4 stroke has issues starting, and dies after choke is turned off

mark20

Well-Known Member
Joined
Sep 26, 2018
Messages
1,145
Ok. I spent about an hour today trying almost every combination. Turn the air mixture a little, then try to adjust idle. It got to the point where the air mixture screw was all the way in, but my motor wouldn't idle. I got my motor down to very low RPMs where it sounded like it was struggling to run. Do you think the issue would have something to do with my clutch instead of my carb? I don't really know, just throwing an idea out since nothing else will really work.
you have to find the sweet spot, usually its about 2 1/2 turns out (screw the mix all the way in, then turn 2 1/2 turns out) should be good enough to adjust the idle.

also if its the clutch try lifting the bike up, does the rear wheel spin? if so add a bit of oil to the bushing (gold thing in the middle, 2 drops is enough)
if not then mess with it some more.
 


TurboJettaJMo

New Member
Joined
Apr 2, 2020
Messages
10
Above posts are correct, it's no secret. Anyone who's owned a HS 49cc for any amount of time will deal with above issues. I blame it on the ethanol in the fuel. If we had pure gas that carb would hardly ever have any issues, simple and effective design.
The black plastic screw is called a “throttle cable adjustment screw,” as it adjusts the “idle position” of the throttle cable by preventing the throttle arm attached to the butterfly valve from closing all the way. It does not adjust idle, it prevents how open or closed the throttle is when the cable is not under tension. the brass needle screw with the spring on it is called an “idle adjustment screw,” as it literally adjusts the fuel trim at idle. Once you open the throttle this screw does nothing to control air or fuel other than create turbulence. Air intake will be dependent upon vacuum pressure of the intake cycle, fuel intake will be dependent on air intake and atomization characteristics of the diaphragm and bowl. You CAN restrict the fuel flow with this screw, but you likely won’t be able to idle or accelerate if you do as you will starve the engine and it won’t achieve anything close to a 14.7:1 stoichiometric air-fuel ratio and therefore internal combustion will not occur. If you want to adjust the air mix, you turn the lever attached to the OTHER butterfly valve on the carburetor, and close the choke. (ASE certified before anyone gets froggy, i am quite knowledgeable about fuel trim and engine management components. see also: honda gxh50 parts catalog)
Also, I use 100% gas and have nothing but trouble with that exact carburetor. So many issues that the brass idle adjustment screw broke (while not being touched) and the spring sent it down the gutter after needing to be adjusted every ride in oklahoma’s rapidly changing climates and have had to rebuild numerous times due to float/jet sticking and gasket issues and it just not playing nice-nice :(.
 

darwin

Well-Known Member
Joined
May 26, 2008
Messages
3,843
From Honda's own site that black plastic screw is called the throttle stop screw. The brass screw is called the pilot set screw. Those are parts of a carburetor not a gas assist venturi device, capiche?
 

C_Morgan

New Member
Joined
Apr 2, 2020
Messages
6
I'm about to give up. This bike has given me nothing but trouble since I bought it. No matter how I try to adjust, it doesn't idle. It runs now, which is 100% better than before, but lt has proven difficult to ride when it doesn't idle.
 

mark20

Well-Known Member
Joined
Sep 26, 2018
Messages
1,145
I'm about to give up. This bike has given me nothing but trouble since I bought it. No matter how I try to adjust, it doesn't idle. It runs now, which is 100% better than before, but lt has proven difficult to ride when it doesn't idle.
try adding a drop of oil to the bushing (the gold thing near the clutch)
as if its not idling the bushing could be binding

can you show us a video of the bike running? we could help you out a lot better
 

Lowcash

New Member
Joined
Mar 28, 2020
Messages
1
Alright, i've been looking around various threads for the last few days, but still can't find a fix.

I bought a motorized bike last summer from a pawn shop. It worked when I first got it, but had some small issues. I'm young and have never worked on an engine in my life. I didn't realise that the issues were kinda ruining the motor. I just tightened all the bolts and screws and called it fine. Then my bike just wouldn't start so I left it for the winter since I didn't have the time or tools to work on it.

My bike was sitting for a couple months and still wouldn't start. I didn't know what to do and just followed some advice from trusted people to just replace the carb. I bought a new carb and throttle assembly and installed it. After I installed the carb it would start but the belt transmission was smoking, but I just took the cover off and it is fine. Now the bike starts on a closed choke and a little throttle, but tries to run away even after I close the throttle. If I let go of the throttle harshly the engine dies. If I open the choke it dies.

I've seen threads with similar issues, but none with all of mine, and none of the fixes work.
No one I know has any experience with small motors so i'm totally at a loss here.
I had tge same problem sounds like a vacuum leak your carburetor isn't sealed enough.
 

Old Busted Hotness

Active Member
Joined
Jul 2, 2018
Messages
384
Looks like your fuel line is entering the carb thru the bowl drain. That's less than ideal, since the drain isn't regulated by the float. On the other side of the carb you will have a pair of hose barbs: a brass one pointing out and a chrome one pointing down. Connect the fuel line to the brass one.

Also, it looks like your throttle cable is too tight. Bend the bracket just a little to relieve tension on the cable. That will make idle adjustments more effective and consistent.
 

darwin

Well-Known Member
Joined
May 26, 2008
Messages
3,843
Busted is right on that cable housing. Cable housing end needs to be inserted into the cable housing adjustment barrel. Hard to say on the fuel lines w/o a pic of other side of carb. There's 3 lines, drain, overflow and supply line.
 

Wrench

Well-Known Member
Joined
Nov 14, 2018
Messages
1,205
Looks like your fuel line is entering the carb thru the bowl drain. That's less than ideal, since the drain isn't regulated by the float. On the other side of the carb you will have a pair of hose barbs: a brass one pointing out and a chrome one pointing down. Connect the fuel line to the brass one.

Also, it looks like your throttle cable is too tight. Bend the bracket just a little to relieve tension on the cable. That will make idle adjustments more effective and consistent.
Nah, his drain hose is just looped up high. The gas input line is on the other side. In his pic, I don't think he has even hooked up the fuel line yet. But Good eye ya have Old Busted Hottie, drain lines usually don't point up.

Yea I guess one line is a drain line the other line is an over flow line
 

Attachments

Last edited:
Top