Honda Twins banner

1 - 15 of 15 Posts

·
Registered
Joined
·
582 Posts
Discussion Starter · #1 ·
While I was riding my CL175, I noticed some symptoms that I figured were due to a lean condition. The bike was able to idle really well. however it wasn't able to rev past about 7-8k rpm. It was also weaker on acceleration past 3/4 throttle. Finally, there was some blueing on the pipes. So I read here that I should try moving the clip on the needle down, to richen the mixture at 1/2 - WOT.

The clip was previously in the middle of 5 rungs in the needle. I moved it to the very bottom. Tonight when I started the bike, it did not want to start without some throttle. And it was idling very low, even though I had previously had a pretty steady idle. I adjusted the idle screws which brought it up, but that didn't stop it from eventually dying if left alone. I went for a short ride, and it felt great, except when I coasted a bit and it died.

What I'm wondering is if I can 100% chalk this up to the needle position, and if so, should I go back to the middle rung, or go to the next up? (2/5)
 

·
Registered
Joined
·
4,770 Posts
Carbs a subtle things, a couple of millimeters off in the floats is enough to hole a Piston
Move the needle 1 clip at a time ( there's a reason there's 5 possitions not 3)
The idle circuit enters the carb body at the base of the needle but you should be able to compensate for the needle position with the mixture screw and slide stop
 

·
Registered
Joined
·
3,103 Posts
The needle position has no affect on idle, it basically affects mixture around the 1/2 throttle range. If you need to change the WOT mixture you need to change the main jet, then change the needle to suit half throttle needs. Trying to affect WOT mixture by playing with the needle will just have you chasing your tail.
 

·
Registered
Joined
·
582 Posts
Discussion Starter · #4 ·
Is it safe to blame the change in behavior solely on the needle position change that I made? If so i can try and go back to the original needle position, as it was mostly running well before. I does sound like perhaps I could go up 2 jets sizes on the main, at least?
 

·
Premium Member
Joined
·
24,208 Posts
As mentioned carb are subtle things and as such little changes can make big differences. Do one change at a time and only minor changes when doing so. It takes time and patience plus usually a lot of spark plugs.
 

·
Registered
Joined
·
582 Posts
Discussion Starter · #7 ·
I was using a similar, lower resolution chart before and that's where I deduced that the needle may have needed a change, as the drop off occurred just after 1/2 throttle. Now I am sure my idle is too rich due to blackened and soggy plugs that I pulled last night. Will definitely have to go back out at least one clip. Maybe I can do that and then try a small air screw adjustment to see if it will maintain an idle that way.

Luckily I have only changed one thing at this time. So in theory I can chalk this up to the needle position change. Just wanted to make sure that the problem could be cause by the change I made, to be sure I didn't go down a rabbit hole.
 

·
Registered
Joined
·
8 Posts
easiest way to explain is this - mixture screw and syncing affects idle - needle affect 1/4 to 1/2 throttle up to 3/4ish. WOT is the main jet.

Set valves and cam chain, then points, then timing. Then look at the carbs. If youre good up to 3/4 throttle do plug chops. Basically get some where you got a stretch of road you can do 50+ on. Put new plugs in. Get up to speed and hold your throttle at about 1/2-3/4 Dont fluctuate the throttle between these but pick 1/2 or 3/4. Mark your grip to throttle housing for 1/4, 1/2, 3/4. Ride with the throttle locked in that position for 2-5 mins. With the throttle still in that position hit the kill switch and pull the clutch at the same time. Hold your clutch and throttle until you stop. Pull plugs and check them. Thatll tell you if youre lean or rich. Adjust your needle as needed. Do the same at 3/4-WOT for the main. I personally like to start with my WOT/main first then with that set, adjust my needle for my mid throttle.
 

·
Registered
Joined
·
2 Posts
The needle position has no affect on idle, it basically affects mixture around the 1/2 throttle range. If you need to change the WOT mixture you need to change the main jet, then change the needle to suit half throttle needs. Trying to affect WOT mixture by playing with the needle will just have you chasing your tail.
 

·
Registered
Joined
·
2 Posts
Mike. I’m so glad you touched on this because I’m having a hard time with getting my bike to idle at low rpm (1500rpm). It isles and responds fenomenal when the idle screw is in and it’s at about 3,500 rpm but when I start to drop the rpms with the idle screw it wont idle unless I keep reving it. I was about to play with the needle position until I read your comment. What do you suggest?
 

·
Registered
Joined
·
2,475 Posts
Unless you are tuning a highly modified racing engine "plug chops" are not really needed. Stock jetting will work perfectly on a stock engine if it does not have vacuum leaks and everything else is working as it should.
TOOLS
 

·
Registered
Joined
·
18 Posts
^^ Plug chops refer to the process of testing the richness/ leanness of your air/fuel mix by chopping (killing) the engine while the throttle is at a certain position. This helps you determine a more specific portion of your carb adjustments, as simultaneously adjusting three variables can lead to hair-pulling madness.

At idle you would only be reading plug for air/fuel mixture. Killing the engine while at 1/4 to somewhere between 1/2 and 3/4 you are reading for proper needle position, and then at full open you are chopping (killing) engine to read for whether you have the proper main jet size. A huge part of carb adjusting is learning to separate which throttle position you're having issues with and then adjusting (jets, clip position, etc) from there. It's def an art, and one I'm still learning!
 
1 - 15 of 15 Posts
Top