83 honda 750 shadow exhaust question ( I'm Baffled)

I bought this bike in running condition, but when i went to do my standard maintenence I found somthing interesting. First this is a v-twin and was fitted with Harley sportster mufflers. ( Bad Idea if you don't jet....I Know) but that's what the guy did. So when I started in on the carbs I found the idle mixture screws were set 5 1/2 turns and 6 turns out from seated position. When I put them back to the 2 3/4 turns out as specified by the manual. ( I figured there would be problems due to the exhaust) And that's exactly what I found. An extremely lean condition that made the bike pop after every accel let-off. So I set the screws back where they were and thought. " Should I re-jet as the prior owner should have?? Or should I try somthing else? I decided the latter as I really don't want this bike to be a gas-hog.
There were only a few options for the latter
1. Get the stock mufflers ( Money is tight) so that wouldn't work.
2. Try adding some back pressure to the sportster mufflers.

Keep in mind that these mufflers don't have a place to put different or adjustable baffles in them. And so........
I welded a 5/8 dia innner diameter washer to a piece of 4" long pipe. I fit the conduit pipe inside the washer flush so picture a washer with a tube coming out of it to 4 inches. ( I looked inside some of my other bikes mufflers and saw somthing similar)
I wasn't sure if this would work as this was adding alot of back pressure but I figured that 6 turns out for a mixture screw is very extreme. And so...I have the washers welded in the end of the mufflers and have driven short distances, just checking to see if the popping would stop. It did with the mixure screws turned to 3 1/2 each. But the lean condition is still present, not as much as before but still there. Here somes my question...
Does anyone out there know if adding this back pressure will harm the engine? The difference is that before I would have to choke the bat snot out of the bike to get her to go and now 2-3 turns of the starter and she's on and idling. So any takers with this one??? Did I hurt things? Am I on the right track? etc...etc....Thanks in advance

 

i think you are on the right track for what you want. you arent going to hurt the engine, just move the power curve down the rpm scale a bit. a 5/8" hole is plenty for that engine to breath through. you could rejet slightly to improve the lean condition, and going from a "40" to a "42" pilot jet wont kill your mileage at all. it sounds like you are very close with the jetting anyway.

 

Thanks for the reply....The exhaust is actually squeezed a little tighter than that...the conduit pipe outer diameter is 5/8 and i'm not sure what the inner diameter of the conduit is but it's smaller than 5/8 plust the exhaust has to but into the bock of the muffler and find it's way back into that pipe?? I also drilled a 6mm hole in each washer for some more relief?