How To Convert Your Vacuum Operated Petcock To Full Manual...

[J6G1Z]

For the most part, the vacuum operated petcock on the VT & FT Ascots works well & usually doesn't cause any problems. There is the potential of the diaphragm forming a leak & then not allowing enough fuel to flow to the carbs/engine, etc. There is also the potential for the vacuum line that comes off the VT's engines rear cylinder to crack & cause a vacuum leak.

I like to run my carbs dry before I park my bike for any extended periods. Then when I go to start it... I have to crank the engine over a few times to create enough vacuum to open the petcock. I really don't like this feature, so on my bike I have modified the petcock to full manual operation.

This modification is extremely easy & will only take about 5 to 15 minutes to perform.

First off, you need to remove the 4 small screws around the diaphragm housing on the side of the petcock. Then carefully remove the housing cover & the parts that are inside. Make sure that you pay attention to the order of the parts as they come out of the housing. You will need to remove the diaphragm & the spring that normally holds it closed. Now you want to swap the spring to the opposite side of the diaphragm & reinstall the parts in their new order. Make sure that you snug down the 4 screws, but be careful not to strip them out. You now have a full manually operated petcock.

There is one other part of this modification that needs to be done. Make sure that you inspect the small vacuum line that runs from the engines rear cylinder head to the petcock. It needs to be in good condition without any cracks or leaks in it. Then you either need to reinstall the tubing exactly as it was prior to the modification, or you can remove the line completely & install a vacuum cap on the rear cylinder's vacuum port.

Now whenever you shut down the bike, you must remember to close the petcock. This has become second nature to me long ago due to riding dirt bikes.

This modification may not be for everyone. If you forget to close your petcock every time you shut off your bike, then it may not be a good idea. I like the fact that when I go to start my bike with empty carbs, I open the petcock & the carbs begin to fill immediately.

Good luck
J.

[Bucko]

There's a big risk to eliminating the auto shut off feature - forget to turn that tap off once and you could be replacing your rods.

Any piece of hose that works will do for the vacuum line, and the diaphragm was still available from Honda the last time I checked.

[J6G1Z]

As the last few lines of my description state... This modification is not for everyone.

If you are forgetful, then I don't recommend it. I have owned several bikes throughout the years off & on since I was about 12 years old. My Ascots are the only bikes that have a vacuum assisted petcock. Closing the petcock has become second nature to me & I would rather have full manual control of it.

Good luck
J.

[scottly]

J, does this work the same on the FT petcocks? I'm getting tired of sucking my petcock on every time I drain the float bowl, not to mention wondering if the lack of vacuum at WFO is adding to my lean conditions on the dyno... 

[J6G1Z]

J, does this work the same on the FT petcocks? I'm getting tired of sucking my petcock on every time I drain the float bowl, not to mention wondering if the lack of vacuum at WFO is adding to my lean conditions on the dyno...

Yes it does. That is where the idea originally came from. The modification is listed in the "FILES" section on the Yahoo FT Ascot Owners Group.

Just take apart the diaphragm assembly on the back of the petcock & switch the spring to the opposite side of the diaphragm so the spring holds the diaphragm open. Make sure that your vacuum line is re-connected to the proper port on the petcock, or just cap it off with a vacuum cap.

It really works slick as long as you are dilligent in remembering to close your petcock whenever you shut down the engine.

Good luck
J.

[FT500R]

Replying to a very old post here but just wondering about why you would have to shut down the petcock everytime?
your float will close the fuel supply right?

Also the european FT's do not have a vacuum operated petcock and I dont think you have to turn those to off everytime?

[J6G1Z]

The float, needle & seat are unreliable for fuel shut off. I learned to close the petcock every time I kill the engine. One of my bikes has a petcock that operates opposite of the others. I accidentally placed it on reserve instead of closed once. The next morning I found about half a gallon of fuel puddled on the garage floor. There is also a risk of fuel flowing into the engine & causing hydraulic lock.