ThatsDax rt High Performance Carburetor

[boredtracker]

I Just isnstalled rt carb....been trying to tune it all weekend...after running it stock...started right up and was bogged down all over the throttle curve,four stoking ..and running hot......got it on the 70 jet...i can say my performance upgrade is marginal(due to my lack of two stroke knowledge no doubt)
A couple things...
I took off the air filter on the 75 jet setting and got some decent top end and the engine overall ran better than with filter on.Four stroking still presen coming out of midrange to topend...then pow ! fast!
Let me also say that Duane was very helpful in all of this...a standup guy in this business for sure.
www.thatsdax.com
Now ( aftrer consulting with Dax on the phone)I have gone to the 70jet Seems to sputter on takeoff, to decent mid range,to a non four stroking exchane into the top end.(NO four stroking present)
(this mind you after only a small test ride duration due to silly real life.)
Also seems to run cooler.I cant help but think im on the right track.
Should i be leary of setups that lean towards no filter ? because with all these configs my filter still needs to be left off!
Im gonna ride around tonite and see how it runs with the 70 after a proper warmup.
I have read the 65 is a common place to land, but my low to mid cant suffer much more...I am actually very pleased with this hobby.Its very fun.
This is a wonderful site for a newbie like me.
Thanks in Advance for any words.thoughts..ideas?
Danno
A little more about my setup and a pic
http://motorbicycling.com/attachment.php?attachmentid=45130&d=1329434669

 

[skitchfish]

It was my experience that leaning it out with 68 did not lessen performance at any level of throttle, but rather made it run even more smooth and with quicker throttle response and more power. If it wants more air such as you taking the filter off, than give it more air by jetting and put your filter back on before something catastrophic happens. My results utilized a high quality oil at 32:1. If your going to lean out your motor by jetting make sure you have some slipperry stuff for fuel and make accurate measurements when mixing as lubrication is key when your motor wants to run on air.
The rt ran smooth and had a nice sound with nice mid-range response, however I could still get 2mph more with old nt at wot. These are just my experiences and observations .

 

[thatsdax]

ive had my rt carb from thatsdax for about a month now runs great with the jet that came with itits got good power at high rpms but seems to be lacking in the low end. i tried steeping it down to a 70 great low end power but WOT it 4 strokes at around 24 to 26 mph so i tired a 65 jet still the same prob the low end is great but WOT = 4 stroking around 24 to 26 mph im thinking i may need a jet around 71 to 74 not sure off hand thou

Try adding some oil. If you are 32:1, try 28:1 and see if that helps. Adding oil displaces fuel and leans out the gas. Richer with oil leans the fuel. Try it and see if it helps. Enjoy the ride.

 

[boredtracker]

It was my experience that leaning it out with 68 did not lessen performance at any level of throttle, but rather made it run even more smooth and with quicker throttle response and more power. If it wants more air such as you taking the filter off, than give it more air by jetting and put your filter back on before something catastrophic happens. My results utilized a high quality oil at 32:1. If your going to lean out your motor by jetting make sure you have some slipperry stuff for fuel and make accurate measurements when mixing as lubrication is key when your motor wants to run on air.
The rt ran smooth and had a nice sound with nice mid-range response, however I could still get 2mph more with old nt at wot. These are just my experiences and observations .

Thanks skitchfish...appreciate your take on the subject.

 

[crmachineman]

Speaking of this RT carb... I'm totally done with the CNS carburetor because the clamp broke for the second time. Does this Dellorto clone have the same problematic design of incorporating the mounting clamp into the aluminum casting? I think it is a bad idea to use aluminum as the material for the mounting clamp.



-Fred

 

[Drewd]

CRC, yes same mounting design but I've got my Dax torqued a whole heck of an amount and it hasn't broken yet. I had another Dellorto clone that had an idle mixture screw and it broke the first time I put the slightest amount of torque on it.

 

[crmachineman]

Huh, Ok. Maybe the clamp is beefier. Still, I don't care for that design approach. My cheesy little "speed" carb. uses a steel clamp; that's the right idea!

How about that idle mixture screw breaking... How could that happen? It's a steel screw right? Damn! that's weird!

Since I've heard good testimony about this carb. I may have to try it.

Thanks,

-Fred

 

[maurtis]

Got my RT today, and ordered a set of smaller jets along with it. Immediately went to the 65 before installing since I figured I would end up near there anyway, lol.

This is a really neat carb, I like it a bit better than the NT I had on there. I had to squish the air filter upwards a bit to fit in the frame, but not horribly so. I am definitely tempted to get a shorty intake manifold now.

Throttle response is AWESOME! But... it definitely feels like I am down a bit on the low end and lost about 1 MPH on top. And I have an intermittent high idle, say 70% of the time. I am assuming this is at the carb/manifoild junction, so I will grab some SealAll later today. I used two tubes of it last week on a different project, I wish I had saved some now, lol.

While trying to tune the carb, I put the 68 jet I was running in my NT carb in, but no real difference. I need to find and fix that air leak first.

My NT was running pretty well, but I could never get the idle as low as I wanted and it pretty much kept the centrifugal clutch semi engaged, so at stops I usually ended up pulling in the clutch anyway. With the RT, when the idle was not running high, it would idle nice and loooooooow.

 

[biknut]

Huh, Ok. Maybe the clamp is beefier. Still, I don't care for that design approach. My cheesy little "speed" carb. uses a steel clamp; that's the right idea!

