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Discussion Starter · #1 ·
hey guys im rebuilding and doing the 720 stroker and wana know whats best for carb choice for this build people say the fcr carbs really wake up the bike with a good port and polish, but if i cant get them will the stock carbs work well if jetted properly?
 

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I think stock carbs will work well for a while if you can't find FCR's right away. If you do more tight and technical riding the 35mm's will probably be better (better low end response). For more open riding I'd say go with the 39mm's as they provide better top end.

I went with 39's on my build a couple years ago (at the time was a 720) but now wish I would have gone with the 35's because I'm back to stock stroke and they don't perform quite as well on bottom end. However, I'm not 100% its the carbs so much as the style of porting. On the top end this thing absolutely screams though!
 

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Discussion Starter · #4 ·
ive never done anything with porting and stuff like that im learning as i go as this is my first ride lol
 

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He has Barker HV porting. The ports are completely reshaped and port floors are raised along with a new intake that is built to. If his build was like mine it didn't have the Tq on the bottom bud mid to top end pull was CRAZY. Don't get me wrong the bottom end wasn't slow at all just not real wheelie happy like most. I honestly don't like the way a 660 front comes up so easy.
 

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ive never done anything with porting and stuff like that im learning as i go as this is my first ride lol
Define what you plan on doing with the bike then ask for advice. Porting, Cams and 35 vs 39mm carbs are all dependent on your riding style. This is my 2 cents and some will disagree with it but there's plenty of truth behind my numbers:

1. Tight woods course, steep hill climbing, farting around with friends.
35mm FCR carbs, Cam shaft that closes the intake valve no later than 52-55 degrees ABDC, Lift keep it under 400", duration keep it under 255 @ .040, Porting with the throats no bigger than 85% valve diameter.
2. High speed open course riding, High RPM, drag racing, farting around with friends.
39mm FCR carbs, Cam shaft -go for it (especially with good valve springs), porting- HV with throats up to 90% valve diameter.

Ok, I know people will chime in and beat me to death over this post but when I say tight woods and steep hill climbs I mean tight woods and steep hill climbs. Good luck
 

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Discussion Starter · #7 ·
Define what you plan on doing with the bike then ask for advice. Porting, Cams and 35 vs 39mm carbs are all dependent on your riding style. This is my 2 cents and some will disagree with it but there's plenty of truth behind my numbers:

1. Tight woods course, steep hill climbing, farting around with friends.
35mm FCR carbs, Cam shaft that closes the intake valve no later than 52-55 degrees ABDC, Lift keep it under 400", duration keep it under 255 @ .040, Porting with the throats no bigger than 85% valve diameter.
2. High speed open course riding, High RPM, drag racing, farting around with friends.
39mm FCR carbs, Cam shaft -go for it (especially with good valve springs), porting- HV with throats up to 90% valve diameter.

Ok, I know people will chime in and beat me to death over this post but when I say tight woods and steep hill climbs I mean tight woods and steep hill climbs. Good luck

my plan is to do the hotrods stroker crank and piston, with stage 2 hotcam, new springs valves, seal guides etc... new clutch weisco or hinson im not sure yet, if i use stock carbs im gunna jet, if i can get my hands on fcrs thats great too... i mainly do trails not much tight woods and no hill climbing...i do some track, but only in the summer at my neibours house, and i do some wide open riding too like feilds..im trying to figure out if fcrs are best, and what typr of porting i should do...like i said im new to the port and polish and im learning as i go... this is my first build so i dnt want to f#$%% it up...catch my drift...i appreciate all the help i can get
 

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my plan is to do the hotrods stroker crank and piston, with stage 2 hotcam, new springs valves, seal guides etc... new clutch weisco or hinson im not sure yet, if i use stock carbs im gunna jet, if i can get my hands on fcrs thats great too... i mainly do trails not much tight woods and no hill climbing...i do some track, but only in the summer at my neibours house, and i do some wide open riding too like feilds..im trying to figure out if fcrs are best, and what typr of porting i should do...like i said im new to the port and polish and im learning as i go... this is my first build so i dnt want to f#$%% it up...catch my drift...i appreciate all the help i can get
First of all, if you plan on keeping the bike and dedicating the next 3-4 years running this dinosaur and you want to go fast then definitely get FCRs -don't give it another thought. But be careful when you buy used FCRs because many have been worked up for alcohol and they require some special attention to tune them back to gas. I quit GNCC type riding last year and i have a dedicated LTR 450 for the ATV Rodeo series so now I do exactly what you have described; Open trails, stay off the real steep hills (I'm almost 50 now) and drag racing. I put the big head on my bike, with 87% throats but I still run the stage 2 cam for the woods. The 13.5:1 piston and the big head works better than I thought in the woods but I did have to drop my gear from 13:40 to 12:40 and still I don't have anything near the bottom end I had with the smaller ported head and standard valve diameter. I like my motor now and on the 200' drags it's faster than most 450s (around 3.9sec) so I'm happy with that. It took some getting used to because the bigger head with bigger throats and valves will launch so easy you don't think the bike will perform until you're next to another bike and you see how fast the power comes on at 3500-4000.

If you have lots of imagination and deep pockets then maybe some conversation with willy regarding the 3 plug set up is due. I keep thinking about it but I simply haven't taken that next step. Good luck
 

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Discussion Starter · #9 ·
ya i plan on keeping it i just bought it may of 2011 and already spent 7000 abouts thats including the 3500 i got it for bone stock... ill never get my money back out of it so y not run her till she dies..
 

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39 mm fcr all the way. You will have plenty of room to grow with these carbs.
 

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He has Barker HV porting. The ports are completely reshaped and port floors are raised along with a new intake that is built to. If his build was like mine it didn't have the Tq on the bottom bud mid to top end pull was CRAZY. Don't get me wrong the bottom end wasn't slow at all just not real wheelie happy like most. I honestly don't like the way a 660 front comes up so easy.
This is very true. With my setup the way it is the bottom end is very close to stock (maybe slightly better). When I built my machine I was not happy with it but have learned to accept it because there is nothing I can do about it now. The top end power (especially the HV combined with the 3 plugger and large carbs) is very, and I mean VERY explosive. I am definitely limited by traction now.

Define what you plan on doing with the bike then ask for advice. Porting, Cams and 35 vs 39mm carbs are all dependent on your riding style. This is my 2 cents and some will disagree with it but there's plenty of truth behind my numbers:

1. Tight woods course, steep hill climbing, farting around with friends.
35mm FCR carbs, Cam shaft that closes the intake valve no later than 52-55 degrees ABDC, Lift keep it under 400", duration keep it under 255 @ .040, Porting with the throats no bigger than 85% valve diameter.
2. High speed open course riding, High RPM, drag racing, farting around with friends.
39mm FCR carbs, Cam shaft -go for it (especially with good valve springs), porting- HV with throats up to 90% valve diameter.

Ok, I know people will chime in and beat me to death over this post but when I say tight woods and steep hill climbs I mean tight woods and steep hill climbs. Good luck
Everything here is very true. I was going to say something along those lines but blueranger has a more specific approach with all the specific numbers than I do so I'll just say +1!
 

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I run 35's because it's not a dedicated drag bike.
 
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