Hi,

I got a GS500F, a calif model (meaning with EGR).
The dealer had removed most unnecessary stuff, but I didn't have enough money for a carb setup.

So, aside from getting the EGR removed, I also equipped the bike with a slightly better free flow air filter. Still using stock exhaust.

Now, when I open the throttle past ~90%, the bike loses power, and speed.
Top speed so far is ~105MPH indicated.

What should I do to get those last 10% working?
Re-jet?
Bore out the jets?
Or raise the needle (if possible)?

Thanks!

Check for diaphragm tears and open the gas cap when (before) you're at that last 10. Two things that supposedly can cause that issue.

The carburetor was just checked and cleaned; the dealer checked it when they did the carb cleaning.
I think the bike is running lean. It still has the stock jets.
I also installed a fuel filter in the fuel line, but it supposed to be a high-flow, slightly oversized filter. So, it shouldn't restrict much fuel at all...

Still wouldn't hurt to check the diaphragms, but everything I've read says in line fuel filters cause more trouble than they are worth, you probably want to take it out.could be that you are lean, but that doesn't sound like typical leanness. Try easy fixes first. Try opening the gas cap (could be that it's not venting correctly), then take out the fuel filter. If neither of those fixes it, use the search function, I'm sure this has come up before.

Does this happen all gears or just in 6th, at near top speed?  If it happens in all gears then you may have a partial clog in the main jet(s).  If it only happens on top speed runs then I can't comment as I haven't had my bike that high yet.

Yeah, i notice it in top speed only, perhaps it's there in lower gears too, but i never really go all out on the throttle, save for the highway.
I changed sprockets, put in a 35t in the rear, which essentially feels like it gave me an 'extra gear'. So my 6th, would be a stock 7th gear. In that gear, my top speed is only 80mph on the speedo, and i know it can do more.
it is also very obvious there.
in my 5th gear, the stock 6th gear, top speed exceeds 100mph barely, after a minute of riding or so. I know it can do another 5 to 10mph!

Wind resistance vs engine power? .. 6th is not good choice for accelerating quick, stomp it to 5th and see if you can replicate situ?

This sounds fairly typical, especially with your current sprockets.  Stock, you normally hit top speed in 5th and quicker than you could in 6th.  I would venture a bet that you are lean, though.  These bikes are lean from the factory, and add a higher flow air filter, and possible fuel restriction from the inline filter... leanness is likely.  To diagnose, do a couple plug chops at different throttle positions to find out where in the range it may be lean.

- Bboy

This bike hits top speed in 5th with stock tires, and if you have a taller/bigger tire in the rear maybe even in 4th.
6th wont let you pull the revs you need to get that top speed.
Cool.
Buddha.

I'm not concerned about top speed. I can upshift if need be.
i know in 6th, even with the sprocket change, i should get to at least 90.
the issue is the throttle, problem exists in all gears. I know I'm running lean, and just wondered if I should bore out the main jet, or if i should just buy new main jets?

I'm scared,  when i bore it out, if the jet needle will still fit?

Btw, the fuel filter shouldn't reduce the fuel flow a lot at all!
I've made sure to get a high flow filter on my bike, that possibly can be used for an engine 3x it's size:

http://www.amazon.com/gp/aw/d/B000C9WJ8K

I'm actually contemplating on installing a vaccum pump, wonder if it could compensate for the loss of throttle at Wot?

Just install a stock/champion/hiflo air filter, or order a jet kit from Buddha and be done with it already!

^This

Have you checked your float heights? I've had this same problem for quite some time due to low fuel levels in my float bowls. WOT feels okay for a second, until the bowls get low then it bogs out. Does that sound similar?

Quote from: MeeLee on December 08, 2014, 10:40:30 PM
I'm not concerned about top speed. I can upshift if need be.
i know in 6th, even with the sprocket change, i should get to at least 90.
the issue is the throttle, problem exists in all gears. I know I'm running lean, and just wondered if I should bore out the main jet, or if i should just buy new main jets?

I'm scared,  when i bore it out, if the jet needle will still fit?

Btw, the fuel filter shouldn't reduce the fuel flow a lot at all!
I've made sure to get a high flow filter on my bike, that possibly can be used for an engine 3x it's size:

http://www.amazon.com/gp/aw/d/B000C9WJ8K

I have tried boring the main jet. Its not possible to do it right. Needle will fit, the needle barely enters the main jet, and why wont it enter a slightly larger hole.

But just so you're clear, you're trying to open a 1.30 mm hole to a 1.325 mm hole in a jet that is round and only about 6mm diameter. I actually experimented drilling a 122.5 to a 125 on an 8mm, and miserably failed. You can drill a pilot a lot easier, but there you're opening a .175 to .2 mm (17.5 to 20)

Given that a set of jets cut to the right size is $8 or so, I wont ever try it even in my rat bike.
Anyway you are likely lean, but a diaphragm leak - for it to come in @ 90% throttle, I would really really expect the leak to be far far far too small to ever even be able to see. A tiny rip, the smallest you can see in 1 diaphragm will get the bike not making over 60-70% throttle. Its worth checking out, but I really really doubt it.
You could try a 80% throttle plug pull, but it will be dangerous - you get it to 80% throttle in 6th gear and hold speed for 5-10 sec, then without shutting the throttle hit the kil lswitch, pull the clutch in and pull off the road. Then remove the plugs and check em, and wait a few mins before pulling the plug, time wont affect the reading, it will keep you from burning yourself. So please be careful all around.

Cool.
Buddha.

My first project will be to raise the jet needle.
i read online my issue is common with more freeflow air filters, and also would compensate for the loss in acceleration between 5 and 6k rpm (according to what i read).

My issue is definitely from taking away the EGR and installing a less restrictive air filter.
The removal of EGR caused the bike to run leaner overall.

the stock airfilter becomes restrictive at higher than 7k RPM, and the new airfilter works just as good as the stock one below 7k rpm, but above 7k, or open throttle allows better airflow.
That's why the bike loses power at high rpm, because the A/F balance is off at higher rpms and throttle opening.
the current filter seems way less restrictive than the stock one (was only $12 at amazon).
Probably very similar to a k&n freeflow or ram airfilter/intake.

If raising the needle won't work, I'll have to rejet.

Float bowls are ok. Diaphragms are ok.

/Rant
No, no, no, just no.
What you're referring to as EGR might be the PAIR system, I think, and that practically pumps clean air into the exhaust, has no effect on being lean or not.
A less restrictive air filter is less restrictive at any given RPM. It's lean at WFO because that's where it's always been lean, and now it's TOO lean to work alright.
Raising the needle might be necessary, but not for full throttle operation.
Thats's what rejet is for, duh. Even I know that.
/Rant over

I have to disagreewith that.

The stock air filter is good for low rpms, but is restrictive at higher. you know by unscrewing the filter, and lifting it gently 1/2 in out of the box. When revving you can feel the filter get sucked in the box too much.
The filter i bought has much better breathing, and is much less restrictive, even at higher rpm,
it doesn't get sucked towards the box as much.

What? ... I recognise the reasoning. ... but what!? ...

How much airflow restriction produces how much suction back into the box. . Ok yes that would occur. .. also would occur with any vehicle with different cfm filter rates! ...

The jump from that to the reasoning of 'its too restrictive for the bike' ... is the what?!

Go on amazon, buy the $12 filter, and see for yourself.
i wonder if Suzuki purposely got those stock air filters,
no bike I've ever owned had this much back pressure due to a restrictive filter.
and yes, it was a clean stock filter vs an aftermarket one.