The Honda Owners Club

Hi,
my CB750 DOHC (83) has a problem with oil emulsification.
I do long journeys, about 100 miles around South Wales, so the oil is upto temp.
The mayonais works its way into the jets so I have to clean the carbs quite often.

I was told that the CB900s were prone to this as it was a design fault.

Any one got any idea.

Cheers

I've had a few of these motors and not had the problem. I can only think that your breathers must be blocked. I would clean them out and make sure none of the breather hoses are restricted. Also maybe worth checking your compression pressure as blow by may be building up crankcase pressure. I assume you are using a good quality oil.

Regards

Chimpy

Chimp Boy wrote: I assume you are using a good quality oil.

Regards

Chimpy

Many cars used to suffer with this problem, it was also a design fault. They got round it by using Semi or full synthetic oil.
Its caused by oil getting red hot & cooling/condensing & condensation falling back into oil thus emulsification.

I don't have experience on this bike, but as you know the emulsification is mixing oil and water, on the old mini, this was a design fault, however it can also be a sign of a small water leak. What confuses me is how it is getting to your carbs, you should not have either oil or water there!

jimmyb wrote:I don't have experience on this bike, but as you know the emulsification is mixing oil and water, on the old mini, this was a design fault, however it can also be a sign of a small water leak. What confuses me is how it is getting to your carbs, you should not have either oil or water there!

Cranckcase breathers usually feed back into the airbox. To do with U.S. emission laws I think. Instead of venting oil mist to the atmosphere, the oil gets passed back into the airbox and theoretically gets drawn into the engine and burnt. Except it usually accumulates in the air filter, clogging it...............

Landcrab wrote:...I was told that the CB900s were prone to this as it was a design fault...

The CBF's of the early 80's had their fair share of design faults but this is a new one on me.
As mentioned already i would suggest you check both crankcase vents. These vents join via a 'T' piece and enter into the top of the airbox. At the rear of the airbox are two vents, the higher one goes to what is sometimes know as the scum box and as the name suggests is there to collect all the yucky scummy stuff that can build up. The lower vent must be open to the atmosphere. A common trick is to position the lower vent pipe down and near the final drive chain which helps with chain lubing.
Also as mentioned, you need to make sure you use the right oil. You MUST NOT use normal car engine oil. These bikes have a wet clutch which is rather unrefined by modern standards and normal car oil will be pounded to pieces by the clutch and soon fill the scum box to overflow.

zkptn wrote:Also as mentioned, you need to make sure you use the right oil. You MUST NOT use normal car engine oil. These bikes have a wet clutch which is rather unrefined by modern standards and normal car oil will be pounded to pieces by the clutch and soon fill the scum box to overflow.

Which Oil would you recommend ?

Cheers Witch

Witchmaster wrote:

Red V Four wrote:Also as mentioned, you need to make sure you use the right oil. You MUST NOT use normal car engine oil. These bikes have a wet clutch which is rather unrefined by modern standards and normal car oil will be pounded to pieces by the clutch and soon fill the scum box to overflow.

Which Oil would you recommend ?

Cheers Witch

'ere, hang on, I never said that! it was 'zkptn', not me!

Hey Red sorry dont know what happened there I just used the quote button and it put you name in I didn't notice that

I have edited it know

Witch

I use Putoline Super DX4 in both my F's. It is a little more expensive than Halfords own brand but I dont have any scum and frothy shite problems and it suit a wet clutch.

bnOil used is Castrol Actevo GP 10-40 fully synthetic.
Oil breather pipes are brand new.
But

Scum box was connected to the bottom vent pipe. Have rectified this so will see how it goes.

Cheers for all the advice.

If any of you Welsh boys are around on a Sunday morning I am normally down the Downs cafe of the A48.

See ya.