Power on the main jet

[Guest]

It's running a new 4->2 exhaust (Mac I think), and a stage 3 dyno jet kit.

I've finally had the chance to get the '82 gs650 on the highway to see how it performs when really pulling and it's struggle to get over 55mph.


Isles good, plenty of chunk when running on the needle jet. It appears the main jet isn't the right size or the fuel isn't getting through.

Any tips? New main jet? Bigger or smaller?

[tkent02]

It's running a new 4->2 exhaust (Mac I think), and a stage 3 dyno jet kit.

I've finally had the chance to get the '82 gs650 on the highway to see how it performs when really pulling and it's struggle to get over 55mph.


Isles good, plenty of chunk when running on the needle jet. It appears the main jet isn't the right size or the fuel isn't getting through.

Any tips? New main jet? Bigger or smaller?

Is it rich or is it lean?

Hard to tell from here.

I would guess it's too lean, but I have nothing to go on.

[Steve]

As tkent asks, "rich or lean?"

Are you running a stock airbox or pods?

If you have the stock airbox, you might be running a bit rich with Stage 3.

.

[tom203]

You good some fun ahead of you with this odd K&N dual filter mentioned previously

http://www.thegsresources.com/_forum/showpost.php?p=2020055&postcount=5

At least with individual pods, the carbs don't get any influence from any other carb. With your setup (interconnected intakes) the intake pulse from one carb is doing something to its roommate . With the stock airbox, this "something" is spread over 3 roomies not focused on one.

[Oliverstrother]

yes, its running pods. I'm not sure if its rich or lean. i think thats my main problem.

I'm not sure the intake pulse effect could be this dramatic, there really is very little power on the main jet.

[tkent02]

I'm not sure the intake pulse effect could be this dramatic, there really is very little power on the main jet.

The main jet is the one for high power, full throttle wide open operation. Try a bigger one. See if it's still too lean.

[tom203]

yes, its running pods. I'm not sure if its rich or lean. i think thats my main problem.

Well ,find a nice place, force bike to go at 55mph for 5 minutes, shut off coast to stop,and pull plugs. bring gloves

[tkent02]

If it's lean you may burn valves in five minutes. Put in bigger main jets first.

[Oliverstrother]

any recommendations on how much bigger I should go? they come in increments of 2.5 right? It has 160s right now.

[tkent02]

What size is in it now? I believe 110 is stock? are you running pods or the stock air box?
At which elevation are you mostly riding?

[Oliverstrother]

its running pods, and an aftermarket exhaust. ride around sea level all the time. it has 160s in right now.

[Steve]

any recommendations on how much bigger I should go? they come in increments of 2.5 right? It has 160s right now.

CAUTION, WARNING, BE CAREFUL.

Those 160 jets are NOT the main jets that you need to be changing.

The main jets are the ones in the middle of the float bowl.

Your stock jets are 110. For pods, you might need to add 3-5 sizes. For your pipes, maybe another 1-3 sizes, both of them depend on how freely flowing those items are. That means that you might need anything from 4-8 sizes up from stock, or anything from 120-130.

Along with upping the main jets, you will probably need to shim the needles to raise them.

.

[tkent02]

Steve, he's already got a Dynojet kit in it, but he hasn't mentioned which size jets.

Should have an adjustable needle anyway.

[Steve]

Steve, he's already got a Dynojet kit in it, but he hasn't mentioned which size jets.

Should have an adjustable needle anyway.

True enough, I missed that part.

The 160s are still the pilot air jets, though.

.

[Oliverstrother]

ok, quick update. The bike has been taken to the edge of the freeway. plugs pulled. scrubbed gently with a wire brush and the bike was then thrashed at full throttle for 5mins.

The bike pulls smoothly to aroung 45-50mph, then struggles to get much beyond 55mph. Kinda pulls a little, then retards a little. but very little power to go any further.

Pulled one or two plugs and they look lean.

The Dynojet kit <http://www.dynojet.com/pdf/3310.pdf> comes with two main jets (the one in the centre when the bowl is removed) options (DJ155 and DJ160)

Currently has the DJ160's in it.

As its running lean, I guess I need to enlarge the size of the jet a little.

How much bigger should I go for a first try? 162.5? 165? 167.5? 170?

As its not only running lean, but also not really making any power, I thought try the 170s?

Any advice would be much appreciated.

Ols