cant get engine to idle right

[joweaver88]

Ok so I have been messing around with the throttle cable adjustments for awhile now and just cant seem to get the engine to idle properly. I havent touched the idle air screw since I did the rejet and I am kind of afraid to until I better understand this. Anyway here is the behavior I am seeing...

Engine runs fine, I can turn the throttle all day long and it will happily keep roaring away. And if I have the choke ever so slightly open (like just a couple mm, *very slightly open) it will also idle happily at about 1000 rpm. I can rev it a bit and let it sit there and idle for 20 min, well after the engine is warmed up and ready to go, but the second I close the choke the rest of the way (again only a couple mm) the idle drops to like 700 rpm and just lopes and lopes until about 10 secs later it dies with a very unpleasant "ka chunk!...errr" noise.

I have tried adjusting the throttle cable turnbuckle a million times to no avail... the difference between 700 rpm and 6000 rpm is only like 3 threads so its damn near impossible to get it to idle just a bit higher than 700. The closest I got to 1000 rpm was ~1700 rpm and it would keep idling, but thats a really high idle and isn't right... it should be idling at 1000-1200 rpm tops. Of course I tried readjusting it down just a hairs width but it immediately dropped down to 700 again... there is just not enough play there to fine tune the idle.

This leads me to believe the engine might be running lean at idle, as evidenced by the difference the tiny bit of choke makes... with just a tiny bit more fuel it idles fine.

So what should I do? Should I play with the idle air screw?

I am running a K&N lunchbox filter, vance and hines full exhaust, 150 main jets, 40 pilot jets, 2 washer per needle, and 3 turns out of the idle air screw. According to the rejet spreadsheet the two other people who reported with my setup mentioned that it was perfect but lean at idle... which is exactly what I am seeing. So maybe I should just leave well enough alone and use the choke when idling to compensate?

What would you do?

[HPP8140]

make sure exhaust valves are not tight

[joweaver88]

make sure exhaust valves are not tight

I already checked the valve clearances, all 4 are in spec.

[bombsquad83]

Make sure your idle circuit on your carbs is clean.  Don't be afraid to go out another full turn on the idle mixture screws.  Once you get it so it will run, check your plugs after letting it idle for a few minutes.  If the plug is white, then you are lean on that cylinder.  If it's black, then you are rich.

You might also want to check your carb sync once you get it to run at idle without choke.

[joweaver88]

Make sure your idle circuit on your carbs is clean.  Don't be afraid to go out another full turn on the idle mixture screws.

I cleaned the crap out of the carbs when I rebuilt and rejetted them but I can double check. What specifically should I check?

I also just synced my carbs the other day... almost perfectly synced.

[bombsquad83]

Did you take the mixture screws out completely?  Take them out and clean the passage that goes up into the venturi.  Be careful not to lose the spring, washer or oring that are under the mixture screw. Also clean through the two small air jets in the bottom of the mouth of the carb.  One feeds the pilot (idle) circuit, and one feeds the starter circuit.  Also clean the small fuel jet that is integrated into the bottom of the plastic float.  It sits in the bottom of the bowl and is often clogged.  It will cause the choke circuit to malfunction. 

When I say clean, I mean use carb cleaner jetted through the passages and then compressed air to follow.

[yamahonkawazuki]

Isnt idle speed adjusted down at the carb?!

[The Buddha]

Yea adjust idle speed.
If that fails - try opening the air srcew +1/2 turn out.
Cool.
Buddha.

[bombsquad83]

Yes I missed the obvious because I assumed you did it..  The idle speed is adjusted with the big brass knob that comes out at the bottom of the carb.  It should never be attempted to adjust idle speed by tightening the throttle cable.  In fact, there should be a little play in the throttle cable when properly adjusted.

