Best carb size?

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jasonp

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justrandy said:
What's the best carb size for the webcam .390 cam type rider?
Stock CV style carb off a early raptor 350 or suzuki z400, with a raptor intake manifold. 34mm for more torque and reponse and 38mm for more top end. (up to 85mm bore).
 

jasonp

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justrandy said:
Why not a non-cv type?
because you will loose torque with a flat slide design and since the this is a slower reving 2 valve motor it doesn't really take advantage of the flat slide carb. You do gain it back at the top end but it just doesn't have that broad range of power and response.
This is from experience.
 

justrandy

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How about a regular ole roundslide non-cv? I've found true cv's don't have throttle response.
 

yamarider

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I've noticed with the CV carb on my dr350s that they really do have crappy throttle response compared to most carbs. Of course maybe it also seems bad to me because i'm used to a fuel injected raptor with a PCIII and the accelerator pump program... throttle response on that thing is WHAM, the dr350 just kinda starts chugging along at it's own pace no matter how quick i rip the throttle. Everyone i've talked to about my bike claims that the flat slide is the way to go and the cv's are crap. Maybe this is just the particular mikuni cv that suzuki used on these bikes though?

And i did have a flat slide pumper carb on my warrior, the edelbrock, and there was definitely no noticable loss in power anywhere in the rpms. Maybe that's not due to the design of the carb itself, maybe it was just tuned in better than my stock carb was, but i didn't experience this loss of torque with a flat slide on a warrior.
 

justrandy

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I thought the whole idea of flatslide was bottom end???

Here's a quote from the Sudco catalog, "Mikuni’s original flat valve (flat slide) carburetor, the TM Series Carburetors provide significant performance improvements over older design round slide carburetors. Air flows faster and smoother through the TM Series venturi due to the flat slide configuration and the jet blocks which help create a smoothbore effect. The high velocity of the air flow means a stronger vacuum at the needle jet, providing more precise metering and better throttle response."

Faster flow means more bottom end and probably less top end.
 

jasonp

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justrandy said:
I thought the whole idea of flatslide was bottom end???

Here's a quote from the Sudco catalog, "Mikuni’s original flat valve (flat slide) carburetor, the TM Series Carburetors provide significant performance improvements over older design round slide carburetors. Air flows faster and smoother through the TM Series venturi due to the flat slide configuration and the jet blocks which help create a smoothbore effect. The high velocity of the air flow means a stronger vacuum at the needle jet, providing more precise metering and better throttle response."

Faster flow means more bottom end and probably less top end.
Flat slide carbs basically can flow more air per MM and over say a CV or round style of carb of the same MM. They also effectively meter fuel better then other styles of carbs as the vacuum signal is greater at those jets. I find I have to run smaller jets then both stock and round slide carbs that are used on this engine per given of mods. One thing I will say is that I found that my bottom end is flat in the power and then really starts to pick up in the mid range and top. This was just after dialing in the jetting and getting it dead nuts on, comparing to a CV. A CV style will mantain maxium airflow volecity at a wide range of rpm points and throttle position. Which means maxium torque. I found when I'm coming up a big hill and lugging the engine if I give it a bunch of throttle fast the engine will start to become flat on the power slightly, now with my CV carb I can gas the bitch and she will stay in the meat the whole time.
CV's are great for all around power, flat slides are great for mid and top end.
Response will be greater with a flat slide with an accel pump for sure. I think I would look for a FCR or CR style if I wanted a flat slide.
 

justrandy

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I found with the stock carb I could open the throttle up fully and then start counting before it revs all the way out. With the 38mm mikuni roundslide I have now, the response is instant and lowend is brutal. Just punch the flipper and the front end comes up.... No delay or stumble.... Even with this air filter and no box: http://www.knfilters.com/search/product.aspx?Prod=RX-3770

I'm waiting on another needle to see if I can refine the off-idle cruising, but for trail busting it seems there's little room for improvement (other than a cam and more rpm). I think a dial-a-jet would probably clean up any inconsistancies in fuel mixture and add even more throttle response.
 

griff

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YamaRider said:
I've noticed with the CV carb on my dr350s that they really do have crappy throttle response compared to most carbs.
A lot of DR350 carbs were absolutely HORRIBLY setup at the factory. Even if you keep the stock airbox and exhaust, a proper jetting will clean it up enormously.

