[74chaparral]

my sleds a 74 chappy ssx 440. i have quite a few questions...

what is the best way to adjust my carbs..?? everytime i ride i have to get new plugs. im running ngk-br9es. it seems like my left cylinder loads up and fouls my plug out. my carbs are synched and clean. at first if i hit full throttle from take off it bogs down then when i release a bit it will pop pop then take off. i have to eeze the throttle then floor it if i want it to open up like it should. there is many aftermarket parts on this engine so idk i think its a spark problem sumhow. cuz if im not gentle with the throttle it seems like it will bog down. i have to listen and feel if its running rite then i can open it up but only sumtimes it will most of the time if i just try to floor it it will bog down then i have to back off the throttle till it runs rite then i can hit it all the way.. COULD IT BE my coil? any help is very appreciated. thanks alot everyone

 

[RJ Gleason]

First off, stop using resistor plugs, the ET ignition can not handle it.
Use B9ES instead, this should also solve the fouling issue.

 

[74chaparral]

okay i didnt know that.. when i got the sled last year thats what was in it and it was screamin. soo b9es. do u think my coil has anything to do with it also.. thank you oh im pretty sure it has a tiger cd ignition?? should i still run b9es

 

[RJ Gleason]

Single coil with two wires on it, or two separate coils?
Single coil would be CDI and needs the resistor plug, two coils is ETI and uses non-resistor plugs.

Unfortunately, I can not find anything in any of my manuals on that engine as it was a manufacturers build only.
All I can find is that is is 438cc and uses 2 BN40 carbs.

 

[74chaparral]

it is a single coil. and yes it has 2 carbs.

 

[RJ Gleason]

OK then, you want the resistor plugs.
You might find more info here;
http://vintagesleds.com/bs/index.php
http://www.vintagesnow.com/index.html

 

[74chaparral]

Thanks rj.. do u know how to adjust the bn40 carbs.?? the only setting screw is on the left side and i was told to start at 1 1/4. but i cant seem to get them working properly. any suggestions??

 

[RJ Gleason]

I have nothing on those either unfortunately.
You will have much better luck getting help on the Vintage sled forum.

 

[Old Man]

There should be 3 adjusting screws. The one on the left is the Idle Mixture and 1 1/4 turn out from gently seated is the initial setting. On the right side the top screw is the High Speed Mixture Screw. 1 1/4 to 1 1/2 turns open is the initial setting. Clockwise rotation of either of these two screws leans out the mixture.

The lower screw on the right is the Idle Speed Screw. Adjust after engine is at operating temp until the desired idle speed is obtained.

I guess the big question is have you disassembled and cleaned the carbs? Adjustments don't help much if the carb is clogged up or has worn parts.

 

[palmrose2]

There should be 3 adjusting screws. The one on the left is the Idle Mixture and 1 1/4 turn out from gently seated is the initial setting. On the right side the top screw is the High Speed Mixture Screw. 1 1/4 to 1 1/2 turns open is the initial setting. Clockwise rotation of either of these two screws leans out the mixture.

The lower screw on the right is the Idle Speed Screw. Adjust after engine is at operating temp until the desired idle speed is obtained.

I was thinking that this Chappy is running Mic float/butterfly carbs. If true I think there are two screws. Idle speed and idle mixture. High speed is controlled by main jets like VM Mic. Idle speed screw sets against throttle shaft and should be pretty obvious. Pretty sure idle mix is on top in vertical position.

 

[Old Man]

I was thinking that this Chappy is running Mic float/butterfly carbs. If true I think there are two screws. Idle speed and idle mixture. High speed is controlled by main jets like VM Mic. Idle speed screw sets against throttle shaft and should be pretty obvious. Pretty sure idle mix is on top in vertical position.

"have a 74 chaparral 440 it has 2 42mm mikuni Spill-Dam carbs. bn042

DOES ANYBODY know how to adjust these!! thanks alot guys"

http://www.snowmobileforum.com/vintage-snowmobiles/58162-mikuni-s.html

He's talking about the Mikuni BN carb which is the diaphragm carb with a butterfly throttle. Totally different carb from the Mikuni B carb. In 1974, all Chaparral sleds used the Mikuni BNO 42 or BNO 38 diaphragm carbs.

 

[palmrose2]

"have a 74 chaparral 440 it has 2 42mm mikuni Spill-Dam carbs. bn042

DOES ANYBODY know how to adjust these!! thanks alot guys"

http://www.snowmobileforum.com/vintage-snowmobiles/58162-mikuni-s.html

He's talking about the Mikuni BN carb which is the diaphragm carb with a butterfly throttle. Totally different carb from the Mikuni B carb. In 1974, all Chaparral sleds used the Mikuni BNO 42 or BNO 38 diaphragm carbs.

Whoops.

 

[74chaparral]

There should be 3 adjusting screws. The one on the left is the Idle Mixture and 1 1/4 turn out from gently seated is the initial setting. On the right side the top screw is the High Speed Mixture Screw. 1 1/4 to 1 1/2 turns open is the initial setting. Clockwise rotation of either of these two screws leans out the mixture.

The lower screw on the right is the Idle Speed Screw. Adjust after engine is at operating temp until the desired idle speed is obtained.

I guess the big question is have you disassembled and cleaned the carbs? Adjustments don't help much if the carb is clogged up or has worn parts.

the carbs are clean and have no visible problems. there is a what i understand a mixture screw on the left side of the carb and there is a small screw on the right sides that seems to have to be all the way in. there is also a screw with a nut on the top of the carb with a bent washer so it cant turn unless i bend it back down then i can turn it out but they are both all the way down. idk i tried adjusting them and nothing was different.. ????

 

[Old Man]

Sounds like your inlet needle and seat may be worn on the carbs. Most parts are hard to come by for the BN carbs. This link may help.

Mikuni Needle Valve Conversion