I want more power but with a good smooth curve.

[Silvermachine81]

I clowned around with my engine when I was younger and dumber and added all the usual High performance mods using goods brands and not going stupid on the cam size etc.
After tons of dyno time I just cant get rid of a big hole in the mids.
I think its the porting job and 38mm Mukuni RS's that are causing an over carburation/bad mids effect.
Its fine from 0-4000, majorly bad (you should see the dyno chart) 4-6500, Strong after.

Ive got a spare brand new head (still in the box) and have been thinking of just going back to a stock head and new valves but still running the not overly high lift webcams and putting the original (New Zealand Wire Wheel spec) 36mm roundslide mukunis back on.
Anyone else been through the same...???

BTW, Everything is set right.

The bad mids cant be dialed out so it has to be the head/carb combo....

By all accounts from what ive been told by people, The 38s are just to big unless youve got a seriously big engine with a really good port job.
For street use they are a bit of a joke cause they are the equivalent of putting 44mm CV's on which is ludicrous.....But I was young and stupid;-)

HELP!!

 

[Dink]

Stock capacity? What exhaust? what jets? Which clip on the needle? GSXR 38 mm flatslides? What ignition? What valve clearances? What is your compression reading?
Dink

 

[Anonymous]

After tons of dyno time I just cant get rid of a big hole in the mids.
I think its the porting job and 38mm Mukuni RS's that are causing an over carburation/bad mids effect.

If you have gone to all that effort and not got results, perhaps your porting isn't as good as it could be. To achieve what you want sounds like you need to do some epoxy filling of the ports instead of making them bigger. Most of the time hogging the ports out does not produce the desired results. Smaller is often better. Check this site out for some good tips and a well done series of articles on filling the ports for more and smoother power:

http://mototuneusa.com/thanx.htm

It is the high velocity porting series you want to look at.


Mark

 

[Silvermachine81]

Stock capacity? 1134
What exhaust? Star Racing Street Sidewinder.
what jets? N/A as im not using the stock carbs, ones that come stock with mikuni RS's just need tweaking and maybe the odd main jet change.

Which clip on the needle? Tried that no change except the hole moved or dropped 2 horsepower through the mids.
GSXR 38 mm flatslides? RS Mikuni 38mm Flatslidses, The real ones.
What ignition? Dyna pickup/dyna coils.
What valve clearances? 0.6...? Whatever the manual suggested.
What is your compression reading? Never checked but it was 10.25/1 pistons, engines in pieces now.
Dink

 

[Silvermachine81]

Lets try that again.........

Stock capacity? Wiseco 1134
What exhaust? Star Racing Street Sidewinder.
what jets? N/A as im not using the stock carbs, ones that come stock with mikuni RS's just need tweaking and maybe the odd main jet change.
Which clip on the needle? Tried that no change except the hole moved up or dropped 2 horsepower through the mids.
GSXR 38 mm flatslides? RS Mikuni 38mm Flatslides, The real good ones.
What ignition? Dyna pickup/dyna coils.
What valve clearances? 0.6...? Whatever the manual suggested.
What is your compression reading? Never checked but it was 10.25/1 pistons and was harder to turn over than standard, engines in pieces now so cant find out.

Also cams were dialed in to 108 & 109 as suggested by manufacturer.

 

[Dink]

Just a quick aside! You cant have an 81 GSX1100SXZ as the "Z" says it is an 82 model, return it to as close to stock as possible, you have THE rarest of all Katana's there.
BTW yes I am aware that your vin plate says 81, BUT it is an 82 model, Suzuki changes to the following model year from the 7th month of the previous year.

Now back on subject, your exhaust is your problem. A sidewinder is a drag system and is only designed to run flat out. it is possible to run one on a street bike but your increased carbs are causing the problem, you may be able to refine it out by playing with your idle jets, as it is the transition from idle to main that is causing the problem and the sidewinder is not helping.
Dink

 

[Silvermachine81]

Mid to late 1981 on the papers....I think..........

But I hear exactly what u are saying.


Yes, The pipe...I think thats the correct name.

There's the pro stock twisty pipe, The cross over headers (drag/no baffle) version for the weekend racer....
And mines the no longer available cross over headers with baffle pipe (which doesnt actually line up with the exhaust mount so I had to get that moved).

Heres a curve I found on the net of an 1166 kitted gsx.......

Hes got 28.5 inlets/25mm exhausts and a bigger motor......

Perhaps im being greedy expecting more than 110 at the back wheel :? with stock valves???

Im sure it the carbs and obviously so are you and most guys seem to run 34-36's with larger engines than mine so maybe I should just put it back together with the old (Really time consuming to adjust) carbs and go play at the dyno for a day.

