strange throttle response
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6th Gear
Joined: Aug 2005
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strange throttle response
Alright I need some help trying to figure this out on my 77 sporster. I recently rebuilt the carb and everything appearst to be working perfactly and everything is in order there. The timing is nearly 100% dead on and just put new plugs in. After the bike is been running and at normal operating temp. If I open the throttle to wide open the bike will just stall spuert and then die completely. Now if I slowly and I mean slowly and gradualy open the throttle it will do the same thing usualy just staps and sputters but usualy catches itsself and will start running normaly. Yet if I were to open up to say about 1/4 throttle like I were if I were riding the bike and starting from a stop it will act normaly. At first I though the wide open throttle thing was the accelerator pump going bad on the carb, so I rebuilt it and com to find the check valve in the AP was stuck open and the diphram on the pump itself had a ton of tiny holes in it. So I rebuilt the carb and it starts up just fine but the throttle response is so werid I'v never seen this before in my life and I can't make heads or tails over this. The only thing I can think that it can be it the ignition system but I'm not familiar with it enought to go though each componant one by one and test them. I"m leaning towards a fualty coil or possible points going out, yet again. I'm open to any sugestions and input becuase I"m totaly lost from here and need some direction.
Thanks
Gary
Thanks
Gary
5th Gear
Joined: Oct 2005
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RE: strange throttle response
I'm not at all familiar with your '77, but I had some questions about rejetting my new 1200C and I called Yost Performance Products in MN. I still can't believe how helpful and how willing to help they were. Blew me away. Ya gotta be OK with the tech end, but the guy I talked with gave me the answers. He clearly was a long time HD rider and he clearly knew everything there was to know about the carb on my machine. If there's any chance that parts from Yost are in your carb or might solve your problem I'd give them a call. They're on the Internet.
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Joined: May 2005
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From:
RE: strange throttle response
Gary
Two things come to mind here, one is a problem still with the accel. pump and the other would be in the ignition. If you check your breaker plate in the nose cone (that's asuming you have points yet) the lead for the points could have a broken wire inside the insulation and when the plate advances it seperates. I would also replace the condenser if so equipped.
Two things come to mind here, one is a problem still with the accel. pump and the other would be in the ignition. If you check your breaker plate in the nose cone (that's asuming you have points yet) the lead for the points could have a broken wire inside the insulation and when the plate advances it seperates. I would also replace the condenser if so equipped.
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6th Gear
Joined: Aug 2005
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RE: strange throttle response
I"m pretty sure the carb is working propely, it runs fine while it ideling. No more fuel is being forced from the accelerator pump and into the incomming air like is was before the rebuild. I can see fuel getting squirted into the carb when I apply a lil throttle so I know the accelerator pump is working. The gas itself is another probelem. The engine is spose to be running on leaded 98 octane and you can only get93 unleaded at the pump. There is a place here in Houston that sells that kind of gas that I need but its all the way on the other side of town. I'v tried adding lead and octane addatives but they arn't really doing anything, unless some of you guys know of some better brands that what I"m using. So I know the gas itself is a problem but I don't think the wrong gas will make it respond and act the way is it. I just replaced the points and condenser about 6 months ago and readjusted them after I put rebuilt the carb. I guess its witht he advancing weitghts behing the points plate, but I'v never open them up before and been inside there before. I know its just lil springs and counter weights but I'm not too familiar with this type of ignition system.
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Joined: Dec 2004
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From: Texas! Ya mean there's someplace else?
RE: strange throttle response
Don't worry about the octane; the 93 will work fine. Sounds like you need to look at the advance mechanism. If things get too worn in there, when the flyweights move outward to advance the timing, they'll hit the back of the plate. That stops the weights from going to full advance, or slows the rate they go to full advance, and can cause the engine to spit, sputter, and just plain run lousy at the higher rpms.
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