Idle Problem?

[miami fanatic]

I have a novarossi 421b motor it starts up and runs but if you take your finger off the trigger it dies. I Tried to screw the idle screw in but if i do the carb wont open so i think it is as far as it can go can i use my transmitter to adjust or am i not tuned correctly on my low speed needle and high speed needle?

 

[bOOm]

The opening in the carb shold be about 2-3mm from closed. If the idle adj. screw is as far in as it can go, you can adj. the idle using your throttle trim however, make sure your engine won't cut out when you hit the breaks.

 

[Rolex]

Do you have a rotary carb or a barrel carb?

 

[miami fanatic]

I think they call it a slide carb. its not a rotary carb

 

[Rolex]

Sorry, you're right, slide carb. I think barrel and rotary are the same.
Now, if you turn your idle screw in, the slide won't move with the throttle trigger?
DON'T adjust the HSN or LSN. That's not the problem. This is mechanical. It needs to be adjusted correctly. You can't do it with the trim tab. It should idle with the trim tab a full zero.

 

[miami fanatic]

What do you mean by mechanical? If i screw the idle screw any further it locks the barrel and it wont move i back it off a little and it opens up again.So how do i fix it?

 

[Rolex]

I'm having a tough time trying to figure out what's wrong here. Take off your air filter, and look in the carb. When you hit the throttle, it opens wide. When you are full OFF throttle (idle position) how much of an opening do you see.
Turn the idle screw both ways while looking in, and tell me if it's opening and closing. I can't quite figure out why it's locking the barrel.

 

[miami fanatic]

When i hit the throttle it opens all the way up.when i turn the idle screw it closes it to where theres a small crack its not shut all the way. Then it starts to unscrew it self from the carb. if i screw it in further it locks up the slide and it wont open its open about 1mm.

 

[Rolex]

I'm starting to thing that there might be a LSN problem here.
At idle, the widest part of the opening should be about 1/16th of an inch. If it looks about right, you might be having a LSN problem. Try richening it while the car is running. Just use minimum throttle...just enough to keep it running. When it starts to run at a higher RPM, then adjust your idle screw, and let us know how it is.
I can't believe I'm doing a solo on this one.

 

[miami fanatic]

thanks ill try that tomorrow and let you know thanks again

 

[miami fanatic]

I richened the low needle but now it idles high for about three seconds then the idle comes down if you try to pull the trigger it acts like its loaded up then all of a sudden it goes but feels sluggish after idle comes down if you let it sit it dies about three seconds later. I tried leaning the high speed but didnt help. The temp at idle is about 170ish. Any suggestions?

 

[mr_bob]

set the carb to where it idles fine and then sung up the idle screw just enough and then make sure the carb still opens

that should fix the problem

 

[Rolex]

Adjusting the HSN has nothing to do with idle, so leave that alone for now. It's only for WOT. You can safely lean out your LSN some more if you're only getting 170. I get about 205 at idle, and 240 running on a dirt track. So, lean it and adjust your idle screw again, since the idle will be getting faster.
If you still can't get it right, you might have an air leak somewhere.

 

[miami fanatic]

I have checked for an air leak changed fuel tank and lines everything seems fine i have the idle screw in as far as i can go it doesn't make much difference if i richen the low speed or lean it idles kinda high then wants to die i think I'm just going to turn my throttle trim up on my radio i now have it at zero. Any other suggestions?

 

[Rolex]

I think it's time to take off the carb, remove the needles, and give it a thorough cleaning. It doesn't take much to clog something where it will run, but it just won't run right. Denatured alcohol and an air hose. Do it several times. To get back to the present settings, turn the needles in and count how many turns till they close, then back them out and remove them. When you reassemble it, close them and then back them out the same amount of turns, and see how it works out.

 

[miami fanatic]

I took the carb completely apart and cleaned it put it back together and tried it same thing it idles fine then slowly gets lower and lower then dies i would say about two-three seconds.It's idling at 190-200 so i think thats good after running it hard up and down the street full throttle then full brake then full throttle again the temps are around 240 so i think I'm tuned right i still have the idle screw all the way in. It seems like it idles kinda high after i run it hard like that but then it slowly gets lower and lower then dies. Any suggestions?

 

[Rolex]

Your temps are great, both at idle and hard running. Now you're dealing with something I haven't run into yet. You'll have to wait for someone else to help you on this. I tend to think it might be an air leak somewhere, since everything else sounds fine.

 

[miami fanatic]

I have put a new tank and new fuel line on it and there is no sighns of oil on the motor so i don't think i have an air leak on the motor any where else?

 

[Rolex]

The air leak I'm referring to would be internal. Either the O-ring seal around the carb neck, or the back plate on the engine. Also check the screws on the cooling head, and make sure they're tight.
Any one else have some input here for this guy?

 

[mr_bob]

guys it can't be an air leak cuz if it was the engine would rev and then shut off or just rev like at wot


so its a carb/gas problem

is your back pressure line connected might also be called feul return line


the fuel tube from your exhast to the top of your gas tank