Petcocks vaccum or no vaccum?

[jchristy456]

ok so here's another dilemma for the you guys to solve. A most of you know their are two type of petcocks for me to choose from. What do you recommend? I'm using the stock 77 mukani carb. I know this decision will affect what sort of intake manifold i get. my initial thought would be to just get a manual petcock.

 

[pcoumbe]

Search the forum using keywords : "vacuum vs non vacuum petcocks" It was a pretty good recent thread with a lot of input and opinions.

 

[650Skull]

78E/SE 79F/SF and all later tanks had Vacuum petcocks. So without information on what Year/model bike or tank you are using the answer is a guess

 

[gggGary]

The vacuum petcocks (78 to the end) use a different bolt center to attach to the tank so if you don't have vacuum petcocks (77 doesn't) you won't be changing over. There are non vacuum replacements available for the vacuum bolt center tanks. I like vacuum petcocks and with a competent overhaul a good quality parts kit and a clean gas tank they work great. Leave one of those out and you will have grief. The intakes with vacuum taps are nice for doing carb syncs which must be done to make the bike run correctly.

 

[grepper]

Gary has it right.
Personally I've had little luck rebuilding petcocks. I have one xs650 with and one without.

The problem with manual petcocks is always remembering to turn them on and off. With them off there's enough fuel in the bowls to go about 1/4 mile or so. More times I'd like to admit I've ridden off only to have the bike die 1/4 mile later.

 

[xjwmx]

I had to do an emergency job on my vacuum petcock and I disemboweled it and added one of those red lawnmower shutoffs from the parts store. The problem was when I rebuilt it I didn't smooth the aluminum faces that meet the diaphragms and as the diaphragms aged and lost compressibility it dripped from there.

I might convert it back to vacuum sometime but I think it would be handy to keep the red shutoff there.

 

[jchristy456]

ok i forgot to mention. I'm going to be using the monstercraftsmen "p-nut" tank. If i get manual petcock i'm guessing to dont need the intake manifolds with the airbarbs? I'm basically trying to figure out two things. What petcock to intall and what intake manifolds to buy so i can fianlly mount my newly re-built carbs.

 

[aldo5468]

ok so here's another dilemma for the you guys to solve. A most of you know their are two type of petcocks for me to choose from. What do you recommend? I'm using the stock 77 mukani carb. I know this decision will affect what sort of intake manifold i get. my initial thought would be to just get a manual petcock.

Personally, I value the safety element that vacuum carbs in good operating condition have: when the engine shuts off, the fuel supply to the carbs shuts off.

 

[grepper]

Personally, I value the safety element that vacuum carbs in good operating condition have: when the engine shuts off, the fuel supply to the carbs shuts off.

Yup, me too. But if he's going with a non stock tank, finding a vacuum petcock to go with it might be difficult.

And, without vacuum petcocks the only use for the carb barbs is for tuning,

 

[650Skull]

ok so here's another dilemma for the you guys to solve. A most of you know their are two type of petcocks for me to choose from. What do you recommend? I'm using the stock 77 mukani carb. I know this decision will affect what sort of intake manifold i get. my initial thought would be to just get a manual petcock.

Yup, me too. But if he's going with a non stock tank, finding a vacuum petcock to go with it might be difficult.

And, without vacuum petcocks the only use for the carb barbs is for tuning,

How would any one know.

This is another case of.............. a question that has no information to relate to to be able give an answer for the posters situation

 

[XSLeo]

From what I can read from this thread, the op can't spell. They are Mikuni not Mukani. He also doesn't know much about his bike. He says stock 77 carbs but when asked to id the bike he ignores this and says he is using a p-nut tank.
I can assume it's some sort of cut, hack and weld bobber.
Even with that I will try an answer. Depending on the tank petcock fitting is you can use either a vacuum or regular petcock.
The 22 mm fittings, you can get either. My Harley has a vacuum petcock. It has the 22 mm fitting.
You can use which ever you want.
As far as carb holders with or with out vacuum barbs, get the ones with vacuum barbs. Makes syncing the carbs easier.
Leo

 

[jchristy456]

Ok so thanks everyone for your time and knowlage on the subject. Its really been helpful. So after a lot more reading and research i think i'm going to go with a manual/gravity fed petcock. by the looks of it you can order the intak manifolds off of mikes xs with the air barbs but you can also order some plugs to plug them up. i thnik thats the route i may be going. If i'm missing somthing or anyone has anymore thought or input to this idea i'm all ears!

Thanks DOODS!

 

[XSLeo]

Don't get the carb holders from Mike's, the ethanol gas eats them up 9in just a few hundred miles. Get Yamaha or search Ebay for Tour Max. JBM Industries sells ethanol resistant carb holders too.
Leo

 

[jchristy456]

Thanks Leo. I know i'm a horrible speller and i dont really proof read what i write anyways. I'm sorry for not describing what i'm doing with my bike more. Thank you for taking a stab at answering my question. I will do my best to check my spelling.

Thank you and sorry.