carbs are giving me a headach? can use some help.

[shark1979]

i have a 78, with a pamco ing. i am running a 155 main jet. my needle is in the middle setting. (it has 5 notches) i have tried it with the needle in the bottom notch, and one up from the bottom. bike has bad popping through out bottom end, and mid range. i can not seem to get this out in any of the settings. i have been looking at the carbs on mikesxs. but hate to buy new ones if mine can be tuned. i have read the carb guide on here. my problem is i am not a carb guy. i can never seem to get them rigth. what do you all think?

 

[Gordon]

You should have the BS38 carbs on that machine. The main needle setting is for high speed only, and work's in combination with the pilot and main circut's. Most problems are in the pilot circut, as these are very small passage's and very hard to get clean. I suggest you re- clean them, put your needle back in the middle, and go to the carb guide here for all the info you will ever need on all the carb's.Do not start with changing jet's yet, because if the pilot cicut is plugged up, they won't help. By the way, are you running the stock exhaust and air filter set-up? If so, cleaning has got to be your problem. In the carb guide, there are picture's of where the varios passage's are, and tip's on cleaning them. Not too bad once you get an understanding of them. The rubber boot's can and do crack, so a thorough inspection is also needed.

 

[shark1979]

i am running pod filters and short open exhaust

 

[Q Tip]

it's your open pipes.

 

[5twins]

It could just be that your mains are too big, way too big. You should probably need, at most, a 145 main. Personally, I would start one up on the pilots, needle leaned one step to slot #2 from the top, and 142.5 or 145 mains.

 

[Sundie]

lol - 155 is *way* too big. run 30's on the pilot, 135's on the main, and put the needle in the middle, *possibly* the second from the bottom. Going bigger than 140 on the main just ensures you're wasting fuel. and, since i find that open pipe guys *rarely* run wot and over 6k rpm, 135 will do you fine.

oh, and if your bike is squeaking at idle, pop your choke bodies off and *very very lightly* skim coat the seals with 1194 and re-assemble. They're problematic in their warping.

 

[gggGary]

Please note that there are several models of BS38s and they use different sized mailn jets. At over 30 years old we have no way of knowing which BS38s are on there unless you ID them by the pictures in the carb guide or post a pic of yours looking in the intake side so we can ID them. We will assume you have read understood and followed the carb guide because any "tuning" without that is worse than useless. Some cheap pods create their own problems by blocking air vents at the intake. No one asked about 'snych", carbs that are out of synch will cause backfiring. Before carb work, cam chain adjusted, valves set, compression checked. Intake and throttle shaft leaks are popular problem areas also, spray carb cleaner while running will show them up in a hurry. Oh if you have not read the mikes XS carb thread on here do so. Those to say the least are no answer for "not a carb guy" owners.