P.S, Last time I went to a dyno it was a seven hour drive and it was a piece of junk :x :x ........Now theres one about two blocks away

BTW, the bike looks totally stock except for the pipe :wink: , I was real careful about that detail, Unlike some people I know with monoshocks etc :roll:

 

[Dink]

We have a member here with a 5/81 GSX1100S, and mine is a 7/81 GSX1170SZ, mine is running an umbranded 4 into 1 and stock carbs rejetted and I am pretty confident it is making more than 110 RWHP, you only need see what it does to a CBR1100XX to know, I am 2 and a half hours from the nearest dyno and work six days a week so I see no way of being certain of its output , but I know it is way stronger than a GSX1100EFF (1150 for the US). Most of its extra is in the cams , as on disassembly I discovered that apart from the cams the cylinder head was entirely stock.
Dink

 

[Silvermachine81]

Thats excellent info man!!!

Mine should be way stronger with all those toys attached so there must be a bit more to it but im sure i will get the minor stuff sorted out on a dyno.

It just the big problem I have to sort first so I might have to find a set of 33's so I can play curve comparisons on the dyno between the 3 sets of carbs.....

I have a book where the author shows the benefits of putting 'SMALLER' carbs on high-performance streetbike and how for the sake of 2hp up top you get heaps more in the usuable midrange area......Factories know big hp figures & big top end sell bikes and wins stock bike racing classes so sometimes overdo the carb size a wee bit......
Change em and you suddenly got the street beast from hell.

Man if I knew that 10 years ago....

Maybe you should try some 33 smoothbores, 34 RS flatslides or something in the carb dept cause they would really get your one going....Slide carbs just make a bike really really come alive and if you do it right (unlike me) youll be the drag strip (I mean traffic lights) king!!

Anyway, If it can blow a blackbird with stock carbs on then youve got one strong machine 8)

 

[ronin1166]

I'm a loooong way from being an expert...
But it sounds to me like you have major reversion at 4000 (where your 'hole' is). Not enough intake velocity - engine isn't sucking hard enough at that RPM to mitigate it it. Kevin Cameron's Sportbike Performance Handbook has a nice discussion on this phenomenon. It's not at all uncommon...been plaguing engine builders for decades.

IMHO, RS38's (and/or pipe) are too big. I'd sell the 38's and find some 36's.

NO two engines behave the same - even with the same parts. Waaay too many variables. As many, many famous engine builders have stated throughout history: "it's all in the combo."

Oh, and BTW: Heard of Dale Walker's "Frankenzuki"?
160+ RWHP. Stock-valved '81 GS1100 head - with RS36's!!!

Good Luck dialing it in, and keep posting your findings.
Ted

 

[Silvermachine81]

Yes that describes it, A major reversion....

Between 4-6500 and the sheet goes nuts and bounces up and down like a yo-yo.
And as I stated before, None of the usual tricks helped at all.

The not very experienced dyno dude just stood there scratching his head saying "That should have done some thing but theres no change what so ever........

The pipe isnt that big real plus ive heard good things about it with is why I got it over a vance & hines.

Sounds like a new head (or at least exopy port the old one), and slap the old 36mm's back on.........

Cheers Guys, Youve been real helpful

 

[Anonymous]

Check out Rosco15's site:

www.rccracing.com

And his horsepower outputs with various levels of tune:

My bike with stock pistons, stock head, stock cams (stock displacement ? 1073cc) made 113 Hp and 75 foot pounds of torque. I do have a pro drag race only pipe, 36 mikuni flat slides, and a dyna msd ignition. When I put in a low compression 1166 wiseco kit and kept the stock unported head and cams I got 128 Hp and the torque was around 80 something. I degreed the stock cams to 110/110 but haven't run it on the dyno again. I picked up about 2 tenths so I think I'm probably over 130 Hp. I'm looking for reliability and ease of maintenance.

Ryan

This is from a thread I posted a while ago.

