No top end

[fireburster]

93 bandit 400, dynojet kit 1. 25k miles.
I had another forum member camarojon come over sunday and look at the bike. We moved the e-clips up and down and that didnt to change much, up made it jumpy like it was surging then cutting out. We moved it down but that didnt help. Its like its not getting enough gas he thought. The plugs look black around the threads but the top was white like lean. I have the air fuel screws at 3 but ive tried 2 and 2.5, nothing seems to fix going over 55-60mph. It seems like it has power when driving around town but once you go out faster you have no power and giving it more throttle seems like it does nothing.

We checked for vacuum leaks and didn't find any.

Jon thought it needed bigger jets as its starving for gas, i dont know what size comes with the dyno jet but i know the package with 100 on it is empty.

Im really starting to think with 25k miles on it and sitting for some years that maybe its just old and done. I like riding it and would like to continue but i also dont want to be ruining it more then it already is.

[canyonbreeze]

http://www.dynojet.com/pdf/3134.pdf

Comes with 96 and 100 jets.  My 91 B400 has the DynoJet kit and the 96 jets.  The needle clip is on the 3rd position, right in the middle.  Recently turned over 30,000 miles and easily gets to 100 mph.

[fireburster]

I was in the middle with my e-clips at first also and 3 turns out on the a/f screws. It really feels like its not getting enough gas.

Thanks for the input on your bike, it could just be the bike and nothing will help it.

[tomacGTi]

If everything is stock (including snorkel and filter material. UNI is as close to stock as you can get, still needs to be a bit richer though.) the DJ 100/96's should be fine.

It's when you start drilling holes, changing the filter material and popping out the snorkel that you're heading into uncharted territory.

[camarobandito]

Wow its been a long time since I have posted here!

Your bike is running extremely lean. It has the classic symptoms, pinging, surging, white flaky plugs, and overheating. It overheated so bad, when I rode it, the fan kicked on from a cool start in about 3/4 of a mile. It couldnt have been much more than 70f degrees out. I thought I heard some pinging before it shut off and coasted at about 75 mph and 10k rpm.  Grabbed the throttle and it would sputter a little then die again. Came back to life when pulling the choke in slightly.

Messing with the idle mixture / af screws and syncing the carbs won't help you with this situation. That's why they are called idle mixture screws, they are for idle, and just off idle. They will have little to no effect in a high load situation. That is why it runs pretty good around town. Like it told you Saturday, how I have always set the a/f ratio on every carb I have ever worked on with the idle mix/af screws. It doesn't matter if it is on a motorcycle or car, I turn them in slowly one at a time until it runs crappy, then I back them out about 1/2-3/4 of a turn. No 2.5 or 3 turns, and no need for any fancy gadgets

Even if it is worn out, its seen better days but its not that bad, it still wouldn't just cut out like that. You are going to have to get your hands dirty. If it was my bike I would dismantle the carbs, clean and inspect them, and go up on the main jet.
You currently have the dj-100 mains, I would order a set 104's and 108's. I would also go 1 step colder on the spark plugs. While you have all that apart, you might as well pry off the valve cover and check the valve train assembly.

Call Dynojet their number is
(800) 992-4993. You have the DJ style jet get p/n DJ-104 and DJ-108. It says on their website they are $2.00 each.

Maybe your wife can give you an advance on your allowance!

Plus it was like this when you bought it, so the PO prob just put in the jet kit, rode it around town and never opened it up, or just didn't care.

I hate to sound like a jerk, but just turning a screw, and trying to find some magic potion to spray on the chain won't fix your problem. You are just going to have to tear into it. Its pretty easy, just time consuming, and a big pain, not just only in the neck!

Camarobandito

[fireburster]

Yeah i figure opening the carbs is next, thanks for replaying. I willing to put the time im just hoping someone else had the same issues before i start ordering a bunch of stuff i may not need.  Ill check into the jets and get them ordered.


Whats the colder spark plug the 9s? I know i need to replace those for sure.

thanks again for coming and messing with it.

