Author Topic: Running rich  (Read 194 times)

Offline Kilted1

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Running rich
« on: August 12, 2018, 04:47:36 PM »
Hi all!  Early this summer I bought a '93 GS with only 3300 miles on it.  Obviously it had been stored for years, with fuel in the tank of course!  But it ticked over nicely with some starting fluid so I went for it knowing I'd have a project rebuilding the carbs and de-rusting the tank as well a thousand other little things.  All this has been done but it's running rich.  I have no power at low RPM, blowing puffs of black sooty smoke out the tailpipe, and the plugs come out covered in dry soot.

When I initially pulled the carbs off, the anti-tamper plugs were already missing telling me that someone had (probably) been there before me.  I didn't think much of it at the time but noted it as interesting.  I've replaced everything in the carbs aside from the floats and slider/diaphragm assembly which are in good shape.  All the O-rings and brass bits are new factory spec.  Everything from the float needle & seat to the choke plungers to the hidden O-rings at the top of the needle tube has either been replaced or thoroughly cleaned and inspected.  The fuel level is just where it should be, at the bowl gasket.

I have the fuel mix screws down to about 1/4 turn out and it's still super rich.  This seems near impossible for a bike that's notoriously lean.  I haven't even looked for vacuum leaks, at this point I'd invite one as that would lean it out.

Can I lower the float level?  If so, how much?

Can I install smaller pilot jets?  If so, what size?

Is it possible someone has drilled the pilot hole in the carb throat to a bigger size?

I just read a thread about a blocked vent tube causing similar issues.  I'll check that but early in the process I had stuck needles and there was fuel coming out the vent tube so I'm pretty sure it's clear.

Any suggestions would be welcomed.  I have managed to put a couple hundred miles on it and it's a great ride.  But I'm just about ready to push this thing in a ditch and walk away!

This forum and the Wiki have been invaluable throughout this process.  I wouldn't be this far without you!

Offline sledge

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Re: Running rich
« Reply #1 on: August 12, 2018, 05:02:10 PM »
If someone who doesn't know what they are doing has been into the carbs.........need I say more  :sad:

If you tell me what country you are in I can tell you what the factory manual states are the correct jet sizes and settings for your year. :thumb:

Offline Kilted1

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Re: Running rich
« Reply #2 on: August 12, 2018, 07:01:57 PM »
I'm in the US.  I could list from memory what jets are currently installed but my memory has been shown to be faulty.  (Was that 27.5, or 37.5?)  :)  I'm fairly confident that it has what it should but a second opinion would certainly be welcome.


Offline Kilted1

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Re: Running rich
« Reply #3 on: August 12, 2018, 11:34:42 PM »
I just had a thought inspired by another thread.  Could it be the choke pungers not sealing?  I've verified that they're moving easily and all the way and everything seems to be okay with them externally.  Internally they're just a flat rubber plate pressing against the end of a tube in the off position.  If it were leaking, it would cause pretty much what I'm seeing.  No?  Opinions?

Offline The Buddha

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Re: Running rich
« Reply #4 on: August 13, 2018, 09:37:01 AM »
Floats are likely high. Likely not sealing, or just adjusted wrong. BTW the float tang will wear and adjust itself high and I find every other year I have to reset mine.

Otherwise, Its pretty hard to get this bike to go rich, of course 45 pilots will do it, but those are impossible to find, and why would anyone even do that.

Cool.
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Offline sledge

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Re: Running rich
« Reply #5 on: August 13, 2018, 05:47:49 PM »
This is what the manual says....

Float height: 14.6mms +/- 1.0mms
Main jet: #122.5
Pilot jet #37.5

Offline Kilted1

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Re: Running rich
« Reply #6 on: August 13, 2018, 10:05:20 PM »
Thanks for the replies, gents!  Guess I need to tear it down again and verify but I'm fairly certain that the pilots are as suggested and the float level is, if anything, at the high end of tolerance which should result in a lean system.  The main jets are either 120 or 140 but again my brain is cooked so I'll verify before tinkering further with the floats.

