I must be a sucker for an old dog. Recently got my 290 Sherco bucket of bolts going and I've come across a 1992 280 Aprillia climber that needs a bit of TLC.

It starts and runs but only on the choke.

I've cleaned out the carb, swilled out the tank and put fresh premix in. The carb and airbox rubbers are sealed tight and it's got a new plug BP5es.

I should say the bike has stood for a long while.

Any ideas from the good people of TC?

I'd go back over the carb again, perhaps get it cleaned in an ultrasonic tank. If it'll only run on choke that's telling me a blocked jet / passage. What carb, I can't remember that long ago!! would the Sherco carb fit to give it a try? Might not be jetted right but should give you an indication.

Hmmm, they're both Dellortos. Couldn't hurt to swap for a try.

Maybe needs more than a squirt with carb cleaner then you think?

I've shared this before but thought you might like to see me riding my 92 Aprilia, bit of inspiration for your project perhaps!

https://youtu.be/UqcqkP5qN5s

You don`t have the two vent tubes connected do you? Also the choke circuit has it`s own jet.

The vent hoses have the cut in them. I'll strip the carb more carefully this time, do you reckon swapping the carb from my Sherco is worth a try as Steve suggests? Can't hurt can it?

Where is the mixture screw located?

Between slide and intake then it's a fuel mixture screw.

Between slide and airbox manifold then it's a air mix screw.

They work un opposite way, completly turned in:

air mixture screw: max. fat

Fuel mixture screw: max. lean

Anyway for both screws 1 and a half turn is the standard setting for both screws.

Edited May 5, 201610 yr by pschrauber

Clogging:

You might again take a very close look to the bottom screw that holds the bowl and the main jet.

The hollow inside the bolt or screw is wider then the thread hole for the main jet the bottom to of the hollow is the deepest spot of the carb inside there can have been collected a bit of crud with the time that can be collected by the gas flow and provide a clogged jet.

I would too unscrew the mixture screw and give the inside a good clean flush with carb cleaner and compressed air. The small O-ring might be insufficient too.

Any other channel of the carb and the bowl (there is one too) I would give too a good flush with cleaner and compressed air.

It's often just small thingies that can change the behavior a lot ...

Edited May 5, 201610 yr by pschrauber

Thanks pschrauber,

I've the stripped carb in an ultrasonic cleaner now. Once I get it out and dried off I'll list what sizes they all are so maybe you helpful folks can make sure they're the right sizes.

There was a lot of crud in the choke.

look for the secondary jet hidden above the long pilot jet that sits in the corner of the float chamber.

Right now I'm stumped.

The carb is spotlessly clean yet it will still only run on choke.

Am I looking at main seals?

Can be the seals, very much work.

 

There is no air leak and the carb is clean Mmmh ... fuel supply is OK, jets are the right ones??

Change the carb since you have one.

I agree with stan post #10, your carb has two pilot jets, one hidden deep beneath the outer one. You might not have discovered the second one (most don't) and its plugged.

I'll look for the second pilot jet, tried swapping the carbs but the Sherco has a smaller diameter mouth on the reed block. Bugger.