Topic: 72 honda cb350f carb help

[Adb350f72]

Hello everyone, new to the forum. I'm looking for some advice on getting this 350f running smooth. To try and keep things short, I've rebuilt the top end after discovering the rings in #4 shattered. Luckily no damage to the cylinder. New rings/honed, valves cleaned and lapped, NOS top end gasket kit from Japan. Had someone rebuild the carbs to save me some time. Let's just say for a small engine repair shop he should pick another business to run. So after a few linkage repairs and I thorough cleaning in a hot tank, I ordered another set of carb kits from 4into1 and did them myself. So here's where I am at, I bench synced the carbs and set slides at 1/8 with a bit. Didn't touch anything else. Installed the carbs and it fired right up and wanted to idle at 9k. I pulled the carbs and stared over. This time I turned the idle screw on 1 1/2 turns from contact. Set the slides to 7/64 (one size smaller in my drill bit index) and adjusted the full throttle stop so the slides just peak down, maybe 1/16. Reinstalled and now she won't run on anything but choke. I've ran through all the A/F from 3/4 to 1 1/2 turns out. Still not running right. Anyone got suggestions?

[Adb350f72]

So, update, I installed new points and condensers, did the static timing. Running better now. Idle is still hanging A/F is at 1 1/4 turns out. Seems to be running rich. The bike smells like fuel. Think I may pull the carbs back off and check the floats. I have them set around 21-22mm from the base to the bottom of the float. It sits on a slight angle thats why I'm saying 21-22mm what spot on the float should I be taking the measurements from? And with aftermarket kits should I set them to 24mm like I've read somewhere?

[Flyin900]

Do not use any brass parts from the 4 into 1 kit they are not the same as the original Keihin brass parts. The after market float valves are always different than OEM, yet if the FSM calls for a 22mm float level set it at that not a higher level. Bend the tang on the float to get the new valves to set to the right spec.
Always clean the original OEM brass and reuse and if not buy a new OEM pieces if one or two are damaged.

These kits these vendors are selling are from China and suspect in quality at best. A OEM Honda kit will cost $60 a carb, where you can buy the whole fours sets from some of these vendors kits for $30 for the entire set of four?

[Adb350f72]

I agree with the quality... it's not there. The original parts that were in the carbs when I got the bike were not stock parts. At least they weren't identified with the star or any other marking for that matter. I am in Ontario Canada. And apparently honda has discontinued the carb kits for this bike so I resorted to 4 into 1. Everything is working just not to where I would like. I'm hoping to dial it in a bit better, and keep my eye out for factory parts

[Flyin900]

Welcome I am in Barrie area and yes if they are all aftermarket parts then likely you will have issues somewhere in the RPM range, with the aftermarket parts being out of spec. Are all the tiny holes in the emulsion tubes clear, as that is where the air and gas are mixed. If they are even slightly plugged you will get a rich condition, or if they are the wrong size from the Chinese crap then they will never be good.

I have restored a number of the CB350F and CB400F's in the past and great little bikes. The carbs are relatively simple, yet finding parts maybe an issue. There is a guy in the St Catherine area on Kijiji who was selling a load of these CB350F bikes earlier this year. He still has a few odds and ends available and a new ad posted on there today with what he has left.

[Adb350f72]

Everything is new (aftermarket) other than the floats themselves. Emulsion tubes are new as well. She winds out pretty good just hangs the idle around 2-2200rpm inconsistently . I just went up and down the street though. I need to take out for a good ride but want to make sure I have done everything I can do to give it the most optimal conditions to run. I will look through kijiji and see if I can find him. Thanks for that, I haven't been on kijiji for a while.

[Robbo]

Since you can get the bike running on choke, warm it up and then do a compression check on all four cylinders (if you haven’t already done so).
Also, check you are getting spark on all four cylinders while you have each plug out.
Make sure all four exhaust header pipes are warming up equally when you start the bike.
If it starts on choke and runs on all four cylinders, you are heading in the right direction.

My CB350f has floats set at 21mm and air screws are 1 3/8 turns out.
She starts and warms up from choke with the idle adjustment screw needing to be turned in.
Once the bike warms up, the idle rises and I need to take it off choke and turn down the idle adjustment screw and it will maintain a steady idle at 1200 to 1400 rpm.


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[Flyin900]

Robbo you have an issue with your carbs, as that isn’t a normal procedure. There is a fast idle ramp adjustment that the FSM specs out with a specific clearance on the choke mechanism setup. Your carb setting isn’t catching the ramp properly, if you have to do that procedure.

When you close the choke that is set up properly it should not only close the choke plates on the carbs. It also increases the idle speed up to around 3K as the ramp opens the throttle slightly too. Your adjusting this manually with the idle screw.

Most owners only clean the carbs and don’t check the other adjustments noted in the FSM, such as the throttle stop adjustment and the fast idle adjustment.

[Flyin900]

Everything is new (aftermarket) other than the floats themselves. Emulsion tubes are new as well. She winds out pretty good just hangs the idle around 2-2200rpm inconsistently . I just went up and down the street though. I need to take out for a good ride but want to make sure I have done everything I can do to give it the most optimal conditions to run. I will look through kijiji and see if I can find him. Thanks for that, I haven't been on kijiji for a while.

You should check the cable routing and look for any bends in the cable that maybe causing it to hang up. Also check the cable tension where they mount on the carb cable brackets, as one that is off slightly can cause the same hang issue. Check you have no vacuum leaks with propane torch gas flowed around the carb insulators and if the idle changes you have a leaking carb insulator.

Just plug Honda CB350 into Kijiji and his ad will come up with a picture of a red CB350F side cover as the identifier.

[Robbo]

Robbo you have an issue with your carbs, as that isn’t a normal procedure. There is a fast idle ramp adjustment that the FSM specs out with a specific clearance on the choke mechanism setup. Your carb setting isn’t catching the ramp properly, if you have to do that procedure.

When you close the choke that is set up properly it should not only close the choke plates on the carbs. It also increases the idle speed up to around 3K as the ramp opens the throttle slightly too. Your adjusting this manually with the idle screw.

Most owners only clean the carbs and don’t check the other adjustments noted in the FSM, such as the throttle stop adjustment and the fast idle adjustment.

Wow…I can’t believe I have been doing it wrong for all these years.

Thanks for that valuable info.  I found a pdf from the FSM and made the adjustment (it was nowhere near spec.).  It now works perfectly.

Thank you so much .


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