Re-post of I will ask again

[Anonymous]

Ive only had my 1977 GS750 for just over 4 months now and I just stripped the carbys down to clean them and replace the needles and seats.

I noted that the main jets are 125.5 and that the manual states 105 is the largest.

It also has a very large 4-1 transac muffler on it, and the bike has never been on the dyno.

Does anyone know a good jet size to start with? Ive been told by a 57yo ex motorbike racer, that 110 to 115 would be a good starter.

Also it does have the K&N open aftermarket airfilters but I will shortly be changing back to the original airbox and aftermarket (K&N) washable filter!

Any ideas on jet sizes anyone (that hasnt already answered the question)

[SqDancerLynn1]

the original filter was a washable foam If you want to figure it check

http://www.thegsresources.com/_forum/viewtopic.php?t=17814

determining modified jetting

[Dink]

Several points,
1) most forum members are US based and have no idea what a Tranzac is!! BTW Tranzac are a horrid C&N exhaust.
2) yes 125.5 jets are Way to big for a 750 streetbike.
3) I agree that individual pod filters (of any brand) are a bad choice.
4) I believe that your best solution lies in re-installing the plenum chamber only, and using a singlepod in place of the stock air filter casing.
5) IMNSHO you would then install a jet of 105 to 110 size, check float levels, especially that all are set the same, and balance the carbs everytime you change anything.
6) a close look at your points and condensors wouldnt hurt either as a weaker spark will also make a bike appear to be running rich.
Dink

[Detman101]

What the hell?

This is the third time now?

Do you know how to follow up on your previous threads?

You click on them and use the "DOWN" key on your keyboard to see what others have written in response to your questions.

Yeesh,
Dm of mD

[Anonymous]

Several points,
1) most forum members are US based and have no idea what a Tranzac is!! BTW Tranzac are a horrid C&N exhaust.
2) yes 125.5 jets are Way to big for a 750 streetbike.
3) I agree that individual pod filters (of any brand) are a bad choice.
4) I believe that your best solution lies in re-installing the plenum chamber only, and using a singlepod in place of the stock air filter casing.
5) IMNSHO you would then install a jet of 105 to 110 size, check float levels, especially that all are set the same, and balance the carbs everytime you change anything.
6) a close look at your points and condensors wouldnt hurt either as a weaker spark will also make a bike appear to be running rich.
Dink

Thanks for your reply Dink (and wife of Dink)

The statements you have made were forwarded to and have been backed by my retired racer friend, he also suggested jets not larger than 115 for the current config with 4 single K&N airpods and the transac 4-1, and not larger than 110 with the standard airbox and K&N single filter with the 4-1 also..... so far thats 3 good opinions ive had....

The floats were all checked and double checked, also using the special tool that shows the float levels whilst the engine is running. They are all at the correct levels, and are all within .45mm of each other.

I have checked the sparks, new condensors and points as a precaution on Friday, and friday night I rode 350Km to Bundaberg, today I rode 450Km home via the sunshine coast. all up for the exactly 801Km journey the bike consumed 76 litres of fuel, the exhaust has a powdery black over it and the plugs (when I got home and checked) were still powdery black. I will be checking the jet needles in the morning as indicated by KW in another reply.

at least now it will idle and runs nicer, one thing I have noticed though, it seems to flattten off at about 120km/h in 5th gear like its starving for fuel?? its weird, and the plugs still run a powdery black but at least now its not dumping so much out the rear anymore!

After I check the jet needle heights then I wil change the jets and have it synchronised.

Thanks to all that did help for the informative helping hand, to all the rest , ](*,)

[saaz]

What condition is the motor in, in terms of compression etc?

Tranzac is pretty bad. I borrowed a Hanco, a very similar relative, some years ago to use while I repaired my Megacycle pipe. It made less power than standandard, was very restrictive and made the power band very flat as you described.

Getting a decent pipe would make tuning much easier. With the restrictive pipe you might have to go for the larger jets as the motor cannot suck very hard, and with the pods this just makes things worse.

