83 VT500C Too Lean/Cooling Issues??

[kadinga]

1983 VT500C ~20K km, new pipes, 2 recent trips to the shop for carb work followed by a short road trip and here's where I stand:
Sounds like Im making popcorn every time I decelerate (shop claims - exhaust gasket leaking where mufflers attach), starts easy/idles nice/rides well until the engine gets hot (aka 2+ hours on the hwy). After that, I have to hold the idle part way open at lights, occasional backfire at lower rpm/starting and it feels ready to stall <2500 rpm. Note: upon passing the 2500-3K mark it wakes up and rides like nothing happened.
My suspicion is resetting the stock jets wont adequately compensate for the new pipes and/or I need to repair the cooling system.
Can I please get some input before I bash away at this?
Thanks a ton!

[kadinga]

Forgot one more thing: I average 55-60 mpg and just replaced the oil/filter and spark plugs

[Easy Rider 2]

Originally Posted by kadinga

Sounds like Im making popcorn every time I decelerate (shop claims - exhaust gasket leaking where mufflers attach),

After that, I have to hold the idle part way open at lights, occasional backfire at lower rpm/starting and it feels ready to stall <2500 rpm. Note: upon passing the 2500-3K mark it wakes up and rides like nothing happened.

Don't panic. Fix what you KNOW is bad first; the exhaust gasket. Remote possibility that the exhaust leak is directed such that it is CAUSING a slight overheating.

Then, what makes you think it is overheating?
Could be a vacume leak or head gasket problem.

If you have an old-fashioned "real" butterfly choke, you might try applying a bit of choke when the problem arises......to see if you really have a lean condition.

Your best bet, especially since you have a shop that is already familiar with the bike is: (after the exhaust gasket is fixed), ride until the problem arises and plan your route to be AT the shop about that time......so they can SEE the problem as it is occurring.

Good luck!

[litnin]

Originally Posted by kadinga

1983 VT500C ~20K km, new pipes, 2 recent trips to the shop for carb work followed by a short road trip and here's where I stand:
Sounds like Im making popcorn every time I decelerate (shop claims - exhaust gasket leaking where mufflers attach), starts easy/idles nice/rides well until the engine gets hot (aka 2+ hours on the hwy). After that, I have to hold the idle part way open at lights, occasional backfire at lower rpm/starting and it feels ready to stall <2500 rpm. Note: upon passing the 2500-3K mark it wakes up and rides like nothing happened.
My suspicion is resetting the stock jets wont adequately compensate for the new pipes and/or I need to repair the cooling system.
Can I please get some input before I bash away at this?
Thanks a ton!

When you replaced the pipes, did you put in new exhaust gaskets?
It's always a good idea to do so, if you didn't, but that doesn't
necessarily mean that they are leaking.
This requires you to clean the bike after-wards, but it will tell you
if the pipes are leaking at the port.
Sprinkle some baby/talc powder around the ports. On the bottom side,
where it won't collect, put some on a piece of cardboard that you can
hold up to the pipe.
Start the bike and rap the throttle a few times.
If the talc puffs out, you have an exhaust leak...
If you have a leak, fix that first.
If not, move on to the carburetors.

If the exhaust does not leak, what you are describing sounds like your idle jets are not supplying ample fuel.
You'll need to do an RPM drop test on the idle circuit.
Once you get that, ride it and see how it does.
If it still pops on decel and idles a little goofy, you want to
richen up your idle mixture just a tad.
Do it in about 1/2 turn increments.
After market pipes generally change the air flow characteristics
and usually lean out your mixture.
Adjusting the pilot jets can usually compensate for that.
However, when adjusting the pilot circuit, if you get more
than about 3 1/2 turns off base, you'll want to go up one
size on the pilot jet and then do another RPM drop test at idle.

You also need to keep an eye out on the plugs.
The plugs will tell you what your engine is doing.
Pull them an look at them.
If the tip has a powder white color and or pitting around
the ground strap, you are too lean and need to get the mixture richened up.
If the tip has a lot of sooty black carbon on it, you're running too rich.
If it's got a nice chocolate brown /tan color around the insulator of
the core, and the tip is nice and clean, your mixture is in good shape.

[kadinga]

I know I have a slight exhaust leak, my main focus is the carbs.
When I took the bike in last they said they "readjusted the jets". My concern is the manual clearly states the jet needles are NOT adjustable. It ran better after each visit to the shop but I still have major problems after harder rides.
What are my options? Larger jets? Or will a *proper* tune up solve the problem? Yes, she runs smoother (when hot) if I apply a little choke. The plug seat is sooty and the tips are white. I get the feeling my bike leans out the more it warms up.
Also, could someone please explain an "rpm drop test" and location of the pilot screws on my bike? Im fairly new to working with carburetion although I understand the principles.
thx again

[Easy Rider 2]

Originally Posted by kadinga

Yes, she runs smoother (when hot) if I apply a little choke.

Your mixture is leaning out as the bike heats up. An "adjustment" will not fix it. There is a PROBLEM when hot and that problem needs to be located and fixed.

The fact that YOU are "focused" on the carbs doesn't mean that is where the problem IS; might be, might not be too. Changing jets or adjusting needles is NOT the solution.

I know you aren't buying this at the moment but FIX THE EXHAUST LEAK FIRST. It may be your only problem; if not, no harm done.

It is also possible that your valves are WAY out of adjustment and when hot, are causing it to run lean.

Did I mention cracked rubber boots around the carb(s) or a vacume leak ??

Also, you included "cooling problem" in the thread title and then didn't mention it again. Do you have reason to suspect it is OVERheating ?
If so, that could be a contributing factor.

[litnin]

Originally Posted by kadinga

I know I have a slight exhaust leak, my main focus is the carbs.

First things first, you need to stop focusing on the carbs and focus
on getting the exhaust leak fixed.
You can focus all you want on the carbs now, but when you burn
an exhaust valve from that leak, you're gonna have more problems
and you're not going to properly tune the carbs until that leak is fixed.

Second, no, the stock needles are not adjustable.
You've added pipes and you've likely changed the air flow characteristics
enough to lean out the motor.
AFTER you correct the exhaust leak, you'll might need to buy and
install a jet kit that has a little bigger jets and needles that are
height adjustable.

The RPM drop test is how you set your idle jets.
You basically start out at a set point, which is usually somewhere around
2 - 2 1/4 turns out on the pilot screws.
You start with one cylinder and run the screw in (lean) until it the RPM
starts to fall.
Once it just starts to fall, you start backing it out until it starts to increase
and then fall out again.
Count the number of turns between the first fall and the second fall and
split the difference.
That will give you a baseline that you can start with and make minor
adjustments from there.
Do this on both cylinders and you want to set your idle speed at the start,
and again after each cylinder.
It would be a VERY good idea to sync your carbs after doing this
and after rejetting.

If you do ANYTHING with the carburetors before fixing that leak,
you are just (pardon the expression), pi$$ing in the wind.