High performance pipes

[Craig]

I will have to check with my tuner to get more info. I will see if he can jump into this thread.

Craig

[Billy Ricks]

That range is right where the accelerator pumps do their thing. You can try pulling the pump rod out and run without the pumps so you can get the jetting right then reinstall the rod to get the pumps working again. When you first nail it with smoothbores you have to roll the throttle on rather than just whacking it open. They'll bog the engine if you don't have enough rpm's spinning and you just yank them open. Once you get it up to redline after whatever gear you were in you can just yank the throttle open after shifting, but you have to regulate the throttle a little and downshift when you first nail it.

[Billy Ricks]

One thing I'd take a close look at is float height considering where your flat spot is.

[80-81, GS 1100]

One thing I read once was that some 4 into one pipes have a
flat spot that a 4 into 2 into one pipe does not have.
Could that be what the tuner is referring to?
In the picture, you have to look closely because
the exhaust does end up on one side with both
systems but supposedly there is is difference.
Don't see how it could make that big a difference
.........

[Craig]

Float height is spot on

[Nessism]

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.

[49er]

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.

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.

[Dink]

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.

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

[Dink]

Float hight is spot on

Your results DO NOT agree!!

Dink

[Craig]

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

[oldschoolGS]

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

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

[1150 Jay]

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.

[1150 Jay]

I meant to say "Next size smaller jet needle" to add more fuel. Smaller in diameter of course. Sorry

[rapidray]

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.

[Billy Ricks]

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.