Honda-SOHC

SOHC.co.uk Forums => CB350/400 => Topic started by: Bradders on July 28, 2023, 08:09:32 PM

Title: Very bad running.
Post by: Bradders on July 28, 2023, 08:09:32 PM: Evening all,

Riding into work this afternoon when suddenly my bike loses power, runs very rough and noisy. It now won’t rev above 4,000 rpm and stalls anywhere near tickover. It’s all happened very suddenly and has up until now been running nicely. Any ideas where I should start looking and what might be wrong with it? Thanks in advance.
Title: Re: Very bad running.
Post by: Sesman on July 28, 2023, 08:10:34 PM: Start looking in gumtree..😁
Title: Re: Very bad running.
Post by: Sesman on July 28, 2023, 08:11:57 PM: Seriously though, start with fuel and move onto ignition?
Title: Re: Very bad running.
Post by: K2-K6 on July 28, 2023, 08:13:54 PM: Start it from cold, run for 20 sec, check if all exhaust pipes are warm at the head.

If you've two cold, it's likely one of the ignition circuits, so which one's if that's the case.
Title: Re: Very bad running.
Post by: Bradders on July 28, 2023, 08:28:04 PM: Quote from: Sesman on July 28, 2023, 08:10:34 PM
Start looking in gumtree..😁

I must admit it sounded terminal!
Title: Re: Very bad running.
Post by: Athame57 on July 28, 2023, 08:39:05 PM: I remember having this kind of trouble a few years back, bike forever on two pistons. I'm sure I just changed the coil belonging to the offending pistons and that solved it.
Title: Re: Very bad running.
Post by: Sesman on July 28, 2023, 08:40:25 PM: Yes, must admit the diagnostic process can be a real challenge, especially for me. Stay with it and keep us updated, we always get there in the end. Could be as simple as a broken wire or restricted fuel flow.
Title: Re: Very bad running.
Post by: robvangulik on July 28, 2023, 08:45:57 PM: Or restricted air flow, not by any chance put your gloves under the seat, or rain gear...
Title: Re: Very bad running.
Post by: Bradders on July 28, 2023, 09:44:58 PM: Thanks for your replies guys, hopefully 🙏 it will be something simple.
Title: Re: Very bad running.
Post by: Oddjob on July 29, 2023, 03:07:14 AM: Quote from: Bradders on July 28, 2023, 09:44:58 PM
Thanks for your replies guys, hopefully 🙏 it will be something simple.

Roo then.

Sorry Roo, couldn’t resist.
Title: Re: Very bad running.
Post by: Laverdaroo on July 29, 2023, 08:23:56 AM: Ooo, underhand Shot from Stockport there

Sent from my iPhone using Tapatalk
Title: Re: Very bad running.
Post by: Bradders on July 29, 2023, 10:57:52 AM: Morning. Have had a quick look at my bikes running problems. Started and switched off as suggested after 20 seconds and it appeared that 2 and especially 3 exhaust pipes were cooler than 1and4.
Changed the plugs but still the same, took off the points cover and started the bike again and the points for 2 and 3 are sparking like mad! Any ideas why that might be? Sorry my knowledge is very limited.
Title: Re: Very bad running.
Post by: McCabe-Thiele (Ted) on July 29, 2023, 11:04:29 AM: What is the visual condition of your coil and leads at the coil under the tank?

Is there any sign of the outside of the leads being cracked especially where they exit the coils. You might see some arcing of the spark if it's dark enough or an absence of spark at the plug end.
Title: Re: Very bad running.
Post by: Bradders on July 29, 2023, 11:20:18 AM: The coil leads look fine with no cracking or arching. Am I right in thinking a bad condenser could cause points arcing?
Title: Re: Very bad running.
Post by: McCabe-Thiele (Ted) on July 29, 2023, 11:24:33 AM: Condensers are a magic little cylinder to me they can work perfectly for years then suddenly fail or give trouble.

Apparently reliable new ones can be hard to find - others here will give you sources.
Title: Re: Very bad running.
Post by: K2-K6 on July 29, 2023, 01:32:09 PM: Definitely looks like the condenser is failing on 2&3 system.

Temporarily, it may improve if you open that points gap slightly to at least keep the cylinders running as a possible bodge, while waiting to get a new part.

Failing condenser stops the points switching load cleanly, with the energy wanting to spark out there rather than competently operating coil function.

They are pretty slow on two cylinder aren't they, and sound like a bag-o-spanners :)

Very minor fault though, and when correct it'll be back to smooth again.
Title: Re: Very bad running.
Post by: Bradders on July 29, 2023, 02:26:59 PM: Thanks K2-K6, I have some spare condenser’s that I can try, it certainly sounded like something terminal. Any gotchas to fitting condenser’s?
Title: Re: Very bad running.
Post by: K2-K6 on July 29, 2023, 02:34:39 PM: Quote from: Bradders on July 29, 2023, 02:26:59 PM
Thanks K2-K6, I have some spare condenser’s that I can try, it certainly sounded like something terminal. Any gotchas to fitting condenser’s?

