4K RPM Idle, Slow Throttle Response, Etc.. First Kat Problems, HEEEELLLPPP!!!

[mustang78]

Hey all, i'm a decent mechanic but this thing has me stumped, not to mention the limited time i have to work on it... Lets say i bought an 89 750 from my neighbor with an unknown carb problem, i pulled the carbs off and cleaned them(light cleaning, 2 main jets were clogged..), put back together and she idles at 4K.. he said it has happened before but usually gets better the more he rides it, i also put some carb cleaner additive in the tank. The little brass tube on #2 carb was broken at the bottom so i fixed that and i'm 99% sure it doesn't leak but i'll have to check in the daylight. Any ideas so far? also what are the petcock positions? i run it pointed straight back.. i checked the floats and none seemed to be sticking, the bike is completely stock with 1,800 miles on it, wrecked once but fixed by first owner. If i put on the choke the idle goes even higher, all i had was starting fluid so i sprayed that all over the carbs while it was running and it didn't change much, if any.. I'm 90% sure my throttle cable isn't sticking and i'm sure the intake boots are on the carb all the way, but the airbox to carb boots are not completely on, it shouldn't cause problems though since it's just an intake and not sealed, right? Also if i blip the throttle it takes 1-2 seconds for the RPM's to jump up from an idle(yes it idles if i click the kill switch really fast, but climbs quickly to 4K after that), it's a huge PITA to ride like this, thanks for any help!

Also what are the petcock positions? i keep hearing about a prime position.. i run it pointed straight back usually. And where are the idle air/fuel mixture screws? i'd like to reset those to 1.75 turns out correct?

Edit: found where the air/fuel mixture screws are, looks like i need some good cleaner(sea foam in a dish?) and will disassemble the carbs friday when i get off shift( i work 24hrs thursday)

[yngveny]

Welcome to KR

Petcock positions are described here: http://katriders.com/wiki/index.php5?title=Petcock
If it does not run wit the petcock pointing straight down I think you have a vacuum problem.

[mustang78]

Thanks, it does run with the petcock down.. i thought that was off, no wonder i couldn't get the carbs to run outta fuel lol

[JokerZwild]

lol youd be waiting a good long time if you just filled it up!try to keep the air box on and closed as your trying to tune it ...it requires a certain amount of restriction in order to run correctly.

[Kreylyn]

Hey all, i'm a decent mechanic but this thing has me stumped, not to mention the limited time i have to work on it... Lets say i bought an 89 750 from my neighbor with an unknown carb problem, i pulled the carbs off and cleaned them(light cleaning, 2 main jets were clogged..), put back together and she idles at 4K.. he said it has happened before but usually gets better the more he rides it, i also put some carb cleaner additive in the tank. The little brass tube on #2 carb was broken at the bottom so i fixed that and i'm 99% sure it doesn't leak but i'll have to check in the daylight. Any ideas so far? also what are the petcock positions? i run it pointed straight back.. i checked the floats and none seemed to be sticking, the bike is completely stock with 1,800 miles on it, wrecked once but fixed by first owner. If i put on the choke the idle goes even higher, all i had was starting fluid so i sprayed that all over the carbs while it was running and it didn't change much, if any.. I'm 90% sure my throttle cable isn't sticking and i'm sure the intake boots are on the carb all the way, but the airbox to carb boots are not completely on, it shouldn't cause problems though since it's just an intake and not sealed, right? Also if i blip the throttle it takes 1-2 seconds for the RPM's to jump up from an idle(yes it idles if i click the kill switch really fast, but climbs quickly to 4K after that), it's a huge PITA to ride like this, thanks for any help!

Also what are the petcock positions? i keep hearing about a prime position.. i run it pointed straight back usually. And where are the idle air/fuel mixture screws? i'd like to reset those to 1.75 turns out correct?

Edit: found where the air/fuel mixture screws are, looks like i need some good cleaner(sea foam in a dish?) and will disassemble the carbs friday when i get off shift( i work 24hrs thursday)

If you have the idle adjustment backed off, and it's idleing high, the most likely issue is it's running lean.

Does this bike, or has it ever had a jet kit installed?

The 3 main factors for idle are float hights (14.7-15mm I think is the right height to start with), air/fuel adjustment screws (2.5 if your carbs are stock, 1.75 is a little lean), and pilot jet sizes (only changed if you have had a stage 3 kit installed normally).

If not jet kit, then turn out the air/fuel screws starting at 2.5, then increas .5 as you go. If you have to go past 3 full turns...

You may have clogged pilot jets, double check them or...
You have have drilled out pilot jets (someone did instal a jet kit at once time). If that is the case, you may have to run as far as 4.5 turns out for the bike to idle.

All tuning for these carbs should be with all vacuum lines pluged off or installed as normal, and the air box on the bike.

Krey

[mustang78]

As far as i know it's completely stock, basically 1 owner bike.. tomorrow when i get home i'll pull the carbs and check the air fuel mixture screws and set em at 2.5 turns out, they might need new O rings so i'll do that if they've been leaking. I'll check the rubber carb to intake boots too and put the air box on the carbs this time, it's a PITA to put the airbox on once the carbs are on the bike.. Also check the throttle cable to make sure it's fully closed, the horrible throttle response raises a red flag for me too.... If those things don't help i'll check for vacuum leaks thoroughly, and disassemble the entire carbs and clean them piece by piece. I've never taken off the black carb tops, could there be a problem i could be skipping under there? i also have a single vacuum guage so i'll hook that up to the carbs one at a time and see if any are different than the rest.. even at 4K it's worth a shot, i'll use the carb 101 write up to guide me through it too, Thanks for the replies guys, i'll keep you updated on what i find...

[Kreylyn]

What I did...

With the carbs off, I mounted the airbox, then installed the air filter, then installed the carbs on the boots.

Each time I needed to adjust the air/fuel screws or float height, I just pulled the carbs with air box off the entirely, made my adjustments, and put them all back on.

I never installed the air box more than once, as it always stayed attatched.

Krey

[JokerZwild]

The black Carb tops are what houses the diaphram for the sliders. Take caution when pulling that apart. make sure you dont tear that rubber apart. And if it is ripped at all... it needs to be replaced.

[mustang78]

Good news! I followed the carb 101 online deal on here and completely disassembled the carbs and found a clogged pilot jet or two.. also missing one of the rubber plugs that support the float housing and keep fuel from going directly to the bowl so i made my own rubber plug that fits in there snug and is just as tall as a factory one, also the idle was adjusted too high and not all butterfly plates were the same. The air/fuel mixture screws were all over the place anywhere from 3-4 turns out so i set em at 2.5 turns out, no ripped O rings and the diaphrams were in great shape.. put it all back together and she runs perfect!(aside from a missing choke cable.. i put a keyring on it so i can hold the clutch in with my bicep and pull on the ring with my left hand, starting it with my right lol are they hard to come by?) I took it for a little spin(expired tabs) and had a blast! it's nice riding at lower RPM's and not fighting it the whole time Thanks for the help everybody and maybe this thread will help someone in the future

[redciv1]

Glad to hear. Choke cables are inexpensive. I got mine from Cheapcycleparts.com. You give me inspiration. My bike idles to high