I want more power but with a good smooth curve.

[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......

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

[saaz]

I think Dink is on the money here. As a package it is not working as it should (ie an arm tearer!) Porting may be a suspect, but getting a decent pipe on may make a world of difference. Drag and really average pipes can tend to worsen performance. A proper road/race system tuned for road performance would be a good bet. Modern cannister designs are a lot better than the old syle ones. As some have mentioned, porting can often destroy performance, but I would fix up the pipe first.

[Silvermachine81]

I think Dink is on the money here. As a package it is not working as it should (ie an arm tearer!) Porting may be a suspect, but getting a decent pipe on may make a world of difference. Drag and really average pipes can tend to worsen performance. A proper road/race system tuned for road performance would be a good bet. Modern cannister designs are a lot better than the old syle ones. As some have mentioned, porting can often destroy performance, but I would fix up the pipe first.

I have an old cycle world with a 1230 kitted 1150 with the same pipe as mine and it puts out 145 RWHP. These pipes work for power.
Perhaps the road pipes just help with the mids a bit more

[Silvermachine81]

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......

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

Well one of us is gonna work it out first and I think that will be you my friend cause I just dont have the time or money to F**K with mine anymore. Its gonna stay in the shed in bits......
Just private message me once you get somewhere dude as it might inspire me to get my *@%^$*@%^$*@%^$*@%^$e together.

I think your carbs are fine.

So maybe its the pipe or maybe its the porting??

God, If that Dale Walker dude can get 159 RWHP with a stock head then we are both doing something wrong

Hell, I only got like 110 with my 1134 kitted engine and ive been *@%^$*@%^$*@%^$*@%^$ing around with this thing on and off since 1992

Id expected 125 at least but if Dale Walkers got that much then I better go buy that magazine and re plan my whole project

[Anonymous]

So maybe its the pipe or maybe its the porting??

Or a combination of both...Big ports will do what you have, with problems down low, then come on - BANG! - up higher in the revs. A 4-1 pipe will cause a hole in the torque curve at about half the tuning RPM, and a straight megaphone will also cause a serious reversion problem at lower RPM. The 4-1 part cannot be eliminated, it is inherent in that header configuration. The megaphone part CAN be solved by the addition of a reverse cone after the expansion cone. Even a small lip (10mm or so) makes an AMAZING change in the response. If your pipe has a muffler core after the meg (or the muffler IN the meg), this is a bit hard to arrange, though.

God, If that Dale Walker dude can get 159 RWHP with a stock head then we are both doing something wrong

I never said the head was stock, I said that he used RS36 carbs. He ported the head, cut the intake spigots shorter and reangled them, and other trickery learned from decades of tuning drag bikes and the thing is now 1168cc displacement. But he did use the stock valves, yet another indication that big power can be done without major modification.

Check out Rosco15's site for some dyno charts of his drag bike in various states of tune:

https://www.rccracing.com

Ryan has about 130rwhp with an 1166 kit, stock head (ports, cams, valves, etc.), degreed cams, RS36 carbs and a Star Racing Pro pipe. Pretty good if you ask me. I think an epoxy port job would add another 10hp or so, with a nice flat torque curve.

Mark

[Silvermachine81]

Thanks Mark,

That magazine probably isnt on the shelves here yet (otherwise it would be the more expensive air freight edition).

I will look out for it.

I am gonna do that port thing one day as my head, with its enlarged ports will be pretty much toast anyway (If it is the cause of some of the problems in experiencing).

As for the pipe, I dont mind a dip in the mids cause it stops me from wanting to go much over 4000 when riding normally (Cant risk the speeding tickets anymore).
If I have to race someone then I can stick to 6500 and above but I would expect more than 110 rwhp so that may just be the head/carb combo and im sure a bit of cleverly placed epoxy will help with that

[kz]

Just private message me once you get somewhere dude as it might inspire me to get my #### together.

I will let you know if I have any success.....

/Karl

[Anonymous]

I didn't read this thread until today, but Dink is right.
It's an exhaust problem.
If you're replacing the exhaust with a 4-into-1, a general rule is: longer headers = more midrange power; shorter headers = more top end power and less midrange power.
Get a decent exhaust for your purpose and I'm sure most of the problem will be solved. Fine tune with rejetting.

[Silvermachine81]

Just private message me once you get somewhere dude as it might inspire me to get my #### together.

I will let you know if I have any success.....

/Karl

Cool, Thanks

[mike J]

Not trying to hijack this thread but I just bought a set of RS 38 flats slides the other day. Luke, do you know what jetting you have in your bike? Right now my 1150 is stock and I want to try them on it. Mike J

[lhanscom]

I don't know what the jetting is, as I haven't had to mess with them yet. I do have them off the bike though, and can take a look in the next couple days. Keep in mind that my bike is far from stock, so what works for me probably won't for you. Also, you'll want to at least have pod filters, and a good exhaust to use the 38s, otherwise your air volume will stay the same as before, but your velocity will suffer.