Also, LRP is rubbish, go for premium unleaded. My Gs1000 runs badly with LRP. The GS has hardened valve seats.

[Anonymous]

What condition is the motor in, in terms of compression etc?

Tranzac is pretty bad. I borrowed a Hanco, a very similar relative, some years ago to use while I repaired my Megacycle pipe. It made less power than standandard, was very restrictive and made the power band very flat as you described.

Getting a decent pipe would make tuning much easier. With the restrictive pipe you might have to go for the larger jets as the motor cannot suck very hard, and with the pods this just makes things worse.

Also, LRP is rubbish, go for premium unleaded. My Gs1000 runs badly with LRP. The GS has hardened valve seats.

Saaz, compression is good, (165psi even on all cyls)

Well the transac came fitted already, its a really fre flowing unit though, minimal back pressure. I will look into changing it though!

I dont run ANY of my 6 bikes or 3 cars on LRP.

Both the 1977 GS750 owners and workshop manuals states "gasoline used should be graded 90 octane or higher in research method, preferably unleaded or low lead"

[KEITH KRAUSE]

Dink, why do you say K&N (or any) pod filters are a bad choice?
Do you mean in this particular case or at all times?

[Dink]

Keith my own opinion after years of watching countless people struggle with "performance enhancing" pods, is that they are way more trouble than they are worth.
I base this on a few other things too.
Our GS's are and always were Torque monsters, partially because of the designed in inlet restriction provided by the plenum air cleaner design installed ex-factory. Pods remove this restriction nd reduce lower and midrange torque, Top end horsepower is pretty much useless on a big bore nowadays with ever tightening speeding restrictions etc. So in my opinion the "power increase" offered by pods: mostly top end in my experience, is close to useless as to use it in anything but first gear will very nearly get you shot (this is particularly true in Oz).
The other problem is the often times difficult set up (re-jetting etc) to run them, I know from your posts Keith that yours was relatively trouble free, but as we all can see from many posts on this forum that a lot of other people arent "enjoying" the experience, I believe that the problems often presented by pods and the attendent re-jetting to be far more trouble than than they are worth.
BTW this is my own opinion, and I have no problem with anyone choosing to or not, but if I am asked, my answer is always that they are more trouble than they are worth.
Dink

[saaz]

With a few engine mods pod filters make some sense. I know on mine just the switch from airbox to the oval K&Ns made all the difference in getting the tuning right as tha airbox was just not able to flow the air.

Pods on a standard motor do not make that much sense as the motor is not restricted by the airbox that much.

The main benefit of my overall mods is that it is stronger down low than standard...but the up top improvements can rarely be used...apart from perhaps first gear sometimes!

[Hoomgar]

I can go either way but only because I know someone who can set them up for me. I am afraid that due to the truth in what Dink said if I were left to do all the work myself a stock air box would be on it's way back into my bike.

In our area Dink we don't have the speed issues you do down there and around here it is the opposite of what you describe concerning that. Most guys who own older bikes will gladly give up some low end to gain some top end. It's what we need to keep up with the modern bikes out there. Without it, I have cruisers blowing me away! 8O

[KEITH KRAUSE]

Dink, good reply and I know what you mean.
Actually, my re-jet did not go well at first because I learned the hard way that U.S. '79 GS1000's came with two versions of carbs. The ones built earlier in the '78 season had richer designed pilot circuits. Models built after September '78 came with a modified pilot circuit that closed off one of the passsages to the main bore. This rendered the pilot screw useless. I went nuts trying to jet for this until I looked in there and saw the one tiny hole plugged with a cap. Lesson learned.
I agree that if the owner does'nt have the ability or the patience with jetting, then they should not go with pods. My bike runs much stronger than stock at all rpm's, but I have more mod's than just the filters so I can't say in my case what they contributed to the low/midrange.
I believe they are the most important part you can change to gain power and if you jet right, you'll have no complaints. The advantages far outweigh any negatives.