Alternate throttle tube for 660 Skorpion?

[zippy49]

Hi all, I'm looking at fitting an aftermarket throttle tube such as the "Throttle Tamer" from G2. Of course they don't list them for MuZ (or even KTM). Can anyone tell me what other, more common makes/models have compatible throttle tubes? I'm looking to get more leverage off of closed throttle to open those pesky flatslides.

[edfmaniac]

Something is wrong if the stock tube doesn't provide enough leverage for you. It is a very long throw throttle tube which is why a lot of people swap it out. And even though the guy from Topham told you that they can be a little sticky when engine braking, I can guarantee that Mikunis don't require super human force to get them to open. They are very common carburetors and come highly recommended by one of the most respected individuals to participate on this site. I'd take them completely apart, if you haven't already, and have them cleaned in an ultrasonic bath to make sure there isn't any varnish built up on the slides or slide bushings.

Maybe try some new throttle cables? Mine were pretty draggy after 50K miles.

[zippy49]

Unfortunately, none of the 'respected individuals' you reference has answered my questions about this problem. Yeah, there's something wrong all right...zero support from the seller, Vintage Spoke. These carbs are brand new. So now the stock carbs are back on, and the flatsides are for sale. The throttle is completely free and the bike runs quite well, just getting the jetting right at this point.

I have swapped carbs on at least five different Yamaha thumpers, and have never had this problem.

[edfmaniac]

I wouldn't blame Vintage Spoke. They are just a distributor. Didn't you get the contact info for Topham in a different thread. They are the one's that build the carbs and will have the technical expertise that you seek. I still think you ordered the wrong carbs since they were so cheap. Mine came out to just over $900 after shipping and seem to work fine in the garage. I haven't had a chance to drive the bike on the road yet since I'm still recovering from my accident but I'll let you know if I have the same problem you did while engine braking.

[zippy49]

VS got the carbs directly from Kedo, the German distributor. Kedo's website listed them specifically as a replacement of the TKs. They were cheaper partly because I had to make an adapter for the RH side. Mikuni builds the carbs. Topham is the German distributor (and perhaps modifies them similarly), and I did ask their advice...which was also no help at all. As you said, many others have been using this very same carb, so it is hardly the 'wrong' one. No one has been able or willing to tell me what difference there is, if any. And I had never heard of your 'asymmetrical' setup until you posted about it.

This is moot, as the bike is back to stock. It's simply not worth the time, money and effort as I have several other bikes to tinker with. I'll bet you will have similar issues, especially if you are running the stock fuel tank as the mods needed to make the linkage fit do not help the cable alignment. And BTW mine worked fine in the garage, too!

[edfmaniac]

Hmmm. Most of your research is not in the same ball park as my research and personal experience over the last couple of months but I don't really feel like debating it. Just know that if you ever want to get top quality personal service from a Mikuni distributor, you can deal directly with Stephan Topham in Germany. http://www.mikuni-topham.de/englishsite ... glish.html

At least you know you can get 60whp out of a stock set of carbs because I've done it. Good luck!

[edfmaniac]

You had me paranoid about the carb sticking issue so I forced myself to go throw a leg over the bike and run it up and down the farm to market road in front of my house. Jetting is damn close, maybe a tad rich and everything else seems to work as it should. I took it up to redline in 3rd, coasted in gear until the rpms dropped to about 7000 and then opened the throttle back up with no issues at all. If anything, the spring return on the Mikuni's is a little weaker than the stock carbs making for easier throttle input on my bike. Can't wait to get it back to the dyno for fine tuning the jets and needles as well as seeing what gains were made.

[edfmaniac]

For what it's worth, I spoke with Stephen Topham again at Mikuni-Topham in Germany. He did confirm that your carbs are virtually the same as mine aside from the custom jetting, bore size and adapter ring. He recommended raising the idle so that the minimum gap in the slide never gets to the point that it creates enough vacuum to cause a problem. The idle on my bike is set to about 1700rpms anyway so maybe that's why I never noticed the problem you were having.

[zippy49]

Tried raising the idle, didn't help. Got a fresh set of stock carbs on now, just getting the jetting right. I ran it this morning, it still surges a bit at small throttle openings and stalled twice during hard stops. Otherwise, it's roadworthy.

[zippy49]

Update - choke plunger was sticking. Right now the only mods are the 135 MJ and big K&Ns (no airbox). Runs great, all I wanted really. But it has been a two year journey!

[phoenix76rb]

Glad you finally got it sorted, Tom. The frustration evident in your earlier posts eerily echoed my own feelings at various points during various projects in my motorcycling past. Not fun to have to work through those situations!