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High performance pipes

  • Thread starter Thread starter Craig
  • Start date Start date
Something is seriously wrong if you were getting 100+ hp with the MAC pipe and now you are getting 75 hp. That's not a flat spot, that's the grand canyon.
 
Nessism said:
Something is seriously wrong if you were getting 100+ hp with the MAC pipe and now you are getting 75 hp. That's not a flat spot, that's the grand canyon.
Click to expand...

Agree with this. Have you changed any other tuning parameters since swapping from the Mac 4-2 to the V&H 4-1? Your symptoms smack of leanness on the needle and main jets.
 
Craig said:
Sorry...I should have told more info. 1166cc kit. Higher lift- longer duration cams. Cam sprockets at approx 108 and 109 degrees. Mikuni 36mm smoothbore flatslides + pods. Dyna ignition. It has been on the dyno and we cannot get rid of the flat spot in the mid range. We feel it is the pipes. Any ideas.
Click to expand...

Get a better Tuner, this person is dangerous to you, your bike and your wallet.
Better still learn to do it yourself.
Get a Dynojet kit as a start.

Dink
 
Thanks for the input! I will talk to my tuner and let him read this thread. He did a great job on my ZRX when I went to a different pipe and carb kit...but is having problems with this bike. Talk to you soon.

Kind regards...Craig
 
Dink said:
Get a better Tuner, this person is dangerous to you, your bike and your wallet.
Better still learn to do it yourself.
Get a Dynojet kit as a start.

Dink
Click to expand...


a jet kit is not needed for RS carbs.

I have a simiilar setup on my bandit 1200:

1157cc with 9.5-1 compression
GSXR cams
RS36 flatslides with pods and a dual outlet pingel
Hindle full system (4-2-1)

I have a small dip at 5500rpm that is common with a real 4-1 full exhaust system, but in no way should you be down that much on top end.

A V+H 4-1 is gonna flow a lot better than a Mac system and there is no reason why you cannot tune the bike to work with it.

First, are you using the stock petcock? At high rpm, your stock petcock could be starving the bowls for fuel. Either way, I highly recommend a dual outlet Pingel. The RS carbs are set up for dual fuel lines.

Second, how did you get the 108/109 numbers? Every aftermarket cam I have seen and used for the GS1100 specify 110/110 centers. I know the numbers are arbitrary, but setting a baseline may help.

Third, you must tune the main first and then work down from there. You are looking for an A/F ratio of around 13-1 from 7000rpm and up. I would start with the 125 mains, the RS36's come out of the box with 130's. I found the 130's too rich for my Bandit, I tried 127.5's and finally settled on the 125's (per several dyno runs).

Also, the acc pump is almost not even needed. It comes out of the box set ON at 1/4 throttle and OFF at 3/4 throttle. Try resetting it to come on at 1/2 throttle instead.

As Billy said, you must roll the throttle on with mechanical slide carbs. From what I have read, It is almost unheard of to have to change needle design with the RS carbs. Your setup is pretty mainstream, be patient and make one change at a time.


Good Luck, Ed
 
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I think that the Mikuni flatslides are notorious for having problems in the mid-range due to not enough fuel flow. I had a set of 38's that had this problem and it wasn't until the bike was put on a dyno and an exhaust gas analyzer was used to actually find this out. If you put in larger needle jets (or fuel tubes) I think this will cure your problem. I put in the next size larger fuel tube, AND the next size larger jet needle and problem solved. Instantly.
You can get the parts from Sudco.
 
I meant to say "Next size smaller jet needle" to add more fuel. Smaller in diameter of course. Sorry
 
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The VERY first thing I do when installing flatslides on any bike I build for someone is to back the accellerator pump ALL the way OFF! Trust me, do this & THEN start tuning! With the mods you have I would start with the 130 main if you aren't high altitude. Then go from there. Also, an A/F meter makes it SOOOOO much easier & faster to figure out. Good luck, Ray.
 
And don't be so locked into the float height you have set up. You can change the mixture of the entire mid-range by raising or lowering the fuel level in the bowls. That's why there's a +/- 1mm in the specs.
 
This is one of the most interesting threads ive read in quite a while.
I also had almost the same experience with my 1100 (RS38's, 348 webcams, Mild Porting, Wiseco 1134 10.5-1, Star Racing pipe).
Nothing fixed it on the dyno and the (not very good) tuner was completely bemused.....
98 rwhp and a hole the size of the Grand Canyon.............
 
Got angry, pulled the motor apart, looked over everything, gave up, sat it in shed (4 years ago!!) and occasionally I look on here for theories as to what could be wrong.
Have had a few ideas to try and will attempt to put it back together one day soon.
I might order those carb parts as suggested above as this time I want it to go together right!
As a side note I too thought all was perfect on my bike when it was together but after over-analyzing the engine during the past few years ive realized much more goes into these things than we sometimes think and one thing slightly out can cause a huge chain reaction, making something appear to be at fault that wasnt ;-)
 
Well, we haven't given up yet. We are trying a few things with the cam timing. I will post my results as they come in. I have too much invested to let it sit in the shed!
 
rapidray said:
The VERY first thing I do when installing flatslides on any bike I build for someone is to back the accellerator pump ALL the way OFF! Trust me, do this & THEN start tuning! With the mods you have I would start with the 130 main if you aren't high altitude. Then go from there. Also, an A/F meter makes it SOOOOO much easier & faster to figure out. Good luck, Ray.
Click to expand...




taking the acc pump out of the picture for tuning purposes is excellent advice. That would have saved me a few headaches the first time I ran my Bandit on the dyno.

an A/F reading is absolutely necessary and will make the tuning process much easier.

Good Luck, Ed
 
I also think your problem is jetting as ive never seen anyone have a problem with the V&H exhaust. When I had problems I actually thought of ordering a V&H myself!

Tuners always seem to blame the pipe but that V&H pipe is in use on thousands of modified GS's all around the world and always seems to perform well.

Cam timing wont solve your problem, I've been down that track too so you really need to pay close attention to everything youve done and triple check it, then wind the accelerator pumps adjustment screws RIGHT OFF and work on your midrange.

Also check your compression as that could be part of the issue.

You never know quite what could be causing this so be meticulous.
 
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