Walbro 990 carb needle settings and tuning advice

delta_kilo

Senior Member
Messages
122
Likes
0
I just ordered a Walbro 990 carb. I figured I'd ask what the needle setting should be to start tuning from since I doubt they will be right when it arrives in the mail.


Also I have read do a high speed pass and then shut the engine off and check the plug to see if it's a brown paper bag color. I'm guessing that would be the high speed screw but what am I looking for to test the low speed side? On my T-maxx you'd cut off the fuel and try to get the engine to die within 2 or 3 seconds. I'm just guessing but I'm thinking it probably isn't that easy on this.


So need some tuning advice.
 
G

Guest

Guest
The high and low needles work together. When you have good plug color you're golden.

Base settings can be around 1-1 1/4 low and 1 1/4 - 1 1/2 high. That will get her running.
 

delta_kilo

Senior Member
Messages
122
Likes
0
So OK I'll start there. Am I just looking for the blue smoke color coming from the exhaust on full throttle runs? No blue smoke "lean" to much blue smoke "rich" Check the plug color after each pull?

Oh forgot to ask. Do I need to adjust both the low and high needles at the same time or adjust them independently of each other?
 
G

Guest

Guest
Do them independently so you can see the outcome of your change. Don't forget to break it in a bit before you start to tune. Let her stay rich (base settings) during break in.
 

delta_kilo

Senior Member
Messages
122
Likes
0
Ok sounds good. The break in process from what I'm reading is basically let it warm up to temperature idle wise then shut it off cool down and your good to go?
 
G

Guest

Guest
There are many diferent ways. You can do some up to temp idles. You can do some easy laps to get up to temp. They all work. As long as you get that ring sat your ok. Use reg 2 stroke oil for break in. After that you can switch to synthetic.
 

Deluge

Senior Member
Messages
7,914
Likes
7
Location
Tucson, Arizona
delta_kilo said:
So OK I'll start there. Am I just looking for the blue smoke color coming from the exhaust on full throttle runs? No blue smoke "lean" to much blue smoke "rich" Check the plug color after each pull?
You don't need to look at the smoke color. Some oils smoke, some don't, so you can't really tune off of that. The plug color is what's important.

delta_kilo said:
Oh forgot to ask. Do I need to adjust both the low and high needles at the same time or adjust them independently of each other?
I tune the HSN, and once it's set I tune the LSN.

delta_kilo said:
Ok sounds good. The break in process from what I'm reading is basically let it warm up to temperature idle wise then shut it off cool down and your good to go?
Nah. You don't have to baby it. Do some warm up laps and then drive it how you intend to drive it. This is how I break in my engines.
 

Petrolheadz100

Well-Known Member
Messages
243
Likes
5
Here is a guide for most common carbs bud ... you have to reverse the needle marks as the chart says .

View attachment 14160 View attachment 14160
Good info i went eith what zenoah recommended 1 1/4 LS and 1 1/8 HS and it fired right up after five pulls, I was worried because many people were having problems with the 990 not starting or having trouble to start it this actually starts better than my 668 stocker incredible. I wonder why zenoah says the HS needs to be more lean than the LS, never seen that before but I Guess I see how she runs after I finish the breakin
 

Dusty

Well-Known Member
Messages
84
Likes
21
Ok that sounds weird to me . High needle usually open more than low needle . This is what I have on the zenoah g320 and their factory carb is the 1107 .

1528157738879.png
 

Phill

Well-Known Member
Messages
2,042
Likes
75
Location
Yeppoon QLD Au
Good info i went eith what zenoah recommended 1 1/4 LS and 1 1/8 HS and it fired right up after five pulls, I was worried because many people were having problems with the 990 not starting or having trouble to start it this actually starts better than my 668 stocker incredible. I wonder why zenoah says the HS needs to be more lean than the LS, never seen that before but I Guess I see how she runs after I finish the breakin
I thought the same.
When I had mine on I was running 1+1/4 low and 1 + 1/2 high.
It ran Ok once you got it started but no better than my genuine Walbro 668
 

sunoco

Well-Known Member
Messages
170
Likes
31
Good info i went eith what zenoah recommended 1 1/4 LS and 1 1/8 HS and it fired right up after five pulls, I was worried because many people were having problems with the 990 not starting or having trouble to start it this actually starts better than my 668 stocker incredible. I wonder why zenoah says the HS needs to be more lean than the LS, never seen that before but I Guess I see how she runs after I finish the breakin
where did you buy the 990 from? ddm? did it come in a double box? and did the inner box say -- zenoah/ husky group??? I bought one from ddm-- deal of the day- tested it on a car- just on a stand- not running it on the ground.- as for the new needle adjustments- high speed, my guess is that they updated the brass high speed fuel dump.-- thats what you see in the carbs bore- round brass device. shure there are more updates also. - also- the butterfly valve does not have a small notch across the 3 tiny holes in the carbs bore-- this changes Lsn settings also.
 

Petrolheadz100

Well-Known Member
Messages
243
Likes
5
where did you buy the 990 from? ddm? did it come in a double box? and did the inner box say -- zenoah/ husky group??? I bought one from ddm-- deal of the day- tested it on a car- just on a stand- not running it on the ground.- as for the new needle adjustments- high speed, my guess is that they updated the brass high speed fuel dump.-- thats what you see in the carbs bore- round brass device. shure there are more updates also. - also- the butterfly valve does not have a small notch across the 3 tiny holes in the carbs bore-- this changes Lsn settings also.
Yes my 990 bought with my g290 engine, im serious no kidding 3 slow pulls then 2 regular pulls and she fired right up easier than my 668 sunoco, you may have a bad one
 

sunoco

Well-Known Member
Messages
170
Likes
31
and-- i was on walbros computer site several months ago-- checking part #-s looking at exploded diagrams.-- Walbro said-- 990- discontinued.--- sooo- i am guessing the deal of the day 990 from daves is still being made- just updated-- more user friendly.-- more e-z starting? Thats fine with me !!!
 

sunoco

Well-Known Member
Messages
170
Likes
31
Yes my 990 bought with my g290 engine, im serious no kidding 3 slow pulls then 2 regular pulls and she fired right up easier than my 668 sunoco, you may have a bad one
not at all -- nothing amiss at all with the one i bought.-- it runs cleaner than the old style 990.-- that fine with me !!!
 

sunoco

Well-Known Member
Messages
170
Likes
31
thing is-- g290 is a great engine-- 28mm rod on the crank shaft. if you get it to start that easy-- it should start even more easy on an engine with a 30mm stroke-- why? because the engine produces more vacume- and more pressure----- This is a good thing!! i have a long block g-290 in box. unused.-- and have esp -s newest version top end.- i am just waiting for a 3 bearing zenoah crank case & zen 30mm crank to come on sale-- it will be a 30,5 cc engine.
 

Members online

Latest posts

Top