SOHC.co.uk Forums > CB350/400
Bike over heating after 40 mile ride
Ken4004:
--- Quote from: Ken4004 on May 03, 2026, 07:31:06 AM ---
--- Quote from: exvalvesetdabbler on May 02, 2026, 07:40:01 PM ---I don't think fuel flow is the issue here, you're getting more than enough.
Time to check the easy bits before tearing stuff apart too much
Spare bit of pipe on the fuel tap into a clean recepticals and try the fuel tap in both pisitions
Choke flaps fully open once the leaver is clicked in the open position
Corrosion inside the post where the main jet sits, or fuel getting by the o ring
Float heights are the float valves sealing or allowing the fuel level to rise too much
Clean plugs with a blow torch before trying again. There's always a risk that you have cleared the problem but not burned the crud off the plugs during normal running.
Sounds like you are going through the same mill I did 15 years ago. I replaced all the brass ware in the rebuild kit but the needles and emulsion tubes are not in the kit.
Regards
Dave
--- End quote ---
Hi Dave when rebuilding the carbs I checked the float heights and they were all spot on, did have an issue with float valves and had fuel leaking out the drains so I have changed all the valves and all looks good .
I have drained the tank a couple of times through the tap and flow was good but will check again .
Can you please clarify what you mean by emulsion tubes ?
I am going on holiday for three weeks on Monday so running out of time but will pick this up again when I get back.
Would you be interested in meeting up when I get back for a coffee at a neutral venue it would be nice to meet you face to face, I am only in Copthorne near Gatwick and I see your only in Wimbledon so not far away from each other.
Cheers Ken
Hi Dave sorry I was being a bit thick I know what you mean by Emulsion tubes , when I stripped the carbs they were all partially blocked with hard deposits. I have some very fine drill bits at home so cleaned out the holes with a slightly smaller drill bit and then followed through with the correct size without removing any of the tube material but they were pretty bad but they are clean on all carbs.
--- End quote ---
K2-K6:
--- Quote from: Skoti on May 03, 2026, 06:43:23 AM ---
--- Quote from: K2-K6 on May 02, 2026, 08:42:27 PM ---From this "Just to clarity when the bike died it would not even turn over until it had cooled down" do I understand correctly that it had partially seized, which stopped you turning the engine over ken4004 ?
--- End quote ---
That sets alarm bells ringing especially after a recent engine rebuild.
A partially blocked oil pump strainer gauze screen (possibly with surplus gasket
sealer etc) can cause restricted oil flow to the cylinder head, over heating and eventual camshaft seizure.
I'd pull the sump pan off and inspect the strainer gauze and check the oil filter at the same time.
Good luck
--- End quote ---
It does for me too, and similarly feel caution in checking possible cause is time well spent.
My thoughts also go into running lean, the situation described with high heat long hill, flat spot (classic lean consequence) and motor coming to a stop. Then not re starting but free when cooled .... suggest "nipped up" to me, if no poor oil supply etc that points to classic partial bore seizure.
Skoti:
--- Quote from: Ken4004 on May 03, 2026, 07:57:19 AM ---
--- Quote from: Ken4004 on May 03, 2026, 07:31:06 AM ---
--- Quote from: exvalvesetdabbler on May 02, 2026, 07:40:01 PM ---I don't think fuel flow is the issue here, you're getting more than enough.
Time to check the easy bits before tearing stuff apart too much
Spare bit of pipe on the fuel tap into a clean recepticals and try the fuel tap in both pisitions
Choke flaps fully open once the leaver is clicked in the open position
Corrosion inside the post where the main jet sits, or fuel getting by the o ring
Float heights are the float valves sealing or allowing the fuel level to rise too much
Clean plugs with a blow torch before trying again. There's always a risk that you have cleared the problem but not burned the crud off the plugs during normal running.
Sounds like you are going through the same mill I did 15 years ago. I replaced all the brass ware in the rebuild kit but the needles and emulsion tubes are not in the kit.
Regards
Dave
--- End quote ---
Hi Dave when rebuilding the carbs I checked the float heights and they were all spot on, did have an issue with float valves and had fuel leaking out the drains so I have changed all the valves and all looks good .
I have drained the tank a couple of times through the tap and flow was good but will check again .
Can you please clarify what you mean by emulsion tubes ?
I am going on holiday for three weeks on Monday so running out of time but will pick this up again when I get back.
Would you be interested in meeting up when I get back for a coffee at a neutral venue it would be nice to meet you face to face, I am only in Copthorne near Gatwick and I see your only in Wimbledon so not far away from each other.
Cheers Ken
Hi Dave sorry I was being a bit thick I know what you mean by Emulsion tubes , when I stripped the carbs they were all partially blocked with hard deposits. I have some very fine drill bits at home so cleaned out the holes with a slightly smaller drill bit and then followed through with the correct size without removing any of the tube material but they were pretty bad but they are clean on all carbs.
--- End quote ---
--- End quote ---
Emulsion tubes on a CB400F, also referred to as needle jet set.
https://www.cmsnl.com/honda-cb400f-england_model14639/zestaw-igiel-odrzutowiec_16012377004/
I had the same symptoms on my F1 as Dave so nicely described on his earlier post above.
Went into denial mode when I saw the price, but when I eventually bit the bullet and renewed them it felt like I was riding a different bike. Very happy.
K2-K6:
--- Quote from: Mikep328 on May 02, 2026, 04:16:58 PM ---From the experience with my 400F over the past few years, the bike will run great on E10 fuel with totally stock settings on everything - jet size, needle position, airscrew turns, STOCK type muffler and stock air filter/airbox. As noted, leaving untreated fuel (without some sort of fuel storage additive) in the tank and especially in the carbs for extended period will have bad results.
--- End quote ---
I don't see particular problems either, but here with possibly lean mixture (flat spot etc) it could help compound any effects by containing more oxygen in fuel mix.
There's reasonable margin (there usually is on non accelerator pumped slide carbs) as they have to be set with bias to slightly rich to run correctly (the bog std setup) but with needles dropped plus E10, there's some measure of compound effect that eats the margin provided by standard settings.
My view is that these engine are very sensitive to being run in the correct air fuel range, when everything is fine. Outside that though, unintended consequential problems quickly build.
Ken4004:
--- Quote from: K2-K6 on May 03, 2026, 08:27:42 AM ---
--- Quote from: Mikep328 on May 02, 2026, 04:16:58 PM ---From the experience with my 400F over the past few years, the bike will run great on E10 fuel with totally stock settings on everything - jet size, needle position, airscrew turns, STOCK type muffler and stock air filter/airbox. As noted, leaving untreated fuel (without some sort of fuel storage additive) in the tank and especially in the carbs for extended period will have bad results.
--- End quote ---
I don't see particular problems either, but here with possibly lean mixture (flat spot etc) it could help compound any effects by containing more oxygen in fuel mix.
I am always running the bike on E5 my Triumph I alternate between E5 and E10 so would that be E7.5 ( sorry little joke)
I have had a busy morning , removed exhaust and it’s clear, remove oil , removed oil filter, removed exhaust , remove sump and checked sump filter which had a little debris but nothing I would say would restrict oil flow around the engine.
All back together snd going to re do the timing and re sync the carbs and thats me done for the day.
There's reasonable margin (there usually is on non accelerator pumped slide carbs) as they have to be set with bias to slightly rich to run correctly (the bog std setup) but with needles dropped plus E10, there's some measure of compound effect that eats the margin provided by standard settings.
My view is that these engine are very sensitive to being run in the correct air fuel range, when everything is fine. Outside that though, unintended consequential problems quickly build.
--- End quote ---
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