Loss of Power carburetor culprit

GoldenMotor.com

gebhardm

New Member
Jul 5, 2010
33
0
0
Illinois
Hello all

Well I"ve been busy trying to get my bike to regain its power. I've tried all the suggestions all of you so kindly offered several to no avail (some of the suggestions multiple times to make sure). However I think I have definitely identified the cause of the problem. I think its the carburetor for sure. I was cleaning it and I noticed the needle valve for the fuel allows carb cleaner to blow through even though it is being held in place with my finger. Anyway I reassembled the the thing after getting it back to factory specs (as close as I could) and tested it in the following way.

1. Got bike started and once again very little power and low rpm.
2. Turned off fuel valve and watched the line. Some bubbles started rising up the tube from the bowl of the carburetor as the flow of fuel slowed. The engine suddenly started sounding like it had 3 times the power. (rpm increased, no hesitation at all) Unfortunately this only lasted about 5 seconds and then the engine started to die from lack of fuel.
3. I was able to repeat these observations a second time.

SO I see this as GOOD NEWS because I was thinking of replacing the piston rings. Anyway I think I need to replace the carb. It's an NT and I really don't want another one of them. I want to know if there are any alternatives to the NT carb. There seems to be as "new and improved" NT carb for sale as well as a High performance carb with a air/fuel sdjusting screw. Are there other possibilities?
 

GearNut

Active Member
Aug 19, 2009
5,104
11
38
San Diego, Kaliforgnia
I run a stock "early" NT myself, but the most favored high performance/ reliable carb I have observed at the 2 sites I regularly visit is the DelOrto carb.
The exact model number escapes me right now.
 

bairdco

a guy who makes cool bikes
Aug 18, 2009
6,537
264
63
living the dream in southern california
i love the NT carbs that came on my Grubee GT4. it's the same as the "speed" carb with the pink air box. i dunno if it's the same one you have, 'cause i dunno if they made an older one or not. the only problems i've had is leaking floats and secondary petcocks.

if your bike gains power with the fuel shut off, it's running rich. by shutting off the flow, you're using up the fuel in the float bowl, and as it burns, it runs better.

you said you've tried everything, but it sounds as simple as adjusting your needle clip up a notch, leaning out your fuel mixture, making sure you have a good quality plug and cleaning your filter.

if you go the aftermarket route with a Mikuni or Dellorto, expect to mess with the jetting for awhile, since they aren't made for our bikes, so you'll have to dial it in. probably be more work than figuring out yours.