No Power after warm-up. '82 Urban Express

[motormike]

Just acquired this bike.
It starts very good.
It has good power when cold.
After one trip around the block, take-off is sluggish.
It will reach 30 mph on level ground.
Spark plug is tan and apparently pretty recent.
When traveling at 30 mph, and starting up a slight grade,
the bike will slow to 20 mph very quickly.
If the grade is steeper, the bike will slow even more, to 10 mph.
When traveling at 30 mph on the flat, the throttle is at 1/2 open.
Any farther open on the throttle, and the motor starts to loose rpm and sound
like it is increasing the air-flow, but not the fuel-flow.
I tested compression hot, with throttle WOT and showed 140+ p.s.i. with a reliable gauge.
I am suspecting some carbon build-up in the cylinder.
IS THAT condition likely to rob the motor of power to the extent described ?
I don't think the carburetor is the reason for this poor performance, but will be starting with a complete
dis-assembly and soaking just because i want to see for myself the status of the carburetor.
Your assistance will be helpful in finding the problem.
What are the items I should inspect while having the carb off ?
Please post any opinions and experiences regarding this scenario to help me return this sweet Urban back to it's full potential.

[bfowler]

Hey mike. You definitely have a lot more experience with scooters than myself but the symptoms you describe sound 100% identical to the symptoms that my elite had prior to disassembling the carb. Gave it a good soak and spray and changed the spark plug and it was running like new again. I also replaced the jet, not sure if it was a down jet or an upjet though, can't remember. Hopefully after you clean the carb it'll be running good! Might wanna check the spark gap too

[motormike]

Thanx bfowler...Hoping for the same thing here.

[motormike]

Anybody ?

[swimmingfree]

how is the coil ??? if its week when it get hot it will give a weaker spark???
swimmingfree

[breaze]

The important thing is that it looks good and has good compression - great find - you'll get the mechanics straightened out. I hate to state the obvious, but it sure sounds like your vacuum choke is acting up. When you clean your carb, you might consider changing out the hoses to clear (you'll need 1/4" and 3'16" clear hose) - that way you can see what it is doing. I've had good luck cleaning out the thermal valve housing (piece mounted to the cylinder) by filling it with carb cleaner overnight. It is also well worth opening the small air cleaner element that supplies air to the valve and making sure it has a good filter element in it (any sponge element will do). Easy enough to take the choke out of the equation if you just want to see if it is causing the problem - just cap off the input to the manifold and plug the hose - that is how it should be running once warm and valve closes off. I'm working on an 83 NH80 at the moment (which has the thermal bystarter) and recently finished the Urban we discussed - I've got lots of pics if you need more guidance on the bystarter. Here is a link for more: http://www.hondaspree.net/phpBB3/viewto ... ze#p234931



The other obvious check would be the belt, rollers, and variator. Assuming you have good compression, good drive and driven system, plug, and clean carb, I bet it will run fine.

Oh, and btw, after your experience with Ruby, drain and re-fill the transmission case before any more road tests

[motormike]

Hate to see it go, but the wheels under me never stop turning.
I'm moving on to a NEW bike this time.
Will be my first spanking-new bike since 1996...(bought a Virago 250)
Here's some parting shots of "Keith Urban"
...and one of the NEW whip that awaits me in Georgia...

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[Pete M]

Main jet in the carb Mike. Emulsion tube may add to the fun.

[LMH]

How much was the Sym? They just recently started selling the Syms at the local Motofino place in town.