Idle Problem

killereef · Posted: Sat May 02, 2009 7:46 pm Post subject: Idle Problem

I have a 78 CB550k that I just bought a few dys ago. The bike starts up find with the choke on, but when i let go of the choke the bike starts to die down to an idling postion around 1500 rpm. Then it revs up by itself to about 4000-5000 rpm for about 2 to 3 mins, then falls back down to around 2000 rpm, and then back up to 4000-5000. It goes up and down. When I tried to adjust the idle screw, I would barely turn and the engine would drop and die. I checked the intake boots for any cracks or any damage, but the boots are find. Can anyone help me?

05c50 · Posted: Sat May 02, 2009 8:45 pm Post subject:

Sounds like a classic case of dirty idle jets and carbs out of sync, with a little vacuum leak on the side. How did you check the boots. Sometime they'll leak vacuum without any visible cracks. Has the bike been sitting for an extended period of time? Does it run well enough to ride? Just a couple thoughts.

............Paul

hondacustom · Posted: Sun May 03, 2009 5:49 am Post subject:

this should be in the honda tech help section

killereef · Posted: Sun May 03, 2009 12:40 pm Post subject:

What I also did not mention why riding the bike, around 5000 rpm, the bike splutter. The idle jet has been cleaned and the boot was sprayed with wd40. I did a check this morning while the bike is idling low, I would pull the plugs. Plugs 1 and 4 would kill the engine, but 2 and 3 would not do anything. When the engine is at the high rpm side, i would adjust the idle screw to turn down the rpm to about 1000. The engine has a different sound and giving it throttle sound get and all four are hitting.

Barchetta · Posted: Sun May 03, 2009 4:00 pm Post subject:

What are the mix screws set at? I don't know what you need on a 750, but it should be in the book. Are all the float bowls filling to the same height? I'm just guessing, I'm no pro.

killereef · Posted: Mon May 04, 2009 8:09 pm Post subject:

The idle screw on 1, 2 is at 2 turn out; 3 is 1 1/2 and 4 is 1 1/4. I thick it is not so much my carb but my valves on 2 and 3 are burnt or just stuck open. The bike does have 36000 miles. I am going to do a compression test when I borrow my cousin test kit.

05c50 · Posted: Mon May 04, 2009 8:14 pm Post subject:

Good place to start. No matter how good the tune is, you can't compensate for poor compression. If the compression is low, check valve adjustment, could be overtight valves.

.............Paul