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Discussion Starter · #1 ·
I just put on an emgo dunstall replica exhaust to quiet things down on my '73 cb350. I was hoping it would provide a little more back pressure than the completely open shorty mufflers it's replacing, but it doesn't. It's also a straight-through perforated baffle construction and the bike runs a bit lean I think. Giving WOT from idle or even blipping the throttle quickly from idle, it falls flat on its face at 5-6k rpm or can die outright. For those of you who have made more open aftermarket exhausts work, did you make any jetting modifications and if so, what is a good place for me to start? Should I step up both the primary/secondary mains? I am running the stock air filters and everything on the engine/ignition is in good order and set to spec.
 

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Sensei
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Buy a couple 8-packs of spark plugs.....Plug chops will tell you how well you are jetted.....

ALWAYS better to start richer than you think you'll need... Better a fouled plug than a holed piston.....
 
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Discussion Starter · #3 ·
Thanks, I'll grab some. I just pulled the carbs and I am running primary main of 68 and secondary of 105. Isn't the stock primary supposed to be 70? Again, it's a 1973 CB350.
 

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Discussion Starter · #4 ·
I just ordered a jetting kit from sirius consolidated. I'm going to step up my primary from 68 to 70 and secondary from 105 to 110. I'm just trying to figure out if it is common to have to rejet for aftermarket exhausts when everything else is stock, or if I'm barking up the wrong tree for this problem. For those of you who had to rejet for a more open exhaust, did you have to bump the primary or the secondary or both?

My new exhaust is 27 inches long so similar to stock, but considerably more free-flowing as it's straight-through. Everything else is stock. 0I also got felt seal replacements to rule out an air leak.
 

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Pilot jet? Also I live on long island so I know your pain. Have you thought it also might be your valve clearance?
 

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Discussion Starter · #8 ·
Z320, the clearances are kept to spec on the looser side. I havent checked the slow jet because it idles well and 0-1/4 throttle is fine. I'm assuming its the stock 35 (i think thats it)
 

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Discussion Starter · #9 ·
I notice that over the run of the cb350's manufacture, the jet size decreased on the both primary and secondary mains. Out of curiosity, does anyone know if the actual carb bodies changed at all over that time period? Or was it just the jets? I recall that my 79 cb750 ran better and cooler when I stepped the jets up a tad. By the time it was made in the late 70's, honda was jetting them lean from the factory to comply withh tighter EPA restrictions. Is this the case with the 350?

The primary main decreased from 70 to 68 over its run, and I believe the secondary mains went from 110 or 115 to 105. I just stepped up my 1973 350 from 68 to 70 and 105 to 110, respectively. If honda was jetting these bikes lean by the time my '73 was made, then I guess Im just returning it to the jetting it would have had if it rolled out of the factory in 1969.
 
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