Can't go faster than 80?

[Watcher]

Hello there, first time poster here with a little bit of an issue.

Been riding bikes for over a year now, started on a 1982 Suzuki GS 650 GL.  Didn't quite fit me right, gearing was awful for the highway, and the fuel efficiency left a little to be desired for me.  Got a 1996 GS500 locally a few months ago and tore it down for painting.  Now that it's done and back together I've been riding it around a lot and although I love it as a commuter bike I'm not happy about it's performance when I'm on the expressway.


Here's the issue:

When I am on the expressway in 6th gear around 75-80mph, I can't get the engine to turn over 7000rpm or so.  If I try to open the throttle up more, the bike bogs on me and I lose speed.  It seems to do fine at lower speeds, and I can get the engine to rev up to red-line through 1st and 2nd, but over 60mph or so it won't rev as high and if I open the throttle all the way the RPM seems to hover right around 5-6k and it coughs a lot.  Half throttle I can get the bike to free-rev the whole tachometer.

The previous owner installed a K&N air-filter, and I assumed he didn't re-jet the carbs or re-tune the mix screws and thus was running very lean.  I figured too much throttle = too much air and not enough fuel so it's losing power.  So, I went to the dealer and bought some 130s and when I took the bike apart and opened the carbs up I discovered that there were already 135 mains installed!

So I sprayed some carb cleaner into the lower half of the carbs, closed 'em up, put 'em back in, then thought about the mix screws.  So I did the standard procedure:
Warm bike up, close mix screws, open 1 turn, set idle at 1000rpm, open screws until RPMs don't climb anymore, open an extra half turn, reset idle at ~1200rpm.
Hopped on the bike, felt good around town, merged onto the expressway, topped out at 75-80 in 6th at around 7k.



So it asks the question, what is wrong with the bike?

Is it possible the mix is too rich and I should go down in jet size? (seems counter-intuitive to me but I won't rule it out)
Is it still too lean and should I move up to 140+ mains?
Is my fuel delivery system starving the carbs? (I should mention, the factory petcock is bypassed.  I'm running from the tank's reserve nipple to an in-line on/off through a filter and into the carbs)

Is the little 487cc engine just not powerful enough to haul my overweight butt faster than 80mph? (I haven't weighed myself in quite some time but I'd wager a good guess I'm around 235lbs when I should be 180lbs.  50hp should be sufficient, though.  My 650's 70hp could take me up to 85 no problem...)


I don't have the proper spark-plug wrench or a big enough deep-well socket so I can't pull the plugs to see what they tell me.  I don't get any backfires, pops, gas smell, or any other signs of a engine running with a poor mix.
Valves did look a little white when I painted the headers, which led me to think running lean to begin with, but with 135 mains I'm not sure what to think anymore...




Thanks for any suggestions.


Pics for fun!

[The Antibody]

Well, you have mentioned all the things I would be looking for. Air filter and carbs basically. It's odd that it is only above 60 that there is a problem. What I can say is the bike definately should be able to hit 100+ no problem, so yes the little GS should be able to haul your ass up to that. 

  -Anthony

[Soloratov]

First...that is a VERY nice red...loving that color.

Sounds like you know your way around the bike, so that's good. Also seems like you know what you are doing as far as troubleshooting and adjustments. The bike should certainly get you past 80, but 6th is going to be a bit sluggish in general. Can you rev it up through 5th to say...9-10K? Get it up that high before you hit 6th? By 80, on a naked bike, you are asking a lot of a 500cc motor as far as overcoming wind and still accelerate strong. Either way, yes, you should be able to go faster...just not much, and not quickly...90-100 naked and your weight is probably all it's got. I'm about the same size so I feel your pain.

[fetor56]

It's important to be able to at least look at the plugs.
Perhaps their worn....perhaps their gapped wrong....perhaps the mixture is out................perhaps u want to change them to make sure(maybe to Iridium)

[Watcher]

Thanks for all the quick replies!


Thanks for the compliment on the paint, Soloratov.  It's actually a very dark burnt orange, and it's extremely tricky to photograph.  It's all House of Kolor paint, Tangerine over Galaxy Grey (and it was EXPENSIVE  ).
In direct sun it looks like a bright yellow-orange, indirect sun it looks burnt-orange, in shadow or at night it looks maroon/burgundy, and under fluorescent light it looks red...  I could take a million photographs of it in a thousand different locations in morning-noon-evening-night-indoor light conditions and it'll NEVER look the same or nearly as good as in person!  The pics I posted were taken during overcast weather.
Well worth the price, that House of Kolor paint, as long as you have the skills to air-brush it.

This is more representative of the true color, I think this may have been taken before the clear-coat:




Anyway...

