Full Throttle Bogging

[Guest]

Hi all,

I recently put K&N pod filters on my 1982 GS 650GL and I have it idling fine and running in the mid range just about good, but when I really step on it in the 3/4 + throttle range it bogs and chugs. If I understand correctly, this has all to do with the main jet. Stock main jet is a 110 and I've tried 112.5 and 115 and all had the same issue. I suspect that I need to go higher, since going back to the stock main jet doesn't really make any sense. So before I buy some more jets, what do you guys think?

Thanks

[chef1366]

That is a needle and main jet issue.
Get a Dynojet kit.

[boingk]

3/4 plus range is mainjet generally.

I don't like the dynojet kits, they're expensive for one and do not allow as fine an adjustment as working with stock jetting. I also don't like the atomisation of the Dynojet mainjets... doesn't seem as good as Mikuni originals.

Anywho, I'd go about 120 or 122.5 on the mains. Try 120 first and see how you go. That's about 12% over stock and about right for a bike with pods. If you have an aftermarket 4-1 exhaust then go 15% over, or about 125, but for now try 120.

People also seem to forget that sizes are meaningless by themselves, and 'one size up' for a given jet becomes increasingly useless the bigger the jet is that you are changing from. I much prefer the 'percentage increase' approach as it works well through numerous makes, bikes and carburettors.

Cheers - boingk

[Carusoat]

Thanks boingk, that's essentially what I was looking for. I am not really a fan of the dynojet kits either, and would like to avoid them if I could. I have stock exhaust, so I'll try the 120's and see how that goes

[blowerbike]

That is a needle and main jet issue.
Get a Dynojet kit.

i will guess to say about 5k to 6k is the problem area....and above.
do as bill said and spend the chump change and be done.
GS vacuum carbs can not be tuned 100% without the needles being changed(shape.. not just being adjustable).
dynojet did not get to where they are today by selling sun par kits.
i am in the US and speak of only US parts and tuning.
i only speak of ahhh 20+ years of experience.

[Mekanix]

To be honest I was skeptical of the DJ kits but after trying to tune it on my own with lots of jets and stock adjustable needles I ended up at the same place the DJ kit did and learned why they made the parts and modifications the way they did.

So yeah its a bit of money but most of the work has been done for you. Its more plug and play than well, guessing and you only have a limited amount of things to try before getting it right.

I learned that the cost of an education, time and experience is greater than the cost of dj kits. Its great for the first time to learn it all but its definitely costly and frustrating if you don't get lucky at first.

On my frankintwin It started off at 117.5 mains, I ended up at 150 just to get some response back.

[ozman]

Hi all,

I recently put K&N pod filters on my 1982 GS 650GL and I have it idling fine and running in the mid range just about good, but when I really step on it in the 3/4 + throttle range it bogs and chugs. If I understand correctly, this has all to do with the main jet. Stock main jet is a 110 and I've tried 112.5 and 115 and all had the same issue. I suspect that I need to go higher, since going back to the stock main jet doesn't really make any sense. So before I buy some more jets, what do you guys think?

Thanks

curious to know if your running the pods dry or are you using the k and n filter oil on them ?

ozman

[Carusoat]

Ozman - nope, they're oiled with the K&N oil

Mekanix - I got the 120's and I'm gonna try those tomorrow, and if that fails I'll go with the dynojet, although i really don't want to but we'll see how it goes. I'm assuming I would go with the stage 3 dynojet even though i have stock pipes?

[Mekanix]

Following the instructions, it will say : if you have stock pipe and a kn filter use xx parts in the kit on xx setting.

Your at a stage 1 with just the filter id assume. Stage 3 would be with filter and pipe.

Upping the mains will help but won't make it perfect.

[Carusoat]

Yeah I put the 120 mains on today, and it's much better, but it has a "flat" spot right around 5k rpm. It will kind of bog, but if I really crank it, she'll fly. So I think I'll have to go with a dynojet at some point, cuz you're right it's close, but not perfect.

Stage 1 it is.

Thanks for all your help

[blowerbike]

st. 3 with no air box...
st. 1 is with air box.

[Mekanix]

st. 3 with no air box...
st. 1 is with air box.

Your right http://www.dynojet.com/jetkits/index.aspx

Stage 1
Intended for motorcycles with a stock engine using the stock airbox, air filter and stock pipe. Stage 1 kits are fully adjustable to allow the use of a well designed aftermarket pipes and stock replacement air filters like K&N. Stage 1 kits are designed to improve throttle response and driveability and in most cases power increases of approximately 5% throughout the entire power range can be achieved.


Stage 3

Intended for motorcycles with stock or mildly tuned engines using a well designed aftermarket pipe and individual air filters. In most cases power increases of 10-15% can be achieved. However driveability may be compromised particularly with short stroke, high rpm motors. On some modern engine and airbox designs, individual filters and proper jetting offer no performance improvement yet compromise driveability, in such cases stage 3 kits are not available.



http://www.dynojet.com/pdf/3310.pdf Only stage 3 available in that list.

DJ kits come with different numbers on the jets. They are not the same numbers as mikuni jets.

120 mikuni is not the same as a 120 dynojet.

[Carusoat]

I ordered a stage 3 today, now the worst part...waiting for the parts to get here

[boingk]

Glad the 120 worked for you up top, sorry about the stock needle though.

I coompletely forgot that the US didn't get notched needles. Down here in Aus all the bikes have adjustable needles as we don't have very stringent smog laws for motorcycles.

Hope the kit gets the bike where you want it.

- boingk

[Carusoat]

So, I got the stage 3 dynojet kit on the bike today and it got rid of the "flat spot" around 5k rpm, but...I'm having trouble getting the bike to not run rich. It wasn't running rich before I put the dynojet kit on, and I followed their instructions so I thought it would be fine but nope. I tried lowering the c-clip on the jet needle to lean it out, which helped but it's still way too rich. Then I tried adjusting the pilot screws and still am having trouble with it being too rich. I'll come back to it tomorrow, but thought I'd see if you guys had any advice. Only thing I can think of is go back to the original needles.