Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: Bradders on August 05, 2019, 09:30:26 AM
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Morning. Been having trouble with my 440/4 recently. Starts nicely and ticks over fine( although maybe a bit fast) but it’s very hesitant to rev below 3,000 rpm. Makes pulling away from the lights or riding in slow traffic a pain. Runs nicely otherwise. Problem only occurs when hot. Any ideas what the problem might be ? Thanks in advance.
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Has it always been like this or has it only started since you fettled / adjusted / changed something?
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You should never get into guessing...but mine would be running lean..?
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Hi Julie. It’s not always been like it, just the last 6 weeks or so. Not touched anything on it but only does it when the engine is hot.
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Hi Julie. It’s not always been like it, just the last 6 weeks or so. Not touched anything on it but only does it when the engine is hot.
Most strange....I would agree with Rob, sounds like a running lean issue but unless you have picked up some debris that is partially blocking the idle jets / circuits, I can't see what else would have caused it to start recently. I know a couple of weeks ago, when we had that very, very hot weather, mine didn't feel at her best when the engine got very hot through hard riding but as soon as the air temp dropped back down into the upper 20°'s she was back to her usual running spot on state. What fuel are you using, el cheapo supermarket like i do or the upmarket expensive stuff? For a start, i would put some STP in the fuel tank and see if that has any beneficial effect. If no different, check air screw settings and if no better, report back.
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Thanks Julie. I normally get petrol from my local Shell garage in Sandhurst. When you say STP is that the same as Redex? I have just put another shot of Redex in, hopefully that will sort it. Seems odd why it only happens at low revs ?
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Redex tends to be a cleaning agent, stp a lubricating agent, used to build up cranks using stp.
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Thanks Julie. I normally get petrol from my local Shell garage in Sandhurst. When you say STP is that the same as Redex? I have just put another shot of Redex in, hopefully that will sort it. Seems odd why it only happens at low revs ?
Sorry, yes Redex. Only at low revs suggests idle jets if you haven't moved the air screw settings. Is the throttle cable tensioned properly?
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Redex tends to be a cleaning agent, stp a lubricating agent, used to build up cranks using stp.
Agree, that me getting me additives confused. I have never used STP on anything 🤣🤣🤣
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Redex tends to be a cleaning agent, stp a lubricating agent, used to build up cranks using stp.
Agree, that me getting me additives confused. I have never used STP on anything 🤣🤣🤣
Now it's hesitant and smokes ;) ;)
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"Agree, that me getting me additives confused. I have never used STP on anything"
Not to worry, it is great for building up machinery and engines as it does not squeeze out or wash away, but it is hell on earth anywhere in a "wet clutch" engine, slippery stuff!
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Is adjusting the air screws an easy job to do? Or is it best left to someone who knows what they are doing? ( not me 😀)
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Is adjusting the air screws an easy job to do? Or is it best left to someone who knows what they are doing? ( not me 😀)
It is a very simple procedure....this thread tells all. Thus was talking about a CB350/4 but 400/4's are the same.
http://www.sohc.co.uk/index.php/topic,19585.0.html
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Thanks very much Julie. Will give it a try.
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Actually could be running rich , check you plug colour and air filter first.
The air filters don't have much space around them and any slight restriction i.e. dirty air filter seen to have huge effect on running.
Oddly just had issue with one of mine, thought the air filter was fine but would splutter at 2.5-3 k and was running rich , replace the air filter all fine.
As an side I pulled the dirty pattern filter apart. The inside of the paper/cloth had a waxy feel to it and also quite hard. So although the outside looked clean, the inner bit was causing the restriction. Its was a new filter but had been in a box for 7yrs or so,so over time had gone off, if that's possible or reacted once fitted to vapours. Had me stumped for while.
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Thanks Northy. I checked my plugs last night and when compared to the photos in the manual looked like might be running rich. So for the price of a new filter I think it will be worth trying.
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Hi , did you manage to sort your problem , i have exactly the same problem , mine is bogging down when trying to set of when warm . The carbs were reconditioned a couple of months ago and all was fine . Started doing this a couple of months after . Stripped and cleaned carbs and slow running jets again . Seams to be running rich i think . Would using a smaller slow running jet sort the problem or is there anything else that you guys would suggest . Bike runs fine and pulls great with no smoke , done a colour tune and carb balance.
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Don't change jet size, just keep standard ones and play with air / mixture screws. What are the screws set at at present?
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Julie , they are set to 1, 3/4 turns , i have noticed that I don’t have to use much choke to start the bike from cold . I originally bought this set of reconditioned carbs from Gerben . Might try changing plugs and air filter.
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As above, they would be unusual to need jets away from spec if all is standard.
But running rich is clear to see and feel with no choke starting if ambient temperatures are down.
What length of time has the air filter been in the bike and is it in any way impaired? It's not unknown to get a pattern filter that hasn't got decent flow capacity so inspect carefully to make sure it's OK.
Try taking it out to see if it runs more normally mixture wise just for a test.
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Morning. Not had chance to do any of the suggestions as been away on holiday in Canada last couple of weeks, wall to wall Harley’s out there. K2-K6, could I run it without the filter for 20 miles to test or is that too long? The problem only seems to happen when the engine is hot.
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As long as there is no dust storm that should be ok
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Yes as Bryan says, ok to go without filter for that time.
It may be a good idea to use a vacuum cleaner inside the airbox when you take the filter out to remove any extraneous debris before you start it.
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Julie , they are set to 1, 3/4 turns , i have noticed that I don’t have to use much choke to start the bike from cold . I originally bought this set of reconditioned carbs from Gerben . Might try changing plugs and air filter.
