I have a stock 1977 Sportster that I bought brand new. The only mod done to it was to install staggered dual exhaust from the dealer. The carb is a 38mm Keihin "Butterfly" type carb. I was advised that now I should increase the size of the jets as the bike would run lean with these pipes. I also lived at seal level and I removed the carb and drilled out the low speed jet .003" and I may have installed a larger main jet. Well now I live at 4000' of elevation and the bike is rich at part throttle cruise. It idles okay and accelerates perfectly but that part throttle cruise at about 2100 rpm the bike bucks and doesn't run right. I have finally found a place to purchase the jets but I am looking for the original Harley part number so I get the right ones.
I appreciate the help and advice.

Lisa

 

The parts book doesn't list a model specific jet for any '77 Sportster, just a list of all available sizes.

1978 book calls for:
Main - 27888-78 (1.60mm) over 4000ft.
Main - 27898-78 (1.65mm) std.
Low jet 27896-79 (.65mm) std.

I'd wager the low jet is your problem. If you did drill it .003, you may have turned a .65mm into a 1.30 .73mm... For reference, later Big Twins used a .52/1.75 (stock) with that same carb,

Good luck

 

Thank you "t150vej"!! That is the EXACT INFORMATION I have been looking for!! As I mentioned I bought this bike brand new 43 years ago and I have always kept notes on repairs or modifications that were done. In my searching I found a cryptic note that said "Main Jet #165" and "Low Speed #76". Below that I wrote ".0292 Stock" and ".032" Present". 760mm is a #76 Jet or .029" orfice. This information corresponds to the information you provided here. Looking in the VT Catalolg they have a low speed .75mm jet that works out to be 029" inch. I think at my altitude and the staggered duals with a stock #165 main and a #75 low speed Jet I should be in the ball park.

Thanks again for taking your time to research that in the parts book for me. I so appreciate it more then you know. It's hard to believe that my once new Sportster is now an antique but then again I'm an antique now too.

Best regards,

Lisa

 

You're very welcome and my compliments on keeping your "old friend" around and healthy.

If no V-twin dealer near or handy, try jets r us dot com, they have the real stuff.

Life is so much easier once you get your head around having been alive over half a century

Ride safe

 

Thanks again "t150vej", you're the very best. You're so right about that half century stuff too.
Here's a picture of my "old friend". All stock except for the pipes, oil cooler and windshield. It's a good thing she can't tell stories or I'd really be in trouble.
I'll fill in a report in a couple weeks here when I get the jet in it and ride it again. It'll be like a new bike I'm sure.

Again thanks for your help.

Lisa

 

I "drooled" over a Sportster exactly like that at Central Harley in Shawnee, KS back in 77. Ended up buying an XLCR instead.

 

At one time I fantasized about getting one of those too as I loved the look. But I've never been a good enough rider to actually wring one of those out to their potential. Nice old picture of cool memories.

 

For those that have been following this thread today I finally got the stock #76 low speed jet and installed in the carburetor. I just got back from a road test and the bike hasn't run this good in years. All the over rich cruise bad habits are gone and the bike is every bit as fast as it used to be but now it has a nice smooth cruise and I can get it in 4th gear earlier with out it bucking around. Thanks for the information on the factory jets too.

Just for information if anyone else is facing this issue here are are the jet numbers that were in the bike and what's in it now:

Before: Main #175 .0688"
Low speed #88 .032"

Now: Main #175 .0688"
Low speed #76 .029"

It's just amazing what that .003" made in the performance of this engine. it idles better and has a real crisp throttle as it should.

Again thanks for the help and here is a problem solved with great results.

Sincerely,
Lisa

 

Thank you for the update Mslisa.

It's always helpful to others on the forum to read a resolution to an issue, especially when it's so concisely detailed and well written.

That's a great looking piece of history you have!

 

Thanks for the compliment t150vej, but your help with the stock jet numbers really helped too. So you get great credit here also.

Now on your comment "That's a great looking piece of history you have!" made me chuckle as I thought "I'm a great looking piece of history too"!!