I went hunting for intake/exhaust leaks today using my daughters bubbles. Nothing found. It was interesting to feel the pulse of the engine in the rubber cap I used to cover the vacuum port on the carb. I had never noticed that before.

Removing the vacuum tube and running on prime has two pronounced effects. First, the engine idles faster. Second, the pop on shutdown is louder. I'm not sure if that means it's leaner or richer than it was before. Any ideas? General performance is about the same. I'll fill up with gas tomorrow and see what my mileage looks like.

About a week before I removed the vacuum tube I also switched from a 55 pilot to a 52.5. I don't recall that switch having an effect on idle rpm or shutdown pop. If it did have an effect on the shutdown pop, it has gotten worse without the vacuum tube.

When I shutdown after hunting for leaks the was no pop. The engine was warm enough for me to have pushed the choke in, but not fully warmed up. I expected a very loud bang at shutdown. Can anyone explain this?

One last question, I'm not sure if it's related.
How long does it take for your engines to get up to operating temperature? I generally ride about a mile with the choke out 1 notch, then 4-5 miles at 35-45 mph before the lean surging goes away. Is that normal?

I really need to mark throttle positions. The surging I'm talking about happens the most pronounced in 3rd gear at 35mph. I think that's in the 1/8 to 1/4 throttle range.

The reason I'm still poking at the carb is because of the POP I get on throttle close. Same type of pop I get coming off the freeway and engine braking. It happens more often when I shift at higher rpms. For example shifting 2->3 at 20mph generally produces no pop, while 2->3 at 30mph generally pops.

Thanks for all of the advice.

-D. Dwarf

justin_o_guy2 wrote on 08/29/10 at 17:44:33:

I did. The one on the petcock too.

-D. Dwarf

DrunkenDwarf wrote on 08/29/10 at 17:37:49:


pop on shutdown says lean.
idling faster generally means air leak.

verslagen1 wrote on 08/29/10 at 21:15:00:

You don't think the pressure wave in the intake is strong enough to push out if there was a leak? I can feel the pulse in the rubber cap I used to plug the vacuum port. It seemed strong.

verslagen1 wrote on 08/29/10 at 21:18:32:

So, by removing the vacuum line and plugging the intake to the carb I created a vacuum leak? Or just increased the symptom?

verslagen1 wrote on 08/29/10 at 21:27:58:

I'm not concerned about the engine braking pops. It's the ones that happen when I shift that I'm working to minimize.

I've looked for exhaust leaks, haven't found any. I'll check the idle speed. It's higher than it was before, maybe it was too low.

I figured out why it doesn't backfire when the choke is out. The RPMs don't drop as quickly when I close the throttle.

-D. Dwarf

justin_o_guy2 wrote on 08/30/10 at 09:25:32:

Right.

With the choke out it's too rich to idle smoothly, but runs well otherwise. Maybe I need to change the main jet up a size (or reduce washers). I've been avoiding changing jets (more) until all leaks are found.

-D. Dwarf

This is why I call myself an 80% mechanic. Im just not the guy to get that laaaast bit of tuning done. Ill get it running "allright" & call it good. I just dont want to deal with spending the time figuring out what to do next & how to do it. I KNOW Ill waste a ton of time & someone else with the experience to be able to listen to it & look at the plug & know whats the next logical step to take would walk right thru. Im not ready for that learning curve. The electrode on the plug is white & ashen looking, & the ceramic on the outter ring is dark, so IDK if its rich or lean er Wuttt! But, Ive got soot on the brake lever,,, maybe one day Ill take it up the street to the machine & hook it up..Its 100 bux for the first run & 10 for the rest.

I should just give up. Today into work it was 60 F and 90% humidity. On the way home it was 90 F and 60%. No pop on shift either to or from.

The changes I made from 'baseline' were:
pilot 55 (1 turn out) to 52.5 (1.5 turns out)
removed vacuum tube

It ran better on my way home, so I assume I'm still lean. The bang on shutdown agrees. I'll try 2 turns out tomorrow and see how that does. That puts me back where I started, except for the vacuum tube. I'll have to pull the cap off the vacuum port on the petcock and see if it's collecting gas.

-D. Dwarf

Mine behaves the same way, and regardless of what setting I was trying it never went away. The same with the poofs on shutdown. It sometimes does, and sometimes doesn't. Sometimes a slight very subtle poof, sometimes a louder poof, almost a bang, but not like a gunshot. When i ride to work in the morning, which only 1.2 miles, it does an audible poof when I turn it off. At lunch when I go home, riding almost the same way it doesn't do it. It might have to do with having to ride up a slight hill, and that gets the exhaust hotter than driving with less strain. IDK. It definately changes with weather/temperature/humidity. In summer it's alot more often than in winter. Being easy on the throttle and shifting then doesn't do a pop most of the time. Getting on it and shifting produces pops almost every time.