Kick back on starting when hot

[bill932]

I have a 1971 xs1b that has a BOYER BRANSON micro digital system that calls for a 4.5 ohm primary coil. Bike starts easily when cold but kicks back and hard starting when warm. my coil reads 5.5 ohms when cold and up to 8.0 ohms when heated with a heatgun.I think I have a bad coil. What is your opinion?

 

[TwoManyXS1Bs]

What does your testmeter show when the leads are shorted?

 

[Jim]

A coil is 2 sets of copper wire wound around an iron core. Increasing the temperature will increase the resistance. Depending on what you subtract for your zero set indication that 2many alluded to above, and not knowing what the temperature increase was ... you're most likely in the normal range.

 

[xjwmx]

Yes, your coil is broken if you're able to measure resistance. Revert to stock ignition and save the next $1000. Resistance of wire goes down with heat. Resistance of fubarness goes up with heat

 

[GLJ]

Resistance of wire goes down with heat.

 

[Jim]

Yes, your coil is broken if you're able to measure resistance. Revert to stock ignition and save the next $1000. Resistance of wire goes down with heat. Resistance of fubarness goes up with heat

 

[Signal]

Check your battery voltage. If the voltage gets too low it upsets the Boyers timing. There is an excellent trouble shooting guide on the Boyer webpage.

 

[bill932]

REPLY TO Two Many xs1b s Put new batt in meter. Leads shorted reads 00.4 ohms. Coil reads4.6 ohms . After riding coil reads 5.3 Sound normal? Coil supposed to read 4.5.

 

[TwoManyXS1Bs]

Are your cold/hot readings of 4.6 and 5.3 as displayed on the meter?
If so, subtract the 0.4 ohm shorted-lead value to get the true readings of 4.2 and 4.9.

Those values would be just fine...