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Starting issues...all comments welcome!

  • Thread starter Thread starter kwest187
  • Start date Start date
In a vacuum petcock there is a diaphram. When the vacuum line draws a vacuum, it allows fuel to flow to the carb(s). No vacuum, no fuel. Extremely safe, no fuel on the floor in the morning, just the best of the best.
The needles have nothing to do with starting, don't bother.
You need to be concentrating on your pilot screws and their passages. Are the pilot air screws 2-3 turns out?
 
koolaid_kid said:
In a vacuum petcock there is a diaphram. When the vacuum line draws a vacuum, it allows fuel to flow to the carb(s). No vacuum, no fuel. Extremely safe, no fuel on the floor in the morning, just the best of the best.
The needles have nothing to do with starting, don't bother.
You need to be concentrating on your pilot screws and their passages. Are the pilot air screws 2-3 turns out?
Click to expand...

Just to clarify a couple of things: a vacuum operated petcock requires vacuum to open the diaphragm to allow fuel flow, the vacuum is created by the engine spinning over (an engine is essentially an air pump..) which is why your bikes stock petcock would have had a second line connected to the now capped port on your carburetor (carb number two, second from the left hand sitting on the bike). That now capped port is the vacuum port. It's free to suck air into the motor to create the vacuum to open the diaphragm on the petcock. A properly working vacuum petcock would NOT flow fuel into that tube. A failing one would. It would also likely flow fuel in any setting, which is bad. The only position that fuel should freely flow without the engine turning over is the prime position. Which, if your bike has sat a long time, you need to fill the float bowls with.

But since you say you don't have a vacuum petcock anymore, you likely have a manual petcock which usually only has an "OFF", "ON" and sometimes "REServe" position. If the bike is off, that petcock should be off. If you don't turn it off, you'll end up with a crank case full of gas and thats very bad.
If the bike is low on fuel, and your petcock has one, it should be set to the "RES" position. This position has a shorter pickup tube that allows that last gallon or so of fuel to reach the carbs.

Lastly, again to clarify, your carbs have pilot mixture adjustment screws, not pilot air screws like earlier model mechanical slide carbs did. The screws on your carbs control the amount of a pre-mixed air and fuel mixture into the pilot/starter circuit. these need to be opened to 2.5-3 turns out as a starting point or you'll not get enough to fire the bike. Just so you don't confuse them with separate air and fuel screws the earlier carbs used if you search around for more info.

Oh..and no, the needle position has nothing to do with startup. The bike will actually start and idle without slides in the bores if the carbs are working/set correctly. The needle doesn't come into play until 1/4 throttle or so.

And you really should pull those plugs and see what they look like. That's an easy and quick way of helping you figure out what's going on. If they're wet, you know they're getting fuel, possibly too much. If they're dry you're not getting enough. If they're black you're too rich, or have been running on choke a lot....etc. No short cuts.
 
Plugs are dry, pilot mix adj. screws are 2.5 turns out...guess I'll crank them out 4 times, if still no start, I'll get bigger pilots-
And the starter relay...still got to pick one of those up today-
 
Understand that throttle plates will appear completely closed in idle position-you might think no air could get thru-but it does. If idle stop screw or throttle cable holds the plates too open, you're defeating the purpose of the enrichment and idle circuits which is to draw mixture thru those little holes. Dry plugs ( when you know the little carb passages are clear) might mean too much air is whizzing by throttle plates ,i.e.,you're not sucking on those holes.
 
Thanks Tom203-I'll double check the throttle plates...I eye-balled them and at the top I see 3 very small holes-I adjusted the plates so the hole closest to the engine appears to be about half covered by the plate/valve-does that seem right-or should I open or close the plate more. ie the sync adjusters-
 
kwest187 said:
Thanks Tom203-I'll double check the throttle plates...I eye-balled them and at the top I see 3 very small holes-I adjusted the plates so the hole closest to the engine appears to be about half covered by the plate/valve-does that seem right-or should I open or close the plate more. ie the sync adjusters-
Click to expand...
Good question! In your case, I'd use a straightened paper clip as a gauge between throttle plate and carb bore to get me in ballpark. First do #3 carb ( the one that idle stop screw hits), adjust by the stop screw; then do the others to match the paper clip clearance by moving their own adjusters. Hopefully, this will be close.
 
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