Too much carb?

Johnny_

Johnny_

Well-Known Member
Local time
2:02 AM
Joined
Jun 22, 2024
Messages
2,692
Location
Born in TEXAS! (Living in MN rn.)
I got the Stihl saw carb on my bike. (090AV). Got the throttle and all hooked up, and finally got the pulse line hooked up as well. I took it for a tuning run today. I got the idle set, and then I ran into issues with the high speed. When it's set so that it accelerates normal, it 4-strokes bad at WOT. When I set it so that it screams at WOT, it won't accelerate at all unless I manipulate the choke all the way up. And THEN it screams. Definitely a speed record I think. (Can't tell exactly cuz the cold goofed up the speedometer.)
Anyways, I'm kinda thinking that may be because the displacement's too small for the carb. Ideas?
 
Johnny_ said:
I got the Stihl saw carb on my bike. (090AV). Got the throttle and all hooked up, and finally got the pulse line hooked up as well. I took it for a tuning run today. I got the idle set, and then I ran into issues with the high speed. When it's set so that it accelerates normal, it 4-strokes bad at WOT. When I set it so that it screams at WOT, it won't accelerate at all unless I manipulate the choke all the way up. And THEN it screams. Definitely a speed record I think. (Can't tell exactly cuz the cold goofed up the speedometer.)
Anyways, I'm kinda thinking that may be because the displacement's too small for the carb. Ideas?
Click to expand...
There are two mixture needles, H & L. How are you tuning each needle? My 090 carb mod runs great on a 66cc/80. Good luck
 
CaveManMechanic said:
There are two mixture needles, H & L. How are you tuning each needle? My 090 carb mod runs great on a 66cc/80. Good luck
Click to expand...
Hey welcome to the forum! Thanks for helping.
Not sure how much I'm turning each needle. I've worked with these carbs a lot and know something's not as it should be. Just to be sure I set the idle silly rich and that didn't help either.
Since it worked for your 66cc/80 it definitely oughta work for mine. How did ya hook up the pulse line? Did you use the PZ19 manifold and just make it work?
Appreciate it!
 
Johnny_ said:
Hey welcome to the forum! Thanks for helping.
Not sure how much I'm turning each needle. I've worked with these carbs a lot and know something's not as it should be. Just to be sure I set the idle silly rich and that didn't help either.
Since it worked for your 66cc/80 it definitely oughta work for mine. How did ya hook up the pulse line? Did you use the PZ19 manifold and just make it work?
Appreciate it!
Click to expand...
Please see my link for photos. Piston port induction. My procedure for new carb install. Caution to gently bottom needles to prevent damage. L 1.0 / H 1.5 turns out. Start engine with full choke. Choke off. Keep bike running & turn idle stop up. Turn L needle in until RPMs rise & back out a 1/4 turn which should establish a decent cold idle in combination with idle stop adjustments. Warm bike up and fine tune L circuit / idle speed. Engine should 4 stroke heavily at higher RPM so turn H needle in until 4-stroking just stops. Just installed a 21mm pumper carb that has better low-end response and similar top end vs the 25 mm 090. External fuel pump works if you don't want to integrate impulse port into intake manifold. Carb will operate on gravity fed fuel, but not to its full potential. Provides a very smooth power band and metering diaphragm design appears to allow carb to work on smaller displacement engines that intended.Good luck


View: https://www.reddit.com/r/motorizedbicycles/comments/1hny6oq/comment/mep3r3m/?context=3
 
CaveManMechanic said:
Please see my link for photos. Piston port induction. My procedure for new carb install. Caution to gently bottom needles to prevent damage. L 1.0 / H 1.5 turns out. Start engine with full choke. Choke off. Keep bike running & turn idle stop up. Turn L needle in until RPMs rise & back out a 1/4 turn which should establish a decent cold idle in combination with idle stop adjustments. Warm bike up and fine tune L circuit / idle speed. Engine should 4 stroke heavily at higher RPM so turn H needle in until 4-stroking just stops. Just installed a 21mm pumper carb that has better low-end response and similar top end vs the 25 mm 090. External fuel pump works if you don't want to integrate impulse port into intake manifold. Carb will operate on gravity fed fuel, but not to its full potential. Provides a very smooth power band and metering diaphragm design appears to allow carb to work on smaller displacement engines that intended.Good luck


View: https://www.reddit.com/r/motorizedbicycles/comments/1hny6oq/comment/mep3r3m/?context=3
Click to expand...

I was gonna put a saw carb on my Avenger, but I got a good trade deal on some parts and got a PZ19 with manifold and I slapped it on. Tuned it and it runs great. I might try a saw carb eventually, maybe on a different engine
 
Johnny_ said:
I got the Stihl saw carb on my bike. (090AV). Got the throttle and all hooked up, and finally got the pulse line hooked up as well. I took it for a tuning run today. I got the idle set, and then I ran into issues with the high speed. When it's set so that it accelerates normal, it 4-strokes bad at WOT. When I set it so that it screams at WOT, it won't accelerate at all unless I manipulate the choke all the way up. And THEN it screams. Definitely a speed record I think. (Can't tell exactly cuz the cold goofed up the speedometer.)
Anyways, I'm kinda thinking that may be because the displacement's too small for the carb. Ideas?
Click to expand...
You have to tune the high circuit with the chain off. Start and warm up the engine and then take the chain off.
 

Similar threads

D
Phantom 85 too much compression
2
Replies
17
Views
627
SilverHeels
SilverHeels
THayne
Super sluggish, exhaust now coming out of carb?
Replies
6
Views
93
Gordy
Gordy
M
Too much Oil ??
2
Replies
11
Views
2K
michael whiteman
M
MinimumVK
Carb clearance, intake length and muffler
2
Replies
17
Views
2K
robe
R
S
Barn Find motorized Bicycle...very old NT carb (i'm guessing)
5 6 7
Replies
64
Views
6K
ShawnTheWeirdo
S
Back
Top