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Discussion in 'Crazy-Awesome almost Dakar racers (950/990cc)' started by sakurama, May 5, 2009.
This Moose Racing prototype windscreen would look totally choice on your bike too, Gregor...
I love this Italians connections
I got me set of stacks in the end of last week. I didn't get to really dig into the box and look at them, until last night. SWEET PETE those are nice looking! Full write-up in progress...
Hope they fit the SM/SE and you get a chance to ride despite the cold. Looking forward to your report.
I have been watching the weather to find a good window to test fit and run the stacks. I have a couple of high torque demand riding applications I specifically want to test them on. It would require the dirt to be soft enough and not frozen slippery-stiff. Getting to run a gear higher in an average drifted corner and sitting on the same steppe of my torque mountain, would be a spiritual revelation to my acc pump diaphragms, throttle stops and fuel economy.
Might have to go to the coast and run on the beach, to get loose enough riding terrain...
I've just stumbled across this thread and I'm impressed! I've had FCR39's on my 950SM for a while and have been steadily working through all the issues you talk about... and the final issue is of course the choke. I wasn't brave enough to try to separate the parts of the carb body, but initially I also went down the route of trying to just add the appropriate parts. I came to the conclusion that it just wasn't going to happen easily enough and changed direction.
I'm 95% finished building an external choke circuit for each carb, controlled with the OE lever and cables. It's turned out a little bigger than it needs to be, but as a first prototype I'm pretty pleased. Best news is it works! I've yet to find the best setting for the air-jet (it's adjustable) and go small enough on the fuel jet (it's currently way too rich!), but I'm close. No pumping of the throttle, one-press starting from cold and a fast idle facility without twiddling with the idle-screws. Yay! Just need a bit more quality-time in the workshop to get the jetting right and make a mounting bracket.
I'll try to get some pictures for you guys the next time I get to go home!!
In the meantime, please tell me where I can buy the 'velocity stacks'. I would really like to try those...
Thanks! I'm impressed you've managed an external choke. I'm flying out tomorrow night for a quick job Monday and I'm going to help Chris do the boring on my set of 39's on Saturday. I'll shoot some photos of the process which will be done manually on the Bridgeport it looks like.
As for the velocity stacks - Chris has a thread in Vendors here. And he finally set up an online store here. He's giving a discount to ADV riders so check his vendor thread to see if there's a code or how that works.
I went from not being too impressed with the FCR's to just loving them. I'm looking forward to doing the fine tuning to get them fully dialed but they've really transformed the bike now. I'm going to try to dig into my 950 engine this weekend and see about pulling a cylinder off so we can check the case bore and what kind of room we have in there. If we can combine these carbs with another 100cc's we'll achieve a level of silliness that would be amazing. That's the sort of thing that would end up making me look into porting. LukasM is responsible for tipping me off on that bike from OZ that's making 122rwhp. Geez, this is how mission creep works.
All right... you said it:
Erm, yes. Stumbled, as in "discovered unexpectedly". Does it mean something else from whence you hail?
I think he means it's a bit like stumbling over a 10' (3m) pile of old magazines. :eek1
So, back in NYC and I've asked Chris to wait on drilling the carbs until I can be there and document the process. It's a bit scary to start drilling into a $1200 set of carbs so if it all goes pear shaped it will be nice to be present. Also, there's going to be time to finally put the bike with it's set of 41's on the dyno and we can finally answer that age old question and knock on the door of popular wisdom - will the 39's make better torque at the expense of top end? Place your bets now folks because later on today you'll have your answer.
But that's not what we're here for right now - today is choke day! Yes today is the day reserved for choking that someone special in your life... er, no. No, today is the day we finally crack the last problem of the FCR's. We hope.
Chris has been working out the idea of how to machine on the 4th axis of the CNC but before you can do that you need to simply test the idea and that's what the Bridgeport is all about. Turns out the passages aren't square which makes it more complicated so the carb has to be shimmed. Here Chris is checking the alignment with an extra long center drill. There's very little meat on the boss so any misalignment and your carb becomes scrap.
Chris measured and ordered several different o-rings and we found one that likes it's new home. Here's the first center drill into the longest passage.
And then it's time to cross your fingers. Actually only I crossed my fingers, Chris had no doubts.
This one blew my mind. Chris brought out the dental mirror to align this passage.
The final passage where the choke will reside.
Then it's time to tap it with a bottoming tap. Done in the Bridgeport to maintain alignment.
And there you have it. The worlds first choked FCR carburetor. All you have to do is remove your seat and reach up inside and pull two small levers and... okay, it will have a cable. We needed to test the function with the choke from the MX carb. It works and all the passages function as they're supposed to. We still need to do some work on the mid plate but this was the lion's share of the work.
Chris will need to make up a dedicated cable to use the handlebar mounted lever and he also needs to make a body housing for the choke plunger. Here's the MX choke and in the background Chris is designing the new choke plunger housing to use with the cables. To test it we'll reuse my old carbs choke cables but they'll need to be cut and resoldered.
So, there's the choke. Chris is an animal. Many have tried but he did it. Hopefully we can finish it this afternoon and put it on the bike to test. Before we do anything though the bike will get strapped down and flogged while wearing the 41s. My guess is about 90% of the folks here with FCR's have gone the 39 route because of the popular wisdom - I know I did. Today we find out if popular wisdom is worth what you pay for it.
Place your bets folks!
Simply awesome work you guys are doing. Keihin says it can't be done, so you find a way to do it cleanly yourselves. Very impressive, very professional.
Sakurama and Co.
It is tiring to say WOW whenever you do stuff. But wow. I think you guys are cool. Top Fecking dollar.
When do you plan to visit Denmark and make my exhaust?
You have to adopt Chris and take him with you to Portland.
It's amazing to watch a machinist that knows what he's doing. Dad has a lathe and milling machine that we use for gunsmithing and a few bike parts. When I move back home I'm going to have to learn how to use those and to weld.
Amazing work guys.
Chris is a rare person in that he he grew up in his fathers garage, then became a mechanical engineer and then a machinist. Typically the three won't agree - theory and reality and practicality - but Chris can see things in a way most can't and that's more valuable than his skill in either individual discipline.
Okay, we ran the bike with the 41's and... Well, I was hoping to hear some guesses. Okay, right after dinner with Gino I'll post the dyno charts. Plus I got my old 950 mill apart. Interesting stuff. Stay tuned.
My Husqvarna TE610 has an FCR41 and it has a choke as well as a hot start button. Am I missing something here or are the twin carbs the difference. I'll go ahead and declare my noobness .
BTW great work very inspiring build.
Yes, you have a different carb. The MX version has a choke. The downdraft does not. Well, it didn't...
I'd say the 41's were better across the board. As long as the stoichiometric ratio was correct I would think that engine would be able to burn any amount of fuel mix efficiently. More fuel, more power. The only way I can think that the 41's would sacrifice anything would be if it dumped so much fuel in at a low RPM that it bogged the engine down.
+2, I'm going with the 41's = more power everywhere