At The Back Of The Pack
Arm chair racerFirst time rider
Hi guys, finally got my atc90 going and its got a real bad flat spot at about 1/4 to half throttle, if you feather it on will rev out fine. Its got a stroker crank and 54mm piston so prob around 130cc now and i have a 22mm mikuni carb. We have gone up and down on main jets, up and down on the needle and played with mixture. All made zero difference
Power User
The day begins with 3WW
Short or long manifold ?
I’ve had a couple were no matter what I did I couldn’t tune the short manifold, as soon as I switched to a long style bapp manifold the problem was solved .
78 atc 90/180cc Dickson Full Suspension
76 ATC90/180cc Nicholson
77 atc 90 Dickson Full Suspension
84 KLT 110/123cc Powroll Racer from 80s
87 atc 125m stock
84 atc 200x Curtis Sparks
84 atc 200x Powroll My race bike from 80's
83 atc70/108cc Powroll blue Xmas Special
81 atc185s HP-ATC full suspension
Performance Shop is Open PM me for Service
My Feedback http://www.3wheelerworld.com/showthr...ck+shortline10
At The Back Of The Pack
Arm chair racerFirst time rider
Yeah its a short sudco
At The Back Of The Pack
Arm chair racerFirst time rider
Why would the length create a flat spot? What manifold would i need? It would need to be low profile as there is not alot of room
Power User
The day begins with 3WW
POSA , BAPP and Rocky all made a long manifold and in my opinion their much easier to tune . The flat spot is a very common issue .
What mikuni carburetor do you have ? VM22 ?
78 atc 90/180cc Dickson Full Suspension
76 ATC90/180cc Nicholson
77 atc 90 Dickson Full Suspension
84 KLT 110/123cc Powroll Racer from 80s
87 atc 125m stock
84 atc 200x Curtis Sparks
84 atc 200x Powroll My race bike from 80's
83 atc70/108cc Powroll blue Xmas Special
81 atc185s HP-ATC full suspension
Performance Shop is Open PM me for Service
My Feedback http://www.3wheelerworld.com/showthr...ck+shortline10
At The Back Of The Pack
Arm chair racerFirst time rider
Yes correct
At The Back Of The Pack
Arm chair racerFirst time rider
What size main jet would you say it needed roughly?
Roostin' Away
Arm chair racerRoostin Away
I agree with shortline on the long manifold. We are running the same set up in several trikes and are running a 100 main with either a 30 or 32 pilot. I am also running a 24mm on a bored out 110 with a ported and matched head with a long manifold. Runs flawlessly.Originally Posted by vroomy
90 nickolson Bored and Stroked "The Good"
Big Bore 110 Pauter frame "The Bad"
90 Bored and Stroked “vey’s frame” "The Ugly"
110 JSC frame Bored and Stroked
flat track build. “Shop trike”
1974 original 90 X 2
1974 Original 70.
At The Back Of The Pack
Arm chair racerFirst time rider
Any of you guys have manifold you would be interested in selling?
Power User
Roostin Away
POSA is probably the easiest and best to tune a carb on.
* 1978 ATC 90/180 Pauter PJ1 / Springer "Team BAPP" Bike *
* 1980 ATC 110/180 "Danny's Machine Works" 3D Sprint Dune Bike *
* Nicholson 500 Race Bike *
* HPATC Yamaha RD350 "Big Moe" Trike *
At The Back Of The Pack
Arm chair racerFirst time rider
Whats POSA?
Just Too Addicted
Arm chair racerJust too addicted
POSA is another manufacture of aftermarket parts from back in the day. They made a long aluminum intake with the mounting studs already installed on one side of the intake.
* 1970 US90 Red
* 1978 ATC 90/180 Helm&Son, Bandito /3D springer. ( Spaghetti Winder )
* 1978 ATC 90/128 Bandito / Ace Williams Springer.
* 1980 ATC 110/ ? Helm&Son, Dickson Full Suspended
* 1981 ATC 110 MTC Full Supended
* 1985 ATC 200s
*1986 ATC 250R/310 2"+ Westcoast Swinger
http://www.ebay.com/usr/jwheeler760
At The Back Of The Pack
Arm chair racerFirst time rider
Are you certain you have a genuine mikuni carb. There's a lot out there that are fake. I had a similar issue in the last week with a vm26 on a 110. I was way too small on the pilot. Pilot controls idle circuit to about 1/4 throttle and needle controls 1/4 thru to around 3/4. Main is WOT top end. If youre experiencing issues below 3/4 main won't change a thing. Air screw is also only for idle and 1/4. Pilot jet and needle are your issues. If you have a genuine carb.
Power User
The day begins with 3WW
Here's an image that illustrates what effects where in the carb tuning process.
Here's another site that illustrates it a little differently. Most carbs work under the same basic concept/idea.
http://kawtriple.com/mraxl/carb/mikunicircuit.html
At The Back Of The Pack
Arm chair racerFirst time rider
Thanks for the info. A paid alot for carb and came in mikuni box etc so i hope it is genuine. Its got a 30 pilot, starts easy and idles great. Just seems any adjustments i make just goes bad to worse. Never had such a hard time tuning a bike
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