exhaust and air intake mods and effects on carbs

I just bought a 1981 yamaha maxim 550 for $200. Bike runs and seems mechanically sound. Ive been looking at all these awsome bike you guys are building, and now im gonna start my project. Im thinking about going with a hard tail and a cust om exhaust. would love to also get rid or the big ugly airbox and get some pod filters. My question is if i go with the chopped exhaust and pods and i mess with my carb jetting is it going to do long term damage to my motor? just worried that the bike wont burn off all that extra fuel. worried about gas in my trans oil and all that stuff. I have one more question because i know you guys are the experts. Has anyone had any trouble with there bikes coming apart where they were cut and welded for the hard tail. any and all advice will be helpfull guys. thanks. my name is rob and im in shelby nc. I build freightliner trucks for a living. and i can weld and have some mechanical skill. i figure i would much rather learn from your mistakes than make them myself. I will add a pic of my 550 later tonight. thanks again.

 

Here is a pic i said i would add of my 1981 maxim 550. I think i did ok for $200

 

Welcome to the site. I haven't hard tailed mine but if done properly and the frame is in good condition to start with you should be ok.

Pods and custom exhaust will require rejetting. Should you get your jets and carbs set up properly then it will have no ill effect on the motor.

Run too lean too long and you'll melt a piston.

 

thanks man. this is an awsome site. im so glad i found it. seems like a lot of cool people with a lot of bike building knowledge.

 

Whats your plans with the exhaust?

 

Sounds like you think the exhaust mods and pods will make your bike run rich. You will be introducing much more air into the carbs and will be running lean (not enough gas) and will have to rejet to get the proper air to fuel ratio.

This alone does not adress the fact that your airbox to carb boots are shapped to flow air smoothly into the carbs to properly raise the carb slides. With pods, the airflow is turbulent, and no matter what jetting you chose your bike will not run as well as the stock set up.

Doesn't mean I haven't ditched the airbox, but am constantly designing ways to achieve stock potential.

PVC pipe intakes with one pod filter seem to be the best alternative right now.

Currently working on a PVC pipe intake incorporating the original airbox to carb velocity stacks.

 

Adding Velocity Stacks will help Bring the problem under control.

But, the SPEED of the UNRESTRICTED Air will most likely REDUCE AIR Pressure at the ORIFICE which supplies AIR to the MAIN AIR INLET JET.

The MAIN AIR Jet ... NEEDS enough Air to be able to SUPPLY the Volume needed to be drawn-up through the Drilled Air Ports of the EMULSION Tube.

An unrestricted Air Flow lowers pressure at the orifice.
Insufficient Main Air robs the Air needed to assist Main FUEL to pulled-up into the Intake Stream.

 

i was thinking about a custom 2 into 1 exhaust. on both sides of the bike. brobably way shorter and cooler than the stock set up. i am going to put baffles back in the pipes so i have some back pressure. want to definately go with pods for the look. not really worried too much about horse power. what i thought about doing is installing the pods and taping them off untill i can get the bike running the way i want. then fab something to put under the foam on the pods made if metal or plastic to cover and slow the airflow down. that way you wont be able to see it. i got this idea from a bike mechanic buddy of mine. he isnt crazy about the frame mods i want to do. but i think thats because he wants me to pay him to build me a bike. im going to hard tail this thing anyway though. can anyone tell me what is the best type and size tubing i need to get for the frame mods?

 

started tearing the bike down. here is a shot of what it looks like now. ive got a tube bender and a welder. all i need to do is decide if i want to stretch this thing a few inches or keep the wheel base the same. im only 5 ft 4 so i want the seat low. not exactly sure what i need for tubing yet but im working on it. theres a race shop not too far from me that builds bikes.im sure they can get me what i need. ill be posting a lot more pics of my progress as i go.

 

You're playing "Catch-up" to a discussion we had about limiting Air Flow awhile back.

While a reduction of Cubic Feet per Minute seems like the OBVIOUS plan to get Air Pods within the parameters of allowing them to be Fine Tuned; the PROBLEM to be overcome is TURBULENCE.

The Turbulence at the Carbs Intake Horn REDUCES Pressure at the Orifice which provides AIR to FLOW to the AIR JETS.
Rather than having a Column of Air rushing straight at the Intake Horn; the Air Flow CURLS and SWIRLS at the Intake Horn and rushes into the Combustion Chamber failing to accomplish three important processes.

The Turbulent Vortex at the front of the horn REDUCES Air Pressure at the Orifice, which provides the supply to the AIR JETS.

