As Hobe suggested, the comp is the issue (assuming there's no other serious mechanical issues).

A change in timing will also mask the problem..for a little while anyways.

Just remove the stock comp and you'll see the problem...the ramps will probably be polished and maybe a lobe or two even damaged.

 

If the only gearing change you are making is from 32T to 30T, the change in torque will be 32/30 = 1.067, or 6.7%. Still worth doing IMHO!. All gears will be more usuable.

I changed the compensator on my 03 Dyna from 25T to 21T, which is a 19% increase in torque. That is VERY noticeable!

 

I'm not lying and I'm not stupid and I'm not crazy, the HQ 500 cam did get rid of the bang on start up, it starts super now, before it took all it had to start at times and banged like hell now it doesn't. Sure do wish I could put a sound clip on here, it sounds almost like my Sportster starting now.
I thought most true performance cams lower cranking compression, that alone should stop the bang, and as I said before I have a friend with same bike same performance upgrades and a different tuner (I have an SERT and he has a Powercomander) and it stopped the bang on both bikes.
Just for the record I do tend to treat my bike like a rented donkey quite often.

 

Thanks for the numbers. A friend suggested I change the sprocket before I do cams. I might be happy with the increase in power without having to break into the motor.

 

I was actually referring to going from the 34T engine sprocket to the 30T engine sprocket which is mutually exclusive with the SE Compensator since the 30T sprocket has no compensating assembly on it, not the 30T trans pulley. I think that is the 30T sprocket in question from Badfinger in addition to the already improved (over the '07 and '07) gearing on the '09 bikes.

 

Its not just the starting clunk its all around. starting and stoping

 

As someone else has already mentioned this issue isn't just a start up issue, in fact it is likely no problem at start up. The problem is under acceleration or hard decel, you will get a clunk in either case, and it can get pretty severe. I can speak to this as I can reproduce it any time with a blip of the throttle, or a quick downshift.

As far as non stock cams lowering compression, well most of the time this may be true, but it is the duration that determines this. Some cams such as the SE 255 can buck this theory, so it depends on what cam you are talking about.

But from your post it sounds like what you are talking about is starter kickback, and this is common on HD bikes, particularly if you start a heat soaked motor. You are correct that if you replace your cams with something with more duration you will effectively reduce dynamic compression. If this is the case you will likely reduce start kickback, but you are also likely to reduce the motor output potential from the cam swap. Typically when swapping to cams with more duration you want to increase static compression to compensate, and to maximize the performance potential from your new cams.

Now once you start getting to this point you will find that you are really hammering that stock compensator, as I can verify. Unfortunately once you reach that point there isn't much else you can do, the SE comp is about the only option available. Once you head down the road of performance upgrades it seems to never stop, so now i need a new SE comp, with my performance cams installed.



Hobe

 

Just to add, was up in Idaho in May, you guys have some beautiful riding up there. Spent 12 days riding and covered about 5400 miles, and a fair number of them were in Idaho.

Ride Safe


Hobe

 

with the stock compensator there would be times when i'd hit the starter button and it'd sound like i slapped the primary cover with a piece of 1X4 wood. with the se compensator, it's much more of a direct drive from the starter to the motor via the primary chain. the spring setup in the stock compensator is just too weak. when you go with a compression increase, the se compensator is really needed. even in a stock motor it's a nice improvement.

 

I only occasionally have any problem with noise or kick back when starting. My problem is that I'm pretty aggressive on up shifts and the thing often sounds like it's trying to destroy itself in these instances. Should I expect an improvement in this regard?