Question about exhaust/jetting

[JoshD]

My girlfriend has a 92' US model Bandit 400.  Both her and my friend who have ridden it say that it will not climb over 70-ish MPH and I've read that a stock bike should do over 100.

We took the carbs off and inspected them.  Everything looked to be in good shape, the jets were all clean and the o-rings looked OK.  There was a very small amount of fluid in the floats, and one or two fuel screws did not seem to be the same as the others.  All jetting was stock, 102.5 mains, etc.

The bike has a 4 into 1 V&H exhaust.  Not sure if this is a full system or a slip on, but she also has the entire stock exhaust (header/pipe/can). 

What do you guys think would be the best direction to go with this bike?  It probably wouldn't hurt to check the float level and sync the carbs.  I'm not sure if it would be better to install the stock pipe on the bike and see how it runs, or if she should buy the F.P. jet kit and keep the Vance and Hines.

I rode the bike briefly in town last year, which doesn't do much good because I've never ridden a 400 I-4.  However, it seems to start and idle fine, the problem seems to be with top end power.

Thanks for the help!

[tomacGTi]

Search for posts by PitterB4.

He had that same exhaust setup before he sold his bike a couple of years ago and was closing in on jetting that pipe.

[PitterB4]

Yeah - I had the V&H pipes, a modded airbox and a K&N.  I started with the FP jet kit.  I ended up going way bigger on the mains (110s maybe???), maybe one notch down on the needle and as I remember was way out on the a/f screws.  It would certainly do over 70.     Like Randy said, search my posts.  Good luck!

[JoshD]

Thanks for the help guys!  Pitter, do you think the FP kit is needed or do you think we could get away with switching to a larger main?  She is not worried about performance as she is a new rider, but I want the bike to at least have the same performance as a well running stock bike.

From my past experience, what you are really paying for in a jet kit is the needle.  At $130 I'm thinking it probably wouldn't be worth it in her situation if I could get some larger mains for $4-5 each.

[PitterB4]

I would agree that you're paying for better engineered needles.  Putting the stock exhaust on would be far easier and cheaper...  well, free.  Why not try that if you're not worried about performance.  In fact, if you have no intention of wringing the little 400 out for all she's worth, I'm SURE you could sell that V&H here pretty easily.  Aftermarket exhaust for these bikes is in high demand. Just a thought...

[JoshD]

Putting the stock exhaust on would be far easier and cheaper...  well, free.  Why not try that if you're not worried about performance.  In fact, if you have no intention of wringing the little 400 out for all she's worth, I'm SURE you could sell that V&H here pretty easily.

^^^ is almost exactly what I told her.  You know the saying about leading a horse to water....Looks like I might just try getting some larger mains for now, or sneaking the stock pipes back on, but that will be a loosing battle.

[tomacGTi]

Run the same mains as thief is running as a starting point then. He's running factory needles although they're adjustable clip. You'll have to use washers to bring the needle up as well.

It is a drag that jet kits are expensive but you are truly paying for the needle. I know between my DJ needles and factory there is a very pronounced difference and FP actually include a reference chart to start out from. May save you some headaches in getting the bike dialled in. I think interfuse had measured all three at one point and posted the numbers.

That or throw on the stock headers, some 105 mains and call it good. Like I said, if you type in jetting into the search in the FAQ as well as the B400 forum, you can follow along in all of our trials and tribulations...

[hangin_biposto]

Also, is  your air box lid stock? 

Hangin_biposto's bike was very sensitive to having the airbox top lid off or having holes drilled.  Put the original airbox lid on, and it ran much smoother with the factory pro jetting.

[JoshD]

Yes, the airbox lid is stock.  I think the previous owners did nothing to it except for exhaust.

[JoshD]

UPDATE-

You guys will either laugh about some of this or I'll get one heck of a lesson on tuning!

Here is how the fuel screws were set, turns from closed-

4.5, 1.5, 3, 1.5   

I changed them all to 3 turns out as a starting point.  The floats, if I measured them right, were set at 13mm.  I changed them to 15mm.  Went with a 110 main to start with, and changed the destroyed factory air filter to a sheet of UNI foam.

Put it back together and after much cranking, it started.  It did have a badly hanging idle.  I noticed there wasn't much slack in the throttle, and after turning the bars to the right, it revved right up.  I will adjust the throttle cable today.  Not sure if the hanging idle is due to the fuel screws, no slack in the throttle, or something else.

Also, do the stock needles come with a shim?  There are very small shims, maybe .5mm or so, on these needles.  From the top, its clip, shim, then spacer.

[tomacGTi]

That is just about my setup but I think you're going to have to go way richer on the jets. Check the database, I've been updating up there but since my needles are narrower, my mains will be a bit smaller in comparison to a stock needle.

That is the factory setup for the needle, I'd move the washer under the clip and see how the midrange reacts. It should be fine, may need another washer.

The Uni filter flows much more than stock as well, keep that in mind. It isn't K&N levels of flow, but it will make jetting a bit more of a PIA.

[JoshD]

Thanks for the info Tomac.  With the other parts, I also ordered a set of 120 mains if the 110's were too lean.  We don't have any good bike shops nearby.

I'm not sure what you mean by moving the washer under the clip, it is already under the clip.  Are you suggesting buying additional washers?  If so, where do you get them from?

[tomacGTi]

You can get additional washers at Radio Shack, the size is important so it doesn't hang up in the slide.

Order going into the slide should be washer (s), clip, plastic spacer, spring if you are to lift the needle.

Hanging idle with everything synched up and revs set at spec indicates rich. Dropping below and coming back up indicates lean (at least in the idle circuit anyway). FP's high RPM CV tuning guide is a must. There are links to it everywhere.

[gsxr400 racer]

or simply a sticking hand grip