hey all!
I've got a '90 ZX 750 F, and i took off the stock air box.. that thing is rediculous and it probably robbs me of power.
so i stuck foam filters on the carbs. i've been told if i don't upgrade my jets, that it'll run too lean and burn up the valves.
is this true? how do i know if it is running lean and can i help it by adjusting the pilot screws?

 

The last I heard you had a couple of seals leaking and a couple of screws stripped on ya... i guess you got that fixed and got this thing running huh...awesome dude!!

If it's running too lean, I believe you are going to have to change the jets out.. which you should be experienced in now!! lol

Does the bike, when you drive it, pop out the exhaust at all? If not, it should be fine. If so, rejet time....

 

The way I've always checked to see if my bike was running too rich or too lean was to take it out for a normal ride then pull out the sparkplugs after the ride and look at the porcelain on the top of the plugs. If they are black and greasy looking, you are too rich, if they are a whitish yellow color, then you're running too lean. An optimum setting and the plugs would look light brown. I don't know how long you've had your old plugs in there before you did the mod, but I would get new ones as it would be more accurate. Also, like Bigrig said, if the bike is popping, you are prob too lean.

 

yeah.. i've got my stuff done from before. I have to drill out another bolt, one of the screws on the front brake master cylinder.
after i do that, i can put my calipers back on. and i have to get new tires on the wheels today. i started her up yesterday for the first
time after putting on the new filters. it was having a little trouble getting past 6k rpms, but that could very well be because i didn't give
it any time to warm up.. so as soon as i get those tires and brakes on, it'll be time to ride.

 

Sweet!! Have you pulled a plug to look at it's condition yet? Does the bike pop?

 

Okay, so i rode the bike around for a little while yesterday.
i do think that is lacking throttle response on the midrange. i have to
floor it to get the power i want.

so this is what i've done to the bike. i've got four foam filters on the carbs. no stock air box.
the top line that went from the charcoal canister to the airbox is hanging unplugged, and i know that has something to do wth the fuel vapor vent that runs from the carbs. There's a line that runs from the vaccumm switch to the air box which has been removed. Now, those reeds let fresh air into the exhaust? i'm thinking, the reed open upwards, meaning they need vaccumm, which isn't there. That going to be a problem? what if i took the reeds out?
anyways, with that out, i have noticed that it sounds like a third muffler. its not excessively loud, but you can hear it. there was a vaccumm line that run from one carb to the vaccumm switch, which i have plugged on the carb side.

i've also had this problem (since before i did the work) of the engine not always returning to idle rpm.
i'll pull in the clutch and it will still be running a 3-4k rpms, throttle wasn't stuck or anything. to fix it, i either have to engage the cultch at less than 3k or i usually just turn the idle control *** on the carbs down for a second.

i haven't gotten the chance to check the condition of the plugs yet, but i will do that later today.
should i adjust the pilot screws? or has anything i've done negatively affected the bike's performance? i want power from this 750!!

 

Hope I am not backing up here but have you got the right jets installed yet. If you call dynojet and tel them what bike you have, exhaust and filter they can get you the right kit for your bike.

The cost about 100.00 bucks but they work and you get a free dyno run afterwards so you can check the af mixture and the HP of course.

702-399-1423

 

Nahh, i don't have the bigger jets needed to power the bike with those new filters.. and i stuck the air box back on, and it has more power than it did before with it off.
so, the stock intake stay until i have the money for new jets.. i also took out my emissions control

 

So, after the bikes warmed up, is it running more like it's supposed too now??

 

it is now, with the stock intake..