GS1000G Jetting for 4 into 1 exhaust

[Guest]

Hi,

New here, so firstly it's great to find such a dedicated site~!
Looking forward to sharing information

I have a 1980 GS1000G with a 4 into 1 system. Runs ok but I have gone with some advice and ordered 42.5 pilot jets and 120 mains in the hope to release some hidden ponies.

Question I have is around shimming the needles (adding washers) to lift the needles slightly. How many washers/shims do I add to each needle? 1 more only or more than that?
IMG_3738.jpg
Thanks!

[Steve]

Welcome, but we are going to need some more details before we can offer any meaningful suggestions.

I am going to have to assume that your stock jets were like the ones we were blessed with here in the USA. 40 pilot, 115 main. There should be NO need to change the pilot. You only need to change jetting when you change airflow. You could run velocity stacks on the intakes and straight pipes on the exhaust, but when the pilot jets are the ones metering the fuel, your throttle butterflies are what is causing reduced airflow. That will not change.

Wide open throttle is another matter. From your picture, it appears that you have a stock airbox. That will minimize jetting changes. The changes required by the 4 into 1 will depend on how much more air it can flow. Without meters to measure that, you can get a decent idea by listening. A quieter exhaust (yours looks decent) will be quieter because it is restricting airflow, so will only need minimal changes in jetting. However, a louder, competition-style exhaust will require larger jets.

Shimming needles is not just adding washers, it is replacing a larger spacer with several thinner washers. When you have the needle apart (don't your needles have more than one slot? ), look for the large nylon spacer at the top. Replace that with a shorter stack of thin washers (might be 3mm washers) to raise the needle. The needle is pushed up by the spring. The only way the needle will sit higher (richer mixture) is to lessen the height of what is above the clip. If you have multiple grooves for the clip, move the clip down (toward the pointy end). With your setup, you might only need to go one notch.

.

[salty_monk]

117.5 Mains. Stock Pilots, raise needle equivalent to about half the spacer. (two clips if it had them - the Canadian ones do).

You only need the bigger pilots with Pod Filters. Even with a K&N inbox I didn't need them . I tried every combination possible at some point, stock airbox & K&N inbox with 4:1 is where I ended up.

[tools99]

I actually haven't had the carbs apart as yet so cannot reply on what size the current jets are.
I will respond back here once I see what's what and also whether I have adjustable needle height..

thank you

[Steve]

I actually haven't had the carbs apart as yet so cannot reply on what size the current jets are.

And yet you ordered replacements? HOPING they are different (larger)?

If you happen to have any more extra money just lying around, I do accept donations.

.

[tools99]

They're only $2 buck each so I won't loose sleep over it. can always give them away to mates anyway. people in my circles always playing with carbs.