Author Topic: Stock carb tuning help needed  (Read 2207 times)

WTF304

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Stock carb tuning help needed
« on: August 03, 2015, 05:25:37 PM »
I'll start by explaining what's done, the kind of riding i do and the shape of the bike.

As far as any real mods performance wise not much, just normal maintenance. ... removal of the snorkel tube, new air filter for the stock air box system. Regularly change spark plugs, the stock carb is runing if memory serves me correctly a 55 pilot and i went up to a 160 main. Front sprocket is a 16 and I'm waiting on a 40 tooth rear to come in, hopefully it'll relax the engine a little more for when i do run down the highway, and an emgo muffler and i removed the core not just for more then already a loud sound .. the engine seem to run a little hotter with it in.

The riding is mostly commuter, a few times i go run an errand  or just go for a ride. Mostly back roads, lots of hills and bends, few times I'll get on the highway just to open it up and cruise and it is faster for those times that i just want to get home or where I'm going a bit quicker. Anyone who has ridden a highway on one of these knows my concern for a more relaxed engine rpm at 65 - 75 mph.

The bike was in pretty good shape when i got it last year. Spent the winter giving her a good once over to make sure she was up to the task. I've done pads, rebuilt both calipers, tires, fork seals and progressive springs, a set of CB550 rear shocks, bars and grips, clutch and EBC springs, front master was rebuilt to. Chased down a few oil leaks which was no big deal, check valve lash and adjusting them accordingly. Some preventive maintenance on the starting system, new clutch cable .... i could go on but we will say i was real anal about what i didn't / did like and what i wanted.

Lately she's developed a bit of a bog and doesn't seem to have the same pepp she did before, use to pull real good in all gears no matter the speed... incline etc. I'm thinking the 160 main is what could be the issue, possible it could be the air cut valve in the carb not entirely sure. Think I'm going to my local Honda spot and downsize on the main jet to maybe a 150 or might even put the 140 or 145 i have back in. Idles fine i had a fuel problem a while back but it was a leaky fuel line which obviously i replaced. I have been reading about everything i could find from the dyno run post and anything else i could when i have the time. The bike has about 14 K on it now ... don't think it's a mechanical problem as far as compression,  timing , etc... but i will do the necessary  tests just to validate.

I've been thinking alot of doing away with this stock carb and go to a regular slide type carb ... never did like CV styles much. Any suggestions on what to run on it with minimal changes as far as the intake manifold, air box, and possibly the throttle setup like the push / pull cables ? ... I'm open to ideas.

WTF304
Mike

scottly

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Re: Stock carb tuning help needed
« Reply #1 on: August 03, 2015, 07:26:36 PM »
Hey Mike, does the bog occur mostly between 3000-4000 RPM? Is the porcelain on the spark plug bone white? If yes, consider going to a larger main jet instead of smaller. The largest available size is a 190, and with my low restriction air filter, was still too lean. With the stock airbox, and the snorkel removed you may not need to go that large, but I would try a 170 at the least.

WTF304

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Re: Stock carb tuning help needed
« Reply #2 on: August 04, 2015, 02:38:37 PM »
The stock air box system is on the bike the snorkel is removed ... the break up is higher up in the rpm range somewhere between 4 - 5200 rpm i believe. Usually the plug has got a little soot on it but it does have a little white to the center. I've been trying to play with the screw a little while riding. ... i removed a little bit of the stopper molded to the float bowl so i can adjust on the fly. Idk if bigger is what i should do but it was a thought .... maybe I'll get a few sizes both higher and lower ...

WTF304

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Re: Stock carb tuning help needed
« Reply #3 on: August 04, 2016, 07:29:51 PM »
Well it's been a while since I've been on here and there has been a few changes since. I did go down on the main jet to a 147.5 ... definitely lost the bog down but it feels like it's limiting power output, the pilot is a 58. I have gone back to the 15 front sprocket but i dropped more in the rear to i think 36, before i changed the main i hit 93 mph and had more to go but i didn't push it past that. I have an emgo shorty 17" muffler open ( no baffle ) and yea she's kinda loud, I'm definitely going to go back to the 160 and I'm going to get one of each two sizes up ... all in all she's still running and still moving, hope all you guys are still enjoying yours aswell.

triguyracer

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Re: Stock carb tuning help needed
« Reply #4 on: August 05, 2016, 08:34:38 AM »
Have not been on the forum for  some time ,here is what worked for me as far as carb jetting ,I have a White Brothers pipe with the suppertrapp style baffles,4 disks still a bit loud, bike has  16 front sprocket and a 41 rear,the jetting that works great for me with no bog or flat spots is a 180 main with the needle shimmed 25 thousands and a one up on the pilot jet ,had to make the shim out of a small washer that was 25 thou if you do this remember that the needle needs to drop all the way down in the slide as you put it back togeather, be carefull of the outside dia of the washer you use if the out side dia is larger than the clip on the needle it will not drop down all the way in the slide but will look like it does,yes I know there is no clip on the needle but that was the best way to describe the top of the needle and what keeps it from falling.The shimming of the needle made a big diff ,until I shimmed the needle, all the going up or down with jets just moved the flat spots,The bike has the air box removed and using a Uni filter

triguyracer

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Re: Stock carb tuning help needed
« Reply #5 on: August 05, 2016, 01:55:32 PM »
Forgot to mention did you check the fuel petcock its a vac type and they do fail a regular type petcock can be bought on ebay cheap and you will know if the gas is really on and flowing freely.Got rid of my stock vac type petcock right away when I got my bike 

WTF304

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Re: Stock carb tuning help needed
« Reply #6 on: August 08, 2016, 05:28:54 PM »
I did not do away with it .... one of the other members had posted about swapping around the diaphragm in it so it worked like a regular one, which i did also a long time ago. I did go back to my 160 main ... definitely better but another factor i did not think of is possibly mechanical. Could be compression which i doubt or just normal wear and tear.

triguyracer

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Re: Stock carb tuning help needed
« Reply #7 on: August 09, 2016, 05:14:29 PM »
Check your valves if you think it is mechanical , tight ones cause low compressian