Pilot jets work range

[Anonymous]

I just bought a 1981 GS850G, and it runs a little lean on low revs but great above ca 4000. It's got standard airbox and exhaust, but instead of the standard filter there's a K&N. Now, I covered the big air hole in the airbox (there's a big hole towards the lower rear and some smaller holes in the bottom - is that standard?) after which it runs a lot better up until ca 4000, where it just wants to die. My conclusion is that to get the proper mix through the whole rev range, I'll have to rejet the carbs.

But I was thinking maybe I just need to change the pilot jets (and leave the airbox as it was)? Does anyone know how far up the rev range the pilots are at work? Any other tips?

Thanks for a great site!
/Par

 

[Anonymous]

good question..im not sure if the pilot works thru the rev range also, but it seems as if it would..i`d have to say yeah.

 

[Jay B]

Air Holes

Air Holes

The only holes you should have are 2. One on the rear of the air box where the air gets pulled in and one on the bottom where a rubber hose goes through. Other than that the airbox should be pretty much closed up when it's put together properly.

 

[Anonymous]

It's not really a rev range thing. It's more a combination of RPM and throttle plate position. The pilot jets are part of the midrange circuit and would definitely -still- be in play around 4000 RPMs even at WOT, but you'd be transitioning to the mains i'd suspect. If it were me, the first thing I would do is raise the needle jet a notch and see what happens. I'm assuming you are in a lean condition that does -not- clear up above 4000 RPMs. Hope this helps,

Tim

 

[robertbarr]

Here:

http://home.att.net/~robert.barr/tunerange.jpg

I haven't tried posting a link on this new system yet -- I guess we'll see how it works.

RB

 

[Anonymous]

Thanks for the help. I guess I'll make it a winter project after all - right now I just want to ride.

What I've done as a temporary solution is to cover the big airbox hole with an aluminum plate from the inside, and then I drilled 13mm holes in it and tested iteratively until the engine got sufficient air in the high end. It really works, it runs a lot better now.

I got the idea from an old off-road I once saw that had pre-drilled holes in the airbox, and came with rubber plugs for fine-tuning the air mix. If you're not after extra bhps but merely an even and smooth pull, this is a cheap and easy alternative to rejetting. Also, it takes about five minutes to remove the plate, drill a new hole, put it back and test again. Just make sure to wipe off any chips from the drill before putting the plate back in the airbox.
/Par

 

[Jay B]

Air Box

Air Box

I'd love to see what whole your talking about. On my 81 850 GL besides the 2 big cover holes on each end theres only the two I mentioned before.

 

[Jay B]

Lower Rear

Lower Rear

That hole in the lower rear. Is it rectangular? Does it have a s shaped tube comming out of it that is the same size and shape as the hole? ( maybe 1/2 inch wide by about 2 and 1/2 to 3 inch across) If so thats where air is supposed to be comming in but there should be an s shaped intake hose there

 

[Anonymous]

Jay,
it sound like the hole you describe, only there's no s-shaped hose in mine. I didn't know there was supposed to be one. What's that for anyway-to protect from dirt? But yes, that's the hole I partly covered from the inside.

But on the other hand I'm not sure we have the same airbox types. There's an imprint saying "GS1000" on mine (but there's also one saying GS850, so). And I remember thinking when I saw a GL on a picture somewhere that the chrome lids may be a bit smaller than on mine, maybe to make room for the different seat? Looking from the inside of mine, it also has several holes in the bottom, protected by a plate at approx 1/4 inch above them. (It may sound strange but it looks very stock to me.)

But I'll do some serious research, and take some pictures next time I take it off.

/Par