I don't really recall the max RPM in 5th or even 4th.  I'm usually a pretty modest rider, not really flooring it everywhere.  I typically ride the engine no higher than 7-8k around town before I upshift, so I'm usually in 6th by the time I hit the end of the access ramp to the expressway and at appropriate hwy speeds (60ish).
I'll give it a test ASAP and post the results here.  Looks like rain any minute now and the next few days aren't looking dry so it might take me a few days.



I'll agree that the plugs are pretty transparent when it comes to determining engine issues, I'll try to get ahold of the right socket ASAP.  I only have a Std size plug socket at the moment and my biggest deep-well metric socket is a 15mm and it looks like I need a 17 or an 18...


They are NGK plugs, not sure if they're iridium or not.  Either way, what is the gap spec on them?  I'll check it as soon as I can get them out.

[Erika]

It should be able to go past 80 w/out bogging. But why so fast? Are you in a hurry? Still, I would also be annoyed knowing my bike bogs when it shouldn't.

[Wagoneer]

I'm 240lbs, probably 250 with gear, with a naked GS500 and I can cruise comfortably at 140kmh. Albeit, I'm getting pummeled by wind, but I can roll on the throttle and easily bump it up to 150 or 160 in 6th in a hurry. No bogging, no feeling like power is running out (although I'm sure above that it will be). Haven't found top speed yet, but the little twin has surprised me so far. This is with jets (whatever the standard suggested upsize is, I forget), K&N drop in, and full Jardine exhaust.

High speed bogging is usually a perfect example of wrong AFR's. The engine isn't under enough load at lower speed for the bad mix to show.

I'd check the plugs quick before you melt something.

[Watcher]

It should be able to go past 80 w/out bogging. But why so fast? Are you in a hurry?

Clearly you haven't driven in Chicago 

On surface streets everyone does at least 5mph over the speed limit (usually 10 over will get you by comfortably), and the local interstates are like America's Autobahn.  If it says 55mph you do 65 in the slow lane...  As you get closer to the "passing" lane you speed it up to at least 75, and even then many people will be trying to go around you.

Problem is, everyone drives like an ass.  The fast lane is "go fast or GTFO" since people like to ride your ass (especially since people don't know how to use the left lane properly and will "cruise" in it and not move over for faster vehicles), and the "slow" lanes seem to be populated by semi's and idiots so on a bike you have to be in the left two lanes just to be safe.  The price of being there is to go fast.

Hell, just today I hesitated on passing an early 90s Chevy Blazer with bad shocks and a bad steering dampener that was "walking" in it's lane.  I thought the driver would loose control and cross lanes, roll it, or spin out any second!  He was in the middle-left and I was in the left; eventually he wised up, got over, and slowed way down to calm his truck down...

A few days ago I got caught in some heavy rain heading home from work.  I was going 55 in the 55, in the far right lane, and I look in my mirror and a driver is only about a car's length away from my back side.  I gesture to back up a bit, and they get the hint for about 5 miles and do it again.  I repeat with a gesture to kindly f**k off, and they went around.

I can't even tell you the last time I saw a state-trooper on the road.  Certainly they don't patrol the interstate every day, and often times I'll drive for weeks without seeing one.  Problem is, with such a reduced enforcement presence and with so many drivers with such a blatant disregard for speed control ordinances, you can't really do anything about it anymore.
People see a car pulled over on the expressway and they push the pedal down even more.  Why?  He's busy, and there isn't another cop for miles...

If everyone is doing 20 over, how do you pull someone over for speeding?  Hell, you'd be pulled over for going the speed-limit on the grounds of "impeding traffic".

Until the staties start doing mass ticketing with the whole force covering a 10 mile stretch, driving all offenders into an oasis where more officers are waiting just writing tickets, it will remain America's Autobahn and I'll be going with the flow...


So, that being the case, having room to move faster will keep me out of physical trouble.  Not that I'd hold the bike at 100mph, but being able to speed up 10-20mph to pass someone, change a lane, or avoid being merged into would be very welcome.







... Sorry about the tangent 

[Wagoneer]

Sounds a lot like Ontario...

I try to avoid highways here like the plague, but sometimes we just have no other options unless you want to add on 30min to your 2 hr drive. We have people going 100kmh in the left lane thinking they have every right to do so and then we get traffic jams in the right two lanes from people trying to pass and, truckers and other vehicles going 100. If you go on the REAL autobahn in Germany it's like heaven. It's unbelievable how the flow of traffic there can be so smooth with 4 lanes while we get bottle neck traffic jams with 8 lanes. Just shows how far highway etiquette can get you.

[Watcher]

Just shows how far highway etiquette can get you.

