Carby High rev sputtering

Discussion in '2-Stroke Engines' started by zmikecuber, Sep 4, 2016.

  1. zmikecuber

    zmikecuber New Member

    I have a 66cc 2 stroke engine. The carb is the red NT speed carb. This one:

    All was running good until recently, it started sputtering at seeming mid-range rpms. In addition, occasionally when I let off the throttle, it continues revving and then comes down. Also, it jerked while letting the engine run without pulling the throttle.

    Found that my exhaust gasket had blown, so I replaced that. I also disassembled the carb, cleaned it out with carb cleaner and re-assembled it. Also, tried to put electric tape around where the carb clamps on, because I read that a leak there could cause the engine to continue revving after the throttle was let go.

    Put it all back together, put in a 32:1 fuel to oil ratio, and ran it.

    It jerks like hell. It will rev up really high, and then go really low even when idling with the clutch disengaged. Then it kills. Giving it throttle causes it to rev up and down. It's reaaaaally bad.

    Anyways, does anyone have some suggestions? I checked and fuel is going to the carb. Getting good spark. My gut tells me that something's up with the carb.

  2. zmikecuber

    zmikecuber New Member

    Also, adjusting idle screw, choke, etc. didnt really help anything.
  3. Frankfort MB's

    Frankfort MB's Well-Known Member

    You've probably got a air leak at the intake or your carb is running lean

    (If you have an air leak you will run lean so try not to get confused on me;))

    Take a quick look at the plug.... The tip of the plug should be about this color

    If it's black then something is REALLY wrong with your engine

    With all the symptoms it should be a light tan color or even white.

    Attached Files:

  4. zmikecuber

    zmikecuber New Member

    It's darker than that, but not black.

    Also, it had/has extremely poor low end power. It's impossible to start from a complete stop unless I start peddling. Even then, alot of the time it sounds like it's barely firing until I get going a bit faster, then it sounds better.

    Also had alot of fuel leaking from the spark plug area.
  5. zmikecuber

    zmikecuber New Member

    I put an NGK spark plug on it... I will take pics tomorrow.
  6. Frankfort MB's

    Frankfort MB's Well-Known Member

    Make sure your plug is tight, and I'd check your head as well....

    I'd go ahead and take head off and flip the head gasket over then tighten everything back up
  7. Frankfort MB's

    Frankfort MB's Well-Known Member

    Just do a head check;)

    I typically don't have a very good one so its nice to take a second and make sure everything is there:D
  8. I was having almost the exact same problem, Electrical tape just gums it up it has never worked for me.

    What I did was extend my fuel line I put new fuel line on before extending it.. You can go to Home Depot and get 20 feet of it for under $5.

    Also so sick and tired of air leaks. Before I put the clamp onto the intake manifold? I used some high temperature J-B Weld and fill in the cracks/ Expansion slot on the card if you want to call them that.

    He has to do this quickly while the J-B Weld was still a little pliable I put the clamp onto the carburetor and tightened it down quickly
  9. Also going back to lengthening my feelings I noticed when it was running I was getting a lot of bubbles in my line after the fuel filter.

    So I when I put the new line and I put a loop in the line before The fuel filter then beyond the fuel filter I left about 4 inches of fuel line going to the carb I also was getting fuel leaking on my car in on the case crankcase. But not on the spark plug this was due to old fuel lines slowly leaking. And running down parts of the bike and engine dripping on other parts of the engine when I thought it was leaking from there it was actually dripping from other parts of the bike Engine parts.
    I had also put a 2 foot extension on the back of my muffler to clear my rear wheel so I would no longer get soot. On my man. As soon as I remove and replace all the lines and reattach the carburetor I no longer had any problems except for the jerking when I start off and to stop there when it starts jerking while you're paddling stop pedaling and pull in the clutch and give it gas and the engine will write up. But I think the main problem was the length of the fuel line because I no longer get that fluffy bubbly gas going into my intake manifold into the engine. I also think by removing the two foot quarter inch copper pipe on the end of my muffler. Was causing too much back pressure and actually cause an air leak in my carburetor.

    So that's what works for me and fix my problems
    You might want to try extending your gas line.
    And try a little bit high temperature J-B Weld in the compressions lines where you can attach it to the intake manifold.
    I have an offset intake manifold because I have carbon filter air filter. With NT SOEED CARB. Good luck to you I really hope this helps you definitely like to hear fuel line go and get that 20 foot fuel line from Home Depot for 5 bucks.

    Last edited: Sep 5, 2016
  10. zmikecuber

    zmikecuber New Member

    Will try to flip the head gasket. That's just removing the top four nuts that surround the spark, and then flipping that gasket right?
  11. zmikecuber

    zmikecuber New Member

    Cool, I will definitely try this. Fuel line sounds like a good idea. Also for the JB weld, is that going to permanently attach the carb to the intake manifold?
  12. This is a test my last 3 post did not post. I had replied to zmikecuber's post more than 3 times. this is just a test.

  13. Yep that's all you do
  14. jaguar

    jaguar Well-Known Member

    aluminum head gaskets can only conform to irregularities in the surface once. Then throw it away.
    I think even a new one is trash. I just make my own from hi temp gasket material.
    Holly and Frankfort MB's like this.
  15. zmikecuber

    zmikecuber New Member

    Found out it was a problem with the switch so it wasn't getting enough gas. Fixed! Didn't reply earlier because got busy with school/work. Thanks guys.
  16. Got problems myself how to solve I use the idle screw turn up the idle idle great in the cold now its fairly warm when I go to a stop the damn thing revs up can't turn it down throttle is a little bit damage but it should still function now when I accelerate feels like I'm only getting 1/4 throttle come to a stop damn thing revs out of control tried taking idle out limited effect check the cable still functioning I do have oil a thin layer of oil on the cylinder maybe got to be another bad motor.
  17. Frankenstein

    Frankenstein Well-Known Member

    Rpms and power are 2 different animals.

    Have a slight air leak on the carb or manifold and you'll get lots of high rpm reving when you hold the clutch, but as soon as you let it go that lean condition makes for bad torque/hp... When you get up to speed (if you get up to speed) you'll get a bunch of weak high rpm, so you can't go very fast against any slight incline or wind..

    Even leaks in your crankcase will make problems (like crankshaft arm seals) and bring low power and high reving when the clutch is disengaged. Can even get hot enough to autoignite too, meaning it runs even without spark, kill switch won't kill it and pulling the plug wire also doesn't do anything. You'd have to kill the motor by stalling it or making an attempt to run it with the choke on to make it too rich.

    Now a nice way to check if an air leak is causing that you can use something like brake cleaner to spray a tiny bit where the different parts come together, wherever you'd see a gasket. If it's leaking the cleaner will dramatically change the speed of the motor one way or another. You can use plain water in a spray bottle, which also works to find leaks.

    Give it a shot, worse that could happen is you don't have one.
  18. Just fix it an hour ago it was a frayed cable after invetigating closer thanks for your trouuble shoot though.
    I still feel it does not have enought power or throttle so after lunch going to the cable to make readjustments to see if I can get more speed from more needle pull suck up the slack adjusters. This is my fourth tank 16:1 I hope when I thin it well burnn beeeetter and accelerate faster.