carb longevity

[sofadriver]

re; my 900SS/SP

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At 18,000 miles, my carbs are showing classic signs of wear. Not exactly a testament to Mikuni quality.

I'll pull them apart this winter for a thorough cleaning but I doubt I'm going to see much improvement and re-building is usually a waste of time and money.

Dropping a grand on Keihins seems the only real solution but I'm wondering about their life expectancy.
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[Howie]

Running rich?  More than likely needle jets are worn.  More of a Ducati problem than a Mikuni problem.  The slides tend to rattle around, causing the jets to wear.  Yep, this does not happen on the flat sides, but you can buy an awful lot of needle jets for the cost of flat sides.  Properly set up flat sides are amazing, the only down side is no choke.

[sofadriver]

you can buy an awful lot of needle jets for the cost of flat sides.

exactly.........it's a big expense to justify when i don't have any experience with them.

[bigiain]

Running rich?  More than likely needle jets are worn.  More of a Ducati problem than a Mikuni problem.  The slides tend to rattle around, causing the jets to wear.  Yep, this does not happen on the flat sides, but you can buy an awful lot of needle jets for the cost of flat sides.  Properly set up flat sides are amazing, the only down side is no choke.

+1

The carbs on my 750 motor were still working fine, with their 4th set of replacement needle jets but no other parts replaced, with over 180k miles on them. I'm pretty sure the slides will _eventually_ wear enough to need replacing, but I threw a belt at 293,000km (~183k miles) and the replacement 900 motor I put in came with carbs (which'd done ~10,000km oir ~6k miles).

18k miles sounds a little early for needle replacement to me, I get between 50,000 and 70,000km (~ 30 - 40k miles) before I feel the need to fit replacements. By 50,000km my fuel economy is starting to drop noticably, and by 70,000km it'll be running rich enough that it'll burble and stutter when cruising on the flat at 80kmh (50mph).

What symptoms do you mean when you say "my carbs are showing classic signs of wear"?

big

[koko64]

 

[motoxmann]

The carbs on my 750 motor were still working fine ... with over 180k miles on them ... I threw a belt at 293,000km (~183k miles)

[PhilB]

My original Mikunis had worn out by 185K and I replaced them.  I tried rebuilding first, but it didn't work.  In addition to worn slides and all that, the mixture screws had corroded and could not be adjusted.  But I think that's a fair life for a set of carbs.  The OP probably just needs needles and maybe a rebuild.

I looked into the flatslides, but my bike is my daily driver, so for me flexibility and rideability take precedence over added performance.  If I was still in SoCal, I might have gone with the flatslides; there I might go for years at a time without using my choke.  But at the time I was working in Cleveland, and have since moved to NH, so having a choke and good cold weather running have suddenly become a lot more important.  I got a lightly used set of OEM Mikunis for $250, out those on, and good to go for another 150K plus.

PhilB

[sofadriver]

running rich enough that it'll burble and stutter when cruising on the flat at 80kmh (50mph).

What symptoms do you mean when you say "my carbs are showing classic signs of wear"?

big

That's exactly what I'm refering to.
It feels like they are out of synch.
I can get them perfectly synched at idle (using a Twin-max and then a water tube manometer). As soon as it comes off idle they read out of synch again (along with the burble and stutter thing) . Also, the mixture screws don't seem to have much effect.

[bigiain]

That's exactly what I'm refering to.
It feels like they are out of synch.
I can get them perfectly synched at idle (using a Twin-max and then a water tube manometer). As soon as it comes off idle they read out of synch again (along with the burble and stutter thing) . Also, the mixture screws don't seem to have much effect.

That'll be your needle jets worn oval then.

You want a pair of these:

http://www.ca-cycleworks.com/products/fuel-carbs/factory-pro-needle-jet

big

[sofadriver]

That'll be your needle jets worn oval then.

You want a pair of these:

http://www.ca-cycleworks.com/products/fuel-carbs/factory-pro-needle-jet

big

Perfect!
Thanks!
What all comes in those kits? (when I click on "description" or "specifications" I get nothing)

[bigiain]

Perfect!
Thanks!
What all comes in those kits? (when I click on "description" or "specifications" I get nothing)

The link above is just a needle jet.

The jetkit:

http://www.ca-cycleworks.com/products/fuel-carbs/factory-pro-titanium-kit-3896

contained (back when I bought one in 1999 or early 2000) from memory: 3 pairs of main jet (135, 137.5 and 140 sizes), two pairs of pilot jets (42.5 and 45), two new needles (with a significantly different taper to the stock ones) and softer springs to match, and a full set of allen head stainless screws to replace the phillips head screws holding the carbs together. And some instructions.

If you've got airbox and/or exhaust mods, it's likely to be worthwhile rejetting when you replace the needle jets... (Don't expect any miraculous power gains from a 750 motor though, you'll probably notice an improvement in fuel economy though, and probably changes to the way it warms up in the morning)

big

[sofadriver]

hmmmm.............3 sets of mains and 2 pilots  .......... doesn't sound like much fun

i think i'll give ca-cycle a call on monday and discuss this a little more

thanks, guys.

[motoxmann]

I recently bought a factory pro jetkit as well. between adjustable floats, adjustable fuel screws, 2 sets of pilots, 3 sets of mains, and 5 positions on the needles; there is PLENTY of adjustability for all types of weather and any type of stock or modified setup on a 750 so long as stock cams are being used