bs38 or bs34 ?

[Scrambled]

My '78 came with stock bs38 , the early model ,no factory preset on the idle mixture. I want to squeeze a few more horses out of it , so is it worth while rebuilding and re- jetting them ? Are the bs 34s better ? Can I use them ? Or should I just buy performance carbs ? The bike is running good with the stock 38s, but I am going to be putting an electronic ignition in it, a 2into1 header and free flow muffler, K&Ns irridium plugs , thats about it, just a few bolt on performance bits , no need to tear down engine cause it runs nice (low miles ) .

 

[5twins]

You have one of the best sets of the 38s, the latest and most refined. The 38s are supposed to make a bit more top end power than the 34s because they're bigger. The 34s are also a nice carb, even more modern than the 38s, but can be harder to tune because they are more E.P.A. strangled. The choice is yours but I wouldn't switch unless my originals were no good.

In your list of proposed mods, don't use K&Ns, get UNI pods instead. They work better, are cheaper, and are easier to tune with.

 

[Scrambled]

You have one of the best sets of the 38s, the latest and most refined. The 38s are supposed to make a bit more top end power than the 34s because they're bigger. The 34s are also a nice carb, even more modern than the 38s, but can be harder to tune because they are more E.P.A. strangled. The choice is yours but I wouldn't switch unless my originals were no good.

In your list of proposed mods, don't use K&Ns, get UNI pods instead. They work better, are cheaper, and are easier to tune with.

Good, thanks ! You probably saved me a lot of money and grief . Now all I am going to do is rebuild and rejet. And buy the Uni-pods. I guess I can get more midrange by adding more teeth to the rear sprocket. Should work, I am building a vintage style scrambler.

 

[5twins]

If you do want to make a carb change and want better midrange, use a '76-'77 set of 38s or the 34s. The '76-'77 38s came with the richest midrange settings (largest needle jet) and make great midrange power. The 34s make good midrange power simply because they're a little smaller. Smaller carbs are better in the midrange but lose some on the top end. Your '78-'79 38s were set up to produce more top end power (larger mains) and as a result, the midrange power is down some.

 

[Scrambled]

If you do want to make a carb change and want better midrange, use a '76-'77 set of 38s or the 34s. The '76-'77 38s came with the richest midrange settings (largest needle jet) and make great midrange power. The 34s make good midrange power simply because they're a little smaller. Smaller carbs are better in the midrange but lose some on the top end. Your '78-'79 38s were set up to produce more top end power (larger mains) and as a result, the midrange power is down some.

There is a sweet stock '77 for sale not far from me , it only has 14000 klicks on it and it has been listed on Kijiji for a couple of weeks . Now I am really tempted to buy it (just for the carbs ). The guy is only asking $2000 , I wonder how low he will go ?

 

[retiredgentleman]

My 78 SE was equipped with a 36 tooth rear sprocket as stock. I changed to a 33 for better gearing on the highway. The 36 gave great acceleration around town.

Does your 78 still have a 36? If not, put a 36 on the rear, if you want the quick snappy acceleration.

 

[Scrambled]

I want to go even bigger than that . I don't need to go much over 60mph , and I do want my scrambler to have some real off road ability , so I figure somewhere in the 50 tooth range and I should be doing third gear clutch wheelies no problem.

 

[retiredgentleman]

I want to go even bigger than that . I don't need to go much over 60mph , and I do want my scrambler to have some real off road ability , so I figure somewhere in the 50 tooth range and I should be doing third gear clutch wheelies no problem.

Maybe try something around a 40 tooth, you may be surprised just how low a gearing that will give you.