Lack of power after new exhaust and carb

[blackfox]

Ok so I drllied out the drag pipe header port. It ran better but still couldn't get up hill and lots of 4 stroking.

So yesterday I Jerry rigged my old stock nt carb on and adjusted the float a little bit.

That thing is running like a top now.

Even more power than before which it should be.

Only it still 4 strokes threw whole power band.
I still have to play with the throttle as long as I hold it in the right spot it will 2 stroke and fly like nobody's.

Major problem is the throttle gets stuck or something.

 

[Steve Best]

So, where is the throttle when it 4strokes? Full or half throttle?
I'd guess it 4 strokes at full throttle? Main Jet is too rich.
Find where the cable, grip or throttle barrel is sticking and free it up or buy new.

 

[6blueoval9]

The

Ok so I drllied out the drag pipe header port. It ran better but still couldn't get up hill and lots of 4 stroking.

So yesterday I Jerry rigged my old stock nt carb on and adjusted the float a little bit.

That thing is running like a top now.

Even more power than before which it should be.

Only it still 4 strokes threw whole power band.
I still have to play with the throttle as long as I hold it in the right spot it will 2 stroke and fly like nobody's.

Major problem is the throttle gets stuck or something.

The Metering rod on the NT operates from idle to 3/4 throttle.. Anything above that the main jet takes over.

Did you play with the metering rod C clip?.... There should be 4 to 5 grooves on the metering rod...i forget what I read but moving the clip up or down changes the mixture either richer or leaner... From what I've read most find the clip being on the second Grove from the top as being a common adjustment.

This is the thing with the NT carb... It's not fine tuneable and you can only tune to find the best "ball park " and be happy with it.

Invest in a good carb as this can carry over with you for future mods and even different engines as they wear out or blow up... I say the same for an exhaust as well.

I'm guessing your exhaust is more of a design factor to look good on the bike and thats great but it's not a power maker and it could even be the excessive back pressure from the tiny tubing causing a 4 stroking issue as the back pressure sends all that excess fuel back into the cylinder.

Play with the NT carb some more, if you can't get it running with no four stroking or a clean throttle response then I would look elsewhere for the issue like the exhaust or maybe a weak ignition spark... Plug maybe?

I found this on here.. Maybe it will help
https://motoredbikes.com/threads/nt-carb-tuning-basics.24867/

 

[Steve Best]

All good advice Blueoval! One has to learn to walk before you can fly.
The lack of adjustment features of the NT carb is exactly why it is the perfect carb for learners.
If someone cannot figure out how to get one jet and a needle to work, MORE adjustment features will only deepen the confusion.

As for power, the NT is plenty big for 3 times the stock power output.
I have played with several of the common carbs for these motors.
No significant power gain to be had over the NT.

As designed, these engines are simply amazing for what they do.

 

[KCvale]

What spark plug are running?
Get an NGK.

 

[blackfox]

The

The Metering rod on the NT operates from idle to 3/4 throttle.. Anything above that the main jet takes over.

Did you play with the metering rod C clip?.... There should be 4 to 5 grooves on the metering rod...i forget what I read but moving the clip up or down changes the mixture either richer or leaner... From what I've read most find the clip being on the second Grove from the top as being a common adjustment.

This is the thing with the NT carb... It's not fine tuneable and you can only tune to find the best "ball park " and be happy with it.

Invest in a good carb as this can carry over with you for future mods and even different engines as they wear out or blow up... I say the same for an exhaust as well.

I'm guessing your exhaust is more of a design factor to look good on the bike and thats great but it's not a power maker and it could even be the excessive back pressure from the tiny tubing causing a 4 stroking issue as the back pressure sends all that excess fuel back into the cylinder.

Play with the NT carb some more, if you can't get it running with no four stroking or a clean throttle response then I would look elsewhere for the issue like the exhaust or maybe a weak ignition spark... Plug maybe?

I found this on here.. Maybe it will help
https://motoredbikes.com/threads/nt-carb-tuning-basics.24867/

 

[blackfox]

I have played with the c clip. I got 4 slots and I put it at the top a while back and it helped a little for 4 stroking back when all was stock.

I haven't messed with it this time around it's still set on lean as possible.

Just the pipe is for to chopper look but is suppose to be a racing drag pipe. I am thinking of cutting and finding the right expansion chamber and right place to cut it in and weld it there.

 

[blackfox]

I'm running NGK B7HS

 

[blackfox]

Oh and suppose to be performance cdi and wire.
Wire looks cool doesn't make it better.
The cdi looks exactly like the stock cdi

 

[Steve Best]

II am thinking of cutting and finding the right expansion chamber and right place to cut it in and weld it there.

Even back in the 1970s I was making pipes for my CR250 and DT250 following the formulas of Jennings, Blair and Smith. A tuned pipe can make or break an engines power characteristic. I have some tuned pipes I want to try on the bike engine, but I have to get the basic engine running right first. I apologize but I haven't been doing much work on the motorized bikes this summer. It has been Blasters and KTMs this summer, and incorporating some of the lessons I learned from the bike engines.

A simple pipe with a free flowing muffler (and quiet so you can hear detonation) is an important tuning tool. Length of a pipe on a 2 stroke can still have a significant effect on where the power happens but has much less effect than a tuned pipe so you can see what the core engine can do.

I gotta tell you Blackfox, you are going about this wrong, trying to modify your way out of tuning problems with "high performance" parts. Spend the money ($10?) for a selection of jets in the 60-68 range and a bunch of plugs. Even the $2 Chinese plugs will work great. Read up on "Plug Chop" tuning and get that stock motor running great. You will love it. Then get to the basics, set your squish to 0.030", modify your stock head's chamber, but most of all, learn to be a real mechanic and tuner, not just a part swapping hack. Use a torque wrench, seriously experiment and test your changes.

Find out what really works and what doesn't.

But first of all, get it working.

In industry, we have an important trobleshooting principle (of many): Return it to its "as designed " state.
Stock, these motors will work fine. If you modify things you will never know if the problem is a basic thing, or the mods.