1995 Harley Evolution engine

[Barbarian]

I know this is definitely not a
Harley forum, but I thought I would throw this out anyway because it's hard to find an intelligent place to talk about Harley Engines.
My Harley makes this wierd sound when I blip the throttle sometimes. It does it more often when it's not completely warmed up. I can only describe it as a fairly loud "pfft" sound that is coming from the carburator. It comes with a hesitation, but it's totaly different from the normal bog you get on a 4-stroke dirt bike. Is that a backfire? If it is, any suggestions on what might be causing it?
The bike has 44,000 miles on it. It has semi-open exhausts, a screaming eagle air filter, and a screaming eagle street cam.
The main jet is several sizes larger than stock. It was modified and jetted before I bought it.

 

[u8dirt]

Sounds like a lean condition. How do the plugs look? Depending on the lift and duration of that cam, and the better flowing exhaust and air cleaner, you're getting alot more air that you will have to compensate for with jetting.

 

[ChopperDave]

If it is spitting out the carb it is too lean for sure. Assuming your top end is in good shape, exhaust pipes may be a problem. Also, Evo motors are not built with "blipping" as a priority. You are supposed to "roll on" the throttle. Sounds like your pilot jet is perhaps one size to small.

 

[jaction125]

Could also be oil pressure relief. My brothers bike was pumping oil through the carb, found the problem to be a stuck oil pressure relief valve. I wouldn't worry about it, but that's just me and my .02

 

[gwcrim]

On most HDs with after market mufflers and air cleaner, the idle mixture screw needs re-adjusted. There are differing opinions on whether the stock main jets are OK but pilot or slow jet probably needs to go up a size.

If you do Yahoo Groups, this is one where you will get a straight scoop from guys who build some serious street engines.

HD Performance

 

[crf450infla]

I had a similiar problem with a super glide. If it get better after it warms up check the intake manifold gaskets ( more like o-rings).

 

[Barbarian]

Thanks for the responces guys. Even after the motor is good and warm, it still seems to pick up and run a little stronger if I pull the choke out a bit. I did up the pilot one size from stock several months ago, and that seemed to help a bit. Now that it's getting colder, I'm thinking about going up one more and possibly raising the needle a clip position. I'll also check for air leaks and the oil pressure relief.
That "pfft" noise through the carburator is wierd, something I've never heard on a dirtbike.

 

[gwcrim]

Did you tinker with the idle mixture screw? Once you go up on the pilot you fine tune with the idle mix. Raising the needle can help too as those two circuits do have some overlap.

 

[Barbarian]

yeah, I've been messing with that also. I think it's at least 2.5 to 3 turns out right now.
The bike had the stock size pilot, so I have a sneaky suspision that whoever modified it before me just dropped in a bigger main jet and left everything else alone. I'll look at the needle and the position it's in next time I have the tank off.
Working on street bikes sure is a pain, you have to be soo careful not to scratch anything, and something like taking the tank off can be a half hour job. (For me)
Thanks for the help everybody.

 

[webbrace]

It really sounds like the pilot jet, but also check the vacum hose coming off the back of the carb, the VOES switch,and the seals between the heads and the mainfold. Real common spot for a leak.Or just grab a 42mm Mikuni and solve all your problems..