Just watch where all the little insulated washers/components go on the electric terminal post.

The circuit passes through that junction without touching anything that could give a path to earth. If it earths unintentionally, that coil won't run at all as no switching will occur.

Just careful diligence as you disconnect and re-connect the new condenser. Low risk, but puzzling if you get them wrong.
Title: Re: Very bad running.
Post by: Bradders on July 29, 2023, 02:49:32 PM: Thanks K2-K6, will try and fix them in the next couple of days.
Title: Re: Very bad running.
Post by: Oddjob on July 29, 2023, 03:35:28 PM: Swap the condensers wires over to the other points, see if the sparking follows it.

If so, change the condenser.
Title: Re: Very bad running.
Post by: TrickyMicky on July 29, 2023, 11:28:01 PM: I had exactly the same problem a few years ago. It was not long after I had replaced the complete points back plate with a nice new fully fitted out pattern one. First failure was miles from home, the very nice RAC man was familiar with these bikes and diagnosed a faulty coil, and we travelled back home on his lorry. New coils fitted, problem re-occured about a month later, so like you I removed the points cover and ran the engine and it looked like firework night. Still had the original 1976 backplate which was re-fitted along with two sets of genuine(expensive) points. No more problems!
PS the condensers are the original factory fittings, 47 years ago, the other problem with the pattern plate was difficulty in trying to get the correct timing for both sets of points. Try and stick with originals if at all possible. Have fun. Mike.
Title: Re: Very bad running.
Post by: Bradders on July 29, 2023, 11:56:26 PM: Quote from: TrickyMicky on July 29, 2023, 11:28:01 PM
I had exactly the same problem a few years ago. It was not long after I had replaced the complete points back plate with a nice new fully fitted out pattern one. First failure was miles from home, the very nice RAC man was familiar with these bikes and diagnosed a faulty coil, and we travelled back home on his lorry. New coils fitted, problem re-occured about a month later, so like you I removed the points cover and ran the engine and it looked like firework night. Still had the original 1976 backplate which was re-fitted along with two sets of genuine(expensive) points. No more problems!
PS the condensers are the original factory fittings, 47 years ago, the other problem with the pattern plate was difficulty in trying to get the correct timing for both sets of points. Try and stick with originals if at all possible. Have fun. Mike.

Hi Mike, My backplate is original but not sure about the originality of my points or condensers. If you think genuine points are expensive try original condensers, David Silver is charging over £50 each original condenser!
Title: Re: Very bad running.
Post by: Oddjob on July 30, 2023, 01:41:08 AM: I have original points and condensers, all in genuine Honda packaging, however they ain’t cheap but cheaper than DS, let me know if you’re interested, try and problem solve it first though, I only want to sell if it fixes your problem not for them to sit in a drawer because it was something else.
Title: Re: Very bad running.
Post by: Bradders on July 30, 2023, 09:13:12 AM: Thank you Oddjob. I’m sure I have my original ones stored somewhere so will try them first. Thanks for the offer. Chris.
Title: Re: Very bad running.
Post by: Bradders on August 05, 2023, 07:38:02 PM: Evening all. Have finally changed my condensers , sadly with no improvement. Number 2 and 3 points are still arcing like mad. Any suggestions what I might try next?
Title: Re: Very bad running.
Post by: Bryanj on August 05, 2023, 07:40:59 PM: Clean the contact faces with a diamong file DO NOT use sandpaperas the grains are actually glass and will act as an insulator
Title: Re: Very bad running.
Post by: Bradders on August 05, 2023, 08:04:58 PM: Thank you Bryanj, I will try that next.
Title: Re: Very bad running.
Post by: Bradders on August 11, 2023, 11:24:17 PM: Evening, have fitted my spare points to my bike after giving them a thorough clean with a file, also reset the points and re set the timing. The bike bike starts well and runs much better but sadly the points are still arcing. Any suggestions what I could try next? Thanks.
Title: Re: Very bad running.
Post by: McCabe-Thiele (Ted) on August 12, 2023, 09:54:07 AM: If you switch the coil for 1 & 4 with 2 & 3 does the arcing issue move to 1 & 4?

Are the LT wires & connections between points & coil all in good condition?
Title: Re: Very bad running.
Post by: Bryanj on August 12, 2023, 12:45:56 PM: You will always get some arcing, depends on intensity and colour, if the condenser was bad the running would be off
Title: Re: Very bad running.
Post by: Bradders on August 12, 2023, 10:07:27 PM: After a lot of faffing I’ve managed to get my bike running quite nicely now, although there is still quite a bit of arcing on 3 and 4. I’ve decided to book my bike in to the mechanics that I use to check it for me. Thanks for the advice given to me on this subject.