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Jetting for mufflers

  • Thread starter Thread starter Beemer
  • Start date Start date
Beemer said:
Good Morning.
Does anyone recognise what mufflers these are? 4 into 2. The carb's are running stalk jets presently and these are fairly open pipes. (A bit loud.)
http://www.techimo.com/photo/showphoto.php/photo/9301/size/big/cat/500/ppuser/68

Any recomondations for jetting?
Click to expand...
I don't know what pipes those are but they appear to be freer flowing. If so, the jetting will be effected. The bluing header at #4 suggests the mixture is lean. I assume the stock air box still has its lid?? Carbs must be clean and no intake leaks before jetting tests. Also, check timing and valve clearances. The carbs must also be vacuum synched to get uniform/acurrate plug reads.
Take some full, 1/3 and minimal throttle position plug tests. Do what the plugs/performance say.
Just for your GENERAL info, a pipe like that typically requires maybe two full sizes up on the mains. Your stock mains are #95. So that would mean 105, if not larger. This is strictly a guess and plug reads will help you decide what to try first.
The jet needles may have to be raised too. 1/3 test will tell you.
Simple richer pilot fuel screw (underneath) adjustments may be all you need for the pilot circuit jetting. For just a pipe, an additional 1/2 turn out may be all that's needed. Fine tuning will be necessary. Adjust side air screws for best idle.
 
Hey Keith.
The pic is from a few weekends ago when I picked up the bike. The blueing problem has been fixed with either the plug replacement or cutting back the spark plug leads a 1/4" or so and resetting the boots or removing an inline fuel filter. Confirmed that the pet cock is working good with vacuum and all, although valve is glued into the RUN position. New fuel line. New points and condensers installed a couple of weeks ago. Checked and corrected timing with a timing light and re-gapped the points. Autosol removed the blue and left the pipes a nice light gold colour for the first 4" leaving the ports. Removed the carb’s and cleaned up the bowl, (Spray carb cleaner used.) main, and pilot screws and holes. (A flush job) I didn't remove the floats. I noticed a 95 on the main but didn't really pay attention. Pretty sure I saw a 95. I didn't look to see what the floats were set on either. I was in hurry to see what kind of bench mark I had set with just catching up on some much needed maintenance.

Describing the sound the mufflers are half loud. Not an open pipe but a nice guttural sound. Definitely freer then a stock pipe. 1/4 throttle makes people turn and take notice. :shock:

I'm driving the bike but it jerks at low speed. 30 mph, 2nd gear at around a steady 1800 rpm. More or less. The ride needs to be smoothed out for idle speeds just after releasing the clutch lever.

Chain and sprockets are new with a .8 slap. Tomorrow after work I'm going to install new intake O-rings. I'm going out now to remove the carbs and deal with the float position and jetting for these pipes. (It would have been nice if who ever installed these mufflers jetted for them too!)

I doubt if I'll go to K&N's although they sure would be easier to get at the carb's. That air box really makes it a tight squeeze removing the carb's.

Thanks for the help Keith. I'll be back.
 
Oops! Forgot.

I finally got the bike to show that it has a power band. In the beginning I couldn't get the bike over 4500rpm without it powering out and back firing at gear changes. This behaviour is gone but now I'm trying to get the power band to be quite a bit more powerful.

In 5th I fully rotate the throttle, the bike lags.
If I back off a bit I get more power but no where near what I should be getting. In 5th gear the bike doesn't take off like it should at just before 5000rpm and up to 8500. It peaks at around 6200rpm and doesn't pick up speed any more. Just maintains the speed.

The stuttering at low speed/rpm and the petering out of the power band at an early stage of the fun and the loudness of the pipes leads me to believe that there is a jetting issue at hand.

I'm going to cut back the leads a bit more and I'll buy extensions if I have to.

Do extensions rob any sparking power?
 
I don't think it's your spark plug wires. Listen to Keith and jet with throttle chops. The plugs will tell the tale. I'm 99% sure you're lean on your main jet and your needle circuit.
 
P.S Really nice looking bike and pipes. Looks just like mine with better pipes.
 
Yup! 95 main and 15 pilot.

After my description and finding stock jetting on board, should I still go with 105 main? What should the pilot change to?

I'll have one shot at this tomorrow sinse I get home just before the dealership closes. Quick shower and off to the dealership.
 
Beemer said:
Yup! 95 main and 15 pilot.

After my description and finding stock jetting on board, should I still go with 105 main? What should the pilot change to?

I'll have one shot at this tomorrow sinse I get home just before the dealership closes. Quick shower and off to the dealership.
Click to expand...
If the ends of the plug leads are clean, leave them be.
Does this bike idle quite a bit higher from cold to hot? Some of your symptoms could be from an intake leak. I always recommend changing the manifold o-rings if the carbs are out. Incorrect valve clearances can hurt the breathing and your top speed. A vacuum synch should be done as I said before re-jetting.
After reading your latest posts, I'm gonna say 107.5 for the mains. Just a guess of course. I'd stay with the stock pilot jets for now and just try richening the pilot fuel screws underneath, maybe an additional 1/2 turn initially. Then adjust the side air screws for best rpm using the highest rpm method. Don't forget to take 1/3 throttle tests for the jet needles. The jet needle circuit is the one you spend the most time riding on.
 
My idle, cold to hot rises a little bit. 200 rpm or so.

The leads were suspect at the beginning of all this. I cut them back and it did help clean up the back firing problem 50% or so. Once I changed out the plugs, the back firing went away completely.
...and just try richening the pilot fuel screws underneath, maybe an additional 1/2 turn initially.
Click to expand...
Presently I've turned these out to 1.5 turns.

All that has been suggested will be done after work today. I have O-rings in hand. I need the jets.

