Cobra drag pipe carb mods shimming vs rejetting

[calcruiser]

looking for anybody's experience with shimming the needles for a bike with cobra sixes and baffles in.  my gut is telling me this is the way to go to reduce popping and gurgling.  guts telling me leave the jets alone.  happy to do whatever is best though to get it dialed.  probably try shimming first since it's so easy anyway and seems to me like it would solve the problem perfectly, but feedback is highly valued on this site.  it's my first bike with cobra drag pipes.

[Chrisj CMA]

looking for anybody's experience with shimming the needles for a bike with cobra sixes and baffles in.  my gut is telling me this is the way to go to reduce popping and gurgling.  guts telling me leave the jets alone.  happy to do whatever is best though to get it dialed.  probably try shimming first since it's so easy anyway and seems to me like it would solve the problem perfectly, but feedback is highly valued on this site.  it's my first bike with cobra drag pipes.

I had Cobra pipes on for many years. Didn't need any carburetor changes whatsoever. Bike ran great!!

[98valk]

when g

looking for anybody's experience with shimming the needles for a bike with cobra sixes and baffles in.  my gut is telling me this is the way to go to reduce popping and gurgling.  guts telling me leave the jets alone.  happy to do whatever is best though to get it dialed.  probably try shimming first since it's so easy anyway and seems to me like it would solve the problem perfectly, but feedback is highly valued on this site.  it's my first bike with cobra drag pipes.

when going off throttle all gas engines go lean temporarily thereby the popping.

opening up the idle mixture screws help reduce it, open too much will be too rich and mpg tanks.
there are two types of popping lean is more common and too rich is less common.

[calcruiser]

[/quote]

I had Cobra pipes on for many years. Didn't need any carburetor changes whatsoever. Bike ran great!!
[/quote]

thanks for input, glad to hear that.  i'm going to hold off on any carb mods until i'm sure everything is buttoned up tight. i'll do new exhaust gaskets, install air box mod kit from valk carbs and customs, new intake tube 0-rings, new intake boots, and replace vacuum lines with silicon tubing.  if it still pops i'll fool with the mixture screws.  there is no doubt it's too lean right now.

[calcruiser]

when g

looking for anybody's experience with shimming the needles for a bike with cobra sixes and baffles in.  my gut is telling me this is the way to go to reduce popping and gurgling.  guts telling me leave the jets alone.  happy to do whatever is best though to get it dialed.  probably try shimming first since it's so easy anyway and seems to me like it would solve the problem perfectly, but feedback is highly valued on this site.  it's my first bike with cobra drag pipes.

when going off throttle all gas engines go lean temporarily thereby the popping.

opening up the idle mixture screws help reduce it, open too much will be too rich and mpg tanks.
there are two types of popping lean is more common and too rich is less common.

i think this bike wants more gas.  i'm gonna seal it up tight and see what happens.  once sealed up i'm guessing i'm gonna need to adjust out a 1/4 to 1/2 turn on mixture screws.  shimming probably ain't the best approach on a bike with a hydrolock curse.  appreciate your input.

[98valk]

I had Cobra pipes on for many years. Didn't need any carburetor changes whatsoever. Bike ran great!!
[/quote]

thanks for input, glad to hear that.  i'm going to hold off on any carb mods until i'm sure everything is buttoned up tight. i'll do new exhaust gaskets, install air box mod kit from valk carbs and customs, new intake tube 0-rings, new intake boots, and replace vacuum lines with silicon tubing.  if it still pops i'll fool with the mixture screws.  there is no doubt it's too lean right now.
[/quote]

major source of vacuum leaks has been the vacuum caps on the intake manifold carb sync nipples.

silicone tubing doesn't like gasoline and its fumes. best to replace with Buna-n aka nitrile which is what the factory uses, however there are different grades of buna-n. u need to buy the higher grade type. Buna-N doesn't like sunlight so Viton is a better choice for sunlight if u what zero problems for the next 30yrs.

if your intake manifold o-rings were leaking, the idle would be going up and down due to a vacuum leak. tighten the boot clamps, manual requires all fasteners to be checked every 8k miles.

exhaust nuts only take 7 ft/lbs.

unleaded gas does not color the spark plugs porcelain like leaded gas did, so not an indicator of leaness.

http://www.factorypro.com/tech/tech_tuning_procedures/tuning_carbtune,CV,lower_rpm_engines.html

http://www.factorypro.com/tech/tech_tuning_procedures/tuning_pilot%20jet,%20affect%20of%20size%20on%20idle%20and%20cruise.html

[calcruiser]

thanks 98 tons of valuable info.  didn't know the gas and silicon thing. i checked those caps and look alright, but it's all old stuff.  i'll get the viton tubing.  in my case it was another indicator of leaking intake manifold o-rings, oil pooling on the engine around the tubes.  bikes don't like to sit.  think this one sat for quite awhile.  i know it's a great engine though.  thanks again for your help gettin it right.  i'll rebuild the carbs on it this winter and should be done with it.

[98valk]

thanks 98 tons of valuable info.  didn't know the gas and silicon thing. i checked those caps and look alright, but it's all old stuff.  i'll get the viton tubing.  in my case it was another indicator of leaking intake manifold o-rings, oil pooling on the engine around the tubes.  bikes don't like to sit.  think this one sat for quite awhile.  i know it's a great engine though.  thanks again for your help gettin it right.  i'll rebuild the carbs on it this winter and should be done with it.

"oil pooling on the engine around the tubes."  that is the gasket hi-tack used on the o-rings to hold them in place on the assembly line melting and seeping out. any time there is a vacuum leak on a intake manifold the engine idle will go up and down and never be steady.  Carb rebuild? OEM o-rings don't go bad unless exposed to chemicals they don't like. pull the bowls and clean the main and pilot jets along with the bowls. bowl gaskets will be fine to reuse.