1997 M750 Vertical Cylinder Rich

[greencow]

Got the carbs on the bench, upon closer inspection, looks like the PO fitted a Dynojet needle and spring.  4th groove down from the top.  Definitely not the stock Mikuni needle, this one is tapered, and has more grooves than stock.

Other than that, the needle jet looks pretty good still, maybe slightly ovaled.... Very hard to tell, if it is, it's minuscule.

The choke/enrichment plunger looks in good shape.


Side note, the slide housing o-ring fits a little sloppy.  I used a KL supply kit to refurb these carbs, if that o-ring is ill-fitting, could that cause excess fuel to bypass the needle jet/slide housing?

[Speeddog]

Perhaps, but I've not seen that happen.

Check the rubber tip on the float valve needle.
I had one with a small blister on it, very troublesome.

[koko64]

Fuel tap?  Are you talking about the fuel petcock? 

I replaced the vacuum petcock with a manual one, then capped off the vacuum line to the horizontal cylinder with a rubber nipple.  The only other vacuum line running from the vert cylinder is going to the fuel pump. 

 

[greencow]

So, while I had the carbs on the bench, gave 'em another thorough cleaning.  While I was taking them apart, noticed a LOT of gas on surfaces I wasn't expecting to see it.  Mainly the slide housing, in and around it.  I had drained the carb bowls before taking them off, so that stumped me a bit. 

The only thing that was causing some concern, to me, was the new slide housing o-rings.  Fitment was super sloppy, and the o-ring itself was to large, in diameter.  Threw the old o-rings back on there, just for giggles.

Put about 60 miles on the bike so far, and it's definitely running less rich.  Vertical plug is still a tad to rich, for my tastes, before however, it would foul out with soot after a 15 minute ride.  To the point that I could scrape off a layer of it.

So, dunno for sure if that was problem, as of right now, seems to be.  I changed nothing else since having the carbs off the bike.  Still gonna throw some new needle jets on there, once I get them.  I'll keep you gents updated, thanks for all the input guys! 

[koko64]

 
Those o-rings should be a tight fit so it's good you put the old ones back in. They take a set over time and not all rebuild kits are equal. I leave them be if they look ok, but change most of the others if required. Needle jets should be replaced with Factory Pro needle jets as oem can wear quickly. Look up the Dynojet site for needle position recommendations for your modifications.

[greencow]

So, just to keep this thread updated in case anybody else comes across issues like this. 

Been chasing my tail for over a year with this problem.  After the carb rebuild kit, new needle jets (emulsion tubes), brand new ignition coils from CA cycleworks, etc....  I was still having rich issues, to the point of changing plugs every few hundred miles, or the bike would run like garbage.  Point of note, didn't really have this problem until I did the carb rebuild kit originally. 

Bought the full kit from Litetek, just had the bike out for a spirited ride, and boy does it ever run great.  Time will tell if that was the problem, but seeing as this only started to crop up after using crappy, ill-fitting seals from the first rebuild kit, I'm leaning towards yes.  Pulled hard, felt great all through the powerband, and no more rich puffs of smoke from the exhaust.  Props to Litetek for a solid kit 

[koko64]

Well that seems to back up what I'm seeing. Customers using cheap knock off kits are getting the level of performance they paid for. There are plenty of rebuild kits on ebay of questionable quality at too good to be true prices. Avoid "unbranded" crap.
If oem gaskets and o-rings are in good shape I leave them be. Quality kits from reputable mfrs are pricey, but the only ones worth using. The longevity of oem components is quite remarkable and the needle jet seems to be the main wear item in BDST carbs.
I serviced a dirt bike FCR recently and it was so badly clagged from sitting in old fuel that every jet was blocked and the float bowl was full of blue gel. Disassembly and thorough cleaning both manually and with a sonic bath restored it. Every rubber part was good and stood "proud" of the gasket surface. Incredible quality. The only part replaced was the float needle as I couldnt envisage how to clean it in a timely way without dissolving the rubber tip. I noted how expensive the genuine kit parts were.

[pepeducat]

There is also the phantom O-ring which can interfere with the carburetion.

It is an O-ring internal diameter 5.5mm and toroid of 1.8mm.

[greencow]

Yah, that's the pilot merge cavity o-ring I believe.  Pretty sure that wasn't even included in the first "kit" I put in the carbs.  The Litetek kit comes with a pair.

[greencow]

I'mmmm baaaaaack.  Long story short, bike was still fouling out plugs, not as quick as before, but still worse than when I first bought the SOB.  My last resort was throwing all new jets at it (thought maybe I had reamed them out when cleaning the carbs....maybe?), and a new(used) set of choke plungers.  

Originals were looking    



Bike fired up much faster, gonna throw some new plugs on it and cross the fingers....

**EDIT**

After a couple hundred miles of riding the plugs are finally looking how they should, or at least much better.

That right plug has maybe 200 miles on it, I wire brushed it clean at some point too, still fouled up in no time.

[koko64]

The airbox is drilled and not cut open, correct? 140 main jets? What pilot jets were you using again?