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
carburetor., 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 Changing' 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 after-market 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,
- Remove the throttle cable plate by clamping the screw head going into the
side of the carburetor body with vice-grips. A slight turn and it'll loosen.
Unscrew it with normal Phillips screw driver.
- Unscrew the only other screw holding it on attached to the top of the
carburetor (black plastic spring cover).
- Unscrew the four Phillip screws holding the float bowl to the carburetor.
body while holding it straight up.
- 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
carburetor. No problem. Just insure you slip it back in on re-assembly.
- 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
- Gently turn the carburetor 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 carburetor 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.
- 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.
- 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.
- Carefully replace the float bowl insuring that the chrome accelerator pump
rod goes back into the rubber bellows. Replace the four screws.
- Looking down at the top of the carburetor (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 carburetor body.
- Remove the large spring.
- Carefully remove the rubber diaphragm that encircles the bore of the
- Remove the white plastic spider retainer.
- Remove the stock silver needle
- Pull the throttle slide out of the carburetor. Don't worry it can only go
back in one way.
- 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
- Replace the slide
- Insert the new needle supplied in the YPT kit.
- Replace the spider retainer making sure you don't block the hole you just
drilled out. The spider is keyed and should drop into the right position
- Carefully replace the rubber diaphragm. Don't damage this! Its not easy to
replace. If it doesn't fit, wait 24 hours or until it completely dries out,
it'll shrink into the correct shape and will be easier to replace.
- Replace the big spring.
- 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!
- 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 carburetor 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.