CR's vs TM's vs VM's vs stock - ratio of performance:ease of tuning

ronnie

ronnie

Calm down and sail on
Well, I know this has been long discussed over on the site and the rest of the net. I have searched far and wide but they best I could find was a thread on here (http://www.dotheton.com/forum/index.php?topic=14721.msg145588#msg145588. It explained good bit but it really didn't hit the head on everything. I'm getting closer to this stage in putting my bike together so I wanted to know now what I would be getting so I can be on the look out for deals and also start saving in the piggy for the purchase.

Now, I have a 75 400f bored to a 466cc, a street cam (#3 from webcamshafts), decked head, stock valves with brz guides and 3 angle cut, and the head will be cleaned up to remove casting marks. That said, I don't have stock carbs and I have been putting nice things into this bike and don't want to skimp out on carbs, but I don't want to have to tune for a year getting it right.

From what I can get, TM flatslides are great for performance and are fairly easy to tune. They offer great throttle response all over (accel. pump). CRs i have come to know are great too but aren't as good as flatslides. Then I hear the VMs are good IF you can get them tuned but they dont offer as much tuning ability as the previous two.

And I get the brands and models mixed up and after all the reading I still get confused.

Bottom line is: Which carbs will be the best option for a hot street (but maybe a day at the track every now and then) that are easy to tune AND stay tuned for the price? And price isn't really a problem (previously thinking I would be buying $700 CRs which I accepted as just what I will be having to shell out for carbs give or take).
 
Guess I'll have to use good marketing for this... Haha!

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lol...

Main difference between the VMs and TMs are that the TMs are flat slides and the VMs are round slides (with a couple of exceptions for reasons unknown to me).

Flat slide carbs are generally seen as superior, but they can take some getting used to. Throttle response is immediate and they almost always flow better than flatslide carbs of the same size. Expect to pay for those benefits.

Though I've never had an opportunity to ride a bike with CRs, the general consensus seems to be that these are pretty much the best carbs that money can buy. What makes them so good? I'm not 100% sure.

From a purely technical standpoint, the purpose of a carb is to deliver fuel in a metered amount and restrict incoming flow as little as possible. Atomization of the fuel is also an important factor. Most carbs, with the proper jetting, are more than adequate for the street. In my mind, the important factor for choosing carbs is tunability and a lot of the comes down to how easy the carbs are to work on and how expensive jets and peripherals come in at.
 
Thanks sonreir, that's pretty much what I know now. Just looking for some in depth on particulars, specifics, technical comparison, etc. I hear good things about all of them, but if I'm going to be spending money I like to make an informed decision and would like to get the best bang.

Yea, maritime, I have been in contact with Kiley. He's been a great help with everything 400f..

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I'm on my phone, but I'll get to this thread with what i know shortly. I bought CRs for mine and there's a reason. I'll be glad to share.

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I stand by the FCR/TM flatslide choice for a hot motor, if you're closer ot stock a VM is a great little carb with loads of support.
 
I'm always ready for your shares Kiley!

Swagger, my bike isn't race but its definitely not closer to stock. I'm now looking at haveing to get bigger inlet valves as I need new valves. So I want somethign I dont have to screw around with everytime I get on the bike. I want to set it, and forget it like those rotisserie chickens haha! And support is nice to have too.
 
TM are basically a two stroke carb. It can be adapted for a 4 stroke, but that's where the HCR was designed to fit - or the FCR. CR are awesome race carbs for early 4 strokes. All aftermarket carbs are a PIA to jet correctly but there's a body of knowledge on common applications.

I have seen Amal concentrics and CRs on 400fs. I'm sure that someone has fitted EFI by now.

For a mild tune, stock carbs are probably most cost effective.
 
I don't have any stock carbs so if I'm buying some, might as well do it right. Really I'm just stuck between TM/FCR and CR carbs. They are all moderately same in price..

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Flat slides are super adjustable but that just make more wrong setting and there is still only one correct right it dosnt matter how much they cost
 
I'm not the authoritive historian on Flat slide development, but the way I see it, the TM series were developed by Mikuni for Suzuki Rm series MX bikes originally IIRC and were adapted to work on many different snowmobiles. They developed a modified version for production 4 strokes like the late 80s GSXR called the VM29SS. And they made the RA34 smooth bore race carbs in a gang of 4, plus the TMR series.

So it seems to me that they modified the design to work in a 4 stroke environment. They also took that flat slide design and modified it again to work in a CV form as a radial flat slide on later GSXRs etc.

They did offer a TM33 in a bank that were less severely modified from the original design.

It's not that they can't work on 4 strokes but it seems to me that it was designed primarily for a 2 stroke application. That said, there's no reason why they can't be jetted to work on a 4 stroke but I think that they come with #389 Primary type needle jets which are not as well suited to a 4 stroke application. I don't have a cross reference to a suitable Bleed type N/J.

On a big twin with high enough intake velocity an large air jets, they will probably work OK but getting the fuel slope right across the rev range will potentially be an issue. Fortunately we don't have to worry much about unburned hydrocarbons from large droplets.

I'd like to hear from a real carb expert like Mark at Factory or Ivan, to hear what they think.
 
Well I read that the TMs were originally 2 stroke, but when I looked at sites to buy it didn't specify either or.. Yea, I would like to here from some experts on it or someone with knowledge on either of the two.

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So the next time I come back on the boat I will be buying items to make my engine run.. ie Carbs, and other fuel/spark delivery items.

Is there anyone who has some input or experience with CRs or flatslides? They will be for a 400F with engine modifications, individual filters and custom exhaust of some kind...
 
I bought my first set if TM's back in 1985 or '86.I have since used them on about 10 different motor combo's, both 2 stroke and 4 stroke.I really like them for the throttle response, no comparison to a VM in that respect.
 
Far as I can tell the only difference between a 2-stroke vs. 4-stroke setup would be the needle jet and settings. Jimmer, what differences did you see 2 vs. 4-stroke with the TMs? I can see a difference in the needle jet, shrouded (incorrect term, please forgive) or non....
thoughts? I haven't even begun the leg work on mine yet...soon though.
 
Swagger, that's all I ever hear about them too.. But it's always hearsay. Another thing is that I have heard the flatslides are tall do it poses fitment issues for some...

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I'm never seen anything with that much size restriction but there's always an exception..
 
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