My old DR was the same way, as is A LOT of the guys DR's on my site. Register and maximum-suzuki.com , you wont find a better DR forum for tech stuff anywhere.
 

yamarider

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Griff said:
YamaRider said:
I've noticed with the CV carb on my dr350s that they really do have crappy throttle response compared to most carbs.
A lot of DR350 carbs were absolutely HORRIBLY setup at the factory. Even if you keep the stock airbox and exhaust, a proper jetting will clean it up enormously.

My old DR was the same way, as is A LOT of the guys DR's on my site. Register and maximum-suzuki.com , you wont find a better DR forum for tech stuff anywhere.
Yeah, i already found that site, it is a great source of information for the dr's, that's where i'm getting most of my ideas. Right now mine has the stock exhaust and the 3" hole cut in the top of the airbox with a k&n filter, and from the best i can tell it seems to be dialed in pretty close, at least through the midrange, at least based on plug chops. I haven't checked it at full throttle yet, and i think it could use a little work getting the idle circuit tuned right, the idle isn't as steady as i think it should be. I'm trying to wait until i get an aftermarket exhaust for it, then i'll get one of the t-handle fuel screws and a jet kit and see what i can get out of it.

I'm thinking that it might not hurt to rebuild the top end this winter. It doesn't seem like it burns any oil, it doesn't really show any signs of a worn top end except the power just doesn't feel as sharp as it should to me, doesn't really feel like 30hp. It does have almost 16k miles on it, and from the best i can tell this motor has never been taken apart past the clutch cover. I was thinking about stripping the whole thing down to the frame this winter to check all the bearings, get a bunch of stuff powder coated, and that would probably be a good time to rebuild the top end. I might wait until next winter though, to make sure i'm going to keep the thing for a while before i put too much money into it.
 

jasonp

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justrandy said:
I found with the stock carb I could open the throttle up fully and then start counting before it revs all the way out. With the 38mm mikuni roundslide I have now, the response is instant and lowend is brutal. Just punch the flipper and the front end comes up.... No delay or stumble.... Even with this air filter and no box: http://www.knfilters.com/search/product.aspx?Prod=RX-3770

I'm waiting on another needle to see if I can refine the off-idle cruising, but for trail busting it seems there's little room for improvement (other than a cam and more rpm). I think a dial-a-jet would probably clean up any inconsistancies in fuel mixture and add even more throttle response.
I don't know if I would call the low end brutal for a 350 for what ever mod you do but that is totally cool!
Sounds like maybe you want to richen up on the pilot jet?
 

justrandy

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jasonp said:
I don't know if I would call the low end brutal for a 350 for what ever mod you do but that is totally cool!
Sounds like maybe you want to richen up on the pilot jet?
You guys are just used to it, I'm coming from a 250 quadsport so... :D But you have to admit, warriors are torquey for their size.

I can't go bigger with the pilot because my air screw will fall out. My first though after that was to get a bigger needle-jet, but I figured that would just screw everything else up. So, I've been thru a 6DP1, 6DH3, 6DP17, and a 6F8 needle. Waiting on a 6F5. If that doesn't work, I'll probably have to change needle jets and start over with the needles. My slide is the middle-of-the-road 2.5. I doubt I'll need to change it.

The 6DP1 came with the carb and had good bottom end, but wouldn't rev out even on the last clip (don't remember if it was top or bottom clip).

The 6DH3 was close, but lacked the bottom end of the 6DP1

Can't remember how the 6DP17 was.

The 6F8 was the last one to try and its pretty good on both ends, but the off idle is too rich... So, the quad either goes full-balls or barely at all... There's no inbetween. Kinda hard to keep it on the trail like that, lol. The front wheels push too much with the back 22's lifting them everytime I gas it.

Anyway, not bad for a $100 carb and a $75 air filter. Think I got the FMF for $50, but had to weld it back together since the guy cut it apart for some reason.

I highly recommend those dial-a-jets though... They're awesome. But I want to get the jetting close as possible first... Its like a puzzle to me. ;)
 

griff

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justrandy said:
I can't.....

....a puzzle to me. ;)
Ok, that was a mouth full... and youre say'n some scary things.

Jason was refering to the pilot jet, not the A/F screw. You need to find out what size is currently in there.

Nothing you do on the needle is going to work right until you have the right size main jet in there 1st.

Just so I'm clear, your engine is stock right, with just the Web cam, right?

