What does "reverse wave" mean?

[poorgradstudent]

I've been riding the bike around with the aftermarket exhaust and opened stock airbox, but I always felt like it rode a little "flat". I know that 4:1 pipes do weird things to intake resonances and can cause holes in the rev range with an untuned airbox. Since each carb is connected together, a reverse wave through one can disturb the other three - this will richen or lean the mixture depending on which cylinder is next in the firing order and what rpm.

http://gs1000e.blogspot.com/2008/05/jet-kit-and-pod-filters.html


I was reading up on this blog from the bikecliff site and noticed this paragraph from when Robert ditched the airbox for pod filters.

What does he mean by "reverse wave"? After reading his entry, I feel like I'm experiencing several issues like this well. I'm running OEM airbox and mikunis on a 1980 GS1000 and I have a 4-in-1 exhaust header with Vance and Hines muffler.

I've been struggling for months now to get the carbs straight, but I know I'm running lean most of the time and I experience the same "flat spots" when throttling beyond 2000 rpm. Also, the power is completely inconsistent and the bike will occasionally "jolt" when pulling the throttle.

I should also mention that I can not, for the life of me, get the bike to idle when cold. Hell, if I can get it to start when it's below 50F outside, that's a good day. And when the bike is finally idling "okay," it will inevitably experience idle runaway as soon it warms up.

It's a mess, and I'm thinking my next step is to completely replace the airbox.

Anyone near Raleigh, NC that could potentially help me out with this project. I've been reading this forums for awhile and have read through nearly every guide, but I still struggle to trouble-shoot my problems.

And then there's the low-idle engine/clutch mystery rattle....

 

[tkent02]

What maintenance have you done? Adjusted the valves? Jetted it correctly for the pipes? Synchronized the carburetors? How did you adjust the mixture screws?

Never had any trouble with a pipe and a stock air box.

 

[poorgradstudent]

What maintenance have you done? Adjusted the valves? Jetted it correctly for the pipes? Synchronized the carburetors? How did you adjust the mixture screws?

Never had any trouble with a pipe and a stock air box.

All, I've done is remove, break-down, and clean the carbs. I have not re-jetted or vacuum synced, and I'm assuming the jets I have are good to go for the 4-in-1 since that's how it came to me. I have all of the maintenance/resto notes from the previous owner and his work looked thorough.

But, it could have been done incorrectly. Problem is, I'm too inexperienced to notice.

 

[tkent02]

No, it needs to be re jetted. A lot of people never change jets, they just sell the bike because it runs like crap.

Nogt idling when cold is a different problem. Do the maintenance.

 

[SocialAnomaly99]

No, it needs to be re jetted. A lot of people never change jets, they just sell the bike because it runs like crap.

Nogt idling when cold is a different problem. Do the maintenance.

What he said ^. I would add that you should take the carbs off and have them cleaned properly to ensure that there is no gunk plugging up your fuel passage ways which would surely cause inconsistent power and a rough idle. Also, be sure that the carbs have the right jets for that exhaust set up.

 

[poorgradstudent]

No, it needs to be re jetted. A lot of people never change jets, they just sell the bike because it runs like crap.

Nogt idling when cold is a different problem. Do the maintenance.

So if I have OEM pilot jets in these Mikuni's, I need to replace them?

Is this what I should get?

http://www.motosport.com/motorcycle/1978-suzuki-gs1000--DYNOJET-STAGE-3-JET-KIT

 

[tkent02]

Probably the stock pilot jets are OK. The main will need to be bigger, and the jet needle will need some adjustment.
VMs are easy to tune, you can do it yourself or go with a kit. The kit is easier if you haven't done it a lot before.
Stage one jet kit is what you need, I think their stage three includes the parts for stage one?


Stock main jets for a VM carbed GS1000 are 95, is that what's in there now?

 

[Steve]

No, the PILOT jets are just fine.

It's the MAIN jets that can cause problems, and the needles also need some adjustment.

