Tune ups, jetting, post-cold weather, etc.

U

UTmotorbiker

New Member
Hey guys, sorry for a new thread if its been covered but I have a few questions.... First, I got the new RT carb from thatsdax.com and I installed it with the RT cable.

I am having a few struggles...it's really got a lot of power in the low end even when it's cold but I have that response only to about 1/2 throttle. After that it lags BIG time up hills and even stalls out. Is this a too rich mixture? I have a couple of jets I have been playing with but I am at a pretty high altitude (4500 ft above sea level) so I'm not sure if I'm getting the right mix. My suspicion is that it's too rich and bogging out because of that but I don't really know. I had the old crappy NT carb going ok but when I switched it out for the RT carb I started having the lagging problems.

I also have gotten an expansion chamber from SBP and I want to install that but I don't really know what the effect will be on the overall performance after installing it.

Lastly, are there good places to get a tune up? There aren't really any dealers around where I live and we just got done with the snow so I just want to make sure it's ready to start riding hard again for the spring/summer.

Any help and suggestions would be great! Thanks!!
 
If you already have the jets, try going a size smaller on the main and see how it runs after the engine is warmed up, if it's blubbering and 4 stroking then go down another size and repeat until the 4 stroking clears up and it revs clean.

If you got the pipe already, go ahead and install it since it'll give you a very noticeable increase in power, then after the p[ipe is installed take it for a ride and see how it does before playing with the jets.

You might need to get a soldering iron or a propane torch and some electronics solder and then get a micro drill bit set and pin vise then you can solder some of the jets you got shut and redrill them to get the size you need. These bits are number sized and the bigger the number the smaller the hole they will drill and most 66cc engines will be in tune with a jet drilled to #72 or 73, but at the higher altitude you live at you might need to try #74 or 75 before it'll clear up and run clean. You can get these microdrill sets from widgetsupply.com and the kit comes with bits sized from #60 down to #80 along with the pin vise to drill with, and the solder you can get from radio shack, harbor freight, or just about any auto parts store that also sells tools.
 
I agree with Dave, if you're going to run a pipe you might as well put it on, no use going through the whole process twice!
I have been trying to get my RT type carb jetted right, too. It seems that if it is jetted right at low to mid RPM, it is too rich at wide open.
I put a smaller jet in, picked up some top end speed but it seemed too lean at low speeds.
The spray bar has two holes, the higher (full throttle) hole being the biggest.

Since I still have a good NT laying around I decided to try some stuff on the spray bar. I took a number 11 exacto knife and twizzled the lower hole a little bigger. Sure enough, it richened up nice on the bottom. Next step would be to try one step leaner jetting, but-

During these experiments I developed a problem with the back tire going flat repeatedly which I've decided to blame on my bike's cheap, low pressure tires. (Genesis Onex, 29) I'm big and I think they are getting pinched or even rolled off the rims in corners due to the low pressure. It only started after they had 300 miles on them, I weigh 255. The miles (or my big white butt) might be softening up the sidewalls.

I have new Contis coming tomorrow with MTB tubes and liners, they can handle 58 PSI. I'm going to continue the carb work after the new tires are on there. Each time I got a flat I was the farthest from the house I usually go. I have a bad leg and 2 mile walks are a major problem.
 
Hey guys, thanks for the input! Not sure what you mean about the spray bar... do you have pics? I don't know my carb that well to know what you are referring to.

I have been toying with doing my own jetting because I am at a high altitude and I don't think the jets are small enough to work for me. I will install the expansion chamber and see what the results are. I'm not super mechanical so we'll see how that goes... It's just been a little frustrating because I had my old NT carb up to about 28mph and I was looking for a cruising speed of around 30mph instead of 25-27mph.

Any ideas for tune ups? I might need to de-winterize the whole thing a bit.
 
Oops -
That RT carb stuff was a little deep for non-mechanics- it isn't necessary unless you get annoyed by little glitches, the carbs run just fine over 90% of the range.

The spray bar is the brass tube in the throat. It brings gas up from the main jet. It is in the center of the carb throat, the holes are the metering jets that are uncovered as the throttle slide is raised. They point toward the engine, the output side.
On mine it is slotted so it can be turned or removed, but I found it very tight and decided to leave it where it was.
If you are new to all this, just get it jetted as good as you can, maybe you won't even have any trouble, since you are at a higher altitude and will be running a pipe.
 
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