Topic: Headlights Get Brighter When Revving Engine

[mkeefe]

Forgive me if this has come up before, but my searches came up with little useful information.

 ('77 CB550F) The headlight gets significantly brighter when I rev the engine, then dims down when it's idling at about 1000 RPM. Battery is new this season, rectifier was recently replaced. Is this something that I should be concerned with? Possible causes? Thanks.

[OldSchool_IsCool]

Get a volt meter and measure battery voltage at the following rev points:

- engine off, key off, kill switch off
- engine at idle (1000-1500)
- engine reved (2000-2500)
- engine reved (3000-4000)
- engine reved (5000-6000)
- engine reved (6000+)
- report results back here

If your generator and rectifier/regulator is working right... well... don't want to contaminate your observations! 

[MCRider]

Forgive me if this has come up before, but my searches came up with little useful information.

 ('77 CB550F) The headlight gets significantly brighter when I rev the engine, then dims down when it's idling at about 1000 RPM. Battery is new this season, rectifier was recently replaced. Is this something that I should be concerned with? Possible causes? Thanks.

First off, to alleviate your fears, in general, that should happen. So now the question is a matter of degree. To determine if it's happening too much, follow Old School's line of questioning.

[bistromath]

Make sure the battery is charged. If the battery is super low because you've been driving a lot in traffic, it'll cause the behavior you're seeing. Top off the battery with a charger and try again. The charging system on these bikes is marginal at best.

[gold72]

my 500 seems to do the same thing

[mystic_1]

Tell us more about the bike, is it stock and if not what mods have been made?

mystic_1

[Pinhead]

Get a volt meter and measure battery voltage at the following rev points:

- engine off, key off, kill switch off
- engine at idle (1000-1500)
- engine reved (2000-2500)
- engine reved (3000-4000)
- engine reved (5000-6000)
- engine reved (6000+)
- report results back here

If your generator and rectifier/regulator is working right... well... don't want to contaminate your observations! 

Before you do anything else, follow OldSchool_IsCool's suggestion. That is generally the very first step when suspecting and diagnosing charging problems.

[feliz]

I have new bikes that do that!! These charging systems are marginal at best. Both my CB750s systems are okay and meet specs but after every ride I put them on the battery tender and it takes 3-5 hours to bring the battery to full charge. Even new(er) bikes I own may take an hour or so but none have ever taken as long as the CBs I currently or have owned. Most of my riding is all or partly in town
though and I assume strickly highway riding would keep the battery charged.

[Pinhead]

I can assure you, that's not normal. My '79 CB650's charging system is just as "marginal" as the 750s and I haven't had to charge my battery since I bought the thing almost 3 years ago. With a little electrical work these problems can be eliminated.

[speedy gonzalais]

Im no expert but what i do know is this is normal in most cases on bikes and cars. The altenator/generator dont produce a full charge when the engine is idle sure it prob wont be the case with brand new altenators but old warn ones it is