Since you still have a stock airbox, the needles can probably just be lifted a bit. If you had pods on there, too, you would then need the DynoJet kit.

Just because you got the bike "that way" does not mean it was proper. As tkent mentioned, it was probably sold because it did not run right.

Power coming on with a jolt when moving the throttle is typical of carbs that need a sync job. Apparently, one is closed more than the others. When you start to move the throttle, it comes 'on-line' as well, giving you full power.

Hard starting, especially when cold, usually points to valves that need to be adjusted. They are probably WAY too tight. With properly-set valves and clean, jetted and synchronized carbs, it will seem that you only have to give the starter button a stern look to get the bike running.

.

Stock main jets for a VM carbed GS1000 are 95, is that what's in there now?

His '80 1000 should have CV carbs, the stock main is 115. With the pipe, might be good to go with 125.

.

 

[poorgradstudent]

Stock main jets for a VM carbed GS1000 are 95, is that what's in there now?

I'm not sure, and I wouldn't know how to tell. The part manual shows "Main Jet (115), PN 09491-23011." Will the dealership offer this part? Or would I need to go with DynoJet stage 1 kit?

How do you even tell the size difference? Calipers? Different gauge wires?

 

[tkent02]

The number is printed on the top of the jet.

Exactly which model is your bike?

 

[SVSooke]

http://www.thegsresources.com/_forum/showthread.php?t=212908

 

[GSXR7ED]

Main Jets

Main Jets

I'm changing the Main Jets on my 750T...112.5s were in there and I'm installing V&H 4-1 pipes this weekend.

Gonna go with 115s but Z1 sent me these:




Ed

EDIT: Rob also recommended changing the Pilot Jets:




I'll let you know how things work out for me if you're interested.

 

[tkent02]

Oh, a 1000G. That blog led to a 1978 1000E.

Just buy the jet kit.

 

[poorgradstudent]

Ha, so the size is labeled right there on top of the jet! Who knew?!

I'll break 'em down, again, and take a look.

Thanks again!

 

[Big T]

If you look closely, or use a magnifying glass, you'll see a number on the main and pilot jets

Record these and check also for a symbol that looks like two interlocked boxes. That means they're Mikuni jets

For a stock airbox and a 4:1,

Pilots 15
Mains 102.5-107.5

Lift the needles one notch

Fuel screw 7/8 to 1 turn out

Air screw 1 1/2 turns out to start

I can't remember, di VH recommend pulling the airbox lid for a pipe only?

PGS, you need to check the Newbie Mistake thread on BassCliff's site and go down the list

Also, you need to put your bike in your signature, so we don't have to constantly guess what you're referring to

 

[Guest]

CV carbs Todd

 

[chuck hahn]

The usual starting point for the mixture screws ( on the top rear of the carb throats ) are 2 out from lightly seated and you fine tune from there.

 

[Big T]

CV carbs Todd

Sorry, the link in post 1 was for a 78E

 

[GSX1000E]

I'm changing the Main Jets on my 750T...112.5s were in there and I'm installing V&H 4-1 pipes this weekend.

Gonna go with 115s but Z1 sent me these:




Ed

EDIT: Rob also recommended changing the Pilot Jets:




I'll let you know how things work out for me if you're interested.

You will not need those pilot jets but you will at least need the 117.5's or 120 main jets. Adjust the fuel screws after the main jet change and report back.

 

[GSXR7ED]

Labeled

Labeled

Ha, so the size is labeled right there on top of the jet! Who knew?!

I'll break 'em down, again, and take a look.

Thanks again!

Yep, I had to put on my reading glasses to see the numbers. The camera got a decent close-up view.

You will not need those pilot jets but you will at least need the 117.5's or 120 main jets. Adjust the fuel screws after the main jet change and report back.

Sir, yes sir!

I was told by MrBill to go up 3. Let's see what he says about going to 117.5s.

I'm good with doing the 117.5s.


Ed