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Wrong mixture after replacing mufflers v65?

Discussion in 'Small Block' started by Auris, Aug 17, 2016.

  1. Auris

    Auris Tuned and Synch'ed

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    Recently I replaced my old mufflers for a set of used stock v65 SP (my bike is not SP) mufflers, which look almost the same only 2 cm shorter. I went for a ride they felt great. But after the engine warmed up it started hesitating when accelerating. It would idle ok, but as soon as I pull the throttle there is a sudden dip, once it passes a certain range the rev catch up. Since then I did almost 300 km with the new mufflers on and now even starting is difficult. I tried adjusting the mixture screw, previously it was just half a turn out, now around 1.5 turns out and seems to have helped a bit, but not good enough. The mufflers are quite loud so perhaps there is an an air leak.

    The spark plugs are black and I spotted black stuff coming out of the mufflers. The previous mufflers were black so I may have not noticed that before. Am I running too rich or too lean? Or is it a coincidence and something else is wrong? I've always suspected the breathing circuit was not a 100%.

    IMG_6462.JPG IMG_6514.JPG
     
  2. john zibell

    john zibell Moderator Staff Member GT di Razza Pura

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    You are running very rich. You need to lean that bike out. Also if the pipes are loud, the internals may be shot reducing back pressure. That will change the flow of your mix through the engine. . Have any intake mods been performed? Also if you open the throttle to quickly, the engine will bog down until air velocity increases improving the mix. I've found the slower you move your right had on a carb bike, the better it performs.
     
  3. Hawghauler

    Hawghauler Cruisin' Guzzisti

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    Sometimes when I run into performance issues, I go back to basics and check all adjustments. Timing, fuel mixture, valve lash, spark (be it points or electronic), check and replace air and fuel filters if need be, adjust or service carbs. As John mentioned, back pressure is a critical component of the system, but it doesn't hurt or take long to check everything. Sometimes issues are coincidental to other actions you have taken. Sure sounds like you are running rich. If all else fails, try the original mufflers again and see if it runs right.
     
  4. Auris

    Auris Tuned and Synch'ed

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    John, what do you mean by "internals may be shot? This weekend I will try to seal the pipes better, maybe that will help. There are no intake modifications. The airfilter is stock and the carbs too. As for what Hawghauler mentioned, the air filter, fuel filter, spark plugs were all replaced a few months ago - right before my trip to spain (3000 km), carbs had a bath and were reassembled using new o-rings. On the other hand I drove through raind and dust, etc. I will check the state of airfilter and fuel filter. I don't know yet how to adjust timing and valves, will have to learn I suppose...
     
  5. john zibell

    john zibell Moderator Staff Member GT di Razza Pura

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    What I mean about the internals of the muffler is they may have failed/come apart/ been removed/ drilled out. I have this suspicion since you said the bike was louder.
     
  6. Auris

    Auris Tuned and Synch'ed

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    Here is an update. Took the mufflers off again and put them back on, but this time used some Permatex super copper silicone to make a better seal. Replaced the spark plugs, replaced the o-ring of the idle speed screw on the left carb (looked very worn). Now the bike runs smooth. Although something strange happened while tuning the mixture of the right carb. Turned the screw all the way in but that side didn't stall, took the spark plug from the other side to test if the right side still runs and it did, with the mixture screw all they way in. I found it to run the best at only half a turn out. Isn't that strange? Couldn't that mean that perhaps the starter circuit is not closing well and therefore providing enough fuel even when the mixture screw is in?
     
  7. john zibell

    john zibell Moderator Staff Member GT di Razza Pura

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    The mix screw meters fuel, not air on these carburetors. Not uncommon to observe this with a DelO'rto, but it just means something is a bit off with the carb channels or pilot jet. The main thing is just to get her running correctly.
     

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