Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: Ken4004 on September 10, 2025, 04:15:28 PM
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Hi everybody
Could you please assist me with the correct routing of cables around the steering area so specifically throttle, clutch , brake lines , Speedo and rev counter with photos if possible.
I want to avoid finding out there routed incorrectly and damaging the cables.
I also had fun and games this weekend starting up the bike for the first time since total rebuild, filled the carbs and fuel leaked out of one of the throttle bodies all over the floor not a good start do carbs off again and checked the float valves which seemed OK throttles back on with same result d as o have bitten the bulletin and bought a DS carb repair kit .
Anyway manage to get the bike to fire once and that was it no more action so checked all the obvious timing, spark, points re adjusted , compression checked again and all looks good so tried again still no joy.
A little bit of head scratching and thought maybe the exhaust is blocked with rust/carbon so I remove the silencer and tried to start again and the bike started without hesitation on three cylinders due to the leaking carb, so lesson learned there.
Didn’t realise that you cannot see straight through the silencer due to the baffle in the silencer so several taps with a rubber mallet and all the carbon/rust came out so continuously tapping and blowing through with an air line both ways then tried flushing out with a jet washer at low pressure then dried it all with a hot air gun and the exhaust seems to be clear now.
Has anyone had a similar problem with a block of exhaust ?
Just waiting for the carb kit now and will see if the bike will start on all four cylinders and then on to the next stage carb balancing probably another learning curve but I am enjoying the challenge.
Cheers in advance Ken4004
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this might help
https://info.sohc.co.uk/download/cb400f-dealer-setup-manual/
Link broken - might need to give the mods a nudge to fix it.
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Ok thanks ,your right I cannot open the link
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Hi everybody
Could you please assist me with the correct routing of cables around the steering area so specifically throttle, clutch , brake lines , Speedo and rev counter with photos if possible.
I want to avoid finding out there routed incorrectly and damaging the cables.
I also had fun and games this weekend starting up the bike for the first time since total rebuild, filled the carbs and fuel leaked out of one of the throttle bodies all over the floor not a good start do carbs off again and checked the float valves which seemed OK throttles back on with same result d as o have bitten the bulletin and bought a DS carb repair kit .
Anyway manage to get the bike to fire once and that was it no more action so checked all the obvious timing, spark, points re adjusted , compression checked again and all looks good so tried again still no joy.
A little bit of head scratching and thought maybe the exhaust is blocked with rust/carbon so I remove the silencer and tried to start again and the bike started without hesitation on three cylinders due to the leaking carb, so lesson learned there.
Didn’t realise that you cannot see straight through the silencer due to the baffle in the silencer so several taps with a rubber mallet and all the carbon/rust came out so continuously tapping and blowing through with an air line both ways then tried flushing out with a jet washer at low pressure then dried it all with a hot air gun and the exhaust seems to be clear now.
Has anyone had a similar problem with a block of exhaust ?
Just waiting for the carb kit now and will see if the bike will start on all four cylinders and then on to the next stage carb balancing probably another learning curve but I am enjoying the challenge.
Cheers in advance Ken4004
Should run fine without the silencer, your neighbors might not like it though....
Just pull off one of the plug caps and fit a spare/old plug in the cap , rest it on the engine and see if it sparks.
If a float valve is stuck open, a gentle tap on the offending carb bowl with a screwdriver handle might seat it. In any case if you turn off the fuel tap once it leaks, the bike should run for a few minutes on what's in the bowls. Also with a cold start, throttle fully closed and choke fully on.
Regarding the exhaust, I had one that rotted from the inside, it just got rather loud.
Regards Dave
Regards
Dave
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Hi Dave thanks I tried all the normal hacks to stop the bowl leaking hence ordering the new kit, I ordered the full kit because it was only two pounds more than just ordering anew valve so will keep the rest of the parts as spares.
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this might help
https://info.sohc.co.uk/download/cb400f-dealer-setup-manual/
Link broken - might need to give the mods a nudge to fix it.
Here's the one from Ash's Dropbox:
[attachimg=1]
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Carb balancing,
Its easier to do a static balance if they are off the bike and I have never improved on that using gauges. I see them as a convenience/diagnostic tool to save dismantling carbs at a later date.
Get 4 small ball bearings from a bicycle wheel.
