kerker 4into 1 exhaust

i scored a clean kerker 4 in to 1 exhaust for my 1982 yamaha maxim 750. i installed the exhaust and it sounds awesome, my only issue is the bike needs jetted. i have the stock jets and do not want to buy a dynojet kit for $70 dollars. i am at sea level and i am thinking the pilots should go up from 40 to 44 and the main jets should go up from 120 to 124. i have the color tune to guide me,i just want to take the carbs off one time if possible. i know it is lean in the mid and upper when i let off after running higher rpm it backfires, not too bad though, also it is not as crisp when doing a normal takeoff from a dead stop. also i do not know about raising the needle with shims or what needle size shim the 750 carb needle uses thanks bruce. also how much is a clean used stock exhaust system worth?

 

kerker exhaust can be adjusted with packing and discs I belive.

what is the color tune showing you?
if you read the color tune instructions it says you can briefly test motor at higher rpms.

each step in jet changes will cost you about 20$ per set.

what comes with the dyno kit?
another member just got a kit with several sets of jets it may be the cheapest way to go

 

i will have to look in to this. i had a supertrapp that had disc added or subtracted thanks

 

if you read this link it will tell you how to guess wha you need
http://xjbikes.wikidot.com/carb-specs

Typical Exhaust Changes:

+2 main fuel jet size for custom 4-into-2 exhaust

or

+4 main fuel jet sizes for 4-into-1 exhaust

but when you get to the bottom of the instructions

Normally, changing to an aftermarket exhaust does NOT require re-jetting, (or minimal re-jetting) as almost ALL of the airflow restriction in the airflow path thru the engine (meaning: ATMOSPHERE > AIRBOX > FILTER > AIRBOX BOOTS > CARBS > INTAKE MANIFOLDS > CYLINDER HEAD PASSAGES > EXHAUST SYSTEM > BACK OUT INTO THE ATMOSPHERE) is within the intake side of this air flow path, and primarily within the stock airbox/air filter. Your stock EXHAUST system can already flow more air volume than the stock INTAKE system allows.

Thus changing only the stock EXHAUST system, with no changes to the intake side of the heads, normally makes NO DIFFERENCE IN TOTAL AIRFLOW, and "no difference in total airflow" means "no difference in TOTAL FUEL FLOW" either, and thus bigger jets are not needed.

could be you just have a tuning issue

 

the bike was running perfect with the stock exhaust, i recently purchased the bike and bought the color tune and syncd carbs adjusted valves and color tuned bike. it runs like new the exhaust has changed the way it runs backfiring after letting off the throttle proves it is lean

 

it is an inexact thing.
drives me crazy because it should be straight forward. to many variables for it to be that easy.

have you re color tuned and synced with new exhaust?

 

HaHaHa (sorry)
120 to 124 is massive, I'd try 122. 40 to 41 would work, the pipes don't matter much at that low RPM.
shimming the needle doesn't really change the mixture only the timing of the transition from pilot to main
stock type air filter?

 

i have not color tuned the bike since i changed the pipe. i did not think 120 to 124 would be so massive. i do have some 122 main jets but the pilot i have are 43 but my low speed adjustment screws are open quite a bit to make it run correct and get the correct color. i might just install my stock exhaust it runs so crisp and quiet with that pipe

 

If you’re only lean on decel you might be able to adjust the pilot mixture rich enough and not need any jets.

 

+1
I went from 40 to 42 pilot jets and after sync and colortune my bike doesnt pop hardly at all on decel anymore. They could probably stand being opened another dimes width, which I'll do when I'm not riding it and remember to do so.

 

i will try just the pilots first.