Carb (?) Issues. Help needed please!

[1970ct70k0h]

K0 3-speed. Old carb and brand new repro from TB have same issue. Only runs on full choke, even at idle. Fuel tank is spotless. Fuel lines and fuel are new. I therefore have no reason to suspect the usual gummed-up, clogged-up issues typical with engines which have been sitting. Intake gaskets seem fine and I don’t suspect an intake leak but I have ordered new gaskets just in case. No amount of pilot screw adjustment seems to help. Thoughts please. Thanks.

 

[Carlo C.]

K0 3-speed. Old carb and brand new repro from TB have same issue. Only runs on full choke, even at idle. Fuel tank is spotless. Fuel lines and fuel are new. I therefore have no reason to suspect the usual gummed-up, clogged-up issues typical with engines which have been sitting. Intake gaskets seem fine and I don’t suspect an intake leak but I have ordered new gaskets just in case. No amount of pilot screw adjustment seems to help. Thoughts please. Thanks.

For some reason it is very lean. Even though it is new the first think I would do is take it apart and make sure everything is clean and no debris blocking any of the holes. If it still runs the same way I would go a couple sizes bigger with the pilot jet until it will at least idle without the choke on and go from there.

Carlo C.

 

[Robert thran]

Spray some carb or brake cleaner or starter fluid around the intake at both sides and see if the motor changes while running,,,if so you have an intake leaking and sucking air..it’s odd two carbs doing the exact same thing..?

 

[1970ct70k0h]

Carb is new, but i suppose it won’t hurt to check For debris. And the starting fluid idea is a great one.

 

[1970ct70k0h]

SOLVED: First off, thanks to those who chimed in to assist.

I still have no idea why the brand new replacement carb from TB wouldn’t run on anything other than full choke and have yet to tear it down for inspection.

I tore down and cleaned the (already clean, no visible varnish of crud, no visible blockages in jets) original carb, soaked it in carb cleaner, and replaced the few gaskets I could from a (very incomplete and disappointing) CHP rebuild kit. I found that the main needle clip was set very lean, as was the float.

The bike started on 3rd of fourth kick and now runs just fine. Further fine tuning of the rest of the engine to follow (timing, valves, etc) of course but I am thrilled that this 2-owner bike (I am the second) is now running for the first time since the 90’s.

I will close here by thanking you all once again!