Hesitant revs below 3,000 RPM when hot.

[Bradders]

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.

[Chris whit]

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.

[Nurse Julie]

Don't change jet size, just keep standard ones and play with air / mixture screws. What are the screws set at at present?

[Chris whit]

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.

[K2-K6]

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.

[Bradders]

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.

[Bryanj]

As long as there is no dust storm that should be ok

[K2-K6]

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.

[Northy]

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. 

[Nurse Julie]

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.

[Chris whit]

Thanks guys , ill try running it without the filter  . Ive got a new one from DS sitting on the shelf .

[ogri211]

Problems when hot could be down to valve clearances have you checked them?

[Bradders]

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.

[K2-K6]

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 

Let us know how you get on Bradders.

[Bradders]

I will K2-K6. Is Dave Silvers the best place to get a new filter from?