4 to 1 header question

[Guest]

ok im gonna get a 4 to 1 header...the megaphone part is dented..i was gonna use a gsxr mid pipe an slip on...will that have any issues?

and do i have to have the dynojet? i have stock airbox an plan on keeping it for a while...

i know i have to jet it up...but wasnt sure if i can just buy 4 new jets an go that route till the pod filters maybe down the road

[Big T]

as long as all the pieces fit togther, no problem

The DJ kit will have Stage 1 (which you need now) and Stage 3 (for pods) parts

[duaneage]

You may not need to rejet. I installed a 4-1 and bumped the jets up 6% and it knocked my fuel economy down. I spoke with a tech at the pipe manufacturer and he recommended stock jets and MAYBE lifting the needles a little after i tested it.

I would make a call to the tech support line for the pipe and if you are running stock intake gear (as i am) I would go with stock settings and try it out. Find a safe, straight, cop free road and do a high speed cut out and pull plugs on the side of the road and see if they are white, tan or black.

Mine were a bit dark with the bigger jets and I've since gone back to stock. It runs a little better, gets the mileage it used to get, and no blued pipes or cut outs under load.

It's very hard to tune a bike on the internet, every bike is different and of course you have to have NO issues like leaking boots, dirty carbs and air filters, or poor compression.

Now if you pull the airbox off for pods, then you are into serious rejet territory.

[gs850cafe]

oh ok ill try that first..im gettin the pipe wendsay i hope..

i had a set of straigh pipes on it for a mile or 2 around town...the plugs were a light tan...which scared me a hair so i went back to stock exaust lol

[duaneage]

The were light tan for other reasons, the pipe was not among the reasons.

Get the pipe on, warm it up, and do a few runs in 3rd or 4th at high RPM and then cut the engine. Do not idle it down. Coast to a stop and pull the plugs.

Do this in a safe location where you can safely coast to a stop and work without being hit. I tested mine on a really tall hill and I cut power at the top. I coasted to a stop on a driveway at the top off the main road. 3rd gear up hill requires the mains full on with max airflow at high RPM. It's a little safer than 120 MPH.

[gs850cafe]

The were light tan for other reasons, the pipe was not among the reasons.

Get the pipe on, warm it up, and do a few runs in 3rd or 4th at high RPM and then cut the engine. Do not idle it down. Coast to a stop and pull the plugs.

Do this in a safe location where you can safely coast to a stop and work without being hit. I tested mine on a really tall hill and I cut power at the top. I coasted to a stop on a driveway at the top off the main road. 3rd gear up hill requires the mains full on with max airflow at high RPM. It's a little safer than 120 MPH.

airbox is sealed very good...new boots filter etc etc..you know the drill lol
but the plugs with stock exaust are nice dark tan/brown...like they should be in a normal condtion...the "straight" exhaust had to lean it out..but the plugs wernt white white...just like a tan almost white...i didnt wanna take risks...

but yea ill run this header down the road n such an pull the plugs...ill post pics too of em

[gs850cafe]

hey i got to looking at this pipe...there no tags or names anywhere...it looks old too

did the 750 or 850 ever come out with a 4-1? (guessing 750 4-1 was same)

it does have the baffle too

[keman]

My kerker 4>1 came off a bike in 1982, hung on a wall for almost thirty years, got shuffled around a garage, then got sold to me. Po said it was a kerker. No tags or markings, finally figured it out by comparing it to another known kerker from the same era. Burned lean enough that I had to rejet . Dynojet does not make a stage one for the 80 GS850, so I went stage three and added the pod intakes to balance. Runs great, good through the whole powerband.

[TheCafeKid]

The were light tan for other reasons, the pipe was not among the reasons.

Get the pipe on, warm it up, and do a few runs in 3rd or 4th at high RPM and then cut the engine. Do not idle it down. Coast to a stop and pull the plugs.

Do this in a safe location where you can safely coast to a stop and work without being hit. I tested mine on a really tall hill and I cut power at the top. I coasted to a stop on a driveway at the top off the main road. 3rd gear up hill requires the mains full on with max airflow at high RPM. It's a little safer than 120 MPH.

I dunno how fast the 650 will go at high rpm in third gear but just about any GS I've ridden (750 on up) high rpm in third gear would be well over most areas legal limits short of the interstate....not busting your balls or anything...



