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What's up y'all, first post here:

I bought a 1976 Honda XL 175 about a month ago and have been trying to get it in reliable riding condition since then. I am fairly close now but am experiencing a frustrating problem.

The problem:

Engine starts first kick and runs really solid for about 10 - 15 minutes. Once reaching operating temperature, performance starts to dwindle and starts to run poorly. Occasional backfires, starts to idle inconsistently, eventually leading to a stall when I pull in the clutch / let off throttle completely. Seems to stall around the exact same amount of time of riding. After stalling it is hard to start, will only start and idle very slowly, any gas given will bog and kill engine. Takes about 15 minutes to recover and then starts normally.

What I have checked:

-First thought it was a possible vacuum lock due to clogged fuel tank vent - Tested by unscrewing gas cap when problem occurred, heard no rush of air and still would not start.
-Recently took it to a mechanic to tune and clean carb - He also checked valve clearances and points timing, and stator.
-Put in new spark plug w/ proper gapping, fresh oil, fresh gas.

Anyone have experience with issues like this? I am thinking it could possibly be the coil starting to go bad and overheat? Or possibly clogged fuel petcock filter? Both things I need to check.

Something else worth mentioning:

I am having issues with the stator putting out too much voltage on the headlight AC circuit and blowing bulbs. However the engine AC circuit is not showing same symptoms / putting out voltage nearly as high as the headlight circuit. Going to put a 12v voltage restrictor / regulator for the headlight. (I understand its a 6v circuit but I have 12v bulbs).

Please Help - Here is a pic for fun

Wheel Sky Tire Vehicle Plant
 

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I imagine any mechanic worth their salt would of checked but I'm guessing you haven't left the choke open...most bikes/vehicles of this vintage have manual chokes.
I'm not very good at the mechanically stuff and most of us over think it and forget to check the simple stuff.
I like to try to help but I'm not smart enough so I've decided to elect myself as a junior part time obvious stater in a bid that I help just one person before they strip their bike down
 

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Honda Tiderls, Ural Solos & BMW R60/6
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I'd suggest testing / replacing the condenser because when they fail they cause erratic sparks as they get hotter, been there and done that many times over .

There is NO VOLTAGE REGULATOR - the battery is what controls the voltage, even to the headlight .

The RECTIFIER is almost certainly bad, new ones are out there, I'd suggest asking the pardue brothers in Florida for their new one, usually far less cost than an N.O.S. one but no quality concerns .

Or, just get a full wave DC bridge OnLine and use that, it's what I do with my old Hondas .
 

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Honda Tiderls, Ural Solos & BMW R60/6
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Well I'll be ! I didn't know that, most older Hondas have only the rectifier .

THANK YOU for teaching me .

The late model CT90 & 110's are well known for blowing their 6 volt seal beam headlights, I wonder if i could retro fit one to one of my oldies ? .

Before making any changes first I'd make it 100 % stock and then see .
 

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I'd look close at the 3 loops of wire at the magneto flywheel, some of that power generated may well be shared across battery and lighting, the lower level stuff used to power one to charge only and the other ran light and you are right, no regulator on many of those. That may have been before turns, which require a pretty even power source to accurately flash.
 
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