And you are trying to use which model 38mm carb exactly?
 

jasonp

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justrandy said:
jasonp said:
I don't know if I would call the low end brutal for a 350 for what ever mod you do but that is totally cool!
Sounds like maybe you want to richen up on the pilot jet?
You guys are just used to it, I'm coming from a 250 quadsport so... :D But you have to admit, warriors are torquey for their size.

I can't go bigger with the pilot because my air screw will fall out. My first though after that was to get a bigger needle-jet, but I figured that would just screw everything else up. So, I've been thru a 6DP1, 6DH3, 6DP17, and a 6F8 needle. Waiting on a 6F5. If that doesn't work, I'll probably have to change needle jets and start over with the needles. My slide is the middle-of-the-road 2.5. I doubt I'll need to change it.

The 6DP1 came with the carb and had good bottom end, but wouldn't rev out even on the last clip (don't remember if it was top or bottom clip).

The 6DH3 was close, but lacked the bottom end of the 6DP1

Can't remember how the 6DP17 was.

The 6F8 was the last one to try and its pretty good on both ends, but the off idle is too rich... So, the quad either goes full-balls or barely at all... There's no inbetween. Kinda hard to keep it on the trail like that, lol. The front wheels push too much with the back 22's lifting them everytime I gas it.

Anyway, not bad for a $100 carb and a $75 air filter. Think I got the FMF for $50, but had to weld it back together since the guy cut it apart for some reason.

I highly recommend those dial-a-jets though... They're awesome. But I want to get the jetting close as possible first... Its like a puzzle to me. ;)
Yeah I would focus on getting the pilot jet spot on first then main jet. Sounds like your trying to get your top end set using your needle jet which isn't correct and you will find that you will have problems no matter how many needles you've tried.
If you are that far out on the fuel screw then for sure the pilot jet is to lean. Anything after about 3 1/2 turns out then the fuel screw will do every little. 1/4 from being in then you know the pilot jet is to small.
If you want info how to get that jet spot on we can help.
Next you have to get the main jet on. Full throttle. You just have to experiment and do some plug chops to see how rich or lean the mixture is. I've found that when running the perfect mixture on this bike it will almost not even color the plug. Simple way to tell though is get it out in 5th gear and rev it in full throttle.. as the rpms come up does it stutter or fall on its face. If it acts like you've hit a rev limiter then you know you are to rich. If the engine dies way to lean. Start rich and work lean until the point where rpms at full throttle rev cleanly to the top with no misses. You will find that the engine will rev higher and higher as you start to lean the main out.
I would recomend putting the stock needle back in and retesting and I bet after dailing in the main you will have no problems with the needle. Easy way to tell if your on with the needle is start with the needle in the most rich position and work lean. How you tell is go back to your 5th gear test at full throttle and get the engine up in RPM's now back off the throttle slightly. Does the engine start to stutter and act like a rev limiter.. ok move the clip up on the needle to lean it out. Keep going until it will run clean and also take throttle with out boging.
 

justrandy

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The pilot jet is right on. The screw is an air screw, not a fuel screw. Turning it out adds more air. So, if I go to a bigger pilot (which I did and had to take back out), the air screw is too many turns out for the spring to hold it in. So, therefore, my pilot is as big as it can be.

My main is right on as well. I have an o2 sensor hooked up, so I can tell what's what. I just have a little rich spot as soon as I open the throttle. Once the throttle is opened, everything is good. Just the part of the needle that controls the first part of the throttle opening is too small.

My o2 sensor.



 

jasonp

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justrandy said:
The pilot jet is right on. The screw is an air screw, not a fuel screw. Turning it out adds more air. So, if I go to a bigger pilot (which I did and had to take back out), the air screw is too many turns out for the spring to hold it in. So, therefore, my pilot is as big as it can be.

My main is right on as well. I have an o2 sensor hooked up, so I can tell what's what. I just have a little rich spot as soon as I open the throttle. Once the throttle is opened, everything is good. Just the part of the needle that controls the first part of the throttle opening is too small.

My o2 sensor.



Right a air screw would be on the side of the carb and does the oposite as a fuel screw. You must have a carb off a 2 cycle, 2 stroke snowmoblie? I really haven't heard of anybody doing it but I guess what ever works for you. I would have bought a carb kit off ebay and could have got it for cheap already set up. I would go ahead and call sudco and tell them what you got and they will help get the needle right. where do you put that o2 sensor? If it is not a wide band or right next to the head then you will not have enough heat for it to be acurate. What type of guage are you using?
 
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