To be clear, you can achieve the same thing in 2nd as well and slightly less illegal speeds...
RPMs, while part of the equation, are not what you're going for here..you need to do chops in the different circuits of the carbs. RPMs can mean nothing in this respect. It's more about throttle position. On CV carbs, which your bike has if it was a 1980 or later model, there is a throttle blade in each carb that is opened directly by twisting the throttle. Think of this as a "primary" valve in a 4 barrel carb in a muscle car (if you're old enough to remember those ). There is also a slide valve, which requires vacuum from the motor to pull air in quickly enough to cause it to lift. This would be similar to a vacuum secondary in that same 4 barrel... Anyway, as RPMs climb, so would the slide. At the bottom of the slide sits the needle, and it rests in the needle jet. The needle jet is fed by the main jet (as is the pilot jet) The needle is tapered, so as the slide lifts, the needle lifts out of the needle jet, and the more it lifts, the more the taper allows fuel to be picked up.

Ok so back to the throttle position. To do accurate plug chops, an good way to know what circuit(s) are being used is to mark your throttle off with tape in 1/4 turn increments starting from closed and ending at WOT (wide open throttle).
Doing this will let you see what position the throttle is in, so that you can keep it there to get an accurate plug chop for the corresponding circuit.
To simply rely on RPMs isn't necessarily accurate because you can be spinning 5K rpm, but once you get up there, you don't need to keep the on the throttle to keep it there...you could be using the pilot or pilot/needle transition circuit just to cruise along at that RPM, but it took a lot more of the needle to get there originally...

Anyway, so mark your throttle sleeve off as I said.
From idle to approx 1/4 turn is mainly the pilot circuit
1/4-3/4 is the needle circuit, and 3/4 to WoT is main jet.

If youre looking to do a plug chop in a particular circuit, you can now simply look down and see that you're staying within the ranges above..

If you're having a problem with the way the bike runs, this will also point you to which circuit may need looked at first, but keep in mind with the CV carbs that they are tuned from the main down. Meaning the main jet must be correct or close to before you move on to the next circuit (needle, then pilot) because the main feeds those other circuits. If the main is too small, it won't feed enough fuel to adequately supply the other circuits.

As to needing to re-jet for just a pipe alone (and retaining the stock airbox) in general you usually have to make some change in the main to get it to respond crisply throughout the rev range. The bike, in second gear when the circuits all are in order, should pull cleanly and crisply from 2K rpm to redline. If there is stutter or stumble, something needs corrected...at which point you can look down at your little taped off throttle gauge and say "oh the needle circuit is breaking up a bit.."

As brought up by duaneage in another thread, we will agree to disagree on this subject. Changes in exhaust flow can have effect on carburetion, as no pipe I've ever used has matched back pressure/scavenging of the stock GS system.

Having said that, the change, depending on the pipe, may be as minor as shimming the stock needle (Doing a search on this will bring up many how to threads) or a bump of a size or two larger on the main, or both.

BUT, and I've said this time and time again; the stock systems flow quite well. They knew what they were doing when they designed them. Especially if youre sticking with the stock box, don't expect a noticeable HP gain. There might be some "seat of the pants" feel changes as the torque band may move around some, but appreciable HP increase isnt much. The biggest advantage to running a 4-1 is weight savings. They're about half as heavy as the stock system...

Hope it helps...sorry if it doesn't

[TheCafeKid]

hey i got to looking at this pipe...there no tags or names anywhere...it looks old too

did the 750 or 850 ever come out with a 4-1? (guessing 750 4-1 was same)

it does have the baffle too

No. No GS model ever had a 4-1 from the factory..

[Steve]

To do accurate plug chops, an good way to know what circuit(s) are being used is to mark your throttle off with tape in 1/4 turn increments starting from closed and ending at WOT (wide open throttle).

Might look a bit like this (your bike may vary):



.

[duaneage]

There was an interesting comparison done years ago on the 1100E exhaust with aftermarket systems, all but one produced less power than OEM, the Supertrap ws the only winner and not by very much.

[gs850cafe]

ok i got the header today...it was black at one time in its life..thats all the info i can find lol..

now is there a performance differnce in stage 3 jet with pipe an pods?

if so ill prolly just buy the pods an jet kit lol...

edit: ill also add this pipe has a welded in baffle...looks like a good weld...its on the outside of the exhaust..

and also where can i get single main jets...since some people said raise the jet size to a 125? or so..or raise the needes.

[whiterabbitt]

z1 enterprises has really good prices on main jets, you can get 2 sets for about the cost of 1 from just about anywhere else.

they are $1.75 ea. if you need large round mikuni's

[gs850cafe]

z1 enterprises has really good prices on main jets, you can get 2 sets for about the cost of 1 from just about anywhere else.

they are $1.75 ea. if you need large round mikuni's

ok good...i think ill bump up the jets an maybe raise the needles...i dont really wanna go with pods and a $100 jet kit that i might not need..

would this be the one i need?

http://www.z1enterprises.com/detail.aspx?ID=4696