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Discussion Starter · #1 ·
Hi , I in the process of building an RC162 tribute bike using an cbr250r mc19 motor, and I would like to find out the carburettor modifications to run with 4 into 4 straight through pipes and open filters .... many thanks Andy.
 

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No need to change any carb-specs for straight-pipes. Stock filtre doesn't pose any restriction, so going with open-filtre won't change flow-rates. Common mods for more power on race-bikes with mods is to lean out mixtures using smaller main-jets.
 

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Discussion Starter · #3 ·
No need to change any carb-specs for straight-pipes. Stock filtre doesn't pose any restriction, so going with open-filtre won't change flow-rates. Common mods for more power on race-bikes with mods is to lean out mixtures using smaller main-jets.
Hi , thanks for reply... I've heard of people drilling a small hole in carb slide and trimming/cutting down the slide spring and also some jet size changes ? I believe there is a member on this site that has built an RC 162 replica/tribute on this site who has made similar carburettor modifications,many thanks for reply Andy.
 

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No, those mods are to richen up mixtures to make up for clogged and dirty carbs. Best to start with fully restored factory-fresh carbs 1st. Then tune from there. Bike is already super-rich from factory and all mods are focused on how much you can lean it out without blowing up engine. Remember that '60s hot-rod motto?

Best way to tune is gathering objective data on AFR. Such as dyno-tuning.

More tools than ever exists for DYI folks. Best is datalogging wideband O2-sensor kit. Records RPM, speed, AFR, TPS if you've installed one. Allows you to analyse specific load & RPM zones for modofication. You'll find that they'll be areas that's too lean (mid-range) and others that's way, way too rich (high-RPM WOT). I've gotten +10% more power simply by leaning out high-RPM/WOT mixtures. Heck, Dave Moss is getting 58-rwhp from his MC22 and he's using smaller-than-factory jets.

Here's link to best datalogging wideband sensor on market. Fully digital on all interfaces. Many of them, such as Innovate, drives their gauge with analogue output-voltage signal. This causes variations in displayed AFR depending upon reference battery voltage. Nice thing about datalogging is you don't have to be staring at tiny 48mm gauge while going down road at WOT and watching out for traffic and constables. Just do your runs, then download to PC and draw pretty graphs for analysis later.

TechEdge sensors.
 

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Discussion Starter · #5 ·
Thanks for all the info ,I won't be racing the bike when finished it will be road legal so I'm just looking to have it set up so it runs /pulls clean through the rev range , but I wouldn't have thought to lean out main jet sizes so certainly some valuable information as a starting point many thanks Andy.
 
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