Got the new exhaust bolted up....buuuuuuut

[slownugly007]

I got my new pipes fitted up and my salvaged mid pipe welded in. The exhaust is a mac 4-1 header with a D&D can and mid pipe off an 89 cbr f3? I snubbed it to about 12 inches and the exhaust really turned out better than I expected, looks wise that is.....buuuuuuuut I cant get it to run? It will start up, barely, after a few tries and when it does it wont stay up for long and eventually dies out. My question is, would running such a free flowing and short exhaust cause problems? I know some people say you need to re-jet when switching to a 4-1, so would you think it needs a re-jet?

On a side note....this thing, when semi-started, sounds like a beast!!!!! If I can get it to run I think I will be very pleased with my junkyard/ebay exhaust system....so far the cost was $50 for used mac 4-1, $50 for thrashed D&D can (also got a bad ass race ready pencil holder from the section I cut off the muffler!!!??) , $15 for new gaskets and $40 for DEI titanium exhaust wrap, $6 for a 6 pack, plus a few hours in my garage. So for roughly $160 plus time, I got a "custom" exhaust! SCORE! Too bad it wont run!!!?? LOL

Sorry I didnt get any pics of the exhaust, I got on a roll last night and it didnt even register. Ill post them up when I get it all done along with a video of the hell roaring sound

Race ready, super light, bad ass pencil holder!!!!

[LukeM]

Hmm...
Too much back pressure will make for hard starting and engine dying.  If it was running well before the exhaust swap, then I suspect something with the new stuff.  How long will it run before it dies?

If the muffler is plugged, the engine may start, but it won't rev very well, and may load up the engine with excess fuel and flood it out.  The more it's plugged, the worse it'll run. Try running it without the muffler. (If you liked it before, you'll probably love it with straight pipes.)

Assuming the new exhaust is good, with the flow opening up, you'll have less back pressure in the engine.  Some would recommend going a bit richer on the carb mixture, and/or going to 1 step larger jets.

I'm sure others will chime in with suggestions.  I hope this helps.
Luke M

[slownugly007]

Thanks for the response Luke! The flow is great in the exhaust, its basically a glasspack muffler. So its a straight pipe with a mesh resonator and fiberglass mat wrapped around it. I was thinking that since theres no baffles or restrictions, it isnt producing enough or any back pressure. Not exactly sure what that means or what it means I need to do to adjust it? For example...more fuel, less fuel, different jets? This is completely uncharted territory for me, Ive messed with car exhausts some but never bikes so I definitely could use some guidance. Would running a K&N air  filter plus the non restricted exhaust cause trouble? Causing the air/fuel ratio to be off or out of whack? Thanks guys!

[Lucky 1]

You need to tell us all the facts.

Year of bike?
750??

Type of intake? Pods?

Main jet size?
idle jet size?
Slide needle position counting from the top.
Mixture screw -turns open?

A photo would be nice.
When you say it will not run do you mean IDLE???
Need to be specific.

[slownugly007]

1981 CB750F SS, stock air box with K&N filter, main jet-unknown (stock?), idle jet-unknown (stock?), the carb adjustments not sure either. I havent torn into the carbs yet.

When it gets started after a few tries it struggles to idle and will eventually die out. When starting it, it will chug a little as if it wants to fire up but it wont fire up until after a couple tries and messing with the choke and throttle.