Stage 3 Dynojet Kit on '81 GS750

[tc80211]

I'm currently on an '81 GS750 and want to switch to pod filters. I have the stock airbox along with stock 4-to-2 exhaust... I was planning on leaving exhaust for now and just doing filters....

My question. Is there another jet kit out there? I pretty much only see the "Dynojet Stage 3 kit"

or should I but the need needles and jets individually? in which case... no clue what size I already have.

Any help would be great. Sorry for re-post if there is already an active thread with this info.

 

[posplayr]

I'm currently on an '81 GS750 and want to switch to pod filters. I have the stock airbox along with stock 4-to-2 exhaust... I was planning on leaving exhaust for now and just doing filters....

My question. Is there another jet kit out there? I pretty much only see the "Dynojet Stage 3 kit"

or should I but the need needles and jets individually? in which case... no clue what size I already have.

Any help would be great. Sorry for re-post if there is already an active thread with this info.

If you plan on doing the exhaust later, wait till then otherwise you will be changing the jetting yet again.

 

[matt1100]

Seems to me it would make alot more sense to wait and do the pipe, pods, and jet kit at the same time. It might be hard to tune and get the performance your looking for without the pipe working with the other components. Balance Grasshoppa

 

[tc80211]

Revisiting this topic... keeping stock exhaust but going pods

Revisiting this topic... keeping stock exhaust but going pods

I like my stock exhaust, but looking to do pods... current jet sizes are as follows:
pilot 42.5
main 112.5
air 170


I assume i would only need to change the pilot and main... what size for pod filters and stock exhaust?

 

[koolaid_kid]

You should never have to change the pilot jets unless it is a totally radical engine. Just buy the Stage 3 kit as it has the Stage 1 kit included. Then install the Stage 1 kit, go through all the excruciating work of tuning the carbs, and hope for the best.
And when you finally realize it is only half done and install the pipe, go through all the excruciating work again.
I run a pipe and pods, and I am not kidding about how much work it is to tune once you change from stock. And you can't run the stock needles once you change; the taper is completely wrong and you cannot adjust them.

 

[tc80211]

Thanks for the info! Maybe I will reconsider at this point. Ha!
Spends my time riding instead of re-tuning...

 

[1_v8_merc]

If this bike is your daily rider, it's not worth it.
If you have like 3 other bikes, then go for it.

 

[JW-GS750E]

I just reworked my 81 750E. When I bought the bike it had a nice kerker header and stock airbox. I added pods and installed a Stage 3 kit. I took it to an expert tuner who explained that not only are the jetting and needle settings critical, but by removing the stock airbox (which is designed for backpressure for the CV carbs) he would have to tune for that aspect too. I know what a pain this process can be with just trying jet after jet, so having an good tuner man is a plus.

 

[Steve]

I took it to an expert tuner who explained that not only are the jetting and needle settings critical, but by removing the stock airbox (which is designed for backpressure for the CV carbs) he would have to tune for that aspect too.

There is no "backpressure" in the airbox, for the CV carbs or anything else.

The biggest thing the airbox does for the carbs (CV-type or any other) is to filter the air and smoothe the airflow.
With different tubes between the airbox and carbs, it won't matter what airbox or what carbs, assuming that both are proper for that size engine.

CV-type carbs do NOT need a restriction on the intake to run properly. Any restriction on the intakes is only to limit air flow to what can be handled by the fuel jets.
If you change to appropriate jets, you can run with velocity stacks, if you want.

It is NOT the vacuum in the airbox or the intake runners (between the carbs and the engine) that lifts the slides.
It is the vacuum caused by air rushing under the slide that causes the vacuum necessary to lift the slides,
so it's air flow velocity, not restrictions, that lifts them.

I know what a pain this process can be with just trying jet after jet, so having an good tuner man is a plus.

Yes, it is, but I don't think that guy is your "good tuner man".

.

 

[posplayr]

I just reworked my 81 750E. When I bought the bike it had a nice kerker header and stock airbox. I added pods and installed a Stage 3 kit. I took it to an expert tuner who explained that not only are the jetting and needle settings critical, but by removing the stock airbox (which is designed for backpressure for the CV carbs) he would have to tune for that aspect too. I know what a pain this process can be with just trying jet after jet, so having an good tuner man is a plus.

Not having heard the conversation, but going from your stated recollections, your tuner is over complicating things. There are many examples of 4:1 and pods conversions, and has been stated here a million times get a jet kit if you plan to undertake this project.

The jet kit have specially tampered needles to account for the increased air flow of pods/4:1 which you can not tune around using the stock needles.

The first step is normally to install the jet kit with the nominal recommendations from the kit or a starting point from someone else's configuration that is similar to yours. There are a whole lot of 16V GS1100E's and alot of 8V GS1000's maybe fewer 16V GS750E's so this should not be a Manhattan Project although I would guess only about 70% of the bikes are "well jetted".

Then get the main jet correct by plugs chops (old school) or Dyno (more expensive) or a WB O2 sensor (my preference). Once that is correct you will probably need to just adjust the needle a couple of time (either up or down) to get it correct. Again a WB O2 is great for getting AFR at part throttle.

AFR background info

http://www.thegsresources.com/_forum/showthread.php?t=164565&highlight=AFR