Lay the carbs on the bench at an 45 degree angle with the inlets facing upwards.
Drop a ball bearing in each inlet and wind open the throttles with the idle adjuster. Which ever ball bearing drops through first, adjust that carb. Keep going until they all drop through within < 1/8 of a turn of the screw.
If the vacuum gages later show an imbalance look for an induction air leak somewhere.
Even if they are way out the bike should still run and rev, it will just sound like a bucket of bolts at tickover.
Float valves stuck. Don't rule out a bent float pivot that gets stuck if it sinks all the way to the bottom. I managed to bend one of mine through freeing them off after they were gummed up with varnish after a lay up. Swapped it out for a spare - problem solved.
Regards Dave
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Hi Dave
I did bench set the carbs using the end of an 1/8 inch drill bit , a method suggested on utube but your method sounds like a better option.
When I bench synced the carbs I did check that the floats were free to more when I was checking the float height but they may be a bit tricky so will check again.
A few years ago I had all four of my z1000 leaking just after I filled up with super market fuel which was contaminated with water, only got half a Mike from the garage when fuel started pouring all over the engine a scary moment with a hot engine.
I stripped down the carbs and they were completely gunned up where the ethernol reacted with the water.
So after half a can of carb cleaner reassembled the carbs and back to normal, last time I put super market fuel in my bike.
I did see a utube video where the guys used only one gauge and 4 shut off valves because he said the gauges on a 4 gauge balancing tool were not accurate to each other so I’ll try both methods.
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Thanks for the link Steve manual down loaded
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Yamaha used to supply one gauge with a rotary valve and it was a bear to use as adjusting 1 carb tends to alter the others.
A DECENT set of 4 like sealey sell is the best, these sets on a blue thin steel backing with plastic valves in the lines are not very good.
The sealey ones aint cheap but are nearest to original Honda i have seen
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I bought a set of gauges a number of years ago, when they came home the one gauge glass was broken so contacted the supplier and they sent a replacement gauge. They are not Sealey unfortunately but they are on a similar vane with the different connections etc. Not sure of there accuracy but each gauge had a calibration screw which was handy so I calibrated them all to the same vacuum source, so at least that would give me a sporting chance.😜
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How about this?
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Best "gauges" were the mercury tubed ones but I suspect those are no longer sold. There is nothing to "calibrate," gravity ensures that!!
I have a gauge set and calibrated the gauges so they all show the same reading from the same cylinder but I've had the carbs off my 400 3 times and have determined that (IMO) a careful bench sync will have them running perfectly.
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Still using my Morgan Carbtune mercury gauges, 30 or so years on. I believe Morgan still sell "vacuum" gauges just not with Mercury in them.
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This carbtune pro has been the only way to go for me. These use stainless steel metering rods. I have bench synced many bikes and it gets it close but never spot on as there are many other factors at play. Never skip a vacuum sync.
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Great advice everyone, I have a set of vacuum gauges but have not used them before and they are the budget ones so probably won’t be much good but I had an idea of calibrating them by linking them all to my mity vac that I use for brake bleeding.
The idea is to set a vacuum and with all gauges connected to the same vacuum source and adjust them together.
I expect there is quite a knack to setting up the carbs and I am sure you all have your own method that you prefer.
I am not sure how often they should be checked but will probably do them when I recheck the timing at 1500 mile intervals.
The mercury gauges look great just the right tool for the job but probably rare as hens teeth now but I’ll keep my eyes open you never know a set might turn up.
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Thanks for all the information not ready on cable routing will crack on with this at the weekend, just the job when it’s pouring with rain just put on some good music and crack on.
I wish I knew what I know now I would have bought a large amount of bike spares years ago but hind sight is a wonderful thing , I dare not try and tot up the amount of money I have spent on this bike over the years.
I can only assume Dave Silvers has a big house !
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Mr Silver once offered to tell me how much i had spent, i declined!
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Yes, I learned that lesson - NEVER review the costs and don't bother trying to make a logical explanation to anyone (other than another motorcyclist) for spending the money. ;)
I just bought a '21 motorcycle in like-new condition and have replaced the perfectly functioning OEM rear shocks, front forks (new cartridges), mufflers, installed a center stand and an ECU reflash. Bike ran perfectly prior to any of this...and still does! ;)