Main Jet size?

[MechMessiah]

I've got an 82 gs650 that I've been trying to get running smoothly and I just wanna make sure I'm heading in the right direction.

The carbs were cleaned (dipped, new rubber, vacuum synced, the whole 9 yards). It's running pretty good right now but there's no top end speed or "pull". All of the carb tuning articles I've been reading say to use a main jet that gives you the strongest pull in 5th gear. How do I know if I need to increase or decrease the jet size?

If it makes any difference I did replace a few jets that had bad threading/drive slots. I replaced them with stock and all the other jets matched the factory recommended sizes. Also, the intake boots and O-rings were replaced as well.

 

[MechMessiah]

How do I know if I need to increase or decrease the jet size?

I'm an idiot. I just remembered reading the plugs is probably the best way to sort this out. No color means too lean, so bigger jet. Wet plug is too rich, so smaller jet. Is that about right?

 

[bobgroger]

Is it stock exhaust and airbox? If so stock size or no more than +1. The BEST way is with an AFR gauge to see what the actual AFR is at full throttle. The days of plug reading are SO 1980's The version that sticks the O2 sensor in the end of the exhaust pipe is less accurate than welding in a sensor bung. I built this one: https://www.14point7.com/products/slc-free
It measures in Lambda instead of AFR but there is a conversion chart. Was $90 with the sensor IIRC and took a couple hours to put togetner. Not the one if you don't have electronics experience though, there are lots of commercial ones available.

 

[Steve]

The days of plug reading are SO 1980's The version that sticks the O2 sensor in the end of the exhaust pipe is less accurate than welding in a sensor bung.

And then what do you do with the bung that is welded in your pipe? :-k

I happen to like the header that is on my bike. I have had it ceramic coated and don't want anything welded in there.

The only option would be to find another header to do that to, but it likely would not flow the same as this one, so it would be a useless exercise.

.

 

[bobgroger]

And then what do you do with the bung that is welded in your pipe? :-k

I happen to like the header that is on my bike. I have had it ceramic coated and don't want anything welded in there.

The only option would be to find another header to do that to, but it likely would not flow the same as this one, so it would be a useless exercise.

.

You put a bunghole plug in it It goes near the end of the collector, if you put it on the inside no one will ever see it. But your choice. It saves a lot of time chasing your tail.

 

[MechMessiah]

Is it stock exhaust and airbox? If so stock size or no more than +1.

Still has the air box and it did have a stock exhaust from a 650L (exhaust for this bike was rusted out) but was just swapped with a Mac 4-1 on Memorial day. I felt no difference in the top end performance between the stock 4-2 and the Mac 4-1. And the jets in the carbs are stock for this bike. 110 if I'm remembering correctly.

As for the sensor idea thanks, but No Thanks. That's just gonna take longer to get the issue sorted out and in the meantime, the bike is still running rough. Plus, that's way more involved than what I can do in the back ally with hand tools. It's also just not my style, I like learning the old school methods.