Bike runs like crap after new mufflers

[Kathos]

I installed new glass-pack mufflers scrapping the stock system.
Bike ran perfect before switching the mufflers.
Vm34 carbs. Pilot jet #25, jet needle 3rd slot before muffler, 1 step richer now.
Bike ran perfect for a test ride to work.
Same afternoon it ran like crap for the way home.
Sputters when I rev it. If I richen the mixture screw to where it doesnt sputter, the rpm hangs a little high before it drops to idle.
Plugs very fouled.
Idle lowers when it warms up, dies when at a stop light.
The bike seems to sputter the worst right off of idle. 1/16 throttle-1/8th throttle.

Just out of curiosity, when you went to a free flowing muffler, was the adjustment to your carbs significant?

 

[webbrs]

Put the old mufflers back on and see how it runs? Sputters, does it pop? Did you just enrich the mix or try to lean it as well? Could you have loosened a ground wire causing intermittent firing? Open pipes should be lean but except for the hanging rpm sounds like you describe too rich.

 

[weaselbeak]

Unless he rejetted I have a hard time believing it got too rich with mixture screw adjustments on open pipes.

 

[Kathos]

Putting on the old ones isnt really an option due to I cut them off :/
The bike does not pop when it sputters. And the low rpm range is where Im feeling most of my issues.
Im going to take a stab at properly labeling each issue Im having rich or lean, and correct me if im wrong.

Sputters when I rev it. Lean
If I richen the mixture screw to where it doesnt sputter, the rpm hangs a little high before it drops to idle. Tuning manual says Rich, however seems to get worse the leaner I adjust the mixture screw
Plugs very fouled. Rich
Idle lowers when it warms up, dies when at a stop light. Rich or something else?
The bike seems to sputter the worst right off of idle. 1/16 throttle-1/8th throttle.
Pilot/Mixture screw adjustment

The bike seems to sputter worse the more I lean the mixture screw out so maybe its possible that my new exhaust made my pilot too lean but my jet needle should be put back to the middle slot?

Also, there are no baffles in my exhaust now so I have less backpressure. I assumed I could tune around this. Maybe the back pressure at idle is much less when compared to stock, and its affect is more noticeable then the mid-range.

 

[Tomterrific]

I believe the bad running is due to the idle jet getting some dirt. Pull the mixture screws and spray inside with carb cleaner. Use the little tube that came with the can.

Check to make sure the carbs are not leaking air. The stock carbs can blow off the manifold but look like they are still secure. Make sure any vacuum lines or plugs are not leaking air.
Your bike would run bad instantly if the pipes were totally to blame.

Tom

 

[webbrs]

That's bad news, if you can't go back to your baseline then your just guessing from here on out. What year is your motorcycle? Any other mods beside the pipes? Points? check your advance. As said, it would seem that if the pipes were to blame it would run bad from the start. Its something else that coincidentally showed up. As said, clean and sync carbs, check spark, check timing, check the throttle shaft seals and the carb manifolds. The fouling could be from a higher circuit like mid range or main and still be lean at idle. Or bad spark/ low voltage. The carb guide gives the best info on tuning as to where the clip should be and other diagnosysis. I deal with air jets so I don't mess with my needle.
Anti reversion cones are your only choice if the reversion thing is your problem but I am not sure if that explains away the rich condition you have, that you shouldn't have, with open pipes.
Do the simplest things first and go progressively deeper into the problem and only do a fix at a time and check your results. good luck.

 

[XSLeo]

Was your previous exhaust stock or something else?
Most times when you change the exhaust it makes more of a difference than intake changes. It sounds like you need to tune the carbs all over again.
I would start by cleaning the carbs. When you changed the exhaust you may have loosened some of the crud in the tank. This crud may have plugged up some of the carb passages and jets.
Leo

 

[Kathos]

Bike is a 79 special. I have a pamco ignition. New Ultimate coil. New E advancer. Chain, Valves, and timing checked one tank ago. Charging system is strong.
Pipes were stock. Chopped them under the foot peg and put my glasspacks there.
Is it possible that, on my way to work (with the richer needle position) I fouled the plug enough to run like crap? My plugs are really fouled, which would cause a weak spark. Maybe I should start with new plugs?
I agree my carbs need retuned. But Im getting mixed messages if Im running lean or rich.