So true...

[codajastal]

Pics for fun!

I REALLY like the colour of your bike

[gsJack]

Are you talking about 80 mph indicated or an actual 80 mph, speedo error on GS is 8-10%?  When you bog down at 75-80 mph have you tried dropping to 5th to see if it will go faster?  Redline on stock geared GS is over 100 mph in 4th if it will pull it, power drops off fast after 8500 rpm on a stock GS. Do you have stock 16/39T gearing, might have been modified by PO.  Were you on level ground when bogging down?

I had my 97 GS up to 110 mph indicated once about 11 years ago with 240# me onboard, GS had a big Plexi 2 windshield on it, was in mountains of upstate NY.  Probably about a honest 100 mph.  Made about 4 trips between NE OH and Smoky Mtns back then travelling 70-80 mph indicated and on I-77 south thru WV there was one uphill the GS would just barely hold 80 but would move out easily with a downshift to 5th.

My 97 and 02 GSs have both been stock for the 175k miles I've used them, no carb mods at all.  Here's a list of data from all published road tests of the GSs I've seen:  http://www.gs500.net/gallery/data/500/GS500tests.jpg

[Erika]

Clearly you haven't driven in Chicago 

I guess not. In New York the cops are nazis and really enforce everything, especially towards motorcycles. They hate anything on two wheels for some reason. In fact, we just got pulled over yesterday because our friend had an antique Vincent with old-timey plates. We all asked him, "What? Were we speeding?" Another saying we use when someone is pushing around in a crowd is "What? Are you in a hurry?"

Anyway, that's a groovy color... nice paint job. One thing that has made my bike bog before was a breather tube... the end of it was facing forward and catching a lot of wind back up into the system. I made it face the other way and the symptom went away. Not sure if that 's the case for you, but might be worth looking into.

[bombsquad83]

Sounds like AFR to me.  I would want to rule out compression as well, could be a leaky valve or bad rings.  Past that, you really need to take a look at the plugs and see where you are with the mixture. 

Before you make any more changes to the jetting, I would verify the type of jet needles you have to determine if it's stock or not.  Stock will only have one position for the e-clip, and have 5DH8 stamped on them along with the mikuni symbol.  Also verify that the 135 jets are genuine mikuni; otherwise they could have a different sizing scheme.  Mikuni jets have this symbol stamped on them:


Lastly with the carbs, verify fuel level in the bowls with a clear tube from the drain and the petcock on prime.  The level in the clear tube should reach the level of the float bowl gasket plus or minus 1 mm.  If it's not, then you need to adjust the float height.  Lastly, check for air leaks (spray starting fluid around the seals on all sides of the carbs and see if the rpms change), and make sure the filter is clean. 

What kind of exhaust is that?

[Soloratov]

Clearly you haven't driven in Chicago 

I guess not. In New York the cops are nazis and really enforce everything, especially towards motorcycles. They hate anything on two wheels for some reason.

Really? Where are you riding? I have done some really dumb things...including speeding...20+ over...and never had one even look at me. Granted it wasn't intentionally malicious by any means, just one of those, crap I got caught feelings. I can actually say I don't think anyone I know has ever been stopped by a cop on a bike. That seems odd.

[Slack]

I agree with Erika, it sounds like your carb breather tube may be routed into the wind.  It gives the exact same symptoms your describing.

[Wagoneer]

Good to know someone else uses the helmet hook to carry things! That's how I bring my lunch to work.

[twinrat]

i think you might be lean on your needle.The needle,s in your carbs should have notches in them lift up 2 grooves then try it out .if your needles are to low your main jet will never pass enough fuel even if you went to a 150 main jet.let us know if it improves.

[Watcher]

You know, now that you guys are mentioning it the overflow tube for my carbs is missing.  I have a barb that goes to nothing...
There is a PepBoys right down the road from my work, I'll stop by there on the way back and hook it up if I can.


Speaking if which, weather forecast cleared up so I took the bike out today.  I may have spoke too soon earlier, the highest I can get in any gear is 8k and no matter what gear I'm in I seem to top out at 80.

My boss pulled my plugs, they're iridium and he says they look normal with a slight tendency towards lean.  I trust his opinion, he's been building and racing motorsports longer than I've been alive.
He suggests going up to 140s, I'll be sure to check the breather and needles before hand, though.

I'll also do the outside carb spray test as well.

[Soloratov]

No tube or non-rear facing is a tiny detail, but I can assure you it matters. When I put my bike back together this spring I left the tube off just to test ride...and it ran like crap! It's weird, but that small amount of pressure must make a lot of difference.

Watcher, make sure you spray both side (in and out boots) and around the throttle shaft.