They should be 2 turns (+/- 1/4 ) so close to standard but I'd screw then out a bit, try 1/4 at a time , so could be a easy fix.
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Julie , they are set to 1, 3/4 turns , i have noticed that I don’t have to use much choke to start the bike from cold . I originally bought this set of reconditioned carbs from Gerben . Might try changing plugs and air filter.
They should be 2 turns (+/- 1/4 ) so close to standard but I'd screw then out a bit, try 1/4 at a time , so could be a easy fix.
Should be 2±½ on a CB400/4, which gives a little more leeway to fettle.I have mine set at....No 1, 2 ½ out, No's 2 & 3, 2 3/8 out and No.4 2 turns out. But every set of carbs will be slightly different.
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Thanks guys , ill try running it without the filter . Ive got a new one from DS sitting on the shelf .
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Problems when hot could be down to valve clearances have you checked them?
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Rode my bike today without the air filter as suggested by Northy and seems to of solved the problem. Will try agaiin tomorrow and if ok will buy a new air filter. Also changed the gauze ( Scourer pad ) as it was a bit mucky. Thanks for the suggestions.
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Hopefully you'll find it's the same with a new filter installed now.
A friend with a 400 (years ago and new bike) had been riding to work in the rain, sunny on the way home but the bike just wouldn't run or rev at all once warm. Just about made a detour to the supplying dealer, bike chugging along at slow speed, they had a look at it, opened the seat and took out his waterproof overtrousers, at which point it ran fine again. Mostly blocked the filter box intake with the trousers ;D
Let us know how you get on Bradders.
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I will K2-K6. Is Dave Silvers the best place to get a new filter from?
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Probably DS as I doubt you'd find local stock for that bike. Unless other owners have better direction to buy.
On second thoughts, check Bike-bitz near you in Yately as he may be able to supply and it'd save you the postage charge from DS. If you go from Sandhurst to Yately, when you reach the main road there he's on the right just next to that junction.
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Thanks very much K2-K6. I didn’t even know they were there! Will give them a try.
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Oh just had other thought (like you do ).
It could be the O rings on the main jets are worn or not sealing properly , therefore making it run rich . So if the new air filter doesn't cure it that would be my next port of call.
Does mean the carbs will have come off but its not bad job if know the correct procedure.
However your issue is at low revs so suspect not .... (make up mind Northy! ......I talk to myself lot !) :o ;)
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Morning all. Some of you may recall my original post some time ago. Still having problems with rough running below about 3,500 rpm when the engine is hot, in fact it’s getting worse. Have adjusted mixture screws with the help of my mechanic so think they are probably about right. Changed plugs, air filter as well. Wondered if anyone had any more suggestions I could try. The problem is a lot worse when the engine is hot, almost to the point that it feels like the engine is going to stall when pulling away. It’s driving me nuts!
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In very, very hot weather like some of the days recently, my 400/4 behaves exactly the same and mine is set up 100% spot on. As soon as the air temp drops, she's perfect again.
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Hi Julie. It seems to do it when the weather is cooler as well. Rode it to work at 5-30 in the morning when it was nice and cool but was still the same.
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What are your air/ fuel screws set at?.
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I’m not 100 per cent sure Julie as my mechanic set them up last week. I know he started off at 2 turns out.
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You need to check Bradders, he may have started a 2 turns out but did he end up at 2 turns out or more or less? Correct Air/ fuel mix will make a huge difference to how the bike runs.
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Ok thanks Julie. Will have another look.
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When you first start it have you tried feeling the header pipes to see if they warm up evenly?
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When you first start it have you tried feeling the header pipes to see if they warm up evenly?
I haven’t tried that. Would that indicate if the leads or coils were suspect?
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I think it helps narrow down the options. eg if just 1 pipe warms up slower/not at all (I had 1 faulty plug, or it could be one carb blocked), then if it’s 1&2 or 3&4 points towards carburation as the fuel is fed to them in pairs (eg a blocked fuel tap gauze or pipe might slow the flow to one pair) or if it’s 1&4 or 2&3 more likely ignition.
I had a problem where I believe one worn HT lead was not connected well to the cap on 3, and it seemed to affect both 2&3 warning up, but produced other issues like less power once warmed up.
I’m going a bit off track but I think can be useful to eliminate possibilities or other things adding to the problem making it harder to detect.
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PS I don’t want to ‘mis-promote’ a product, but I am testing Sta-Bil ‘storage’ which seems to help cleaner running, given less smooth, older delicate carb innards ‘may’ be likely to attract more blockages. Something may be clean, but still less ‘non stick’ compared to brand new. Only my theory!
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When my 2&3 were playing up a bit 1&4 used to put out slight vapour for some reason.
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Thanks for the suggestions guys. I will start her up tomorrow and see how the headers warm up.
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It could be a coil or a cap is failing as the engine warms up, when it's cold it's fine but any heat makes them start to fail.
Any chance you can borrow a set of known good coils and caps for a test to see if it still does it?
Is it possible to test coils / caps whilst they are still on the bike?
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Thanks for your advice oddjob. I did look at Ash’s coil repair but it seemed a bit daunting to me. (I’m not the best mechanic in the world.)
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If you manage to check the pipes heating up, even if it’s not conclusive, I won’t regret replacing my 49 year old coils with DSS, plus old caps and plugs. Along with points and condensers that were 20+ years old - it is running really well now, and should for a good long time.
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Certainly a saving if one has time and skill to do it. I didn’t and at £72/pair the DS were much cheaper than some, and should last another 50 years! I’ve kept my old ones in case I get time to do the leads, or to sell to someone who can. My leads were certainly poor. I wonder if the wiring within the coils can also deteriorate after 50 years.