 

[Kathos]

I put new plugs on gapped to .040. Took it for a ride. The idle is smooth and the midrange is strong but for some reason that 1/16-1/8 throttle is very jerky and poppy. Not backfiring but just inconsistency.
If I lean the mixture screw and rev the bike, the popping is worse.
Pulled the plugs from putting around the block and they are already getting dark (Rich?). I havent switched the pilot jet since the old exhaust and it would be very hard for me to believe that I need a leaner pilot.
I have 3 theories.
#1 I need to get a richer pilot jet. Coming from the bike is lean from the popping and jerking symptom.
#2 I need to get a leaner pilot jet. This seems unlikely but the hanging idle being listed as a rich symptom is making me consider this direction.
#3 I dont have enough back pressure at idle. Being that I cannot find a middle ground between the two, is it possible that I need more resistance in my exhaust?

 

[Kathos]

So, just an update.
I tried out two larger pilots on my xs650.
When I tried the 27.5, I noticed that the idle was better. I also noticed that the idle screw actually increased and decreased the idle. I was having a huge issue with the idle returning to normal after revving. It would just rev really high when I revved it. And Higher as I blipped the throttle more. I read up to learn this was a lean condition so I upped the jets again.
When I tried the 30's, the idle was very smooth. It was very easy to set idle and sync the carbs. When I held the throttle slightly open(while in neutral) I didnt get any of the crazy popping that I got before. I took it for a test ride around the block and I noticed Im still getting very jerky acceleration at low rpms. I didnt have time to play around with the mixture screws but I know both sides are 3/4 turns out. I also noticed that my idle still takes a second to come back to normal.
My next step is to play with the 30 pilot jets and the mixture screw. Something tells me I need to go another step richer (or two).
Does this even sound realistic? I went from a 25 pilot to possible a 32.5 or even 35 with a shorter blow through exhaust?

 

[Maurice]

How's WOT operation (main jets)? You need to start there or you'll have a hard time getting it tuned right. There's a number of overlapping effects for main/needle/pilot jets.

Read up on the carb FAQ. Bookmark it.

Applies to most carbs, really, whether mechanical slide or vacuum.

But yes, changing the exhaust will likely require jetting changes, especially if you went to a see-through glass pack from stock.

 

[Kathos]

Thanks Maurice, I refer to that manual (for the vm34) very often. Like the vm34 manual says, I prefer to start bottom up.
I havent taken it to wot since this issue came about. I can say that when I rode it before it starting acting up, I could tell the top end was lean. When I swapped out the pilots, I switched from a 180 main to a 190. I wanted to get the low throttle tuned in before I started going to the high end.

 

[Maurice]

You are right, that is interesting... Looks like you are on the right track.

Going to be some $$ in brass...

Good luck!

 

[nj1639]

Did you use the exhaust pipe reducer when putting the glass packs on or did you just clamp on to the cut off exhaust pipe with the glass packs ?

 

[scabber]

Have you synchronized the carbs since you changed the clip position. The black plugs and clip change and larger main jet most likely caused the problem.

 

[Kathos]

Yes, I sync the carbs everytime I change pilot jets and readjust the idle position.
Yes I used a reducer going from the stock pipes to the larger 1 3/4 muffler. The reducer was welded inside of the muffler and I used exhaust sealant on the stock side. The muffler also has its own bracket that I fabricated so it wouldnt shake around.

 

[nj1639]

Double walled stock header pipes?

 

[Kathos]

Yeah except mine looked like they had 3-4 walls. It wasn't simply a pipe inside of another pipe. I cut it right after the rear bracket before the mufflers.
The reducer fit over the smallest pipe.

 

[scabber]

The sparkplug gap is too big try .032 the rich condition and the .40 gap could be part of the problem. Cylinder pressure plays a part in if the arc will jump the gap.