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Discussion Starter · #1 · (Edited)
i know this has been discussed in the past, and for a while i just ended up keeping the stock CVK carbs, but now i have the bug again and want a little more power and am thinking about some new carbs.

aside from the carbs i really have no intention (at this time or the near future) of installing a big bore, but may throw in some hotter cams at some point.

with that said i am still unsure of what carbs i want to go with. off the bat i will say mikuni's are out of the question. just too expensive. FCR's look nice, but i don't like that they don't have a choke (i am in san diego now, but go to colorado often), and in my opinion (and prove me if i am wrong) but for an 865 engine (no big bore kit) and no headwork the FCR's seem to be a bit overkill, plus from what i hear i don't like having to roll the throttle on the FCR's because if you whack the FCR's the bike will supposedly hesitate. FCR's are around $900. i am also thinking my mileage will suffer a bit with the FCR's more so than the CR's, which is a consideration since i also use the bike as a commuter, ride from san diego to LA, run errands with it, but also love to take it in the twisties and wring it out too! (i ride my bike like it's stolen and consistently get 42mpg.)

i am leaning toward the CR's just because it seems like a nice set up for what i have: stock motor, billet intake manifolds, air box and AI removed, predators, nology coil and wires, iridium plugs and stiffer clutch springs already installed (my clutch started slipping once i moved to san diego from denver and got the bike dialed in here at sea level. it obviously pulls way harder here than it did at altitude). plus the CR's seem like the best as far as a cost-effective alternative to the FCR's because i already have the billet intake manifolds, so if i bought the CR's it would cost me around $579.00. i am also guessing that the CR's are easier to tune than the FCR's (i am a noob but not afraid to tinker and have done all the work on my bike myself). i also wouldn't mind throwing in a set of hotter cams eventually. the one thing i dont really like about the CR's is the stiffer throttle but that's because it's a direct linkage compared to the vacuum design of the CVK's. i have been told the FCR's are easy and smooth because they work of of ball barings.

my other question is what makes the FCR's bog down so much when the throttle is whacked? would headwork correct this allowing more flow? is it worth doing headwork if i dont plan on doing a big bore kit ever?

so as far as a timeline, this is my plan:
new carbs now, then eventually hotter cams, then further down the line possibly headwork (if it's worth it?). just dont have any interest in a big bore kit because i dont want to get into spending that much additional $$$.

i don't have any visions of making this bike superfast and am not going to sink a ton of money into it like some people have done (nothing against it, i just have other hobbies too that cost money!) but want to get the most out of this bike with the resources i have!

so if you were in my shoes and had the options i listed what would you do? what are your recommendations and suggestions? i know a lot of people on here are totally against the CR's and think they are garbage, and the general consensus here is the FCR's seem to be the carb of choice, but i also know there is a collective here that loves their CR's and have heard these will pull pretty hard too!

also, i know the FCR's are equipped with a TPS (throttle position sensor) just like the CVK's, and the CR's dont have the TPS, which has to do with the timing, but have also read that it really makes no difference with not having it on the CR's. any thoughts?

here's a pic of my bike so far:



 

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I love the 42s but if I couldnt have them ,I would buy the 39s.For the little money more the the 39s cost you get alot more carb.The 35s at best are just alittle better then stock.they have have a smaller bore then stock but they dont have the butter fly so they flow just alittle more.The 39s flow way more.Even with these motors bone stock they like all the flow they can get.The 4 valve head is way better then the carbs they put on them.If you go to better cams they even flow better and need more carb.As far as cams go tpusa 813 is the way to go ,dont buy some of the other peoples out of date after market cams.
As far as the tps ,It dont mater much ,with the right timing at wot the bike dont know its there with flat slide carbs that work as they should.
 

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Well this is interesting to me, because over the last few days I've started about thinking carbs.

From what I have read, if I had to choose today, I would go with the FCR39s. This is based on a bit of cost / performance juggling. It would allow further expansion of the motor if I really wanted to do that, but would save a bit over the 42s.

As for the bogging down - I suspect that has to be a setup thing. From what Bonnie1000th is saying, he has to be careful to roll the throttle not because it will bog down - quite the opposite, it will lift the front wheel (he has a BIG bore kit and all that as well - but the carbs are not holding it back).

