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went to straight pipes need help with jetting

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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Here's the story. I cut off the mufflers a few weeks ago and recently welded some straight pipes on. Everything was hunky dory....... for a while. One morning on the way to work it started dying cylinder by cylinder and then shut off. It started right back up again a few minutes later then. I have always had a lot of power of the start and especially in the midrange. The performance even improved when I cut the mufflers off. But after that morning it shut down, I took the carbs off and cleaned them when I put them back on, now I have a mule. There was no power off the start and it hesitated around 5k rpms. Today I took the carbs back off and went from a size 115 jet up to a 125. It runs better but still not good. No hesitation around 5k rpms but still less power and top end. I didn't adjust the float height because I can't get the stinkin pin out for the life of me. I'm considering going up to a 135. I'm still running with the stock airbox on but like I said, I went from the stock mufflers to running straight pipes. I changed the plugs so its a little hard to tell if its running lean, but the heads do look a little pale still. Any suggestions??? I will go to hell and back trying to fix this before I go back to the stock mufflers. I've tasted heaven with these pipes and now I just can't part.
 
What bike? If you have CV carbs you'll need to buy a jet kit. Swapping mains isn't going to do much to straighten out anything other than wide open throttle.
 
mkrohn151 said:
sorry, I have a 1980 GS850GL
Click to expand...

Which is a CV bike...

The main jet & needle control the higher-end performance

Pilot jet controls the lower end...

best to look at K&N or Dynojet (sp?) for a kit... Stage 1, maybe?

Also, you should do something (like a high-flow (K&N or Uni) stock-replacement air filter on the intake side... Airflow mods (or sound mods that increase airflow) should be balanced -> improve airflow on intake and exhaust at the same time...
 
Found this useful info.

"So, straight pipes don't require jetting changes, right? Actually, they usually do. See it's a trick
question. By not providing good cylinder scavenging, at least as good as the stock system, a
couple of things happen. First, more exhaust mixture may remain in the cylinder, diluting the
fresh charge for the next intake cycle. This may also mean that less fresh charge will enter the
engine because we've effectively cut down on its ability to flow air. So now we open the throttle
further in an effort to get some of our power back. But we're not providing as much signal to the
main jet. What this all means is we often end up having to rejet the carburetor(s), usually richer,
to get some of our power and driveability back. Gas mileage usually suffers as well. The
motorcycle may sound like it's fast, but put it on a dynamometer and there may be little to no
gain in power over a good stock system. This is in spite of the stock system's more restrictive
mufflers."

Dm of mD
 
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