[banditv]

if your mains are only 100s, you will be way lean. my 250 has 95 mains and its spot on.
i'd think 105 would be closer for a 400.
and after doing my own carb diaphrams, i'd recommend doing those as well.
will make a huge diff to the way the motor runs

[fireburster]

ok 104 and 108s ordered. now to find time and tear the bike apart.

[canyonbreeze]

The main jets are only going to affect you much on half to wide open throttle.  Is that the issue or is it speed regardless of throttle?  The float level could be off and cause it to run lean.  If lean you'll most likely be getting some backfires as well.

[fireburster]

Mainly i have seen the issue at open throttle with load. If its idling and you rev it it seems normal. But i think it seems doggy in town also. It goes 45 and it revs good but it seems like its not as powerful as it should be.

i think if you have enough straightaway it would eventually get over 55-60 but you have to back off the throttle for it to start speeding up.

Its my first bike so i always assumed it ran like it should. But ive been told it seems slow.

[Maniac]

Have you checked the fuel petcock?

I've got an '05 GS500 sitting in my garage that had been giving me -fits-. It idled OK and free-reved OK, but ran like -crap- and would frequently stall. Turns out there was a problem with the vacuum line feeding the fuel petcock, causing it to not open all the way. I can't remember of the Bandit had a vacuum actuated fuel petcock or not, but if fuel isn't flowing well from the tank, you can get the symptoms you describe.

Of course, it also sounds like you need to rejet, but something else to check at the least. It's possible the silly thing is just clogged up.

[fireburster]

I took the petcock off and cleaned it all out and from what i can tell pours gas fine. Im going to replace my fuel hose once i have it all apart. I think its 5/16 but im going to take it with me when i go back to the auto store.

[camarobandito]

I moved his petcock to prime (that sounded kind of dirty!) when I made a run with it as I thought that could have been the issue and it had no effect.

 Moving it to prime disables the vacuum actuator and lets fuel pass directly to the carbs (as im sure you all know), then I moved it back where it was.
He rode it awhile after that. We took the tank off I re-routed his fuel hose, and plenty of gas came pouring out of it, so I don't think the petcock is an issue.

As for the floats, its possible, but I feel its very unlikely. It zings around town just fine, it doesn't miss a beat and runs pretty good for these bikes. Although they should be inspected, and cleaned anytime the carbs are apart.

His bike is in alot better shape than mine was before I did my GSX-600 carb swap and I put over 10k very hard miles on it before she gave in. It had 32k miles on it when I got it.

It will run about 50-60 just fine, as long as it is not under any load. Just a small hill makes it act up.

canyonbreeze- you are 100% correct about the main jets coming in to play, at half throttle, esp when the engine is in a low vacuum state,i.e. when climbing a hill, or hard acceleration. That is precisely where he has the problem. Plus, the way these bikes are set up, you can't really get past 60-70 without giving it half throttle

In my opinion, changing the main jets is the cheapest, easiest, and most logical thing that can be done. It is so lean, if he continues to ride it like this, it will cause serious engine damage.

If this doesn't fix it, I think the ignition system, timing chain, cams, and cylinder head will need to be inspected, and possibly re-worked. I hope this is not the case!

Camarobandito

[fireburster]

carbs removed!!

They look good and shiney inside the bowls. I didnt see anything gummed up in there. I changed the jets to the 108s.

I noticed im missing 2 washers on the needles, and i have 3 screws that were stripped before i got to them. So ill have to run to a hardware store and get some parts.

Hopefully i can get it all back together as easily as it came off but that never happens for me.

[ywgbandit]

I had a friend that had a similar problem with an old "Water Buffalo" GT 750. It turned out to be 2 things. 1- he had a float that was sticking and wasn't set right for level or drop. 2- the old fuel lines were collapsing inside when the fuel was under high demand. You couldn't see it from the outside but the old fuel lines were made of layers with a nylon reinforcement between them and it had delaminated and the core was collapsing under fuel draw and cutting off the gas. New fuel lines solved the problem. I have seen solid fuel lines get soft with age and do the same thing.