Your comment about the choke concerns me though. I'll have to look into that more.

Since I haven't done it that's all I can offer, but I shall be earmarking this thread and watching it with interest.

I guess it would be very good to hear from people with each of the different set ups, and know what problems they had in set up (if any), how the bikes start and run and so on.

Maybe instead of trying to buy another bike this year I should find another motor and build a mega machine. :confused:

So many projects, so little cash. :D
 

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am leaning towards the FCR's

sbpark,

Sounds like we are at the same point in the decision point curve. In the mod life cycle of my Thrux I am at the point where I am now seriously looking at bigger carbs. I may likely consider a new cam and perhaps some headwork in the future but am unlikely to go much further than that. I have read all the debates regarding the FCR's and Mikuni's on this forum. I have a Mikuni on my FXD back in Oz and it was a huge improvement to the performance so I certainly believe in what they can do. However it is a pricey set up for the 865 so I am leaning towards the FCRs. Up here in NorCal, the temp range is variable over the year so I also had initial concerns over the lack of a choke. From what I have read and discussed with people, the lack of choke has not been a problem. The local Triumph dealers indicate they would charge me a little more for servicing with FCRs however the only work that I would ever get them to do on my Thrux is the valves clearances. A deciding factor for me is the fact that the FCRs would arrive "tuned" out of the box for my setup so its a bolt on and go solution. Therefore I am leaning towards the FCR's as the CR's, which a quality set up, don't seem to give as much bang for the buck as the FCR's.
 

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If i had it to do over i would buy the 42s again ,I think there the best they do cost more though .If you buy the 39s you better buy them from someone that knows how to set them up,not some guy that leaves you in the dark once you get them.
Here is what you guys need to look at if you plan on spending money on carbs,once you buy them they will never be worth the money you pay for them so buy the best you can once because you will spend more later if you are not happy with them .Good carbs will out last your bike so only buy them once.$300.00 on any kind of hp mod is cheap compared to most mods.Carbs are the limit on how good your motor can flow and how much hp it will ever make.Once you get good carbs and see how much more fun these bikes are to ride with hp you will be looking for more,dont say you wont ,I know I been there.These things are way more fun then sport bikes when you get them making some real hp .There like your rideing a beast.Sport bikes come on smooth at high rpms these things put the power on right now and in your face.
 

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That's some good advice. My garage is full of parts I purchased because based on a cost-performance compromise some of which failed to fulfil their role to my expectations and I have then upgraded at a later date. A question, if I was to approach the HP pursuit in an incremental manner (ie as fund became available) in your opinion, what is the logical order for a 865 motor? My guess would be carbs, displacement, headwork, cams?
 

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that sounds like a good order only if you do a big bore kit and head work do them at the same time you will save maybe$150.00 on gaskets that way.You can do cams before or after the only extra would be maybe valve shims that way I dont know what pipes you have but you need some god ones to.,as well as air box kit.
 

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Discussion Starter · #9 · (Edited)
i appreciate everyone's advice but some people may not have read my initial post all the way through.

to restate, i do not care how great the mikuni's are. i cannot afford them, and didn't want to waste any time with this thread turning into a [email protected] measuring contest between mikuni's and FCR's. i've read those threads and am trying to avid recreating those threads and was looking for a comparison based on MY particular wants and needs for the bike. i'm looking for advice based on what i am trying to accomplish.

the reason i tried to be so detailed and thorough is because yes we know the mikuni's and FCR's are top of the line, since i am not planning on going huge (big bore, stroker kit) i wasn't sure if it was overkill to throw on FCR's on a stock engine and didn't think it would do it justice.

i was just trying to match the right carb to the application (not trying to take the cheapest way out, but still trying to stay within my budget, and have nothing against the FCR's, but posted because i don't know a lot about them), and would like advice on which carb is better for MY application, so i tried to include factors like: riding the bike in colder climates, using the bike as a commuter as well as a toy to wring out tin the twisties, NEVER going to do a big bore, may drop in cams at some point, and lastly MAY consider doing headwork, but that is probably not gonna happen. i even mentioned that i have no visions of turning the bike into one of these super high horsepower (well, high HP for our bikes, so it's a relative term!) bikes where you end up spending a ton of cash and also have to update breaks, clutch, etc. like i said i am not against doing it, but i have too many other hobbies and need to share the wealth between them! i just want to say, get to 70-72 HP at the rear wheel (at 63 hp now, possibly a touch more since the bike was last dyno's in denver and i am now at sea level), and thought that carbs and cams would accomplish that, or carbs and headwork with stock cams?

