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Question Posted By: BLUEWHEELER on 7-24-2008
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| Make of Bike: |
H-D |
| Model of Bike |
Sportster |
| Year of Bike |
87 |
| Engine Size |
883 |
| Other info on Bike |
Andrews V2 cams,S&S carb,crane ing.
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| What's your question? |
bike hesitates when you crack open the throttle at any speed unless you keep the rpms up
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| Details: |
I put a yost power tube in the carb,rejetted several times and even opened the external floatbowl vent(closed off the breather side)Ive been told this is a common problem with IHs and EVO883s. |
Answers:
- First, Yost Power Tubes increase the gas flow to high rpm's...they do nothing for instant response. Second, no matter what jets you change they're for flow, not response. Third, you have longer duration cams, again, not geared for response but for higher duration flow. Fourth, if you have a carburetor with a larger sized throat than stock, like a 40MM, 42MM, 45MM...you won't get response because along with the increased valve overlap (lowering your response factor) you lose manifold velocity, the prime factor in engine response. In removing the CV (constant velocity) carburetor, a carburetor that's geared for response because of it's (CV) nature...you altered this factor.
You might look to your accelerator pump...as the accelerator pump adds extra gas to the air/fuel mixture making that mixture heavier and less likely to reversion from the cylinder. More reversion is created when you install longer duration cams geared for higher rpms. The longer duration takes advantage of the velocity coming from the carburetor/manifold at higher rpm's. At lower rpm's...the bike responds like shit. Why? Because you've installed cams made to run in a higher rpm range. Your exhaust also plays a part in this. If you've installed an exhaust that doesn't have enough backpressure...you'll lose reversion from that and your engine wont respond. If your timing is too retarded you'll lose response. I wouldn't blame it on being an 883...the engine you've designed is no longer balanced. In other words...adding a buncha aftermarket stuff from a catalog does not a hot-rod make! You also might want to check for intake manifold vacuum leaks. Spray a little WD-40 around the intake spigots and where the carburetor meets the manifold while it's idling. If the engine slows down...you have a leak. By: 47Knuckle-Dragger on: 7-25-2008
Reads: 219
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