hi, i need some advice. i recently bought a 1990 cbr600 that wasnt running, it needed a new fuel pump and downpipes. i have now fitted these along with a new battery and also changed the oil and oil filter. i am having trouble getting the bike to idle correctly. when i start it, it idles up and down between 2k and 3k revs for about 10 second and then it goes wild and revs all the way up to the red line and i have to switch the engine off.
i have noticed the ht lead to plug 2 seems to have been tampered with and has some insulation wrapped around it.
also i have fiited the downpipes but not put the gaskets on yet, not sure if any of these thing have anything to do with the problem.
o yea and i have tried turning the idle screw down but this didnt help. i have got a video off the bike but dont know if i can post it on here?

 

Has most likely been sitting for awhile and is starving for fuel in some fashion, either petcock, filter, pump, or carbs unable to keep up with the demand of the engine.

You said you replaced the fuel pump, did you also tear down the carbs and clean them, as well as the petcock?

Either that or there is an airleak somewhere along the path, make sure seal between airbox to carbs is in order. As well as the intake boots. Get it started and spray some ether around the intake areas and see if it fluctuated your RPM.

 

ok i will check these, ive also bought new ht leads off ebay to replace the damaged one as i have been doing some research and it sounds like that could be my problem.
thanks

 

Well, I couldn't find any vacuum leaks either visually or with spray. Although I was skeptical new plugs would do anything on account of they only have 11,000 miles on them, the color looked good, and the gaps were right on the money, I figured I should replace them anyway while I'm torn down. I also replaced the air filter while I was at it even thought it looked hardly used. After replacing the plugs and filter with new ones, viola! The bike runs perfect again. That's seems so weird to me. Honda says inspect the plugs at 16,000 and, I think, replace at 32,000. For that particular part number, NGK says they're good for 80,000 - 100,000 miles. I'm not complaining because I'm happy the bike is fixed. I'm just saying that seems a little not right...

 

I had it tore down enough to get to the spark plugs by the time I had checked everything else and hadn't found any problems. I figured even though the plugs had only 11,000 miles on them and had good color and the gaps were perfect, I might as well replace them while I had access. Amazingly, with the new plugs the bike runs like new! It's the goofiest thing I've seen in a long time, but I'm not complaining. It just was surprising on account of Honda says inspect them at 16,000 miles and replace them at 32,000. NGK says that particular part number is good for 80,000! Well, at least the bike is back in business for the good weather. Perhaps this discovery can save someone else the trouble of chasing the wrong things for the same symptom...