SOHC.co.uk Forums > CB750
Carb rubbers
AshimotoK0:
Quote "Forgive me if I am out of order and missed the point but I would buy new rubbers if I were you.😉
Nige. Ps, and good luck"
Beginning to think you are right Nige .. The other thing is the fragility of the alloy carb mounting plate on the K0 (don't ask me how I know this ask the welder I know :( ) I would still like to know if the softening process made them go porous though or the other path of the leakage.
Ash
UK Pete:
Surely they would never be porus enough to let that much air through, the correct f2 clamp is crucial to correct sealing in my opinion
pete
Lobo:
I'd have to agree with you here Pete; the airflow volume would barely be dented by a little porosity?
Poor clamps / new splits .... more believable.
Any mileage Roy, in pressurising the Airbox (Hoover outlet) and then painting a soapy solution abouts the rubbers to look for leaks?
Simon
AshimotoK0:
--- Quote from: Lobo on April 04, 2015, 05:20:59 AM ---I'd have to agree with you here Pete; the airflow volume would barely be dented by a little porosity?
Poor clamps / new splits .... more believable.
Any mileage Roy, in pressurising the Airbox (Hoover outlet) and then painting a soapy solution abouts the rubbers to look for leaks?
Simon
--- End quote ---
When I get back to work Simon I will do some testing and plot the air decay after pressurising. There is a rubber property in the 'Industry' called compression set (CS) . I suspect it may be that the softened nitrile may not have the same CS properties, although the recovery when compressed looked OK to me. Once I have done some tests and consulted the 'oracle' guy, who has worked in the rubber processing industry for almost 40 years, I will post on the US site because they have done loads of softening with essential oils, and we can compare notes.
http://en.wikipedia.org/wiki/Compression_set
One thing I did notice with Roy's parts was that initially there were a few fine threads of rubber came off, which I assumed was moulding 'flash' but perhaps if the rubbers are removed when cold from the bike, then tearing of the surface layer could occur. I never noticed this on the K0 I softened in 2010.
I will also ask DS if he has any technical info on the pattern ones he sells. I suppose it's guys like Roy who have the biggest problem because the ones for the F2/K7 are mega expensive.
royhall:
Thanks for all your interest guys, was beginning to get demotivated with this.
Am off work today so going to take the carbs off yet again and have a really close (magnifying glass) look at this. Am wondering if the rubbers were just too hard before they were softened up. Have got a used set on the way from DK for £26 so I have a comparison. I did notice before fitting the rubbers that the engine side is about 50% thicker than the carb side, and was a fair bit harder. Maybe due to the extra thickness they haven't softened as much on that side. Will know better this afternoon after I pull them again. Will report back.
On another note. My other F2 is fitted with replica rubbers from the USA that are also leaking now. Looking online a great many people are having problems with these, most with air leaks they cannot get rid of. They look okay, but they are very soft and have a shiny finish. Don't think they are made from the correct material. There are some reports that at about a thousand miles these rubbers go rock hard, and one guy reports having a carb actually detach (snapped off rubber) whilst riding. Got these from Vintage CB750, so if anyones tempted to order these DONT. £136 wasted me thinks.
Further thrilling instalments to come. Watch this space. ;D
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