How about that idle mixture screw breaking... How could that happen? It's a steel screw right? Damn! that's weird!

Since I've heard good testimony about this carb. I may have to try it.

Thanks,

-Fred

I run a speed carb too, and I like it a lot. It's 1 mm bigger than a DAX carb.

 

[happycheapskate]

Don't throw it away yet!

http://content.etilize.com/Large/1021069916.jpg

You can take the intake tube off, polish it inside and out, then epoxy that carb on it. Make sure you don't block the hole.

Speaking of this RT carb... I'm totally done with the CNS carburetor because the clamp broke for the second time. Does this Dellorto clone have the same problematic design of incorporating the mounting clamp into the aluminum casting? I think it is a bad idea to use aluminum as the material for the mounting clamp.



-Fred

 

[JonnyR]

the CNS is a horrible carb all around i tossed mine in a box and use a NT now
anything indorsed by the EPA and built by the Chinese cant be good

 

[goofyfoot2001]

I've tried every jet possible and I cannot get this carb to stop four stroking at the top end. Midrange is great until about 21-22mph then it's just useless to give it any more throttle. I do have the intermittant bursts of energy going up hills. Going up a hill would probably make my bowl level as it's angled forward an up on level ground. Any ideas? A smaller sprocket probably wouldn't make the hills around here.

 

[biknut]

I've tried every jet possible and I cannot get this carb to stop four stroking at the top end. Midrange is great until about 21-22mph then it's just useless to give it any more throttle. I do have the intermittant bursts of energy going up hills. Going up a hill would probably make my bowl level as it's angled forward an up on level ground. Any ideas? A smaller sprocket probably wouldn't make the hills around here.

I hope you engine is broken in and running 36:1 mix or higher. If so the jet size you need is probably a 66, or 68. Have you tried adjusting the float level a little lower? Spark plugs also play a roll in 4 stroking. Sometimes an extended tip works better, and sometimes a regular plug is better. Try a NGK B6HS. If that doesn't help, try an extended tip BP6HS. Be sure and roll the motor over by hand to make sure the extended tip doesn't touch the piston top.

If you've not confidant about your float level, start over. Adjust the float higher till it leaks a little at the angle you're running it at, and then adjust it back down, just to where it stops leaking. If it starts losing power on downhills at full throttle, the float level is too low.

 

[happycheapskate]

You can get a stubby intake from Manic, or find another stock intake tube, saw the ears off, and run a hose between them, and mount the carb remotely.

I've tried every jet possible and I cannot get this carb to stop four stroking at the top end. Midrange is great until about 21-22mph then it's just useless to give it any more throttle. I do have the intermittant bursts of energy going up hills. Going up a hill would probably make my bowl level as it's angled forward an up on level ground. Any ideas? A smaller sprocket probably wouldn't make the hills around here.

 

[goofyfoot2001]

I added some hose to the intake to level out the carb. Runs much better. I also am running a B7HS plug. I slightly increased the gap which did seem to make a little bit of a difference. Put a 41T sprocket on and with all the changes it does seem to be running better. Still stroking down hills or whatever you call the weird noise it makes.

 

[happycheapskate]

Like this? I don't care if mine does it. It is a very long stroke for a 48cc engine, compared to weeder/type engines.

http://youtu.be/ZjWYUhmy5aw?t=1m Here I am not WOT but cruising along and feathering the throttle. It grumbles some when decellerating. I like it.

I added some hose to the intake to level out the carb. Runs much better. I also am running a B7HS plug. I slightly increased the gap which did seem to make a little bit of a difference. Put a 41T sprocket on and with all the changes it does seem to be running better. Still stroking down hills or whatever you call the weird noise it makes.

 

[skitchfish]

I added some hose to the intake to level out the carb. Runs much better. I also am running a B7HS plug. I slightly increased the gap which did seem to make a little bit of a difference. Put a 41T sprocket on and with all the changes it does seem to be running better. Still stroking down hills or whatever you call the weird noise it makes.

Hey Goofy, Excuse me if you already know this or its not what you are referring to. When going down hill at speed you should you should either pull in the clutch or give it the gas but do not let just let off the gas and coast in gear or use your engine to slow down. The Harley guys call this " Let'n it eat". Two strokes do not like this because you have the carb closed when doing high rpm and it's not getting proper lubrication. It definitely going to sound like four stroking when you let it eat.

 

[skitchfish]

wow! sorry about the typing and grammar

 

[happycheapskate]

I don't see why it would starve for lubrication if the idle position is high enough that it would run at idle. It will suck what it needs despite engine braking. FWIW you could also do like some moped riders and flip the choke switch on while descending long grades (soaks the engine and accomplishes engine braking, while giving you some more control with the throttle).

 

[GearNut]

The oil is in the fuel. With the engine spinning at a high RPM it draws a LOT of air through the carburetor, at least it tries to. When the throttle is at the idle position the slide is all the way down restricting air flow. The slide needle is also all the way down restricting fuel flow. The engine is still spinning fast only now it can barely draw in any fuel/ air mixture through the almost closed carburetor. A fast spinning engine with barely any lubrication results.
All 2 strokes develop a teeny pool of oil in the bottom of the crankcase during normal operation. Hard to believe I know, considering how the air is pulsing and swirling all around down there, but it is the nature of the beast. This pool of oil can be consumed during extended periods of high RPM engine braking and once it's gone the lubrication really suffers. Short periods of engine braking are harmless. Long periods of engine braking.... Well it's your engine, treat it as you wish.