Another annoying jet thread-16v 750

[claygs750e]

I have a 1980 16 valve GS 750 that currently the CV carbs are soaking in dip and will be ready to reassembly tomorrow. So like others I am confused as to what jets to buy. I will have a MAC 4-1 exhaust and APE pods. Currently the jets are 115 mains and 40 pilots. I am really at the end of my budget to spend $100 for the DJ kit so what main jet would be a good starting point? Can I get by with only upgrading the mains only?

After reading many threads it seems like people are saying that the average is to go up approx. 6-7 sizes at 2.5 increments? So that would make my mains at 132.5. That seems a little high when I hear a lot of people with similar setups running at 122.5?

Please help and sorry to keep up the annoying jetting trend, but this is all new to me.

Thanks,
Ned

 

[tom203]

Everything that I've read here indicates that sure you can up main jet sizes, but without the DJ kit, you will have lousy mid range performance- the stock mikuni needle just won't work well with pods.

 

[Steve]

The general "rule of thumb" is to go up 2 to 4 sizes (on the main jet) for a pipe (depending on how restrictive it is) and about 4 to 8 sizes for pods (depending on how restrictive they are).

As mentioned, what makes the DJ kits worth the money is the needles.

At the end of your budget? No problem. Spend about $100 on the DJ kit or several times that on replacing your blown engine.

.

 

[claygs750e]

It looks like from what everybody saying the Dyno jet kit is the way to go. So do I just basically order the stage III kit for my particular model and that's it?

 

[tom203]

Here's a summary- those who have done this will comment, I have no clue and don't plan to find out

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 2
Intended for motorcycles with a stock or mildly tuned engine using a well designed aftermarket pipe with a modified airbox and a stock replacement air filter. Stage 2 kits are designed for applications where individual filters cannot be installed and for applications where airbox modification improves the engine's performance. In most cases power increases of approximately 8% 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

 

[posplayr]

Here's a summary- those who have done this will comment, I have no clue and don't plan to find out

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 2
Intended for motorcycles with a stock or mildly tuned engine using a well designed aftermarket pipe with a modified airbox and a stock replacement air filter. Stage 2 kits are designed for applications where individual filters cannot be installed and for applications where airbox modification improves the engine's performance. In most cases power increases of approximately 8% 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

Pods and a pipe is Stage 3 and yes the problem is that a 4:1 which has exhaust scavenging at high RPM requires a different taper than the stock needle at mid range. You wont be able to get rid of a mid range bobble where the stock pipe is more linear. The 4:1 effectively blocks flow at mid range which requires a leaner needle (physically larger diameter than stock).

I would suggest at least getting the equivalent sized Mikuni main jets as the DJ kit (remember to subtract 10) and live with the mid range issue.

Or find the guys on ebay that have more inexpensive jet kits, and let them customize it.

Or third option is burn your exhaust valves.