so i get that shes 21 years old and tired but my 1990 CBR 600F is only putting out around 50 HP and it is running off the charts lean. two owners prior to me did a dynojet kit and drilled a but load of holes in the air box. the shop i go to thinks going back to the stock jets and finding a stock air box would be the way to go. im wondering is there any thing else that could be done to get some of that life back?

oh and hears the vid of the event.


YouTube - ‪1990 CBR 600F Dyno‬‏

 

Going back to stock jets and stock airbox will make your bike just that. Stock.

Reason 1 for running lean? Carb Kit is installed incorrectly, main jet is probably too small. Needles might need to be raised a bit.

So, first things first, take your carbs off and clean them, determine what size main jet is in it. The largest size for the DJ kits on the 1990 is a 124 Main. Thats the one you should start with, hopefully the previous owners gave you the rest of the jet kit. If it is not a 124 main jet, you need to do the CV Carb Tuning Procedures Listed Here.
CV Carb Tuning Procedures

Also, before doing this, seafoam each cylinder individually by pouring seafoam into the carbs 1 by 1 and hit the engine kill switch just before you stop pouring. Let it sit each time for about 20 minutes and start it back up (the white smoke is normal). Doing this will clean some of the carbon from the pistons and valves (carbon acts like a sponge to fuel and absorbs it causing your bike to run lean).

After that my friend, get the beast re-dynod. Remember, its a 21 year old machine that has 21 years worth of abuse on it. Prostitutes that get ridden hard for that long wouldn't last.

 

Easy now she’s only a part time hooker, up in the great white north of MN we only get to ride 3 months a year. So it has insanely low mileage for a 21 year old bike(46K).
And it did not come with the jet kit. I am capable of doing the seafoam but I don’t feel comfortable pulling the carb off and trying get to the jets.
So what would you recommend?

 

Try the seafoam first, see what happens. The carbs are very simple to do, its near impossible to screw up, but if your bike is running lean there is definetly something wrong because if anything it should be running rich. If you are not comfortable cleaning your carbs yourself, pour half a can of seafoam into your fuel tank as well, that may help a little, but definetly get those carbs well cleaned. So, if you dont do it yourself, get the shop to do it and also when they clean them, get them to advise on what size main jet is in the bike.

 

They were cleaned and had new gaskets thrown in over the winter because when I got the bike it had sat for two years and was varnished up rather good, wouldn’t stay running without the idle on and ran like garbage. When I got the bike back it rocked asides from the little bit of lag/stuttering on the low end. i wouldn’t even know where to start and im thinking its not going to go back to the same place.

 

mixture screws might need to be turned out slightly.

 

SO finally got all the tools together i needed and pulled the spark plugs and ran a compression check.

first things first. all of the plugs were nice except for the right most plug (throttle side) this is what it looked like.



[img width=447 height=600]http://i177.photobucket.com/albums/w240/tec_in_the_making/fc680327.jpg[/img]

the measurements for the the compression test came up as (from clutch side to throttle side)

130-PSI 130-PSI 120-PSI 140-PSI

and as for he wet test im not sure my oil squirter was long enough to reach all the way down to ware it needed to be. that test came up as.

130-PSI 140-PSI 140-PSI 145-PSI

so as far as the compression test went it doesn't look like any thing too bad for a 21 year old motor. the main concern now is what is causing the carbon build up on the plug. could be bad spark but i don't think that's it. the cables are in nice enough condition, haven't looked at that coil yet. my bet is with how f-ed up my carbs are that one cylinder is running rich wile the rest of the bike is running lean.

 

thats probably the case, that plug on the left is running rich and you can tell the one on the right is running lean from the heating marks on the threads (blueing).

 

the dynojet kit should have an adjustable needle.
you can check the clip position without removing the carbs.
just pull the chrome "bell" on the tops of the carbs.
make sure they are all the same position.
moving the clip down richens it, moving the clip up leans it.
careful with the rubber diaphrams

 

he cant adjust the needle until getting the proper main jet, it wont run at peak performance