883-to-1200: Part III, Yost Power Tube Installation

The last article left off with me disassembling my engine down to the cases pulling the heads and cylinders and taking them off to the machine shop Tuesday. Since dropping them off I continued on with this new experience (God I hope this thing runs again!).

Thursday night (4/2/98) I decided to tackle the Yost Power Tube (YPT) installation. I thought I'd do it in the kitchen (since I live by myself and don't have someone to remind me not to do mechanical work where I make sandwiches etc. Even though there is such a thing as soap and water, some women just don't like the idea.) I pushed everything aside and made room for the carb., screw drivers, vice-grips, paper towels, electric drill, and a coffee cup to dump the gas into from the float bowl.

A long time back, Maurice wrote an article entitled Changin' Jets. I printed it back then and had it handy as I started this task. I also had the magazine article just published showing a pictorial step-by-step procedure for installing the YPT. One thing you can be sure of in doing aftermarket installations is, if you work from the manufacturers instructions, you won't be able to figure out what to do (One exception. S&S has the BEST manual on installing and tuning an S&S carburetor I've ever seen. That company is top-notch. From manuals to customer service, they are the best! IMO). Maurice's notes and the pictorial were invaluable aids to the project.

Tip: If you use Maurice's instructions, mine or the magazine article, be sure to read them completely once or twice so you are prepared for each step with the right tools and parts on hand.

OK, here goes,

  1. Remove the throttle cable plate by clamping the screw head going into the side of the carb body with vice-grips. A slight turn and it'll loosen. Unscrew it with normal phillips screw driver.
  2. Unscrew the only other screw holding it on attached to the top of the carb (black plastic spring cover).
  3. Unscrew the four phillip screws holding the float bowl to the carb. body while holding it straight up.
  4. Gently lower the float bowl watching the float slowly tilt downward. The accelerator pump rod will come out of the rubber bellows on the side of the carb. No problem. Just insure you slip it back in on re-assembly.
  5. Dump the gas from the float bowl into that coffee cup (the one WITHOUT your coffee in it), pat the rubber o-ring type gasket dry and put the float bowl aside.
  6. Gently turn the carb body over take a small crescent wrench or a screwdriver large enough to fit the entire slot of the main jet (brass piece screwed into carb body.) and remove the main jet and the brass tube its screwed into. If the jet is stock, it should have a very tiny number stamped into it like 160 or 165.
  7. Insert the new power tube and #180 or #185 jet included with the YPT kit and screw it down, but not to tight. I'd try the #180 first.
  8. Right next to the main jet set deeply into a narrow shaft is the slow jet. Replace it with a #45 if you have one. Also be careful to use the right size flat blade screwdriver so you don't damage the inside surface of the shaft.
  9. Carefully replace the float bowl insuring that the chrome accelerator pump rod goes back into the rubber bellows. Replace the four screws.
  10. Looking down at the top of the carb (black plastic cover), remove the remaining three screws. That cover has a large diameter spring under it so keep your thumb on it to hold it down as you remove the last screw. Then slowly lift it off the carb body.
  11. Remove the large spring.
  12. Carefully remove the rubber diaphram that encircles the bore of the carburator body.
  13. Remove the white plastic spyder retainer.
  14. Remove the stock silver needle
  15. Pull the throttle slide out of the carburetor. Don't worry it can only go back in one way.
  16. Follow the instructions for drilling the 1/8" hole in the bottom of the throttle slide. Carefully clean out any metal shavings from the drilling process.
  17. Replace the slide
  18. Insert the new needle supplied in the YPT kit.
  19. Replace the spyder retainer making sure you don't block the hole you just drilled out. The spyder is keyed and should drop into the right position automatically.
  20. Carefully replace the rubber diaphram. Don't damage this! Its not easy to replace. If it doesn't fit, wait 24 hours or until it completely drys out, it'll shrink into the correct shape and will be easier to replace.
  21. Replace the big spring.
  22. Replace the black cap or, if you've already got one, install the new chrome cap in its place. As Maurice said, this is the best time to do it!
  23. Replace the throttle cable plate and cinch up that one screw that holds it to the side of the carburetor body with the vice-grips.

Done! Replacing the carb onto the intake manifold will be covered when I describe the entire engine re-assembly process.

Oh yeah, not quite done. Don't forget to clean the kitchen counter before your SO comes home!

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Date this page last modified: 3/18/2005