Help~ CB350 warm up RPM raises bike dies

[Dragonfish]

Ok, I really need some advice. Bike has not run too well, I've been working on it for a couple months. Had bad mufflers and air filters so I replaced them with Nice stock mufflers and Uni foam filters. Tonight I pulled the carbs, bench synced them, checked the float height (26mm Keihin 3D) adjusted the valves which were pretty far off, set the points, synced the throttle pulls, replaced the plugs. I wanted to check the timing (it was done recently) but the battery was stone dead. I jumped the bike and it ran great!!! Better than it has ever sounded. Unfortunately it started doing the same thing it was doing before all the work. As the bike warmed up the RPMs started going up unless I hit the choke. The warmer it got, the worse it ran. Eventually it just won't stay running anymore. I pulled both plugs and they are perfect. It ran for a good 3-4 minutes during this time. I'm betting that once it cools off, it will fire right up again. What would do this? The carbs are stock with 70 primary and 105 secondary mains. The ONLY non stock item on the bike is the Uni filters. What could be causing this?

 

[Sonreir]

How clean are the carbs? It sounds like you're running lean. Possible air leak at the manifold?

 

[my-79-750-k]

Pinched fuel line, clogged fuel line, clogged petcock, air leak, buildup in your intake runner, etc. SOMETHING is causing either your fuel to not flow enough or just not enough air/fuel getting into the chamber when it's warm.

 

[Dragonfish]

Possibly the dumbest question ever... could it just be low on gas?

 

[Dragonfish]

Carbs were recently boiled in lemon juice, brand new fuel lines. Have not checked the petcock but if I disconnect the fuel line from the carb and drain it into a can it flows nice. I did spray carb cleaner at the boots and it backfired and may have increased the RPMs but it was already running crappy by then so I didn't know if it was from the cleaner or not. Also: the carb air/fuel screw is set to 3/4 turn out from closed. For my carb thats what I read is the right setting but every other cb350 thread I read says more like 1.5 turns out. So what is the next logical thing to try? Also if it is the carb boots leaking how do I seal them up?

 

[Sonreir]

If the fuel in the bowls were low, it wouldn't be revving high, it would just die out. Total lack of throttle response would preceed the engine dying. The problem is likely to be too much air getting in somehow.

If you haven't already done so, but a thin layer of silicone sealant (such as RTV) in between the manifold and the head (on both sides of the gasket) and put a thin layer of grease on the inside of the manifolds where the carbs attach. I assume the manifolds are in good shape?

Finally, while you have the carbs off the bike, look them over and make sure nothing came out. A loose screw or something or the sort will cause this problem, too.