The MAIN Air Jet becomes starved for AIR to allow through the Emulsion Tubes Tiny Ports:
a) Insufficient Air Flow through the Emulsion Tube Ports LESSENS the Flow for the SIPHON Effect.
b) Is too weak to ATOMIZE that Fuel which does get drawn-up.
c) The Non-Atomized Fuel enters the Intake Stream as DROPLETS, ... NOT a mist. The BURN at Ignition is less efficient and the Engine fails to make good POWER. (Flat spots).

Regulating the Intake Volume will NOT fully address the problems caused by Air Pods.
Taking measures to insure that AIR **IS** Supplied at the Air Jet Orifice needs to be addressed.

Velocity Stacks.
Air Jet Supply "Bypass"

That will help.

TWIN VINYL HOSES INSERTED INTO AIR SUPPLY ORIFICE SEALED WITH BATHTUB CAULK PLACED AWAY FROM TURBULENCE WILL HELP PREVENT AIR JET STARVATION.

 

ok cool i understand now. thanks for the advise man. this is definately a great site. i have a question though. what is the best way to prevent trash from getting into the tubes?

 

I sold them Carbs before being able to prove it.

But, I'd be willing to bet that just running the Tubes on back as far as you can ought to do the trick.

The Vortex is at the Mouth of the Horn.
There must be some "Good Air" lingering-around at the back of the Pod.

 

Rick,

Doesn't the little oval inlet at the top feed the Pilot fuel jets? I thought the problem was with the main jets? So what does your rig do? (I'm sure it helps, I'm just wondering why?)

Also, the velocity stacks on my bike go about another 2 inches or so into the airbox, do we need to keep the entire length or cut it down? Does it fit inside the pod or around the outside, and if it goes inside, how far?

Final question, how much do you recon you need to change the size of the jets by? I need to order a new set off Chacal. I was going to order a stage 3 kit off Dynojet, but it seems cheaper (and I learn more) if I do it myself.

 

Okay here is my stacked pod break down. Should be self explanitory, short rubber is what came with the pod, I run 132 mains, stock pilot, and needle shimmed one click on the dyno jet needle

 

The Oval Orifice IS the AIR Jet Opening. (Sounds Presidential)

The arrangement on the Left looks like what you should try.
The Pod is long.
I'd try to run the Bypass Hoses all the way to the whole length of it.

I have no idea which JETS to recommend.
If this experiment proves to be successful on a running bike; you'll likely be rewarded with a LESS LEAN Mixture as a result.

You are the Pioneering Bypass Experimenter.
I hope its effective enough to let you do some Tuning that will require less rejetting attempts to solve the Lean condition.

I think you might have less success than the Members which have designed the PVC Uni-Pod Manifold.

 

StreetBrawler..

Thanks for that.. What size mains did you start with? My mains are likely a bit smaller than yours for whatever reason Yamaha decided to change everything around in the E-II model, I'll first try with some jets by stepping up from my current ones by the same amount you did, and see where we are. You prolly started with 120's, I think mine are 106, so I'll go up to 118 and see what happens. Do you have a stock exhaust or an after market one?

Rick..

Thanks for the words of encouragement.. I've some clear tubing that should fit, we'll see where we end up.. From your experiments, did you actually take the tubes out of the pods somehow or just cut them so they just reach the ends.. I think I'm going to do the latter, since it invoves less mucking around with anything, and I can't really see what difference it will make.

I've never done anything like this before, so I've a mixture of excitement and trepidation. I think I might find some 2nd hand velocity stacks to do this with so I can put the bike back to stock if the Swiss authorities don't like the change in emisions this creates.

 

pic wouldnt upload last night. here is my progress. will probably cut the frame today.

 

My experiments ended when I sold the Carbs.

All I know for SURE, ... is:

With hoses in the Orifice to let MAIN Air reach the Emulsion Tube, ... MORE Fuel **seemed** to be getting drawn-up through the Emulsion Tube. That Fuel Flow was in a remarkably better pattern leaving the Emulsion Tube.

The Smoke was still Turbulent as it entered the Horn.
Swirling in.
And, it was only ONE Carb. I have no idea what would happen with additional Carbs nearby.
So, I surmise ... that adding "Shape" with a Velocity Stack will guide the Intake Flow over the Top of the Emulsion Tube ... LOWERING the Pressure at the EXIT greater than without a Stack and cause MORE Main Jet Supplied Fuel to enter the Intake Stream

 

Ya 120 was stock on mine. The exhaust is custom made 4-2 with a crossover, I ran it for a while with no crossover and just can't leave anything alone for long so decided to put that crossover in to see if it helped, and it did seem to even the powerband out, by the seat of my pants, no dyno or fancy tech diagnoses. I am very happy with my set up, no flat spots and power out the butt. Blows my stocker away, but could also be the wieght difference lol.

 

What size are those pods, to get them to fit on the stock boots?