colinwhisson

I just can't find the info, sorry for an old question...

I've successfully run my Super Tigre s2500 on gas with stock carb, glow ignition, just using an OS G5 plug.

It ran well for two tanks, but yes the mixture adjustments are very fine. I am confident with leaving the ignition as glow with G5 plug, but can see the carb causing grief at some stage if everything isn't spot on.

A walbro carb will be going on with adapter plate. My question is about the walbro's pulse line pump... I want to just run an exhaust pressure line to the tank for pressure. What do I do with the existing pulse line on the Walbro?
Will the carb even work if I block it or leave it hanging in the breeze?

Many thanks in advance.
Col

Ed...Disregard...won't work without pulse line.

Larry882

The muffler pressure will give you a constant pressure. Not a pulse. You could drill a hole threw the engine backplate and mount a pressure fitting there. A Dubro # 539 8/32 fitting should work. The walbro carb doesn't need pressure.
Larry
Conyers, Georgia

spaceworm

Don't give it up. All you need is a walbro carb with a return spring in the pump side of the carb. Some carbs have these springs, but you can add them to regular carbs. With that carb all you need to do is tap the crankcase back and run a tube from a nipple there to the `pulse hole of the walbro. The positive pulse from the engine pushes the carb diaphragm in one direction, then the spring pushes it back, completing the pump cycle. I am not sure of the details, but search here on RCU for "glow to gas conversions", and it should pop up. Good luck

colinwhisson

Thanks for your help guys.

av8tor1977

My Feedback: (6)

You do not need a spring in the carb. The crankcase of a two stroke engine provides both the positive and negative pulses needed by the fuel pump in both the Walbro and Zama carbs. Very few of those carbs have the spring inside, and the ones that do are for four stroke engines. Don't add a spring on your two stroke app; it might cause the pump to not function, or function erratically. Just a pulse line from the crankcase to the carb is all that is needed. There are two bosses on the top of the carb fuel pump cover. Either one can conveniently be drilled and tapped for an external pulse line if your intended carb doesn't already have an external pulse provision. Do not confuse the carb primer bulb connection for being the pulse line. Let me know if you need a pic of this.

AV8TOR

spaceworm

Thanks for the correction. My experiences have been with 4S.

Sincerely, Richard

av8tor1977

My Feedback: (6)

No problem my friend. Just trying to help the O.P. out.

AV8TOR

colinwhisson

Thanks Av8tor, appreciate the info.

A tap in the backplate for the pulse line it is.

Doed this mean drilling the hole and tapping an actual thread for the nipple to screw in to?

(basically if my tapping skills aren't too flash, will some jb be ok to hold it?

colinwhisson

For the backplate on crankcase that is. carb has existing external pulse line thankfully.

av8tor1977

My Feedback: (6)

Yes, you'll need to drill and tap the back cover. It's easy, you can do it. Just buy a drill bit and tap combo so you have the exactly right size, and drill the hole carefully and straight. If you have or can borrow the use of a drill press, that would be great but it's not necessary. If you have some small drill bits, it is always best to drill a smaller hole first, then open it up to the size needed for the tap with the tap drill bit. Then lubricate it with a light oil, make sure the tap is straight, and go slowly. After each turn of the tap once it is well started, back the tap out about a half turn.. This helps clear out any chips. WD-40 actually makes a good lubricant for tapping aluminum. It won't hurt a thing to add a touch of JB Weld to the pressure tap when you screw it in, but trial fit it first, and be sure to clean the pressure tap and your new hole with carb cleaner or acetone before installing with the JB Weld. You'll do fine.

Just to be sure we are on the "same page" about the pressure tap for an external pulse line on the carb itself, here is a pic of a Stihl 62cc that I converted, and a Homelite 30cc that I converted and hopped up that shows the location of the tap. (Don't have a pic of my Supertiger .90 converted to gas with a Walbro on this computer.)

As an aside, note that the Zama carbs are just slightly smaller in outside dimensions, and this sometimes help when you have a really tight fit. I prefer the Walbro carbs myself though.



AV8TOR

av8tor1977

My Feedback: (6)

Also note that www.lambertsrc.com does these conversions and has parts like the carb adapter. He can also convert yours to a roller bearing rod/crank interface so that you can use less oil....

You might find his website and pics interesting in any case.

AV8TOR