Jetting for an exhaust change.

[ajk511]

Hey guys,

So I had my carbs rebuilt back in may due to a sticking float causing fuel to dump out of my left carbs air pod. Ran great for 1k miles and then started dumping fuel again this morning. I've decided to try my own hand at cracking them open this time, and I figured this would be the perfect time to re-jet for the exhaust change I just made. About 400 miles ago I ended up cutting off the stock mufflers and replacing them with a pair of shorty mufflers from Dime City. Just curious if someone has ever run a similar set up and can give me an idea of what jetting size I should be starting off with, and anything else you'd recommend I change around. 1985 GS450L with K&N pods, stock exhaust cut where the stock mufflers go with 12" Shorty Mufflers installed. No other engine related modifications to the bike.


Also, Dime City has a ton of Mikuni VM carbs. Is it worth it to swap the stock 450 carbs for Mikuni VMs? If I did, what size would be appropriate for a 450?

 

[Rob S.]

They may not require rejetting. Dynojet always says the deciding factor is the intake, not the exhaust.

 

[ajk511]

The bike did run pretty awesome with the current set up until the left float started sticking again.

 

[posplayr]

You should at least start with looking at the plugs. Plug chops are very popular as the alternatives are more expensive. If you have K&N pods I'm guessing someone already changed the jetting. The exhaust changes (muffler swap) is not likely to make as much change as was already(should have been) done for the pods.

 

[ajk511]

You should at least start with looking at the plugs. Plug chops are very popular as the alternatives are more expensive. If you have K&N pods I'm guessing someone already changed the jetting. The exhaust changes (muffler swap) is not likely to make as much change as was already(should have been) done for the pods.

It has brand new plugs and I confirmed with the guy who rebuilt my carbs in May that he did everything to factory spec.

 

[60ratrod]

Sounds like some stuff is flowing past the petcock sock. Do you have an inline fuel filter?

 

[smcneish]

Sorry to hijack the thread but I recognized a opportunity to learn something. What are plug chops?

 

[rwnielsen]

Run wide open for a couple seconds, pull the clutch and shut off the engine. Pull over, stop, and check the plugs. It's a way of checking the mixture/jetting. The bigger the bike the more room you need. Be careful, the police are not, typically, understanding

 

[78550GS]

Sorry to hijack the thread but I recognized a opportunity to learn something. What are plug chops?

Do a search and you will find MANY answers to that very question.

 

[JJ]

Run wide open for a couple seconds, pull the clutch and shut off the engine. Pull over, stop, and check the plugs. It's a way of checking the mixture/jetting. The bigger the bike the more room you need. Be careful, the police are not, typically, understanding

Ummmm.... a couple of seconds ain't gonna' cut it. I would say a minimum of thirty seconds (which will cover 1/2 mile at 60MPH). You don't have to be in highest gear, WOT in second is good enough.

 

[ajk511]

Sorry to hijack the thread but I recognized a opportunity to learn something. What are plug chops?

https://www.youtube.com/watch?v=hF3tGEFQ1ZA
Confused me too when he first said it. This video was extremely helpful.

 

[ajk511]

Sounds like some stuff is flowing past the petcock sock. Do you have an inline fuel filter?

Yup. Brand new in May when the carbs were re-done. When this happened before the guy who did my carbs found the float in the left carb was actually cracked.I'm curious to see what's causing it this time. I think I've read somewhere that it's possible for the floats to catch on the bowl gasket? We'll see once I get them apart.

 

[huntb]

Ummmm.... a couple of seconds ain't gonna' cut it. I would say a minimum of thirty seconds (which will cover 1/2 mile at 60MPH). You don't have to be in highest gear, WOT in second is good enough.

How would one keep WOT in second gear for 30 seconds?

 

[60ratrod]

How would one keep WOT in second gear for 30 seconds?

you just have to keep the throttle pinned all the way open is all. that's why they're recommending 2nd gear. 2nd gear should get you at least 60-70mph.

 

[rwnielsen]

you just have to keep the throttle pinned all the way open is all. that's why they're recommending 2nd gear. 2nd gear should get you at least 60-70mph.

That would be worth watching

 

[60ratrod]

It would be the only way to maintain WOT without excessive speed. And what I mean by pinned is keeping the throttle all the way with your hand, no actual pins required

 

[rwnielsen]

It would be the only way to maintain WOT without excessive speed. And what I mean by pinned is keeping the throttle all the way with your hand, no actual pins required

And in doing this, do you have a rev limiter? or just rely on valve float?

 

[rudeman]

you just have to keep the throttle pinned all the way open is all. that's why they're recommending 2nd gear. 2nd gear should get you at least 60-70mph.

You don't think it would peg the tach?! If you can get remotely close to redline in top gear you surely would be able to significantly exceed redline in 2nd or 3rd. To hold it there for 30 seconds? With luck you might make it to 5 maybe 10 seconds before the engine begins to disintegrate.