so in conclusion, how many of you have the FCR's on a stock motor? (this means no headwork, no cams, no big bore kit)? how well do they stay in tune once you get them dialed? are they finicky? how long did it take you to get them dialed? (i'm not looking for something that is needy and always needs tinkering once i get it fairly dialed, but don't have anything against performing routine maintenance, or have something that will let me down when i am ready to go to work. (i mention this because i have heard once you get the CR's dialed they are solid.) how is your mileage now? how are your starts on a colder morning (are you constantly out there messing with the throttle to keep her going until she warms up or can you walk away once she turns over?) even on a cool day i have to use the choke with the stock CVK's even if it's just for a few seconds because it wont turn over with the choke in. also, tell me about how your throttle action is compared to stock? if tuned properly can you hit the throttle or do you always have to be mindful and be conscious of how you are twisting it? i don't want to be on the highway and be in a gear or drop a gear and whack it to pass someone or get out of the way and have the bike bog down or hesitate when i really need it. and eventhough i know there are those out there who have these carbs on bikes that have been bored out i am just looking for how these carbs act if they are tuned properly on a STOCK 865 motor! and if you are a CR fan also feel free to chime in! i still haven't decided one way or the other. anoter factor to really consider is that i ride this bike everyday. it's not just a weekend toy that i take out for a few hours onthe weekends. if it isn't raining i ride the bike and the car stays parked. i just love being on it, even if it's a quick trip to the store or a 300 mile day trip, so that needs to be taken into consideration.
 

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If you go to better cams they even flow better and need more carb.As far as cams go tpusa 813 is the way to go ,dont buy some of the other peoples out of date after market cams.
Please forgive the thread hijacking...:)

Mike - have you had a chance to give the 813 cams a go? I'd like your opinion after you have since you have the experience and I know you don't bs nor have any sort of agenda on who has the best cam going...I'm hoping they live up to the hype.

Cheers,

--Rich
 

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i appreciate everyone's advice but some people may not have read my initial post all the way through.

to restate, i do not care how great the mikuni's are. i cannot afford them, and didn't want to waste any time with this thread turning into a [email protected] measuring contest between mikuni's and FCR's. i've read those threads and am trying to avid recreating those threads and was looking for a comparison based on MY particular wants and needs for the bike. i'm looking for advice based on what i am trying to accomplish.

the reason i tried to be so detailed and thorough is because yes we know the mikuni's and FCR's are top of the line, since i am not planning on going huge (big bore, stroker kit) i wasn't sure if it was overkill to throw on FCR's on a stock engine and didn't think it would do it justice.

i was just trying to match the right carb to the application (not trying to take the cheapest way out, but still trying to stay within my budget, and have nothing against the FCR's, but posted because i don't know a lot about them), and would like advice on which carb is better for MY application, so i tried to include factors like: riding the bike in colder climates, using the bike as a commuter as well as a toy to wring out tin the twisties, NEVER going to do a big bore, may drop in cams at some point, and lastly MAY consider doing headwork, but that is probably not gonna happen. i even mentioned that i have no visions of turning the bike into one of these super high horsepower (well, high HP for our bikes, so it's a relative term!) bikes where you end up spending a ton of cash and also have to update breaks, clutch, etc. like i said i am not against doing it, but i have too many other hobbies and need to share the wealth between them! i just want to say, get to 70-72 HP at the rear wheel (at 63 hp now, possibly a touch more since the bike was last dyno's in denver and i am now at sea level), and thought that carbs and cams would accomplish that, or carbs and headwork with stock cams?

