87 Ninja 750 bogs after 30 mins.

[Green024]

just about since the day I've owned my 1987 Ninja 750f, every time i go for a ride longer than 30-40 minutes, the thing sounds as if its choking or its clogged. it first becomes noticeable when i'm taking off in 1st gear(when its warm), if i lightly roll on it, the thing feels like its hesitating, but if i half throttle it or more, the thing will scream, but eventually after that, every rpm will sound the same, clogged to all hell. This bike has been piped, and the previous owner put on 4 K&N air filters. So, 3 years ago i got 2 new floats do to liquid being inside them.the bike ran good for longer now but still same problem. I realized the gas line from the tank to the carbs (i think. the bikes at the shop and i forget :X) was really short and was getting kinked. so i lengthend it and put a fuel filter in their in case of dirt or rust coming from the gas tank. Then i took the carbs completely apart and made sure all of the little holes in my jets were clean as a whistle, and to make sure my floats are working properly. I did notice that on carbs 1 and 2 on the left side of the bike are spitting a wee bit of gas into the filters.

Currently my bikes carbs are being synchronized and my uncle is looking it over very carefully for any other issues. AND i replaced those K&N's with some UNI air filters.
Also this bike used to have 2 exhausts , but one of the previous owners converted it to a single yoshi exhaust.

My mechanic discovered that my water pump needs to be replaced.

all the places i checked locally and online dont have the water pump or cant get it because its been discontinued. On top if that, while my mechanic was working on a chainsaw, he smelt a funny smoke smell coming from my bike. The key was off and all of my lights were on. Some wire was shorting out and my battery was still connected. so now theres a frickin hole in my electric junction case or fuse box. Luckily he was there to witness the event and stop it before it burnt down his garage. SOOO Im going to try and order a new junction box and find a used water pump at a salvage yard or somethin or maybe a inline water pump for boats?

What could i try to get rid of this bogging down problem? Carb rebuild?

[gpzrider]

Check the spark when it gets hot. My Gpz did the same thing and I kept going over and over the carbs. Finally put inline spark testers on it and realized it was getting random spark from one coil once it warmed up.

[shadelane]

You might laugh at me, but a bad spark plug cap will sometimes cause this. Also check the gas tank vent hose and the vaccume operated fuel valve.

[littlekevin]

troubleshooting fuel problems is the most difficult a good rule of thumb is if you have a problem asking for horsepower (accelerating, climbing a hill) the mixture is rich if you have cruising problems< not asking for power its lean. I would look to see if the last owner rejeted the bike or just installed the filter and pipe hoping to get more power

[Green024]

thanks for the quick replies everyone, as soon as i get some time next week ill look into what youve all mentioned.

[Green024]

So I am back, I replaced all of the spark plug caps, which 3 of them were toast. my coils were ok, but i have an extra set with wires hanging around that came with my caps in case i need it. I got the carbs synced and replaced the water pump, which was leaking a little before.

So none of this changed the bogging down at low RPM's problem once its gets a little warm. i did not even get 10 minutes down the road before it started hesitating in FIRST gear, and then once it got a little warmer it kinda started doing it in sencond, but not as much. So all and all its running a little bit worse than before in regards to the hesitation/bogging aspect.

this friggen machine is depressing me.

As for the good news, The response from the throttle is much better . thats about it for good news. It runs great in the higher rpms in all gears, i can feel the difference from the carb sync.

We discovered that it is the alternator making a ticking squeeking noise when i initially twist the throttle ( most obvious when in neutral). So i will go ahead and get a decent used one from the guy i've been getting all of my other parts from.

Could this cause the problem i am having?
Should i just go ahead and replace those coils? My mechanic never tested them when the bike was warm, because we didnt have the plug caps in yet.

Im at my wits end here, im really about ready to sell it as is, and get a new bike with no problems..... thanks again

[Ole Yeller]

I would change the coils because when you do that, you are eliminating one more thing that it could be.

[Green024]

Ill do that tomorow on my night off, probly change the oil too. I meant to ask my mechanic if he checked the coils when the bike was warm, but it was too late to call.

