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Discussion Starter · #1 ·
So.... I know I’m going to have to entirely rebuild the stock carbs on my recently acquired CM400 that’s been sitting with unstabilized fuel in it for 3 years. I was also thinking of (eventually) getting rid of the air box. After reading several threads on here, I am worried that I’m going to go through the entire assessment/jetting process only to have to do it again when I put on pod filters. Not being sure about the compression and condition of the engine, I’m leaning towards getting the pre adjusted mikuni setup from SpeedMotoCo in order to save myself some headaches and improve adjustability/flexibility moving forward.

What do you all think of this? Am I jumping the gun? Do Mikunis offer a significant advantage to justify the cost?


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I would asses the condition of the motor before I decide on carbs. The best carbs aren't gonna fix a non solid motor...
 

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Discussion Starter · #3 ·
I would asses the condition of the motor before I decide on carbs. The best carbs aren't gonna fix a non solid motor...
Exactly, Rob, but the way I see it; if I have to rebuild the motor, my time can be spent on that, and if it’s solid than I won’t have to factor major carb tuning into the equation. I’m trying to avoid running a long term project just to get it on the road.


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Discussion Starter · #4 ·
So I’ve gone through the bike and solved the PO’s starting issue by doing a good cleaning of carbs and air box/filter.

After more reading on this forum and seeing their condition, I’ve decided to keep the stock carb setup, but I definitely need a new air filter (old one contained a mouse nest).

Any recommendations on a good brand for a replacement air filter?

Also looking for opinions concerning replacement carb boots


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It's hard to advise on this. I'll say the the stock Keihin CV carbs are more versatile when dealing with altitude changes. Because of the design, constant velocity, they tend to regulate fuel better with larger altitude changes. Rejet is advised for continuous operation over 4-5,000 feet but not ness'y if it's temporary and that is only dropping the primary main one size.
Carburetor operation is always dependent on air density, higher elevation means thinner air requiring less fuel and inversely. If you're always running in the same +/- 500 foot elevation the Mikuni setup will be fine and you'll even be able to exceed the elevation numbers some before having to rejet.
All that said if you keep the stock setup go thru the carbs slowly and carefully, they take time to get right the first time around. Don't expect to do them in 1 day.
 

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Discussion Starter · #8 ·
Thank you LDR. The information regarding altitude in your response is particularly pertinent to my situation. I live in south central New Hampshire at 000’-1500’ above sea level and regularly travel to the coast. From what you are saying the flexibility of the Keihin carbs would suit me much better. I guess I’ll start cramming for the build.

I see that you recommended buying the Honda brand carb rebuild set, but all such sets I find only contain the gaskets. Do you have a link or part number for a Honda set that contains other parts such as jets and float screws?


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Jets are only needed if they're damaged or permanently clogged. Otherwise you use the originals except for the primary main which you want to increase one size. Jet R Us is a good source for those.
Besides the gasket kit you will want new air cut valves, aftermarket ones are fine. If you have the VB21 carbs with Black floats then aftermarket float needles are fine. The VB22 with White non adjustable floats require using OEM Honda float needles. Yes, you can use the Black floats on the VB22's.
The only kits that offer all the jets and everything else are usually wrong on the jets and the rubber used for the gaskets is not quality.
 

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Rebuild the stock carbs with Honda kits ( It is not that tough, just do it right the first time) and keep the stock air box. Make sure you put a new Accelerator Pump Kit on it and go one size up on the primary jets, then sync the carbs. Why do this? Because they run great this way and you will save $300. My 2 cents.
 

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^^+1^^
However ... IF a set of carbs are complete sh*t.. or non come with a used bike purchase...
what are say the "best" affordable replacements???
 

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I put mikuni vm32s on my cb450 because I got talked into them as an upgrade, and I thought my original carbs were damaged. I had nothing but tuning problems. I ended up taking my bike to two different mechanics and they couldn't rectify my stumble off idle after multiple jetting attempts. Rebuilt my stock carbs and they worked way better as soon as I put them back on, especially off idle throttle response. The mikunis did perform well at open throttle, but I ride mostly in the city.
 

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Discussion Starter · #13 ·
Do you think it would be ok to go with an aftermarket accelerator pump kit, in order to save some money on the rebuild?


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One of the stock carbs on my 71 CB350 is done. Rather than find one vintage replacement I'd rather get two new options that I can tune in to do the job. I'm completely new to all of this. The most mechanical work I've done in the past includes oil changes and brake maintenence. So I'm learning as I go. When swapping out carbs what would be wrong with using something like this

NASIBO Carburetor Fits Honda Rancher 350 TRX350 350ES 350FE 350FMTE 350TM 2000-2006 https://www.amazon.com/dp/B07CB1L29J/ref=cm_sw_r_cp_apa_L4ozBb244EF74

Thanks for the help. Seems like this is the best thread to fit this into.
 

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One of the stock carbs on my 71 CB350 is done. Rather than find one vintage replacement I'd rather get two new options that I can tune in to do the job. I'm completely new to all of this. The most mechanical work I've done in the past includes oil changes and brake maintenence. So I'm learning as I go. When swapping out carbs what would be wrong with using something like this

NASIBO Carburetor Fits Honda Rancher 350 TRX350 350ES 350FE 350FMTE 350TM 2000-2006 https://www.amazon.com/dp/B07CB1L29J/ref=cm_sw_r_cp_apa_L4ozBb244EF74

Thanks for the help. Seems like this is the best thread to fit this into.
Most of the 350 folks use the Mikuni VM series carbs as replacements. There several threads in the 350 Fuel section concerning this. For the SOHC 400/450 series engines reviews are mixed as for using them.
That NASIBO carb may fit and work for your 350, haven't come across that carb before.
 
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