KZ305 will not go faster than 50 mph now

Hi All,

Not sure if this belongs in the carb section but here goes:

I recently took the carbs off to replace an o-ring in the swivel fuel T-fitting between the carbs and it fixed the fuel leak. The bike ran well for 4 or 5 rides and had full power. Now it continues to start and idle well but is sluggish after that and will not go more than 45-50 mph.

I took the carbs off and the bottom bowls and cleaned everything and blew out the jets. I did NOT take the top of the carbs off or remove and clean the pilot screw or the jet needle.  I have read that the diaphrams are hard to find and replace so I didn't want any carb cleaner up there or damage the diaphram s in any way. I did puff some compressed air into the diaphram area and the sliders moved easily.

After doing all that and reinstalling....I have the same problem.

I seek advice on what to do next. I am a noob at this stuff, was my first try at a carb cleaning.
I do have an ultrasound bath available. Thanks.

See if it runs better on one cylinder or the other. Get a spark plug and ground it to the engine and attach the plug wire to it. Go for a quick full throttle test ride on one cylinder. Do the same for the other cylinder and see if the problem is on only one side.
Another check, with the carbs on a work bench, is pull air through a carb with a shop vac while opening and closing the throttle plate. Do the slides on each carb react the same?

Ok will do. Thank you.

I assume you mean to just rev the throttle after grounding the plug or do you mean an actual ride around?

I dunno how I would do the ride while holding the grounded plug.

I mean go for a ride. You want to check things under full throttle under load. Use a piece of wire to strap the plug to engine fins or another ground point.
You could just pull one plug wire, but would risk damaging tke coil, if not attached to a grounded plug.
You are trying to see if one cylinder is pulling much stronger than the other. A 1 minute test ride is enough.

Got it. Will do. Thx

Ok finally got around to doing this.

As I had my spare spark plug and wire for grounding attachment ready I fired up the bike to warm it up first.

Looking and feeling around I see the exhaust pipe and cooling fins next to my right leg gets hot in a couple minutes, the exhaust pipe and fins by my left leg stay cool.

I had tested both plugs for spark earlier and they passed, I swapped the plugs anyway and the left side remains cool and does not warm up.

I wanted to ask if this gives any clues to what might be wrong before going through the carb removal process. Any ideas?
 

Worth checking valve clearances and compression but it does seem like a fuelling issue. You could also swop the coils left to right (I know it sparks outside the engine but it may not produce a strong enough spark when in a pressurised cylinder)

Thanks will probably swap those coils before tearing down further to get to the carbs.