[Green024]

if this does not work, i may look into bringing this money succubus to a kawi dealer (not that it will be cheaper than me buying a part here and there and installing with the help of my uncle but). I dont want to sell this good looking of a 1987 machine, but its costing me quite the pocket full o change to get this problem solved. the alternator i found was 200 dollars, used of coarse. New would be around 6-8 houndred. any suggestions are greatly appretiated

[StarGate]

I doubt you will find a dealer that will even work on the bike. Most dealers won't work on anything over 10 yrs old and some less than that. The techs are trained on modern bikes and don't know how to work on something that old. With a little patience you should be able to find a used alternator/stator on ebay for a lot less than that.

[Green024]

your saying 200 dollars is too much for a used alternator?

[StarGate]

If you're happy with that price thats all that really matters I guess. Value is what it's worth to someone and I know urgency sometimes dictates value. I am saying that used generators/stators generally go for less on ebay from what I've seen. I know this one isn't going to work on your particular model but this might give you an idea if you haven't been checking them out on ebay.
eBay Motors: Kawasaki KZ650 ZX750 KZ750 KZ700 Stator 21003-1083 (item 320282628585 end time Aug-06-08 18:54:04 PDT)

Since yours was used on the 87-90 model 750 ninjas it opens up the possibilities of finding one and if you find an ebayer thats parting out one of those models but doesn't have the stator listed you can always email them and ask if they have one.

[MFolks]

Stator choices:
www.ricksmotorsportselectrics.com [1], Stator - RM Stator - High Performance CDI, Rectifier, High Output Generator,Yamaha Stator, Honda Stator, Stator Repair, Arctic cat ZR stator, Arctic cat thundercat stator, Ski-doo stator repair,Yamaha Warrior stator,Yamaha Grizzly stator,Yamaha Pulse, ElectroSport Industries - Motorcycle, Dirt Bike and ATV Aftermarket Electrical Parts

[spoon32]

Chances are if it had individual filters on it, it also had been rejetted. Going back to a single filter could be causing it to run rich, making it bog down.

[Green024]

It still has individual filters spoon32, i replaced the 4 K&N's with 4 UNI's.
I took off the alternator and belt and noticed it was very dry, chipped and the pullies it was on were shiney, meaning it had been slipping. i brought my alternator in to a guy whos good with car alternators, and he said its difficult to tell if it is bad or faulty without the rectifier.(or did he say stator, or something else, i have a shortterm memory problem, i think its the reefer) anyhow he could only see the positive diodes or whatever and couldnt find the negative ones on it, at least on the outside of it.
he thinks it could very well be not working properly, hard to tell without the negative diodes or whatnot.

SO could it have just been the dried up ole belt? I havent had a chance to go get one yet, but im workin on it.

thanks for your input everyone

[Green024]

well i replaced the spark plug caps and the old beast is running pretty damn good now. ive noticed that i am getting worse gas mileage than i used to get. i was able to get around 140ish out of a tank and now it will barely get past 100.
Ive noticed that this bike is running kinda rich too. when i try to putt around at a constant speed it seems as if its getting too much gas. Its either accelerate or decelerate for this machine. when it starts to sound boggy and $hitty i just open er up a little and that clears it out untill i try riding at a constant speed again. Again thank you all for your advise.
Here are a few pictures..
http://i291.photobucket.com/albums/l...IMG00191-1.jpg
http://i291.photobucket.com/albums/l...4/IMG00189.jpg
http://i291.photobucket.com/albums/l...4/IMG00188.jpg

[Ole Yeller]

Just wondering, why did you replace the K&N filters with Uni's? Are the Unis the same size or smaller?

[Green024]

they are Uni's yes and seem slightly smaller, and dont seem as breathable as the K&N's. I would have left them on but they have been stretched out to the point where they dont want to stay on. I suppose i did not have a great reason to change over to UNI's besides the fact that i dont have a lot of extra money to spend on my bike, and i was not sure if the bike was getting too much air from the K&N's. I would like to test them out now that the bike will stay running for more than 30 minutes, maybe it might help my gas consumption?

[antiq]

Could be someone used Dynajet to rejet for the pods. This would be using a main that is way too big and use a lot more gas.

[Ole Yeller]

Originally Posted by antiq

Could be someone used Dynajet to rejet for the pods. This would be using a main that is way too big and use a lot more gas.

And if that were the case, then, moving to smaller air filters could make it run richer.
As for the K&Ns being stretched out, I run K&N's and I have found that if you
set the clamp too loose they will fall off AND, if you crank it too tight they will pop off. I have to find that 'sweet spot' where they are tight enough but not too tight. Hope this helps.