Unable to Perfectly Tune my Engine...

[Techbiker]

Adjusting the stock NT carburetor on my 2 stroke 70 cc Thatsdax engine has been one of the most frustrating experiences. When I was using the stock exhaust, I downsized the jet from the stock .70 mm size to a .66 mm jet. I picked up a few mph and on acceleration I was 2 stroking more.

Recently however, I added an expansion chamber. This caused my engine to run really rich with the .66 mm jet. Unburnt oil sludge was actually dripping out of the exhaust. I then installed a .64 mm jet and my plug went from dark black and wet to a drier black color. Oil is still dripping out of the exhaust, but not as badly now lol.

I have my e-clip on the highest setting so while accelerating, my engine 2 strokes consistently. However, once I reach cruising speed and load is taken off of the engine, it starts to 4 stroke constantly.

Should I downsize again to a .62 mm jet on move my e-clip down a notch or two? It seems like this might be on the small side for a 70cc engine!

Thanks!

 

[MotorNut123]

I know that the pipe is also tubeable. Look it up cause I am unsure how to tune it but there is a way to.

 

[MotorNut123]

Sorry. Tuneable by tubeable

 

[Bikeguy Joe]

You engine SHOULD break into a four stroke when there is little or no load (cruise condition). It should break back into a two stroke when you accelerate.

 

[r00t4rd3d]

Oil dripping out of the exhaust is not uncommon with 2 stroke engines either.

 

[Venice Motor Bikes]

How are you mixing your gas & oil?
How many miles do you have on your engine???

 

[Techbiker]

I am mixing my oil and gas in a 2 gallon gas can. I also have about 350 miles on my engine. I tested my engine a couple of days ago and it really does 4 stroke most of the time. It still only 2 strokes when I'm climbing a fairly steep hill. I think that I'm going to pull my motor apart and get the crankshaft balanced along with new bearings, although I don't think this will make much of a difference.

By the way, I'm using regular valvoline 2 stroke air-cooled oil at a ratio of 32:1. Do you think that I should try running a .62 mm jet?

Thanks

 

[Techbiker]

I'm under the impression that the stock jet is a .70. A smaller jet will help, but .62 seems like quite a big jump.

I'm currently running a .64 mm jet. Going from a .66 to my current one helped so I'm hoping that a smaller jet will help more. I doubt that I will need to go smaller than .62

 

[Venice Motor Bikes]

Move the 'C' clip on the carb needle to the top position. (away from the point)

 

[Techbiker]

Thanks for the advice Venice, but my e-clip is already at the highest position.

 

[camlifter]

is this a rear rack mount. is the engine setting level, if it's tilted enough to have the carb unlevel it could be flooding the float bowl. check the float level it could be set to high.

 

[Techbiker]

I did install a billet intake in order to increase performance and allow the carburetor to fit in my frame well. My carb is tilted at quite an angle. I suppose that this could be causing problems. I'll put on another intake and see if that fixes the problem.

 

[Alson]

My engine jerks some what after I put an expansion chamber on, it still jerks at 20 so I moved my c-clip up one notch and it semed to get most of the jerking gone. But when I checked my plug it was lite green, thinking it was to lean. It realy suprised me seeing green. I run maxima K2, and seafoam to clean the engine, anyway I moved my c-clip down at the 4th down ran it and checked plug and same colar, but I went 37.6 I usley go 36 but it was windy and the wind would blow two different ways. I want to go back to the 2ed from the top, but I dont want to be to lean. I dont know what to do

 

[poorboys bikes]

I put bigger jets in both my bikes leaving the clip in the middle and both my bikes run great! i get alot more low end torque and a higher top speed. One jet says 7.5 and the other says 7.75, dunno how that relates in size to the stock jet but i got a great increase in performance. regular speed carb running a 60 to 1 ratio on premium gas. my felt goes about 47-50mph with the 7.75 jet in it, spark plugs always wet when i check it! These motors have alot more potential then what most of us are getting from them!!!

 

[2door]

Here we go with the amazing speed claims again. Why is it that every thread dealing with almost every aspect of motorized bikes has to include claims of speeds that are more fantasy than fact?
Tom

 

[poorboys bikes]

I guess that would make me more of a "super moderator" than you wouldnt it!?! Come down to wichita from your little town in colorado and ill prove it!!!

 

[2door]

Yeah, whatever

Tom

 

[poorboys bikes]

I was being kind of a smart ass, but seriously, people dont take the time to make sure EVERYTHING is working perfectly like they should. Im sure you know, being a rod builder, that simple things are overlooked like wheels. Most ppl just go buy some piece O shiny crap from wally world and slap a stock kit on it. Well most of those bikes come with steel wheels and unsealed bearings that were probably very poorly greased, if greased at all. Most of the bolts and nuts are loose, axles arent put in correctly, etc. what im trying to say is I've gone over every inch of each of my bikes to make them go faster and run smoother, ending up at the carb last! But the right wheel size/gear ratio is what made the biggest difference getting my bike to run smooth and go fast!!! And weight is a huge variable too. 50mph on a motorized bike, no prob, i can peddle a bike up to 30!!! piratescycles1.com will help you go fast like me if you want!!!

 

[Bikeguy Joe]

Adjusting the stock NT carburetor on my 2 stroke 70 cc Thatsdax engine has been one of the most frustrating experiences. When I was using the stock exhaust, I downsized the jet from the stock .70 mm size to a .66 mm jet. I picked up a few mph and on acceleration I was 2 stroking more.

Recently however, I added an expansion chamber. This caused my engine to run really rich with the .66 mm jet. Unburnt oil sludge was actually dripping out of the exhaust. I then installed a .64 mm jet and my plug went from dark black and wet to a drier black color. Oil is still dripping out of the exhaust, but not as badly now lol.

I have my e-clip on the highest setting so while accelerating, my engine 2 strokes consistently. However, once I reach cruising speed and load is taken off of the engine, it starts to 4 stroke constantly.

Should I downsize again to a .62 mm jet on move my e-clip down a notch or two? It seems like this might be on the small side for a 70cc engine!

Thanks!

That's just about right. Cross ported two strokes like ours, once set up correctly will usually four stroke, or break back and forth between a two and four stroke condition when at low load/cruise.

 

[ToxicAz520]

My bike breaks back and forth from 4 to 2 stroke as well. One thing to think about that I am learning about these Ht motors is that the smallest change in tuning can make the biggest difference like one slot on the needle or one size on the jet or even placing tape over where the throttle cable goes into the carb to block air there. You just have to play it tho every engine and set up it different but the basics are the same.