Triumphrat

asphyx9 · 09-25-2005, 02:48 PM

I might be inheriting a set of FCR 39mm Flatslides from a friend who is changing out some carbs on his Duc.

I have a couple of questions about them. They are the downdraft type and I was wondering about fitment onto the Thruxton. Would they work?

Has anyone put together their own set of 2 FCR 39's on your Thrux (not the Southbay kit), and if so what challenges did you encounter. How about jetting specs?

I know SouthBay sells a rack with their own linkage system to be a direct bolt-on for the Thrux. I probably would have to use different throttle cable but I am not entirely sure.

whatisit · 09-27-2005, 04:55 PM

Seems to me you'd have to fabricate some kinda 90 degree intake manifolds to use downdraft carbs. I bet that'doffset any performance gained from the carbs, but the obvious bonus would be that you could have two huge velocity stacks sticking up on either side of the gas tank.
I got mine from southbay, but had considered ebaying a pair & making the linkage & rack mounts. I saw plenty of sets of 4 39's, but never any pairs. My time is more valuable than money lately, so I just skipped it. If you do a pair yourself I'll happily pass along any jet/needle info to get you pointed in the right direction though. -Worth the investment in my opinion, whether it's money or time & frustration.

[ This message was edited by: whatisit on 2005-09-27 14:56 ]

asphyx9 · 09-27-2005, 06:08 PM

Thank you for the response, I knew someone out there had some on their Thrux. I also noticed the price you can get FCR 39mm flats from Ebay. So the downdrafts will probably not work to well. I guess another option would be just to get the regular (side draft?) and get those to work with the Thruxton.

The SouthBay kit is a little high in price, but like you said, how much is your time worth (the SouthBay kits is pretty much Plug and Play right?).

I will research some more and share my findings, and hopefully pictures and performance numbers if I can get a rack of the FCR's on my Thrux.

Thanks for the jetting info as well, I will take you up on that once I get them.

Boulder City ay? I was born and raised in Las Vegas, and lived in Henderson (Green Valley) for about 4 years.

BonnevilleBill · 09-28-2005, 01:23 AM

I have the Southbay kit. 60 min. install and I am slow. They run very well much better than stock at all positions.

Rhinoe · 11-04-2005, 11:19 AM

Bonneville Bill, Have you noticed any change in your MPG since the change?

katanaman · 11-04-2005, 07:15 PM

is 39mm fcr's the appropriate size for this engine? just wondering if maybe 33mm-35mm would be any good as the air velocity would be higher( maybe they are not available) what is the size of the stock cv carbs? i have always been taught that the flat slide and smooth bore carbs flow much more and therefore you go smaller than the equiv cv that would be fitted stock..
does this make any sense? pretty tired right now!!!

1409 · 11-04-2005, 08:00 PM

Stock carbs are 36MM, 3MM is not that much bigger 1/8 inch.

04BB...

cafecarl12 · 11-05-2005, 11:35 AM

I was looking at the southbay kit as well, do you feel any performance gain than the stock carbs?

Pete_Twizz · 11-07-2005, 08:36 AM

Quote:

On 2005-11-04 18:00, 04blackbonnie wrote:
Stock carbs are 36MM, 3MM is not that much bigger 1/8 inch.

04BB...

3mm is not much bigger diameter, but the choke area will be 17% bigger, which is significant.

Pete.

katanaman · 11-11-2005, 08:25 PM

So pete, is this a good idea to go for a carb this size on the thruxton?? it just FEELS to me to be to big a carb for this bike, i am sure the performance would be inhanced by a carb around 33 to 36 mm. any guru's out there have a rule of thumb for this? my experience on old GSX engines and such was bigger was not always better, especialy on the street. drag strip is a differant story...