High idle after bike is warm

Hello,
I am new to this forum. I just bought a Kaw 1981 550 LTD in great condition. The bike has difficulty starting but I am able to start with the fuel petcock in PRI. The choke has no effect on starting or running the bike. When the bike is warmed up it starts to race. I lowered the idle adjuster as low as possible but still races at idle. I sprayed carb cleaner around the carb to see if any change, no change. Plugs are new and air filter is on order. Could it be the choke stuck?
Any help would be greatly appreciated.
Thank you,
Dino

sounds like a job for wg;)

you need to clean the carbs and check to see if the butterfly valves are opening at the same time .there has to be some serious blockage for the choke to make no difference.


And welcome to KZR home of the most insane and genuinely knowledgable motorcycle freaks on the net, p.s. we want pics

What butterflies would you suggest he check on those round slide carbs Terry? bwhahahahaa Sorry... you DO have the right idea though... the problem is likely in the synchronization. Bench sync using the procedure in your Kawasaki factory shop manual. The bench sync that was done was done incorrectly and you are out of the range where the idle can be set after the bike is warmed. The factory manaual will tell you to open the idle screw some to open the slides and then close them down using the sync screws. You usually need to turn the idle screw down about 4-5 turns on those carbs as I recall then close the slides so there is about 1mm gap between the slide cut out and venturi. Once you get the carbs on your bike again, sync with a manometer and you should be fine. Once you have the biked warm, set the idle speed. I am not sure why the choke isn't working... perhaps I would clean the gas pick ups that feed gas to the choke circuit but would need to look at the carbs to be sure...

Just a thought, but if the bike only runs with the petcock on prime, perhaps the diaphram in the petcock is leaking fuel into the carbs through the vacum ports? It might be worth a check.

Post edited by: danielcwebb, at: 2006/05/24 19:41

Thank you for the response. Can you tell me which direction the choke lever operates. Also the gas petcock has ON,PRI and RES but no off.When would you normally use PRI and when would you switch to ON.

Thank you,

Dino

The choke arm on the side of the carbs should be oriented DOWN when you are running normally without choke. You lift the arm, that is, pull it up, to actuate the choke. As far as the petcock goes, most petcocks in the 70s were gravity feed and had ON, OFF and RESERVE positions. Folks would forget to turn the petcock to OFF when parking the bike and would have a pool of gas when they returned to the bike as the float needle/seat mechanism isn't the world's best gas shut off. Most manufacturers went with VACUUM actuated petcocks in the 80s. This style relies on engine vacuum via a carburetor vacuum fitting connected to the petcock to actuate an internal diaphragm in the petcock. In other words, when the bike is running, vacuum is produced and the diaphragm allows gas to flow. When the bike is not running, gas will not flow. This type petock has ON, RESERVE and PRI functions. The ON position is the normal position you should have the petcock. You operate the bike, gas flows and shut the bike off, gas stops flowing. RESERVE works the same except the pickup for this position is slightly lower within the tank allowing gas from the bottom to be drawn in. The PRI position bypasses the vacuum diaphragm mechanism and just allows gas to flow. The problem is, if the carbs are TOTALLY DRY, the bike won't run to generate vacuum to pull gas in. A catch-22 situation so PRI allows gas to flow without vacuum control to fill the carbs and get you going. Once the bike is running, switch to ON. The downside to the vacuum petcock is the complication of the diaphragm mechanism which tends to degrade over time and needs to be periodically rebuilt. It it is defective, gas will flow freely when the bike is not being operated in the ON position. This allows the carburetors to potentially flood and gas can then get into your oil. On top of that, gas will also back up into the vacuum line and flood the #2 carburetor. If the vacuum actuated petcock is working properly, it is fine but if the thing needs rebuilt, it creates some very real problems.

Thank you, now it makes total sense. The idle is much better and the bike does not race after it gets warmed up. Now that the idle is running normal I hear a slight miss and little knock from the right side of the engine. Does that sound like the valves need to be adjusted?

Thank you,

Dino

If you have NOT performed normal tune up procedures, DO NOT operate the bike until you have done so. Buy a service manual or Clymer manual for your bike and do normal maintenance proceudres. Check compression, valve clearances, make sure cam chain timing is correct, replace plugs, plug wires, plug caps, clean/lube mechanical advance mechanism, remove oil pan and clean sludge and oil pump screen, replace intake manifolds, change ALL fluids, inspect tires, inspect chain/sprockets and master link and replace or at least inspect brake pads and brake function are what I personally do before I even try and start the bike. MANY costly and frustrating problems are resolved by maintaining and inspecting your bike.