Mark

 

[Dink]

This is a problem a lot of people strike you know!
They build a bike from advertisements instead of building "A Package" as I stated before I have absolutely no idea what brand the 4 into 1 on my Kat is, but who cares it works and rather well at that, I seriously believe your exhaust is your problem, next time it is on a dyno try ripping the baffle out, borrow any other exhaust that will fit, and run it with that, I would be amazed if that did not go further to wards fixing your problem than a carb change, I have often heard that 38 mm flatslides wake an 1150 up like nothing else, so whilst they may be a little big for application, they should work if you go a little light on in the jetting. I may have a lead on an all new exhaust system for your Kat, ask me early in December, a friend and I are developing one that may just do the trick. In fact whilst sitting here typing this I remebered that at the last KatOz run there were two stock block Kat's running exactly the carbs you are and no problem. I must say again, get any other exhaust, most people pay little to no attention to the exhaust side of the equation and suffer because of it, there is heaps of "free" horsepower and torque sitting locked up in any exhaust, many a car builder has been able to free up 50 HP or more through attention paid to the exhaust side of things.
Dink

 

[Dink]

This is a problem a lot of people strike you know!
They build a bike from advertisements instead of building "A Package" as I stated before I have absolutely no idea what brand the 4 into 1 on my Kat is, but who cares it works and rather well at that, I seriously believe your exhaust is your problem, next time it is on a dyno try ripping the baffle out, borrow any other exhaust that will fit, and run it with that, I would be amazed if that did not go further to wards fixing your problem than a carb change, I have often heard that 38 mm flatslides wake an 1150 up like nothing else, so whilst they may be a little big for application, they should work if you go a little light on in the jetting. I may have a lead on an all new exhaust system for your Kat, ask me early in December, a friend and I are developing one that may just do the trick. In fact whilst sitting here typing this I remebered that at the last KatOz run there were two stock block Kat's running exactly the carbs you are and no problem. I must say again, get any other exhaust, most people pay little to no attention to the exhaust side of the equation and suffer because of it, there is heaps of "free" horsepower and torque sitting locked up in any exhaust, many a car builder has been able to free up 50 HP or more through attention paid to the exhaust side of things.
Dink
Also try re-dialing your cams in for 106 centres as this will help midrange.

 

[Silvermachine81]

Thanks again,

You could be right about the pipe....Problem is I dont know anyone where I live cause I only moved here a while ago....

I did build it to a plan actually and each item was meant to compliment the other and judging from everything ive read and learned over the years I have probably only got the porting wrong and maybe the carbs size.
But yes the pipe may be designed to only work from 6500 up as it is a pretend drag pipe....BTW pulling the baffle made it slighly worse in the mids.....

Im seriously thinking its a lack of velosity caused by too big carbs with bored out rubbers with too big ports but I'll try your 106 idea cause ive heard of that before, That could really help

 

[kz]

Hi Silvermachine81,

I have a very simular problem as you seems to have, but I have Mikuni RS36 and have not solved it yet.

You can see my dynochart at http://www.karl.zellner.com/Dynojet1327-1.jpg

My next step is to go for RS40 instead of RS36.

If I understand you correct your next step is to go from RS38 to RS 36.

Maybe we both are on the wrong track???

If you solve the issue with the hole in the midrange, I would be very interessted to here what caused tour problem.

The hole in the midrange should just not be there, I have dynocharts from other engines with almost the same config as mine with no hole.

I have an own thread for the same issue...

In my case the engine is far to rich in the area there the hole is.

Impossible to rejet away, tried alot with needles and jets...... :evil:

http://www.thegsresources.com/_forum/viewtopic.php?t=27597

 

[lhanscom]

Sounds like the porting, check out this article http://mototuneusa.com/think_fast.htm describes how to epoxy your ports to increase the velocity of the mixture. The end result of increasing your port size, and then reshaping them with epoxy should give you a net gain over the stock head. The stock head would probably get you back to decent base line though. Another thing you could try is retarding your cam timing some, maybe back to 106, it will have an effect on your top end, but may change your flow characteristics enough to fix the midrange problem.

 

[kz]

lhanscom

Thanks for your reply,

I'm afraid you are right about that it could be the porting wich has to be redone/improved.

Would you go for the RS40 instead of RS36 in my case?

As I understood from your earlier post you run RS38 on 1229 with good low end.

 

[lhanscom]

If you're having midrange problems going bigger isn't going to help I don't think. My RS38s work great, and they would work well for your application as well , I think RS40 would be too big, and would make your low end bad. RS36 should be good for low and mid, but not have the top end potential of the 38's, or 40's. You're pushing some pretty big hp on top though, so the 36's seem to be working, and I wouldn't change them.

 

[Anonymous]

RS36 should be good for low and mid, but not have the top end potential of the 38's, or 40's. You're pushing some pretty big hp on top though, so the 36's seem to be working, and I wouldn't change them.

Luke,

Don't forget that the limiting factor in flow will be the valve and seat combination, not the carbs. From the power he is making, the 36's look to be perfectly adequate.

Cycle World this month has a feature on a '80 GS1100 roadracer built by Dale Walker (of drag racing fame). He uses RS36 carbs and it makes 159rwhp and 90ft*lb of torque, so they don't seem to be hurting it's performance either...


Mark