carb tuning help after 2-1 install

[donimo]

OK I ordered some 120's, from the stock 117.5's, hopefully that is enough, we'll see I guess. Barring any helpful info,

[donimo]

Also I ordered the "small round" style, I assume this is correct for my BS34SS carbs?

Anyone know if going from a 117.5 to a 120 is enough, I really dont want to waste my time?

It never sputters or backfires, just seems to lose power like you are dragging the brakes a bit, sounds fine, still smooth. and only at WOT

[gearhead13]

These normally take large round mains

[donimo]

gah, I knew that would happen, the only site I saw said that the BS carbs took the small round, why is this so hard to figure out on a bike as common as a GS with BS mikuni cv carbs on it?

[donimo]

I changed my order to 125's see how that goes, guy at the shop thinks that is too much, everything I find here says it won't be enough.

[donimo]

Anybody running the mac 2-1 and stock airbox on a 400/450 and can give me jetting hints?

I read every post on here and most also went with pods (I don't want to) and that changes the game a lot.

[donimo]

I just tried swapping the old "generic chinese megaphone" muffler on, got way worse, sputtering like nuts WOT and down on power everywhere else. Almost seemed corked up rather than lean though.

[Joe Nardy]

D.,

Here's a good guide to carb tuning from Factory Pro. Basically it says to work from the main down to needles and pilots.

This is Dynojet's troubleshooting guide. Between the two you should be able to get your bike running right.

One way to determine which way you need to go on the various circuits is to restrict intake flow (richen) by taping off part of your air filter(s). If the bike runs better in a given range with the air flow restricted that circuit needs to be richener. If the bike runs worse in a given range that circuit needs to be leaner. You've already done a similar test by swapping the exhaust but you don't know for sure if the stock exhaust flows more or less than the Mac so the test doesn't help much.

Thanks,
Joe

[donimo]

It wasn't stock, but I am pretty confused about how different it ran. The mac is 2 tubes welded together:



and the old one is one tube with a hole in ech end, so pretty much the same. but the tube is smaller, so I would think if anything it is MORE restrictive than the MAC, but their used to be 2 of them.

it was night and day, so could the mac actually be choking off the bike instead of leaning it out?

I will check out those pages thanks!

[Joe Nardy]

It wasn't stock, but I am pretty confused about how different it ran. The mac is 2 tubes welded together:



and the old one is one tube with a hole in ech end, so pretty much the same. but the tube is smaller, so I would think if anything it is MORE restrictive than the MAC, but their used to be 2 of them.

it was night and day, so could the mac actually be choking off the bike instead of leaning it out?

I will check out those pages thanks!

Yes, the MAC could be more restrictive than stock. The Dynojet document addresses that question. Still, it's difficult to be sure either way. There are other factors in exhaust design that affect performance. Restricting the input is more definitive.

Thanks,
Joe

[donimo]

OK read those 2, that factory pro one is pretty good! I tried searching but never found anything that good.

I tried plug chops but I have a shortage of roads I can get up to speed like that on and just pull over. The only one is the trans-canada freeway and I am a bit freaked of that road still ha ha.

It seems like this one:

7. Engine accelerates until the midrange then pauses, stumbles, or shuts
down until you back off the throttle. This problem gets worse the higher
the gear used.


But it doesnt really do those, just seems to lose power, it feels like all of a sudden you can only turn the throttle halfway (except it happens at WOT and not part throttle).

With the smaller muffler it sputters and pops and lfalls on its face.

I really wish I could find a replacement muffler that would work on a 2-1, all the ones I can find are the same as the one I have...

[donimo]

ok, I am getting a bit confused here, I haven't messed with the jetting yet as my jets aren't IN yet (stupid local shop grrr)

But if wind it out to redline at WOT the whole way it goes like this:

-good take off

-seems to fall off in power at 4-5k (may or may not be rpm ot throttle related but thats where it seems to happen

- around 6-7k it tkaes off like a raped ape, sounds like a gp race and I have to shift really fast so I don't spin the pistons out the top of the motor at 15k (not literally but that is what it feels like to this newb)

Now keep in mind that these are gross estimations, I am too inexperienced to ride like that on public roads while staring at the tach...

but if my main jet was out I can't see how it would take off at the end there...

plugs look the same as always, tan until the bend then lightening to a more grey colour at the tip

[gearhead13]

Well, my thought is that you have a stock bike modified with a pipe and it has changed your engines powerband in different areas. Normally with an aftermarket pipe you will gain top end and lose low end and midrange. If it was me I would move my needles up or down a notch to see if it helps or hinders the dead spot at 4-5k rpm like you have said. The needles have the most impact at mid rpm ranges. If you dont know if its rich or lean, then go up one needle clip, if it gets worse, then go down one.

[Joe Nardy]

The Dynojet troubleshooting guide says in general if you have problems while adding throttle you're probably rich. If you have problems while at steady throttle you're probably lean.

Try restricting your intake by taping off some of the air filter(s) to richen the mixture. If the problem gets worse then you are too rich. If it gets better you are too lean.

Thanks,
Joe

[donimo]

I took out the fiberglass from the muffler, I have a suspicion that it may have been partially restricting the outlet when i got on it.

i suspect this becaus it seems the problem comes and goes, maybe it is moving around in there...

I will feel dumb if that is what it is, i may still go from 120's to 125's just due to the slight white-ish on the tips of the plugs, still no word on whether that is too much or too little for jetting up?