peanuts
XS650 Member
I had to buy two new petcocks from mikes. the old style as you know have the two vacuum fittings leading back to the intake manifold on each carb. Do I run a tube line from one to the other or not.
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vacuum petcocks
- Thread starter peanuts
- Start date
You can do that. Some like that little mod and say it balances out the idle. Or you can just cap the nipples with blind plugs. I use these vacuum caps from the auto parts store. The 7/32" size is a perfect fit .....
Dan Welch
XS650 Member
So, can I use vacuum petcocks and not attach them to carbs? Just cap them? I have a 77' XS650 but the tank is later maybe 79'
Dan Welch
XS650 Member
I was explained that I will need to modify the petcock valve http://en.650wiki.org/index.php/5.02.1_Vac_Petcock_Conversion
CoconutPete
1979 XS650 Special
1: Buy a non-vacuum petcock
2: Buy 2 of those caps that 5Twins posted
3: Install the new petcock on whatever side you want.
4: Run a line from that petcock to a T
5: Run the 2 lines from the T to the carbs
6: Take the 2 things that you bought that 5Twins posted and use them to cap the little brass barbs sticking out of your carb manifolds.
7: Either leave an old petcock on the non-used side in the closed state or get creative and make a block-off plate to seal that side. I made mine out of JB weld and an old vacuum petcock.
8: Enjoy your newly simplified fuel supply system.
2: Buy 2 of those caps that 5Twins posted
3: Install the new petcock on whatever side you want.
4: Run a line from that petcock to a T
5: Run the 2 lines from the T to the carbs
6: Take the 2 things that you bought that 5Twins posted and use them to cap the little brass barbs sticking out of your carb manifolds.
7: Either leave an old petcock on the non-used side in the closed state or get creative and make a block-off plate to seal that side. I made mine out of JB weld and an old vacuum petcock.
8: Enjoy your newly simplified fuel supply system.
Cafe32
XS650 New Member
Thanks for this - I'm about to do the same on my '79 XS650. I have a question on steps 4 and 5 though - how have you found that to work, does it matter you're feeding both carbs from one petcock? As I type I realize that's probably a dumb question but it's better to ask now. I just hadn't thought about going to a single petcock for both carbs.
That's what I use on my left side. It cracks from heat about once a month so you have to have a never-ending supply. Someday I will get a piece of high quality vacuum hose and put a plug in it and use that. My right side has the original cap that will last for a hundred more years.You can do that. Some like that little mod and say it balances out the idle. Or you can just cap the nipples with blind plugs. I use these vacuum caps from the auto parts store. The 7/32" size is a perfect fit .....
One petcock will deliver enough fuel to the carburetors to run the 650, that one petcock would be enough to run a much larger engine. I've had trouble with those plugs on other bikes, they crack and disappear, all brands seem to be the same material. A vacuum leak will destruct an engine. I've used tygon fuel hose and plugs cut from stainless bolts for a long lasting plug, painted with a black felt marker. Still a good idea to occasionally check that the plug is still there and sealing.
Scott
Scott
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CoconutPete
1979 XS650 Special
No problems with step 4 or 5. The bike runs just fine with one petcock.
I have a tank from an 80' on there right now, so only one petcock opening - no block off plate needed at the moment.
I replaced the carb intake manifolds with non-vacuum ones, so no caps there anymore either.
If you use a vacuum petcock, you'll need to modify it to flow fuel without the vacuum...I've found it way easier to just get two NON-vacuum petcocks (from Mikes) and not worry about the modification. I connect both petcocks to the carbs...but I only use one petcock to run the bike, the other stays off all the time. Works for me.
I've tried the caps, but have lost a few of them at various points...so I use a heavy fuel line and connect both ports together. If one pops off (which hasn't ever happened yet) it's still on the other. My carbs are very well balanced but I'm sure the connected ports help to some degree as well....not really sure about that, but makes sense logically.
I've tried the caps, but have lost a few of them at various points...so I use a heavy fuel line and connect both ports together. If one pops off (which hasn't ever happened yet) it's still on the other. My carbs are very well balanced but I'm sure the connected ports help to some degree as well....not really sure about that, but makes sense logically.
