Query on hanging RPMs/erratic idle

[nuad]

Hi my 12 year old S4 PB1 has this issue that i hope some fellow forumners can advise on.

 

The RPMS are rather erratic, it floats about a little, from 950-1050 rpm at idle.

 

When i close the throttle from the mid throttle position (pulling the clutch in and freewheeling), the Rpms will not go down to the idle speed of 1k, for example from 6k rpm it will descend rather smartly to about 1.6k rpm, hang there and pretty slowly return to 1k, it takes a short blip of the throttle to quickly reset it to 1k rpm.

 

I put it to 1k rpm cos its the lowest end of the recommended idling speed, and research on foreign sites suggest that too high an idle speed causes this, but it did not rectify my issue.

 

Clutch cables and throttle cables seem fine, the carbs have been cleaned rather recently, the engine runs rather smooth so i don't think it could be a carb sync issue, though i cant really rule that out.

 

I tried fiddling with the mixture screws but kinda messed it up, went to a workshop to reset it to stock settings but problem persists.

 

workshop mech says parts of the carbs could be worn and need to be changed, but he was not specific about which parts.

 

I suspect a rich mixture issue at lower ends, maybe i have to change the pilot jet? the exhaust gases have quite a strong petrol smell.

 

any advice appreciated.

[adesmond2]

hi bro.. from what i experience and encounter before..

 

1) carb kanna water -> u have ensure it's not

2) mixture of air & fuel -> a small possibility (maybe you try to check that again?)

3) Check fuel line -> internal might be dirty after long usage

4) carb slider (possible as well, I change mine and it works ok)

5) lastly, carb's part where it "guild" the slider. (have to change the entire carb to get this fix.)

 

Just my 2 cents of comment..

[adesmond2]

double post.. =(

Edited June 6, 2011 by adesmond2

[nuad]

hi bro.. from what i experience and encounter before..

 

1) carb kanna water -> u have ensure it's not

2) mixture of air & fuel -> a small possibility (maybe you try to check that again?)

3) Check fuel line -> internal might be dirty after long usage

4) carb slider (possible as well, I change mine and it works ok)

5) lastly, carb's part where it "guild" the slider. (have to change the entire carb to get this fix.)

 

Just my 2 cents of comment..

 

 

hey thanks, could be the slide sticking, or fuel lines, ill ask mech to check it out, quite scared of fiddling with carbs now.

[adesmond2]

hey thanks, could be the slide sticking, or fuel lines, ill ask mech to check it out, quite scared of fiddling with carbs now.

 

lolx.. what bike you riding?

If KR/SP/TZM, might be needle also.. slowly touch and guide down, see any uneven surface anot..

[CSV]

defintely your carb has issues. check it.

[nuad]

lolx.. what bike you riding?

If KR/SP/TZM, might be needle also.. slowly touch and guide down, see any uneven surface anot..

 

riding a s4 pb1, 4 carbs to touch haha.

[adesmond2]

riding a s4 pb1, 4 carbs to touch haha.

 

that's tiring bro...:giddy::sian:

[MiddleAgedBiker]

Sounds like one or more of the carb diaphragms could be pinched, or might have a hole or tear in it.

 

To check for holes, put the diaphragm against a strong light source.

 

Also check that the slide is not corroded to the point where its sticking to the side of the carb.

[MiddleAgedBiker]

oh yah, also check for manifold leaks. remove the tank and spray carb cleaner around the manifold joints, if the idle changes, you've got a leak.