How do you tune a two needle carb?

[jon2]

Hey you guys great job on all the support for the less experienced nitro tuners!I just got a hold of an OS 2BK carb that fits directly on to a 15FE. Problem is that I do not know how to actually set it to factory settings and then tune it that way!!I really need help. The carb looks similar to the OS 10E carb.but it isnow discontinued. My car takes off like it is loading up and my 2-speed doesn't seem to engage at all.

BTW I have a RTR-3 with a 2speed tranny and I have an OS 2BK carb. I want to get this solved SOON!! HELP!!!!!!:fro: :censored:

 

[kwong2001]

Well when it's loading up and having to clear it, then it's rich on the LSN. HSN sounds too rich too. I'd lean both out a tad. Just 1/8 turn at a time.

It's funny, I know how to tune but can never explain it.

 

[Candyman]

Tuning is usually done in 3 steps. But first you need to reset to factory settings. I don't know the settings for that carb, but usually they tell you to go about 3 turns out on the HSN and 2 on the LSN. If anyone knows for sure, please correct me.

First step is get it running and set the idle a little high with the idle stop. Then drive it. Get the engine up to temp by driving it for a little bit. Then make some high speed passes. If the engine is running sluggish at high speeds, lean the HSN a bit. Usually 1/8 turn at a time and then run it again. Keep doing this until no change in performance is seen. Then you usually want to richen it up about 1/8 turn to be on the safe side. Now, here's where a temp gun will come in handy. You want to try to keep the engine temp comfortable. Usually in the 250 F range. If you don't have a gun, use a drop of water. If you put a drop of water on the head, it should fizzle off in about 3-5 seconds. If it's longer, the engine is still cool. If it's shorter, you're waaaay too hot and need to richen the HSN.

Once you have the HSN done, turn to the LSN. I use the pinch test. When the engine is up and running at temp, stop the car and then pinch the fuel line. The engine should start to wind up and then stall in about 3-5 seconds. If it takes longer, the LSN is a little rich and you should lean it about 1/16 of a turn and try the test again. If it's less time, richen the needle.

Once you have them set, reset the idle so the engine will stay running, but not high enough where the car rolls at idle.

Then you should be pretty close to set....

 

[Nitroaddict]

for a complete guide - click below:
http://www.rcnitro.com/rn/articles/carburetor.asp

 

[tkhoo]

Hi Candyman, may I know that for LSN, I need to pinch the tube at where?? near the carb inlet or any place?? My fuel tube from tank to carb is around 8 inch. Please advice. Thanks.

khoo

 

[SilentHunterKellen]

doesn't matter

 

[tkhoo]

Dosent matter?? If we pinch it near to the tank the ideling will more longer...........like this we will consider the LSN is in rich side.....I think is different answer from different place we pinch the tube.

 

[DarthRacer]

For the LSN factory setting on an OS carb, the needle screw should be just about flush with the throttle arm, but not screwed out past it. If you use the fuel line pinch test, pinch it about an inch from the carb. It should only run for about 3 to 4 seconds. I have lots of experience here. I've had OS engines since my first nitro years ago. Anyway, you can use my suggestions as a base for the LSN, but you should actually tune the HSN first, then the LSN because the HSN has more of an effect on the LSN than vice versa. :yes:

 

[SilentHunterKellen]

Just make sure you pinch the fuel line in the same place if you test it more than once!