On another note, the hose leading from the fuel gage sensor on the tank is presently hooked into the vacuum nipple on #2 carb. Is this correct?

Thanks again for all the help.
 
Last edited:
Beemer said:
On another note, the hose leading from the fuel gage sensor on the tank is presently hooked into the vacuum nipple on #2 carb. Is this correct?

Thanks again for all the help.
Click to expand...


No, thats an overflow or leak tube. Should just be routed down below engine.

Vacuum from petcock attachs to #2 carb.
 
beby99 said:
No, thats an overflow or leak tube. Should just be routed down below engine.

Vacuum from petcock attachs to #2 carb.
Click to expand...
As beby says, the gas gauge overflow line should be routed so any gas would spill out and away from the motor.
With it hooked up to the #2 float bowl VENT nipple, carbs 1 and 2 didn't have adequate bowl venting. Minor (at least) fuel starvation would occur. The correct vent line is 3/16" and approx' 18" long.
On your VM carbs, the nipple at carb #3 is the ONLY vacuum source. CV carbs have the vacuum at #2.
Also, the nipple at carb #4 is for venting carbs 3 and 4. Make sure both vent lines are connected and routed with NO KINKS under the seat along side the air box.
 
Thanks for the hose routing beby. It's been bugging me.

Deesel. Thank you. Best $500.00 I've spent in a while.

I picked up 105's, 107.5's and 110's. I wanted to make sure I covered all possibilities since the bike shop is closed till Tue. It's 95F outside at the moment so I'll wait for the heat to settle down in a bit. I really don't want to leave the A/C of the house.

Hey wait! No gas in the carb's. I can bring them inside....lol
 
Installed the 105's and intake boot O-Rings. The pilot air screw on the bottom of the bowl's are set to 1.5 turns presently.

The test drive.

Still stutters at low speeds but not quite as bad.
Between 2000 and 4000rpm with heavy throttle it sputters.
At 6000 she takes off like a raped ape all the way to 8500.
I haven't played with any screws yet.

The hoses.
#2 is open and resides on top of the air box.
#3 is attached to the petcock vacuum nipple.
#4 resides on top of the air box.
Need to buy hose for the fuel sensor nipple.

How many turns should the pilot screw be set at.
How many turns should the screws on the side of the carb's be set at approx.
Who do I send a cheque to? ;)
 
You need to sync your carbs first. Mark your throttle 1/4, 1/2 and 3/4. First check your mains with a full throttle chop. Pull with full throttle as long as you can and hit the kill switch without letting go of the throttle or pulling in your clutch. When the motor is killed pull in your clutch and coast to the side of the road and pull your spark plugs and read them White is lean, tan is good and black is rich. Adjust the main with full throttle until tan. Then do your needle circuit(you have an adjustible needle) (1/4 to 3/4) Lowering the clip on the notches will raise and richen the needle. Then do the pilot circuit which is the idle adjustment screws and the pilot jet. If you're lean after messing with the adjustment screws from idle to 1/4 throttle then you will have to go up one on the pilot jet. Keith will tell you to do your needle first because you do ride on this circuit most of the time, but it is a matter of preference.
 
Beemer said:
Installed the 105's and intake boot O-Rings. The pilot air screw on the bottom of the bowl's are set to 1.5 turns presently.
Still stutters at low speeds but not quite as bad.
Between 2000 and 4000rpm with heavy throttle it sputters.
How many turns should the pilot screw be set at.
How many turns should the screws on the side of the carb's be set at approx.
Who do I send a cheque to? ;)
Click to expand...
First of all, you haven't done a bench or vacuum synch. It's an important part of the jetting. Basic tuning before jetting. Don't expect good results if you take short cuts.
Then you need to adjust the side air screws using the highest idle method as I said.
Both of these could be causing your "sputter" problems.
Highest idle method: Warm up the bike completely. Turn off and place on centerstand. Initially set each side air screw at 1 1/2 turns out. Adjust throttle cables for correct play. Start the bike and set the idle to 1,000/1,100 rpm's, no more. Starting with any screw, slowly turn it in either direction until you hear the rpm's max out. Fine tune it. Generally, they end up 1 1/2 to 2 turns out. Now reset the idle to base 1,000/1,100 rpm. Repeat to the others one at a time.
Leave the pilot fuel screws where they are for the moment.
Also, don't expect great performance when fully opening the throttle at 2,000 rpm. Allthough a correctly tuned bike shouldn't sputter even under this condition, most people don't ride like this. It's like deliberately trying to make it show a problem.
If a vacuum synch and correct air screw adjustments don't cure the sputter, then I suspect the jet needle needs adjusting. But you have to vacuum synch and set those air screws and take a solid 1/3 plug/performance test first. We need to know how the plugs look at that throttle position after a couple miles. If you find a safe place to test, run it in 4th or 5th gear and chop off. Take a rag and a piece of hose with you that fits snugly over your plugs. The hose will help you remove and install the hot plugs. Careful of cross threading as always.
 
Also, after re-reading this thread. The carbs may still need more cleaning and inner o-rings could be bad. Float levels could be wrong.
Valve clearances need to be checked/adjusted and this should be done before any vacuum synch.
What plugs are in it? Do you have a good bluish spark at all four plugs?
Have you checked/cleaned the coil terminals and other connections such as the battery posts and grounds to frame and motor?
What color are the plugs after just general riding around/testing?
Is the filter clean and is the air box lid ON?
Etc, etc.
I just want you to know that it can get difficult when you take short cuts.
You don't want to mix troubleshooting with re-jetting. Taking care of all other tuning first makes the re-jet much easier.

If you're serious about sending a cheque, please send a few bucks to this great site. :) Future members looking for help will appreciate it.
 
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