I've been bugging you all (particularly Davej) for some time about my part throttle tuning woes. I've tried all the suggestions to go leaner and richer to no avail. Yesterday I think I hit upon the actual source of my problem: my intake/carb
/cam/exhaust combo. Here's the whole story, to the best of my knowledge, please bear with me. I'm no engine builder nor am I an expert mechanic.
According to service records, my bike was fitted with the entire Speed Star Stage IV kit a decade ago, minus the intake and exhaust. The PO
ran a K&N on stock backing plate and Bub
Stubbies. I'm guessing the Stubbies are the reason he opted for the smaller HSR42 instead of the HSR45 that comes with the full kit. This is why I always assumed it had the bigger one. Whoops. The next owner rebuilt the engine (it scattered a piston at some point) and threw a Pro Pipe HS on it, and sold it to me with a dropped lifter, dead battery, and broken air cleaner on it, tuned 32 pilot
97 needle 3rd notch and 160 main
Once I repaired it all and threw a xXx air cleaner on it, I realized it made a gnarly noise while cruising low throttle positions, sounding like the stumble you get when you roll off with a rich setting. It was persistent at the throttle opening I used for cruising and decelerating, from just off idle to 1/4 throttle. I assumed, until yesterday, that it was a rough spot from tuning. It can't be, though, because I've run every size jet and needle I could think of and it doesn't affect it whatsoever. in fact, at any pilot size 25 and up it loads up at idle.
I think that it's due to my setup. Here's why.
-My idle lopes a lot. the rough running down low is probably lope too. The speed star cams have a lot of overlap due to late closing exhaust and early opening intake, which makes for a rough idle and rough low end performance. The intake opens at 11* BTDC and the exhaust closes at 15* ATDC.
-I can hear my slide making noise at idle too, because the reversion pulse of the exhaust flowing through the intake at idle makes the slide click against the carb body.
-Opening up the throttle makes the roughness go away, but if you hold the throttle at a set point below 1/4 or so it starts to lope again.
I know it's the nature of a cam with a lot of overlap, but there's gotta be a way to make it a little more driveable. I pulled the baffle out of the pipe yesterday and found all the packing was blown out. When you run it without the baffle, the reversion is worse because of the lack of back pressure. I put a few hose clamps over holes in the baffle, essentially restricting airflow to give it some pressure. The bike responded great to this as far as torque goes, but the lopey reversion thing is still present.
Thanks for making it through this longwinded post. Here's what I'm left with: Is my diagnosis correct? Can I fix it? Maybe try the proper HSR45 carb, or a different pipe? Different intake? Is it just the cam? Would it be worth it to have a set of Warrior cams ground to fit in my bike instead because they have less overlap? What can I do? Is there a way to tune it out of the bike at all with carburetion?
Thanks to everyone that has helped me, I know I ask a lot of you.