Topic: wait to put on muffler before messing w/ carbs?

[1974blaze]

so i put a 4-1 on (replacing a 4-2) and have not fitted a muffler yet.  possibly unrelated, but it now is hard starting and needs WOT to fire up.  should i wait to put on the muffler (already purchased rev cove shorty) before removing carbs for cleaning?

[WarwickE36]

Hard to tell from your post if the bike was running (or running well) before the exhaust change.  But, I would fit the muffler before tweaking the carbs.  Exhaust will have a big affect on the running of the bike.  Eliminate all the variable I.e. exhaust and intake 3,000 mile tune up etc.. before tuning the carbs.  That being said, if the carbs are dirty/varnished they will certainly need to be freshened up thoroughly before the bike will run properly.

[1974blaze]

yeah makes sense thanks.  fyi, running perfect before.

[Patrick]

If yu think your carbs need cleaning then this is the time to do it. You probably are not planning to ride the bike without a muffler anyway, so you'll have time to mess with them. Have you ever cleaned carbs?

Patrick

[grcamna2]

If you have more a more free flowing exhaust you may need to richen up your main jets some.

[1974blaze]

i have cleaned singles a bunch, on my 78 125s.  this is just 4 times as big i assume?  same otherwise? (75 750f)

worth mentioning i'm in CO at 5k ft elevation, so air is thin.

[Patrick]

The innards of the carbs will be about the same, but you will need to synchronize them. First a bench synch and then a vacuum synhc on the bike. Unlike a dirt bike, you've got to make all four carbs work together. It's not hard.

Patrick

[Ernest T]

Doesn't matter if your muffler was free flowing or not, removing it will change the flow of exhaust gas out of the system.  That will change the way the system fills and empties the combustion chamber which naturally will affect the way it runs.  Put the exhaust the way you are going to use it before messing with the carbs.

[1974blaze]

good stuff guys thanks.

[Ernest T]

Here's some of the science behind the design of an exhaust.  I don't think English was the author's first language but its a good explanation.

"During each cycle of combustion, gas flow in the exhaust produced a wave of high pressure. It is logical to assume that a wave of high pressure should also produce a wave of low pressure. At some point in the exhaust system, which is determined by the designers, some of the waves collide.  When the high-pressure wave leaves the tube, the wave of low pressure that follows it, is reflected back. A wave of low pressure promotes filling of the combustion chamber with fresh fuel mixture. Then the reflected wave of high pressure prevents leakage of the fresh mixture through the exhaust pipe. Next wave of her low-pressure scavenge the combustion chamber. The process is repeated, the bike is breathing evenly and well.

The length of each pipe exhaust system carefully calculated to pressure pulses were required to point at a given time. Properly executed release plays a crucial role in engine performance."

When you shorten the system, the pressure waves are no longer working to fill the combustion chamber the same way they were before.

[Ernest T]

Here's a link with a better explnation.  It won't lt me copy the text.

http://www.motorcycleproject.com/motorcycle/text/exhausts1.html

Read the section on exhaust wave tuning and you'll understqnd why length is probably more important than restriction.

[Rgconner]

Here is another reason:

Your neighbors might still talk to you if you have mufflers on the bike when you run it.

[1974blaze]

hell i don't even like being on it when its this loud.

i will read the article above tomorrow thanks.