1988 FXSTC Problems
Thread Starter
|
Intermediate
Joined: Oct 2012
Posts: 40
Likes: 0
From: Dallas, Texas
And visually I can't see any wires that are grounding out or with bad connections. All the wires under the dash, wiring going to headlamp and handlebars, and the rear tailight wiring all look good. I'm not well versed on the wires that are underneath the oil pan where the starter and main CB are and don't know a good way to check those wire so any help in that department as well would be greatly appreciated. And thanks for all the responses, I hope we can troubleshoot this thing before Daytona bike week so I can ride!
Seasoned HDF Member
Joined: May 2008
Posts: 21,143
Likes: 12,707
From: South Carolina
You are sure that all electrical cuts out when the problem occurs?
Have you looked at the wiring at the ignition switch?
Also take a look at the cables at the starter solenoid, make sure the connections are good.
Last edited by Dan89FLSTC; Mar 4, 2014 at 06:13 PM.
Seasoned HDF Member
Joined: Nov 2009
Posts: 15,705
Likes: 22,718
From: Farmington ,MS
Basic ohms law, the only way you can cause current to increase is to either increase voltage, or decrease resistance...
Ohm's Law as a Predictor of Current
The current in a circuit is directly proportional to the electric potential difference impressed across its ends and inversely proportional to the total resistance offered by the external circuit. The greater the battery voltage (i.e., electric potential difference), the greater the current. And the greater the resistance, the less the current. Charge flows at the greatest rates when the battery voltage is increased and the resistance is decreased. In fact, a twofold increase in the battery voltage would lead to a twofold increase in the current (if all other factors are kept equal). And an increase in the resistance of the load by a factor of two would cause the current to decrease by a factor of two to one-half its original value.
Ohm's Law as a Predictor of Current
The current in a circuit is directly proportional to the electric potential difference impressed across its ends and inversely proportional to the total resistance offered by the external circuit. The greater the battery voltage (i.e., electric potential difference), the greater the current. And the greater the resistance, the less the current. Charge flows at the greatest rates when the battery voltage is increased and the resistance is decreased. In fact, a twofold increase in the battery voltage would lead to a twofold increase in the current (if all other factors are kept equal). And an increase in the resistance of the load by a factor of two would cause the current to decrease by a factor of two to one-half its original value.
That reasoning only applies to a circuit with good connections...throw a bad connection on the load side of a breaker, and it goes out the window. A 30 amp 12 volt circuit is 360 watts...a bad connection dropping the voltage to 10 volts just on the load side of the breaker will pull 36 amps...pop goes the breaker.
Thread Starter
|
Intermediate
Joined: Oct 2012
Posts: 40
Likes: 0
From: Dallas, Texas
Yea the bike will spit and sputter, the dash lights go dim and flicker. If I keep giving it gas it will back fire and pop but it will still run (but barely) . When I don't give it any gas, it will die and then nothing will turn on until the main CB resets.
Seasoned HDF Member
Joined: May 2008
Posts: 21,143
Likes: 12,707
From: South Carolina
That reasoning only applies to a circuit with good connections...throw a bad connection on the load side of a breaker, and it goes out the window. A 30 amp 12 volt circuit is 360 watts...a bad connection dropping the voltage to 10 volts just on the load side of the breaker will pull 36 amps...pop goes the breaker.
A little backround; I`m not a pro motorcycle wrench. I work as an R&D Mechanic for a Aircraft engine manufacturer (32 years so far), I work with these calculations all the time, our engines are heavily instrumented, sometimes you can`t even see the engine because of the amount of wires coming off the test stand.
http://www.ohmslawcalculator.com/ohm...calculator.php
Last edited by Dan89FLSTC; Mar 4, 2014 at 06:23 PM.
Seasoned HDF Member
Joined: May 2008
Posts: 21,143
Likes: 12,707
From: South Carolina
Yes, ohms law=there is no such thing as a free lunch...
HD Forum Stories
The Best of Harley-Davidson for Lifelong Riders
7 Surprising Harley-Davidson Products that Are Not Motorcycles
Verdad Gallardo
8 Best Harley-Davidson Motorcycles Ever
Pouria Savadkouei
10 Worst Harley-Davidson Motorcycles Ever
Pouria Savadkouei
Killer Custom's Jail Break Is The Breakout That Refused to Blend In
Verdad Gallardo
Crazy Bunderbike Build Looks Amazing, But Is It Impossible to Ride?
Verdad Gallardo
Harley-Davidson Reveals Super Cool Cafe Racer Concept
Verdad Gallardo
Engraved Rebellion: Inside Bundnerbike's Glam Rock II
Verdad Gallardo
10 Motorcycles You Should Never Buy
Joe Kucinski
10 Things Harley-Davidson Needs to Fix in 2026
Verdad Gallardo
Seasoned HDF Member
Joined: Nov 2009
Posts: 15,705
Likes: 22,718
From: Farmington ,MS
Tom, watts is calculated by volts x amps, watts are not a constant.
A little backround; I`m not a pro motorcycle wrench. I work as an R&D Mechanic for a Aircraft engine manufacturer (32 years so far), I work with these calculations all the time, our engines are heavily instrumented, sometimes you can`t even see the engine because of the amount of wires coming off the test stand.
http://www.ohmslawcalculator.com/ohm...calculator.php
A little backround; I`m not a pro motorcycle wrench. I work as an R&D Mechanic for a Aircraft engine manufacturer (32 years so far), I work with these calculations all the time, our engines are heavily instrumented, sometimes you can`t even see the engine because of the amount of wires coming off the test stand.
http://www.ohmslawcalculator.com/ohm...calculator.php
Neither is the voltage when you are dealing with a bad connection...OK I am not going to argue the calculations...you got me beat...I do know in 20 years of being an industrial mechanic, I have replaced hundreds of blown fuses that were blown by a loose connection on the load side of the fuse...can you explain?
Intermediate
Joined: Jul 2013
Posts: 47
Likes: 3
From: Flushing
In your case does bad connection equal a short to ground? We are only talking about a 12 volt system here. Now that being said I have seen bad motors draw more amperage.
There is no way to increase amperage without increasing voltage or decreasing resistance. If there is then I have messed up a lot of customer cars along with what I am teaching my students.
If you have a 12 volt circuit and 6 ohms you have 2 amps right? Same circuit "bad connection/corrosion" you have 12 volts 8 ohms gives you 1.5. Now if we decease resistance 12 volts 3 ohms we get 4 amps. And then in all of these systems they are capable of 24w 18w and 48w. All wattage is is a measure of power. you can convert horse power to wattage.
In our line of where we are concerned with ohms law on a bike wattage is not needed ever when trying to diag a SHORT! to ground.
What else is happening when the bike shuts off are you turning going straight on the throttle off?
There is no way to increase amperage without increasing voltage or decreasing resistance. If there is then I have messed up a lot of customer cars along with what I am teaching my students.
If you have a 12 volt circuit and 6 ohms you have 2 amps right? Same circuit "bad connection/corrosion" you have 12 volts 8 ohms gives you 1.5. Now if we decease resistance 12 volts 3 ohms we get 4 amps. And then in all of these systems they are capable of 24w 18w and 48w. All wattage is is a measure of power. you can convert horse power to wattage.
In our line of where we are concerned with ohms law on a bike wattage is not needed ever when trying to diag a SHORT! to ground.
What else is happening when the bike shuts off are you turning going straight on the throttle off?