Occse Posted September 14, 2015 Share Posted September 14, 2015 What is sub air cleaner doing exactly? Does it have any connection of the diaphragms' work? Still have the stuck at 6k problem and really can't find anything. On of the diaphragms has been changed because that look a bit loose, but the stucking problem still exists. Link to comment Share on other sites More sharing options...
Member Contributer mk2davis Posted September 14, 2015 Member Contributer Share Posted September 14, 2015 I believe what you are referring to is a foam filter that is supposed to filter air before it vents. Mine was totally dried out, and I took is off. It does not affect the performance of the bike. Link to comment Share on other sites More sharing options...
Occse Posted September 14, 2015 Author Share Posted September 14, 2015 I believe what you are referring to is a foam filter that is supposed to filter air before it vents. Mine was totally dried out, and I took is off. It does not affect the performance of the bike. Yeah, the small black box. I've changed the foam in it because mine was also a piece of sh/t. Can that be that the new foam don't let enough pressure balance, and because of that the diaphragms can't go the whole way, so I have stuck problems at higher rpm? I don't think that it would get any leak air because it is doing it only higher than 6k, runs smooth 'til that. Link to comment Share on other sites More sharing options...
Member Contributer mk2davis Posted September 14, 2015 Member Contributer Share Posted September 14, 2015 I haven't had mine on for 30k miles. Test yours by taking it off and see what happens. I don't think its your solution, but the easy cheap ones are the best. Link to comment Share on other sites More sharing options...
750 Posted September 14, 2015 Share Posted September 14, 2015 Your sticking diaphragm is very unlikely to be due to that little bit of foam, it's a secondary filter - seemingly does nothing. Got a video of the sliding action problem? Link to comment Share on other sites More sharing options...
Occse Posted September 15, 2015 Author Share Posted September 15, 2015 Your sticking diaphragm is very unlikely to be due to that little bit of foam, it's a secondary filter - seemingly does nothing. Got a video of the sliding action problem? Two mechanics says that the diaphragms are OK. I do want to believe them. I'm searching for any fail in connection with the vacuum system connected to the diaphragms. Air leak due to some sort of not proper connection can do this think? I think it would be noticeable also in lower rpms. Link to comment Share on other sites More sharing options...
750 Posted September 15, 2015 Share Posted September 15, 2015 Are the diaphragms sliding correctly when opening the throttle fully? Can test by simply removing the tank and airbox and turning it over then giving it a rev. There'll be enough fuel in the carbs to do the test. Might be a blocks jet, fuel tube bit inbetween the carbs etc etc...maybe send them off for an ultrasonic clean? Link to comment Share on other sites More sharing options...
TheDutchy Posted September 16, 2015 Share Posted September 16, 2015 Check fuel delivery.. My RC36-1 (1993) would not run above 5.5krpm with the carbs hooked to a seperate fuel bottle for servicing.. Only on the fuel pump it would run in the higher regions.. Could be a fuel delivery problem if the carbs are good.. Link to comment Share on other sites More sharing options...
Beck Posted September 16, 2015 Share Posted September 16, 2015 Isn't the sub air filter related to crankcase venting??.... not fueling.... Link to comment Share on other sites More sharing options...
Member Contributer Rectaltronics Posted September 16, 2015 Member Contributer Share Posted September 16, 2015 In searching around for info about the sub air filter I've discovered that almost nobody knows what the heck it does or why it's there. But it does vent directly into the carbs (no - it's NOT a crankcase vent) so I would advise against dispensing with the filter altogether. Folks experiencing disintegrated filters report finding the filter bits in the neighborhood of their carbs' diaphragms. I found a couple of posts on bikersoracle.com which seems to explain a little about the sub air filter: when you accelerate, the slides are pulled up in the carb body. As a result, air is forced out through a small byepass hole that is connected to a tube. The tubes are connected together and exit to that small filter on the side of the main air filter. the Sub Air Filter [is] connected to the carburettor sides, near the top but below the diaphragm. IIRC it filters the air going in to /out of the space below the carb. diaphragm as that moves up and down doing its CV thing to position the needle. A look at a Honda Shop Manual will show the connection in a carb. set exploded view for disassembly.I don't know why the VFR carbs have this (presumably) sealed chamber. On other CV carbs the Sub Filter does not exist (eg my CBX750) so presumably in those the chamber is open to airflow from the main supply in the venturi. And I know from experience that when that sub air filter gets gummed up the bike runs like crap. Link to comment Share on other sites More sharing options...
Member Contributer burnes45 Posted September 17, 2015 Member Contributer Share Posted September 17, 2015 It filters air so it does not get dirt into the diaphragms. Air has to move on both sides of the diaphragms. Like a gas tank has to vent air in to let fuel out. On most other motors it just vents back into the air box. Not a separate hose and filter. Test on rebuilt carbs [not VFR] was to blow compressed air into vent to see if slide would rise. Most of the time it was at the top on the intake side of the carb. Bottom line I would replace the filter they are still available and cheep $6.00 from Bike Bandit. Link to comment Share on other sites More sharing options...
Occse Posted September 17, 2015 Author Share Posted September 17, 2015 I've put the foam away from this filter but didn't solve the problem. I think I will have to disassemble the carbs. Link to comment Share on other sites More sharing options...
Occse Posted September 17, 2015 Author Share Posted September 17, 2015 Any other tips regarding the diaphragms? Is that visible on the spark plugs if any of the diaphragms are not OK? Link to comment Share on other sites More sharing options...
V4 Rosso Posted September 17, 2015 Share Posted September 17, 2015 Air has to move on both sides of the diaphragms.Yes, but not to the outside, through a filter, where there is ambient pressure. Link to comment Share on other sites More sharing options...
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