so in conclusion, how many of you have the FCR's on a stock motor? (this means no headwork, no cams, no big bore kit)? how well do they stay in tune once you get them dialed? are they finicky? how long did it take you to get them dialed? (i'm not looking for something that is needy and always needs tinkering once i get it fairly dialed, but don't have anything against performing routine maintenance, or have something that will let me down when i am ready to go to work. (i mention this because i have heard once you get the CR's dialed they are solid.) how is your mileage now? how are your starts on a colder morning (are you constantly out there messing with the throttle to keep her going until she warms up or can you walk away once she turns over?) even on a cool day i have to use the choke with the stock CVK's even if it's just for a few seconds because it wont turn over with the choke in. also, tell me about how your throttle action is compared to stock? if tuned properly can you hit the throttle or do you always have to be mindful and be conscious of how you are twisting it? i don't want to be on the highway and be in a gear or drop a gear and whack it to pass someone or get out of the way and have the bike bog down or hesitate when i really need it. and eventhough i know there are those out there who have these carbs on bikes that have been bored out i am just looking for how these carbs act if they are tuned properly on a STOCK 865 motor! and if you are a CR fan also feel free to chime in! i still haven't decided one way or the other. anoter factor to really consider is that i ride this bike everyday. it's not just a weekend toy that i take out for a few hours onthe weekends. if it isn't raining i ride the bike and the car stays parked. i just love being on it, even if it's a quick trip to the store or a 300 mile day trip, so that needs to be taken into consideration.
SB:
Both carbs the 35 CR's and the 39 FCR" will do what you want for your particular application about commuting, rideability, cold start, spirited rides etc,etc.
The only difference is: 39's will give you more power, better fuel mileage and after are dialed in you don't touch them anymore.
 

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Discussion Starter · #12 ·
hell, if the FCR's are solid once they are tuned and can be started on a cold day without a choke and get better mileage than the CR's and more power to boot that's what i want to hear!

i am still kinda leary about no choke. i work nights and would suck to come out after a 12 and a half hour shift at 7-730am and not be able to start the bike on a cold morning and have to wait around for the ambient temp to warm up!
 

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So has anyone in the cooler climes installed the FCR39's? I'm very interested to know about the no choke aspect. Do they not have any sort of enrichener? How do you deal with that - do you just make them run rich at idle or what?

I am fascinated by this for some reason.

As you can clearly tell, I know nothing about these. I only just found out they have accelerator pumps. Well, sometimes you just have to dive in and fish about.
 

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Discussion Starter · #14 ·
So has anyone in the cooler climes installed the FCR39's? I'm very interested to know about the no choke aspect. Do they not have any sort of enrichener? How do you deal with that - do you just make them run rich at idle or what?

I am fascinated by this for some reason.
i am very interested in hearing about this as well!
 

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Well, as you might expect there has been discussion on this before, and here is some of it:

http://www.triumphrat.net/twins-technical-talk/81197-keihin-carburetor-kit.html

Which leads me to believe that the FCR39s start allright in the chill.

I'd still like to hear back from anyone with experience and updates on ANY of the different carbs. It's fun this. :D

EDIT: Hey! Exploded diagram for FCR 39. Doesn't add anything to the discussion but I like the piccie.

http://www.sudco.com/fcrside_diagram.html
 

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So has anyone in the cooler climes installed the FCR39's? I'm very interested to know about the no choke aspect. Do they not have any sort of enrichener? How do you deal with that - do you just make them run rich at idle or what?

I am fascinated by this for some reason.
The FCR's are Racing carbs, they do not have a choke,, but they have an accelerator pump, one for the 2 carbs.
For cold start I mean 24 hrs gap, a week, 2, 3 weeks , you'll open the petcock, blip the throttle half way 3 times and push the starter button, it will start right up and after 20 seconds will tickle at 1000 rpms.
For super cooler climes below 30 degrees, same procedure but just 4 throttle blips.
I hope this help.
 

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It certainly does!

As long as I know there is a starting method for them, I am happy. Probably just a matter of getting familiar with them. :thumbsup:
 

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Discussion Starter · #18 ·
i am starting to see the light...
 

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sbpark....if you want top performance get all your stuff from British Customs. CR carbs with their street cams and maybe head work...u will for sure be happy! I've met you at British Customs before and i know your story
 

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Discussion Starter · #20 ·
sbpark....if you want top performance get all your stuff from British Customs. CR carbs with their street cams and maybe head work...u will for sure be happy! I've met you at British Customs before and i know your story
dammit! now i am back to thinking about the CR's...
 
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