CB 350 carbs

m13 · Post by **m13** » Sat Nov 22, 2008 1:50 pm

My '71 cb 350 is confounding me. The obvious carb problem was a hole in the right float thus flooding. Took both apart, cleaned repaired float, set both levels, and no visibal damage to diaphrams. Set timing and sincronized the throttle plates to open together, Starts right up BUT when I look down the throats while increasing throttle the right slide begins to open about mid range but flutters considerably. The left slide doesn't respond till almost full throttle. Any tips or should I look for another set? I know one of the idle mix screw needles is broken. This bike starts easily without the choke even today at freezing temps. This makes me suspect problems as it wont start at all if the choke is closed. Any help would be appreciated.

e3steve · Post by **e3steve** » Sat Nov 22, 2008 7:03 pm

Service the carbs fully, using new, complete kits -- jets, needles, diaphragms, gaskets, etc. -- then setup. It's obviously waaaaay too rich as it is, and you can't be certain of correct setup with known broken parts and diaphragms that just 'look okay'.

m13 · Post by **m13** » Sat Nov 22, 2008 7:20 pm

Thanks. I'm a bit concerned if I buy second hand carbs I would just be getting a new set of problems but i was assuming that Full rebuild kits with diaphrams were no longer available. Any sources? thanks for the rapid reply

e3steve · Post by **e3steve** » Sun Nov 23, 2008 5:16 am

Assuming yours is in the K2-4 model range with Kei Hins, Retrobikes show them stocked here as KH-0119: http://www.olypen.com/retro/ but you'll need to put in a call or email about the inclusion of diaphragms, by the look of it.

Don't write off your old carbs unnecessarily until you've exhausted all servicing possibilites.

m13 · Post by **m13** » Sun Nov 23, 2008 8:22 am

Thanks I checked out the link and looks good for most parts/minus diaphragms. I'll give them a call. All my web search for diaphragms has only turned up some without slides for around 100 dollars...I'm thinking there must be a better way. I'll go over these carbs again with more detail/give the diaphragms a closer look. Thanks for the help. Maybe my memory is busted but in 1972 I had a triumph trophy and my friend a CB350 and I remember how reliable and relatively smooth the CB ran and hope to acheive that with this '71CB, a bike I recently got for my son.

m13 · Post by **m13** » Thu Jan 22, 2009 10:46 am

I want to thank e3steve for the help with the '71 cb350 that was giving me fits. Just an update. I put in new points, plugs, rebuilt the carbs with Keyster kits (again careful exam of diaphragms showed no problems) I then static timed it and syncronized the carbs. It ran good, had my son happy again to ride the bike to school for TWO DAYS, then in the middle of a ride would no longer go more than 40mph. I'm recovering from a badly busted arm and haven't been able to ride it myself, but according to my son it ran OK but above 35 or so just "hit a wall" and wouldnt go faster. Believe me, I was getting pretty frustrated with it by then and it wasn't helped by my son's dissapointments every time I thought I had "cured" a problem only to have another show up. SOoo I decided to pay a local shop to fix it as nothing I did seem to last.
What they found was one of the new throttle needles had come loose from the slide and of course was not lifting with the slide(see pic- the right is the old, the left the Keyster kit one that failed)This needle I guess is a press fit? and shouldn't separate but it did. I have to admit that when this first occured I pulled the carbs and bowls but didn't think to check the slides/needles. That where us amateurs get into trouble, I guess, not thinking things competely through. The bike runs good again and in spite of the sub freezing temps we have had here lately, he has been riding it regularly again. Thanks again for the support.

e3steve · Post by **e3steve** » Thu Jan 22, 2009 11:09 am

A pleasure. You got there in the end, and that makes for a good result! Hope the arm heals well.