[joweaver88]

Turn signals still arent working out but at least this is!! Ok yea im an idiot I was getting the mixture screws and the idle adjuster mixed up... yea, these things happen with me. Anyway, I adjusted the idle to just under 1000rpm (like 900-950) and it idles no problem... well it does lope a bit and sound like it might stall, but it never actually does, and you know what I will totally take that happily 

[bombsquad83]

It's supposed to be set to 1100-1300 when fully warmed up.  Does your bike not like to be set any higher?  I've found that mine will idle very low until I ride a couple blocks or so depending on temperature and humidity.  I ride with slight choke until it idles at at least 1100.

[joweaver88]

It's supposed to be set to 1100-1300 when fully warmed up.  Does your bike not like to be set any higher?  I've found that mine will idle very low until I ride a couple blocks or so depending on temperature and humidity.  I ride with slight choke until it idles at at least 1100.

No it will idle at 1100 just fine... I thought stock idle was 900 rpm, if it is 1100 I can set it to that.

[ShowBizWolf]

1100-1300    Mine is like that too sometimes, idling low but after a few blocks it's just fine 

[The Buddha]

I set the idle to 1500 or thereabouts. RPM is for oil pressure - so I dont mind it being a bit more ...
Cool.
Buddha.

[LocalGuyLawnCare]

I had this same problem and its nothing you would think it is. Mine was the petcock, it was getting air and the ratio was never right so replaced it. And she idles great now even on a cold start I don't have to use the choke.

[chettski]

I had this same problem and its nothing you would think it is. Mine was the petcock, it was getting air and the ratio was never right so replaced it. And she idles great now even on a cold start I don't have to use the choke.

What do you mean by "getting air and the ratio was never right?"  Air bubbles? 

I started experiencing this problem after I replaced my fuel lines. I'm seeing bubbles every so often.  I'm new at this so I didn't think much of it.   

[The Buddha]

The petcock has a vacuum side and a fuel side separated by a spring loaded diaphragm. If you get air in the vacuum side it will run like crap. Its about the same as an intake vacuum leak ... I've also had a petcock that will let gas through to the vacuum side. That bike will load up and bog with fuel on 1 carb, but be horribly lean on the other carb cos fuel isn't flowing through the right hose too well.

Cool.
Buddha.

[chettski]

The petcock has a vacuum side and a fuel side separated by a spring loaded diaphragm. If you get air in the vacuum side it will run like crap. Its about the same as an intake vacuum leak ... I've also had a petcock that will let gas through to the vacuum side. That bike will load up and bog with fuel on 1 carb, but be horribly lean on the other carb cos fuel isn't flowing through the right hose too well.

Cool.
Buddha.

Thanks Buddha.

I wonder if I created the problem when I replaced the fuel lines? Is there a way to get the air out of the vacuum side? Does this call for a new petcock and vacuum tubes?

[The Buddha]

The petcock has a vacuum side and a fuel side separated by a spring loaded diaphragm. If you get air in the vacuum side it will run like crap. Its about the same as an intake vacuum leak ... I've also had a petcock that will let gas through to the vacuum side. That bike will load up and bog with fuel on 1 carb, but be horribly lean on the other carb cos fuel isn't flowing through the right hose too well.

Cool.
Buddha.

Thanks Buddha.

I wonder if I created the problem when I replaced the fuel lines? Is there a way to get the air out of the vacuum side? Does this call for a new petcock and vacuum tubes?

Vacuum side - by definition has air - just that it has less air than the outside - unless its a true vacuum. Then it has no air. You dont have a problem because of air on the vacuum side, you may have a problem with gas getting into the vacuum side - not saying you have that problem.

OK you replaced fuel lines - did you connect it/route it right ? pinched or hooked to wrong location ?

Cool.
Buddha.

[The Buddha]

OK Sorry I didn't understand your question cos I didn't re read my post earlier.
There isn't a air bubble on the vacuum side. You're getting a constant inflow - from a tiny pinhole leak. That may or may not be happening in the bike. Just saying that's what I meant.
Cool.
Buddha.