Air fuel ratio question.

[courier11sec]

So I mentioned this in another thread, but it was not on topic for that one so I thought I'd start a new one.
My bike, (1981 GS850G, 35,000mi) Had pod filters put on it at some point in the past, and I figured they must've jetted for it since the bike has always started and idled well, requiring choke to start and for a minute to warm up before it will run well enough to ride.
The other night, I was in a hurry to get hom and just decided to ride with the choke on. I was rewarded with low end and part throttle power I didn't know this bike was capable of! I'm sure I need to rejet to take full advantage of this, but are there any adjustments I can make to fatten up the fuel curve down low in the mean time?
Would returning to the stock airbox have the same effect as the choke, as in making my deliver smooth useable power in the low rpm range?
I'm tempted to just ride with the choke on, but it idles at 3000RPM and makes me smell like gas, not to mention the high rate of consumption.
Any thoughts are appreciated.
-Ray

[West]

If the bike idles well when warmed up with the choke on, something's not right.

You sure the machine was rejetted?

[Guest]

It's up to you. Do you know the stock jetting for your bike and is that what's in it? Pods will make you run lean with stock jetting and you are doing your bike no good with this mod. You need to find out what's installed for jet sizes and make a decision whether or not to go stock.

[courier11sec]

West, you misunderstand.
I'm saying I don't think the bike was rejetted and that it idles well with the choke off.
With the choke on, it's at 3000RPM.
I suppose I'll have to tear down the carbs and see what's in them, but I suspect it's the stock jetting.

[West]

West, you misunderstand.
I'm saying I don't think the bike was rejetted and that it idles well with the choke off.
With the choke on, it's at 3000RPM.
I suppose I'll have to tear down the carbs and see what's in them, but I suspect it's the stock jetting.

OK. My mistake. So the rev's go up when you choke it. Sounds like it's running lean & perks up when you choke it because it's getting that richer fuel/air ratio. The other behavior indicates a lean mixture also (better power at higher throttle openings with choke on).

My experience (limited) indicates that the leanness of the mixture caused by adding pods/performance exhaust is limited at low revs - I just opened up my airbox and it starts & runs fine at idle also - the real changes in behavior are at the higher airflow speeds/throttle openings.


P.S. "Would returning to the stock airbox have the same effect as the choke, as in making my deliver smooth useable power in the low rpm range?"

Probably. the best thing to do is find out what you have - maybe it WAS rejetted - badly. Or perhaps raising the needles would do what you want, but without the information on what is in there you are shooting in the dark.



I agree with Chef. Before you do anything else you need to find out just what you have in there.

[courier11sec]

Thanks. Will do. I spoke with someone locally about it and they think I'm probably on the right track. They also suggested raising the needles with small washers. I may tear into it tonight and see what's in there.

[courier11sec]

I just went out and pulled the tops off the carbs. Didn't see a way to remove the jets from the top, but on the needles there was a thin washer on the bottom and a thick plastic spacer on top of the e-clip. I swapped places between the two and the bike runs excellent now! Idle is just as before, maybe a touch rich. Power is there from way down low and doesn't go away up top. I'm very happy about this. The only casualty was a long pair of needle nose pliers I had to grind the tips down on to use on the snap ring inside the slide.
WooHoo!

[West]

I just went out and pulled the tops off the carbs. Didn't see a way to remove the jets from the top, but on the needles there was a thin washer on the bottom and a thick plastic spacer on top of the e-clip. I swapped places between the two and the bike runs excellent now! Idle is just as before, maybe a touch rich. Power is there from way down low and doesn't go away up top. I'm very happy about this. The only casualty was a long pair of needle nose pliers I had to grind the tips down on to use on the snap ring inside the slide.
WooHoo!

The jets come out from the bottom.

I don't know your carbs, but that thick plastic 'spacer' is usually what the spring contacts to keep the needle down in the hole, and transmit the spring force through the e-clip to the bottom of the slide.

Is that plastic spacer the same diameter as the slide bore? If so, and your needle is on top of it, then what's keeping the needles down in their holes?

Gravity?

[courier11sec]

Inside the slide, looking down, you see a snap ring holding a plastic bit with four tabs in a disk at the bottom and a long cone coming up the center.
Removing this reveals the needle and allows it to come out of the slide as it is what holds the needle down.
Near the top of the needle is an "e" clip. Above the clip sits a plastic spacer maybe 1/16th of an inch and below is a very thin washer that rides on a spring. I've simply swithed the two.
Have a look at this:

http://www.bigshaftie.fsnet.co.uk/CARBS.gif

the two bits I'm talking about are labeled #7 and #36.

[West]

Inside the slide, looking down, you see a snap ring holding a plastic bit with four tabs in a disk at the bottom and a long cone coming up the center.
Removing this reveals the needle and allows it to come out of the slide as it is what holds the needle down.
Near the top of the needle is an "e" clip. Above the clip sits a plastic spacer maybe 1/16th of an inch and below is a very thin washer that rides on a spring. I've simply swithed the two.
Have a look at this:

http://www.bigshaftie.fsnet.co.uk/CARBS.gif

the two bits I'm talking about are labeled #7 and #36.

I see. A bit different from my BS34's. I remember running across a reference to swapping the washer & spacer somewhere, might have been here (don't think so) while doing research on rejetting. There was no mention of a spring, though.

If it's working for you, more power to you! (double entendre intended)

Richening your mixture a bit is not too dangerous so sounds like it's all good.

Happy riding.