RPM runs higher with the head light on.

Stillreel · May 9, 2014

With a nod to Hobot "Ole Brit Iron Motto - if it feels sounds and smells like fuel problem check electrics first" ... what electrical component failure is causing my RPM to change from a steady 1100 to 2000 when I run it with the head light on?

Reminds me of the story of a fella who thought D = daytime driving and N = night. Said his car wouldn't go anywhere after dark. Race mode (R) had even worse consequences.

BC

concours · May 9, 2014

Stillreel said:
With a nod to Hobot "Ole Brit Iron Motto - if it feels sounds and smells like fuel problem check electrics first" ... what electrical component failure is causing my RPM to change from a steady 1100 to 2000 when I run it with the head light on?

Reminds me of the story of a fella who thought D = daytime driving and N = night. Said his car wouldn't go anywhere after dark. Race mode (R) had even worse consequences.

BC

Flaky ignition switch.... check it with a jumper wire, or, unplug the headlamp, see if it's the same...

Hobot · May 9, 2014

Oh Oh I think that was one of the first symptoms of buying a Vampire Commando before it got bloody meaner. If a boyah or other potted 'black box' installed spraker installed, they tend to go brain dead over advancing if something causes voltage to drop a few-3 volts. Smells like a loose alternator charge lead to me along with an old or too small or too dry battery. May just be battery terminals the shoe elves are chuckling about.

Stillreel · May 9, 2014

Okay. Its not electrical. After further testing, it NOW appears that is is an airleak around the port side carb. When riding today, I put my thumb over the gap at the base of the slider (airfilters removed) and the idle returned to normal. So I'm thinking its the leaky old AMALs that are causing the high idle. I'll lower the needle (only on one side?!?) to see if that helps.

Next question is what part to replace; chrome slides or the whole thing(s).

On a positive note, the machine sounds great. when I open the throttle.

But it is a constant puzzle.

BC

concours · May 9, 2014

Get new carbs, you can't tune variable, intermittent air leak.

L.A.B. · May 9, 2014

Stillreel said:
When riding today, I put my thumb over the gap at the base of the slider (airfilters removed) and the idle returned to normal. So I'm thinking its the leaky old AMALs that are causing the high idle. I'll lower the needle (only on one side?!?) to see if that helps.

If, as you say, if the slide is excessively loose in the carb body, then air can be drawn in around the slide, causing the high idle.

I don't quite understand what expect to achieve by lowering the needle, as it has little or no effect at idle.

1up3down · May 9, 2014

it NOW appears that is is an airleak around the port side carb.

you could fix the air leak instead of changing the carb jetting.....

L.A.B. · May 9, 2014

1up3down said:
it NOW appears that is is an airleak around the port side carb.

Click to expand...

you could fix the air leak instead of changing the carb jetting.....

I think he means air is leaking past the slide (slider?)?

When riding today, I put my thumb over the gap at the base of the slider (airfilters removed) and the idle returned to normal.

Hobot · May 11, 2014

Worn slide to bore clearance infamous for too fast creeping up idle. I diagnosed one Combat doing that by greasing the slides which tamed idle till grease washed out after 100 miles or so. Anodized slides with one size cut out smaller to compensate for the bore wear worked out well in my case.

maylar · May 11, 2014

Umm... what does any of this have to do with the headlight being on or not?

Hobot · May 11, 2014

Same thing as the riddle of what a baby's bottom a boat bottom and a lemon have in common. Baby and boat's bottoms are always wet.

Matt Spencer · May 12, 2014

Try getting it up to Top Whack , then switch on the lamp to see if it goes faster . :wink:

concours · May 12, 2014

maylar said:
Umm... what does any of this have to do with the headlight being on or not?

The OP came back and reported it was a coincidence, rather than a bona fide symptom. So very often this is the case, a good interrogation is crucial to solving the puzzle as a troubleshooter.

RPM runs higher with the head light on.

Stillreel

concours

Hobot

Stillreel

concours

L.A.B.

Moderator

1up3down

L.A.B.

Moderator

Hobot

maylar

Hobot

Matt Spencer

concours

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