Anyone know why my headlight bulb would be blowing out when I rev the bike? The brightness increases with rev, then at high revs it blows out. I have gone through 2 new lights now. Put another new one in last night, blew out the high beam simply reving the bike in the garage, then the low beam blew out driving down the street. Bike is a year: 1975 Yamaha 175 Enduro. Blinkers work just fine. Only issue is the headlight..

Any help here would be much appreciated!

The battery has to be installed, and in good condition, it acts like a buffer/regulator to keep voltage going to the headlight not going to high.

If you want to stop this, install the correct voltage regulator.
There are only 2 (that I know of) that work... the original Yamaha version (single wire) and the high power 3-wire version.

Hmm. I will check this. I do have a battery though. Any quick solutions here? Just check it's charged and make sure it's not bypassed I suppose? Thanks for the help!

Other than replacing the whole electrical system for a new 12v one, the only textbook solution is to do as DEET says and fit a 6v voltage regulator. If you click on the Tech Library button on the toolbar at the top of the page and follow your nose to Service Bulletins, you will find the official publication from Yamaha on why and how.

A non textbook solution that some say has worked for them is to fit a 12v headlight. I've no idea of the quality of the light when you do this, mind.

Does this model have a rectifier under the tank? If so, check your connections there. If the wiring, connections or rectifier itself is faulty it will blow headlights.

Thanks @DEET. It's the original that was on the bike when I bought it 5 years ago. Didn't have the issue until down the road, say 2-3 years later after I tried changing to some china lighting garbage, then reverting back to the original 6V ones.

I have been installing LED headlights in DT1 to DT400c and have installed Yamaha regulators when there wasn't one and so far they have been working good. I had a 75 DT400 with no regulator and no signal lights no horn no gauge lights and no battery, just headlite tailite and brake lite and I connected a digital meter to the system and revved the bike up to 5 to 6 grand and the meter bounced off 37 to 40 volts a couple of times. That thing blew 6 volt or 12 volt headlight bulbs like a flashbulb and the 1154 tail lights or 1157 12 volt tail lights flashed and were gone. I installed the yamaha voltage regulator and all is good. The LED headlight flickers a bit at low idle but is fine after 1500 rpm
Doug

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