Technical Discussion Topics related to Technical Issues

Diaphragm/Vacuum Piston on VTR Carbs

Old 08-18-2006, 09:52 AM
Thread Starter
Vincent's Avatar
Join Date: Mar 2006
Posts: 83
Diaphragm/Vacuum Piston on VTR Carbs

Can someone take a look in the Service Manual at the images of the Diaphragm/Vacuum Piston on pages 5-10 and 5-14 compared to the drawing on page 5-12. When reinstalling this part, do you want the bell to be down over the piston body or turned out towards the cover?
Vincent is offline  
Old 08-18-2006, 10:34 AM
World Champion
Hawkrider's Avatar
Join Date: Dec 2004
Location: Fulton, MO
Posts: 105,285
Hawkrider will become famous soon enoughHawkrider will become famous soon enough
You want this as on 5-10 and 5-14. I have found it much easier to install the slide/diaphragm assembly into the cover first and then installing the two parts together onto the carb. I minimizes the fumble-fu*k that occurs trying to deal with the long spring. Careful, don't pinch the diaphragm. Also, use one hand to install and hold together the ***'y and the other to guide the needle into the main jet.
Hawkrider is offline  
Old 08-18-2006, 10:42 AM
BeerHunter's Avatar
Join Date: Jun 2005
Location: San Antonio, TX
Posts: 489
BeerHunter is an unknown quantity at this point
You want the diaphram down. Then drop the piston in slowly just until the diaphram contacts the carb mating surface. Use a finger underneath the piston to hold it in place while you seat the diaphram. You can check the fit first by placing the carb top on without the spring in place, to get a feel for how it should look when it is assembled properly.

Putting it all together along with the loooooong stock spring is a bit of a pain in the *** (here, shorter DJ springs are a god send). Using a pen, pencil, or long screwdriver shank as a guide you can compress the long spring into the cap. This will help you get the cap back on without disturbing the position of the diaphram.

Once the cap is in place , you can then remove your finger from the underside of the piston and commence to installing the screws. This is how I do it. Others here may have different methods that could work as well.
BeerHunter is offline  
Old 08-18-2006, 10:43 AM
Senior Member
Stumpy's Avatar
Join Date: Jul 2006
Location: Madison Wisconsin
Posts: 639
Stumpy is on a distinguished road

If you put a very very small amount of KY jelly on slide boot to hold it on carb it is real easy to install. in my opinion just a thought. It works great for me
Stumpy is offline  
Old 08-18-2006, 11:20 AM
Senior Member
mikstr's Avatar
Join Date: Apr 2005
Location: Montreal
Posts: 5,560
mikstr is on a distinguished road
KY jelly huh? lol Somehow I think I am getting wise to the reason you sign as Stumpy, he he

mikstr is offline  
Old 08-18-2006, 11:50 AM
Senior Member
kai ju's Avatar
Join Date: Jun 2005
Posts: 523
kai ju is an unknown quantity at this point
What works for me is to keep the slide at full throttle with a large bottle cap. Insert it into the throttle bore so that supports the slide from underneath.
This keeps both hands free for the spring/cap installation where I follow the same procedure as Beerhunter.
The bottle cap I found that works really well is what comes on the Honda four quart oil containers but anything that just fits in the bore will work.
Don't forget to remove it when you're done.
Kai Ju
kai ju is offline  
Old 08-07-2007, 07:02 AM
Join Date: Jul 2007
Posts: 48
camaroguy72 is on a distinguished road
i was thinking about using some glue to hold the diaphragm in place while i put the cap/spring on... i cant get the rear carb to create vacuum and there are no tears in the diaphragm. think i need to seat it first, then install, but the thing needs to like be held in place while i put it together or it just comes out of the lip on the carb. anyone done that?
camaroguy72 is offline  
Old 08-07-2007, 12:52 PM
superbling's Avatar
Join Date: Dec 2004
Location: South Texas
Posts: 2,553
superbling is on a distinguished road
Kai's bottle cap sounds like a great tip. Hope I remember it next time. Does it have to be Honda brand oil or can I use Mobil 1. What about synthetic? Too early for that? Sorry, couldn't resist.

I put the diaphragm into an umbrella shape (for a lack of a better description) and slowly lower it into the carb until the edges stick into the valley. I use honda's silicone spray to lube the diaphragm which has a slight tacky properties and that helps to hold it in place.

Then add spring and cap together while SLOWLY but deliberately sandwiching it all together. Usually get it right the first or second time.
superbling is offline  
Old 08-10-2007, 07:04 AM
Join Date: Jul 2007
Posts: 48
camaroguy72 is on a distinguished road
it seemed to now work.. so i took some gasket maker meant for gasoline, used a thin layer around the edge of the diaphragm. seated it one section at a time, taped it down, let it dry, removed tape, inserted cover/spring. voila. she runs like a charm.
camaroguy72 is offline  
Related Topics
Thread Starter
Last Post
Technical Discussion
01-19-2013 07:34 PM
Technical Discussion
06-19-2011 06:13 PM
Technical Discussion
09-20-2010 08:54 PM
Technical Discussion
02-02-2010 07:29 AM
Technical Discussion
12-15-2008 06:08 AM

Thread Tools
Search this Thread
Quick Reply: Diaphragm/Vacuum Piston on VTR Carbs

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to and affiliated sites.

All times are GMT -7. The time now is 10:26 PM.

© 2019 MH Sub I, LLC dba Internet Brands