I have a stock 1980 Sportster with the HSR 42. I noticed I'm running rich. Is the default jet needle too small (rich) for the 1000cc? I know the config out of the box is for 1200cc and 1340cc. The leaner neddle is only 10bucks so maybe it's worth the try.

Tom

 

In a single word, I think the answer is yes. The Sportster runs best with a 38mm size carb. The large twins use 40mm and 42mm. I am talking about the 74 cu inch and larger machine here.
I am not saying the 42 won't work on your bike, but if it is rich then put smaller main jet and idle jet in it and try that. Go down only one size. If there is an improvement, go down one more size. Better or worse? Given a choice...I would rather be just a bit to rich than a bit to lean, especially in the summertime when it's hot in most places (I am talking about Texas here)..........pg

 

Thanks, I couldn't find much info on using the 42 on an ironhead unless the motor was moded. I will order the leaner needle jet which is said to only help idle and up to 1/4 throttle. When I bought the bike used it had the carb on and drags. The drags didn't have any blueing at all, that's a sure sign of a rich condition. When I pulled the plugs, all black, not fouling but black. I'll keep everyone informed on the changes.

Thanks
Tom

 

Keep us informed I have also Mikuni HSR42 but plan was put it into bike during wintertime.
Carb is taken from 2000 softail...so jets and needle needs to be changed.
I'm still working on modifying manifold to attach carb in it.

 

What I did notice is according to my manual the Richer needle #96 came standard with my carb and the newer carbs come standard with the Leaner #97 needle. I don't know when that change over may have happened. I hope there's markings on the needle that will tell me which one I have. I think I'll be ordering the #97. My rebuild kit will take about a week to get from J&P. Maybe I'll just open it to check the needle. I'll get back to everyone.

Tom

 

Finally I have some progress on this Mikuni HSR42 project





Just waiting for new O-rings for manifold, after that it can be fired up and tested.

 

Looks good, but I agree with pg - a 42mm (other than a CV carb) is too big for a 1000cc bike (or probably even a 1200, for that matter). You lose too much velocity through a venturi that large with the lower suction provided by a smaller engine. Hope I'm wrong and it works out for you.

 

Everything is worth to be tried, except folk dance and your own sister
It's only 30min job to change original butterfly Keihin back [8D]

 

I have 75' and running a 40 edelbrock quicksilver, motor is bored .20 over and 10:1 pistons. Im actually running a bit lean. I think. previous owner thought he got it dialed in pretty good but I think its still abit lean. Anyways. im very new at this and could be way off, but my motor is just not modded that much and running lean with a 40, I would think you could get the 42 dialed in with the right needles. I may be wrong, in my 2 weeks on this site I have learned to listen to whatever PInion Gear has to say. He seems to be right on the money with just about every question

 

I have a '73 sportster with 10:1 pistons, flowed heads, and a high lift long duration cam that has over lap. the hight and duration is unknown to me as it was in the bike when I bought it. I finally got the cam dialed in and now have a problem with the carburetor. I am running to lean in the rear and just right in the front cylinder. I have what I think is a 42 mm mikuni straight bore with flat slide and a out swept 6"pluneum intake. What would cause it to run rich in the rear and ok in the front? It fouls out the rear spark plug in about 20-30 miles.