SOHC.co.uk Forums > CB350/400

Carb sync

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Nurse Julie:
Oh dear Roy, it does sound terminal  ;D I agree with what you said about learning from the experts, and I think it's great we have such knowledgeable members on this Forum who are able and willing to share their experiences which will help us all and future SOHC members. On that note, I will go and fiddle with the newly rebuilt carbs I'm putting on my CB550 and just hope my very basic knowledge does the job.

K2-K6:
Certainly on here we are fairly well past consumer knowledge and into the back office stuff, if that's the right way to describe it.

I guess discussions about total strip and reassembly will naturally venture into more detail and it always seems more long winded written down than any face to face work through of something.
It's curious that people with low knowledge of any basics take a look at an engine and voice the opinion of how complex it looks,  will when faced with a problem start to adjust any part they can get a spanner on in the hope that they may improve it.
The bit that repeats itself fairly frequently is when someone arrives on forum with a poor running bike which is usually the result of impaired idle circuits, yet they think that a carb balance is going to sort it out. That confusion over which bit affects what is real easy to sort out if it's in front of you, but some of the problems go of for months, with the new owner getting very despondent about their latest bike purchase. If you go through the basics in the right order then it's really quite simple.
I get on some cars where for want of a little routine a problem could be solved, but they've picked out anti tamper seals, adjusted all sorts of stuff and completely lost sight of any rational diagnosis. Then you've got to check and reset everything before you can even see the original problem.
I'm happy taking the time to set anything up to run as it should, but when out using it I just want it to work, no questions asked.

kevski:
Roy i went through your build thread for this bike and am rather surprised you had not rebuilt the carbs, i guess you are beating yourself for this, i personally have never restored a bike i have a preference to preserve and only do what is needed that always includes a carb rebuild brakes and suspension, if i totally restored a bike i wouldn't use it for fear of getting it dirty, so will you be using genuine  parts or after market, i got my rebuild kits from 4 into1 in California and just used the o-rings and needle valves cheaper and quicker than David Silver the valves let by but with every set of valves i have ever bought genuine or not i have had this problem, i then polish the tips and the seat and it always works,  really in short, set every thing as stated in the manuals there is no special formula, bench sync, put it back together and see what you have in hg across the rev range, if it all runs within 3hg you are in parameters and if like me you want it closer tweek it. The one thing i set different is float heights and only by 1mm on the 350 i have them set at twenty two. Having a duff battery may not have helped you with this as the ignitions do like a good battery. Good luck

royhall:
Kev....... You must have missed the bit about me rebuilding the carbs in the restoration thread, it was quite a few pages long as carbs are a real struggle area for me for some reason    (http://www.sohc.co.uk/index.php/topic,8257.90.html)      They were given a really good clean, then done in an ultrasonic bath. They were replated where required and reassembled with new seal kits (the jets and needles etc were cleaned and reused)............ Everything was okay initially after I had sorted the petrol overflow issues, (they even synced well) but soon I developed problems on carb 4, in that it was running so rich it actually spit raw petrol from the exhaust. Thats when I decided to redo the carbs with full refurb kits......... Carb 4's problem was a way over size idle jet, looks like the PO had been cleaning it with a drill and made the hole huge, plus a chunk of float had broken away causing the float height to increase (never leaked from the overflow again though). How they synced okay like that I will never know, but the pictures are on the rebuild thread to prove it?..........So now they are rebuilt for a second time, only this time done properly.............The reason for this thread is to make sure I am setting them up as good as they can be, as they appear to be far more sensitive than the carbs on the 750. So just needed the views of the experts on here so I can learn something..........The real lesson in this is don't assume anything when it comes to carbs (or anything else), you never know what previous owners have been up to.

kevski:
Will look through it again, and you are not wrong about assumption.

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