popoff, even if i did, what would this tell me?
 
ATS_Aaron

ATS_Aaron

X-
Location
Shady Shores, TX
The pop-off tells you what pressure the needle is pushed off the seat. I think you hook it to the fuel inlet line (please someone tell me if that is wrong). Start pumping, the pressure will go up and up and then stop or drop. The peak pressure it reads is your pop off pressure. (again PLEASE someone tell me if I am wrong).

http://kartingtechinfo.com/tech/popoff.htm

Or I think you could modify this with a 1/4 hose to hook to the fuel inlet:

http://cgi.ebay.com/Foot-Pump-w-Gau...ryZ22664QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Aaron

Edit - I went and read the Mikuni manual section on testing pop off. You need to connect the pump to the fuel inlet. Plug the return. Remove the diaphram cover and diaphram. Then start pumping and visually look for the needle to move. Make a note of what pressure shows on the gauge when the needle moves. Do it at least 3 times.
 
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ATS_Aaron

ATS_Aaron

X-
Location
Shady Shores, TX
Oh yeah, ATS_Scott built a very similar engine to yours last spring. He ran a 6M6 cylinder that had been "sport ported" with the templates and then bored to a 701, so that might make some difference (you could search Sport Port and find out what size those are). He ran the following carb settings:

Main Jet : 145
Pilot Jet : 120
High speed screw : 1/2 turns out from closed
Low speed screw : 2 turns out from closed
Needle & Seat : Stock
Spring : 95 gram

It rode great with no hesitations. But Chucky is much more experienced than us with that.

Aaron
 
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