Does it matter if the pilot jets are vented?  ie: have little holes in the sides?  The ones I took out were vented but the ones that came in my rebuild kit were not.  So I later ordered and installed vented jets in the same size.  I read somewhere that it doesn't matter but I'm no carb expert (obviously).  It didn't seem to make any difference in my case.

Thanks again for your input!

Offline The Buddha

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Re: Running rich
« Reply #7 on: August 13, 2018, 10:09:12 PM »
Vented pilots = 1 size larger. So 37.5 bleeds (vented) = 40 non bleed (correct)
Again someone who did that may also have drilled em or done other stuff.
140 mains - yea That's super rich if the bike is stock, but you'd likely feel that over 1/2 throttle rather than at idle - of course bleed pilots and that and 3+ turn air screws could conspire to do ya.
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Offline Kilted1

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Re: Running rich
« Reply #8 on: August 14, 2018, 03:32:51 AM »
Okay, the jets are what they should be, 37.5 / 122.5 and the in situ fuel level was right at the gasket before I tore her down again.  Couldn't lay my hands on the non-vented jets, I have all the other bits but those weren't in the bag.  Until they turn up I've raised the floats (thus lowering the fuel level) by a couple of millimeters.  I realize it's a hack job but at this point I don't know what else to try.  Yes, I may have to make it up on the main jet by raising the needles a bit.  Somewhere, somehow I will find the right balance!   :icon_eek:

But first I have to put it back together...again.

Offline Sarasi

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Re: Running rich
« Reply #9 on: August 15, 2018, 07:28:17 PM »
Have you looked at the air filter yet? I had a stuff up a while ago where the shop gave me a wrong air filter that was basically tubed halfway in. This lead to my bike losing a lot of power, absolutely blackened spark plugs that got black stuff stuck to them, and real jerky reactions while drowning at full open throttle.

Since running "rich" or lean" is a balance of air and fuel, as far as I know, and I have absolutely zero knowledge of carbs, I'd check the air filter first. Just because that's an easy check and it's nice to be able to rule that out.  :wink:
'02 GS500H ("Duckling")
RVS exhaust system | steel braided front brake line | progressive fork springs | R6 '11 rear shock | adjustable brake & clutch levers | heated grips

Offline Kilted1

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Re: Running rich
« Reply #10 on: August 16, 2018, 02:23:39 AM »
Have you looked at the air filter yet? I had a stuff up a while ago where the shop gave me a wrong air filter that was basically tubed halfway in. This lead to my bike losing a lot of power, absolutely blackened spark plugs that got black stuff stuck to them, and real jerky reactions while drowning at full open throttle.

Since running "rich" or lean" is a balance of air and fuel, as far as I know, and I have absolutely zero knowledge of carbs, I'd check the air filter first. Just because that's an easy check and it's nice to be able to rule that out.  :wink:

Good idea!  I have thought of that though.  The filter looks pretty much pristine, white and can see light through it when held up to the sun.  It may very well be OEM given how few miles are on it.  Also it runs pretty much the same with the air box completely removed, air box on but filter out, or fully assembled.  I should probably pick up a new one just out of principle based on it's likely age.

Offline Kilted1

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Re: Running rich
« Reply #11 on: August 20, 2018, 03:34:31 AM »
Just a quick update.  I replaced the pilot jets with the unvented ones in the same (spec) size and tweaked the floats so the fuel level is about 1mm below the bowl gasket (via clear tube method).  Currently 2 turns on the screws.  It's running awesome now!!!  Lots of low end power that I've never had and all the top end it should as well.  No smoke and no smell.  I still have some final tweaking to do but I can at least ride it.  I seem to have gotten the choke cable wrapped around the clutch cable, so if I turn the bars hard to the side it pulls on the cable, partially engages the choke and sends the idle soaring, and I may have the throttle cable tighter than it needs to be.  Easily managed in both cases.  I'm so tickled I want to take tomorrow off and just ride!