83 750ES tuning/odd idle

[Guest]

So I have completed tuning for main and needle on my UNi podded 83 750.
If you've been following along I've went through the carbs, done all the suggested cleaning plus some, and replaced everything. The valves are in spec and the carbs sync'ed.

After settling on a 150 mikuni main jet and leaving my needle at 4 my last thing was to try going up with the pilot jet to get some adjustability on the screws. After putting in the 40's I really didn't notice the difference in idle that I was hoping for. If anything I ended up turning out an additional 1/4 turn past 3, which is where I had it set through main jet tuning. 3.5 turns out had smoke coming out the exhaust when rev'ed (too rich). Either I need to go up more on the pilot, and I'm thinking at least two steps, or something else is wrong.

I decided to record what how the idle behaves after a good long flog last night. The temps were in the 90's by the way.

 

[BigD_83]

The surge seems like a vacuum disturbance. It has a somewhat regular rhythm, so that makes me think about the vacuum diaphragm. It could be bringing in too much fuel to #2 carb, causing it to cut out.

Have you checked the petcock to see if it is functioning properly?

 

[Guest]

Yup. Does it whether it’s hooked up or not and there’s no leak.
No vacuum leaks that can be found either.

 

[Guest]

Hi guys. Spring is here and I'm thinking about the GS again. Recently I watched a youtube vid of a guy who used some "extensions" made from pvc pipe to resitrict his pod setup a bit and increase the vacuum/flow on his CV carbs. He also made cuts to make sure the ridge inside his pod's rubber boot wasn't blocking an airjet hole on the carb horn. The PVC pipe basically works like a crude velocity stack. This got me thining about my problems with keeping the bike running at idle. It would make a lot of sense if it's just a matter of too little flow/vauum at the intake which is not allowing the slide to function resulting in a stall which isn't affected by any jetting changes.

On that note, I believe if I really wanted to "fix" it from this perspective, I could get a new set of Mikuni RS flatslides with accelerator pumps instead of vacuum diaphrams. Parts Giant has a set for the 750 but I'm not sure this bike is worth a set of $800 carbs. It's be nice to know what size RS the 750 uses. Pats Giant doesn't give any specs.

As usual, please share what you think or know.

 

[BigD_83]

On that note, I believe if I really wanted to "fix" it from this perspective, I could get a new set of Mikuni RS flatslides with accelerator pumps instead of vacuum diaphrams. Parts Giant has a set for the 750 but I'm not sure this bike is worth a set of $800 carbs. It's be nice to know what size RS the 750 uses. Pats Giant doesn't give any specs.

As usual, please share what you think or know.

Well, the glib answer is buy the carbs, and if they don't work out, get a nice classic muscle bike to complement them...


Maybe one of the race guys will have a real answer for you.

 

[Guest]

Yeh, saw that vid too. Ichiban, I believe? I love the way he pretends to use the most crappy tools LOL. look, in my experience of tuning and jetting a GS850GN to fit pods is that it's an exact science BUT... It's not rocket science... but ... well.... a bit rocket sciencey. I nearly gave up. Carbs off, carbs on, carbs off again. But when you get your rocket firing you will feel NASA (Not a silly ass) A good sonic clean and inspection of parts is a good start and a little gismo for mix is the Gunson Colourtune. If you haven't heard of it, read about it now. Game changer!

 

[Guest]

No his channel is called GoldGuy.

 

[Guest]

Well, the glib answer is buy the carbs, and if they don't work out, get a nice classic muscle bike to complement them...


Maybe one of the race guys will have a real answer for you.

Perhaps your on to something. Only I'm thinking; yank the old 750 out, squeeze a big motor in from something a bit newer. 1200 bandit? GSXR? Oh that's a rabbit hole without an end I think but a fun one.

 

[chuck hahn]

Could be electrical. Bad coil connection, weak connections where the caps plug onto the plug wires, advance governor sticky...sticky weights or weakening springs are just a few things i think of.

 

[Guest]

So this is what I came up with. I found some fittings that I was able to grind out to make a restricter that also will not block the air jet like the uni filters do alone.
Left is after shaping with a burr on a die grinder.

 

[Guest]

unfortunately not much room on the outside two

intial testing at 45 degrees ambient is an engine that will idle around 1500 maybe a tad lower instead of 2k once warmed up.
ill have to do some daytime testing and I’m either going to scrunch the middle two to match the outside filters which doesn’t seem very scientific or find a way to angle the outside two and balance the carbs.

 

[Grimly]

So this is what I came up with. I found some fittings that I was able to grind out to make a restricter that also will not block the air jet like the uni filters do alone. View attachment 62725
Left is after shaping with a burr on a die grinder.

Better Plumbing for a Better Life!

 

[chris]

Hi, in my opinion the RS carbs are well worth the money, just make sure you use APE or KN pods.

 

[Maddevill]

Could be electrical. Bad coil connection, weak connections where the caps plug onto the plug wires, advance governor sticky...sticky weights or weakening springs are just a few things i think of.

I'm also thinking it may be electrical. When it misses it seems sudden like it's momentarily losing spark

Mad

 

[Guest]

I rewired it last winter, completely. Everything checks out electrically, however, I've had similar problems with the computer going bad. But then I can only test that with another box which I dont have.

Anyway, the temporary restrictors I put in between the air filters and the carbs have shown it's a flow problem. Now my top end, which was great before, is bogging on WOT telling me it's time to jet again. I'm guessing I went too rich compensating for the lack of flow at idle.

I'm also contemplating TIGing up an aluminum air box similar to stock to use instead of pods. The ES frame does not have a lot of room around the intake area to play with and my modifications don't fit. Either a new aluminum air box or when I have my restrictors machined from aluminum, I'll make two offset.