Custom Airbox

And have you ridden a well-tuned stock XJ before jetting for pods?
Dyno results say that pods are not as good as stock, but can be close enough that most people won't notice without making a timed run (or using a dyno).

 

83 XJ750 Maxim, UNI pods, 43/134, stock collector with aftermarket baffles, no mafflers. Factory hitachi carbs.

 

My XJ was well tuned and 100% stock prior to me modifying anything. Considering g that my bike is 105lbs lighter than stock, it’s difficult to compare acceleration wise. But drivability is as good as factory. Starts great, plugs look as should, no hesitation at any RPM, no dead spots, pulls very smooth from idle to redline, steady RPM at 1050.

 

The air box was off on my 650 so guess what im diving into. Granted the patterns are for front, back, top & bottom. The sides will pretty much fall in place.
Its pretty close to stock box dimensions. Only difference will be the use of a spectre 3" maf adapter which will accept any 3" air filter. Final product will be in sheet aluminum & tig welded.
As far as air flow, I'm guessing more than stock but less than pods.

 

Its getting there

 

The jet sizes are going to vary per application and its not that difficult to nail down which sizes to run especially since jets are so cheap. its the overall tuning of the carb which is key, jet sizes + color tuning + needle/plunger spring adjustments + float bowl level adjustment if necessary. I found on my end the float adjustment weren't needed but that doesn't mean Joe Schmoe wont need it.

Pavelk313's carb setup with 43 130 is a good baseline for his open exhaust setup. What i am interested in is if stock and pods are raced side by side on a quarter mile, will the lighter frame make up any difference on the lowend that pods might cause.

 

I have 134 mains. 130s were a bit too lean. Also, as you mentioned, I didn’t just throw new jets in new jets and everything was perfect. Had to do some tuning, once that was done, bike performs great. I would love to race a stock 750 to see where I am at acceleration wise.

 

That would be cool to do.
It would be interesting to test with different variables accounted for. Maybe three runs per rider on each bike (6 runs total) as-is, and three runs with some ballast on your bike to bring the weight to stock. That would give a good indication of what effect your carb setup has, what effect your weight reduction has, and what effect the rider has on 1/4 mile time.

 

That would be ideal, but not very likely to ever happen unless I buy another XJ. Lol
Plus, not sure how I would possibly add a 100+ LBS ballast to my bike.
I been wanting to take my bike to the track but I don’t thing necessary gear to run faster than 14s and I am confident that it should be faster than that.

 

I'm pretty sure I can pack 100 pounds of lead into a tankbag.

 

Downloaded an app today and tried doing 1/4 mile run.
What you know about that 8.1@32 mph Hahahaha

 

Might need calibrated a little

 

You could let me ride it!

 

Back in the 70's People ditched their airboxes for a single filter unit called a Breadbox. It used rubber extension stacks between the carbs and the filter box and worked great. Wasn't that pretty, but it worked and only required one filter to change over time.
Personally, I would ditch the carbs and buy 4 round slide carbs. Block off the YICS channel with a 3/8" steel rod.

 

Why get rid of carbs & YICS when everything work perfectly fine?

 

He has a different opinion. He's not wrong, but neither are you.
Choices, tradeoffs, opinions.

 

Well the reason was CV carbs are a big enough PITA to clean and sync for a stock setup. If you change the exhaust or air(Pods), then you get to go through finding the right jets to use and every time you sync these wonderful CV Carbs, you have to go through the 2 step system of blocking the YICS channel for 1st sync, then unblock for final sync.

The YICS was only used on these bikes and it does a great job, but the carbs, air intake and exhaust all have to be set up just right. If that channel has to be blocked just to start the sync process, you have to wonder if it really does as much beneficial application as it was intended and if all the trouble is truly worth it.

When I blocked mine off for my custom intake and round slide carb setup, I didn't miss it one bit. The system was easy peasy to set up and sync and it ran better and faster.

I don't get upset if people want to keep their bike original or mod it. Blocking that channel off permanently as I stated isn't exactly completely blocked. There's a tool for blocking the channel for the sync process that has rubber grommets on the shaft that completely seal the chambers for each piston, but those grommets have to be replaced after some time. if they were used all the time, the grommets would be completely destroyed in quick fashion.
What I did was to unscrew the bolt on one side of the channel, measure the hole's diameter(10mm) and put a 10mm diameter steel rod through to the other bolt and mark the length of the rod needed, I cut the rod to the desired length(I believe it was 18") put the rod in and screwed the bolt back into place. The rod doesn't completely block the channel for each cylinder, but it's enough to simplify the sync process. Over time, deposits will form around the rod in each cylinder area of exposure and permanently seal each cylinder for even better ease of sync and performance.

Gotta ask yourself, If it was such a great idea, Why was it only used on these bikes and only for so long? To my knowledge it was only used in the 80's on the XJ series. These engines were made great, just difficult to keep them running great(carbs), questionable YICS channel system and a terrible starting design(starter clutch that requires an entire engine tear down to fix or replace). Other than that, these are wonderful bikes.

 

+1 on jet sizes. I just finished a pvc tube using 2 90°'s and 2 T's. Cut to match distances between intake horns, hole saw on the opposite side and sanded straight and glued the 6 pieces cut off to give me about 4" . I put the extra stock fz8 muffler i had on it, jetted with 116s and 43s i ran for about 4 minutes and finally holding my choke on all the way doesn't make my engine rev high, I'm bench synced ready to do running synch valves in check compression was 148-151 all the way across. Have bpr7es so took out the resistor in the caps it's just been too cold to start this I'm afraid mid 30s will not give me a good tune, is that correct?

 

I know this thread died in Jan, but it can still be informative....and related to an exhaust thread.

Factory air boxes are serving 2 main purposes... Restrictor! and Filter. Mostly focusing on the first
That's why they vary in size and shape. It is simply when the manufacturer is designing the engine, they strive to achieve whats known as VE "volumetric Efficiency". I somewhat explained this in the exhaust thread already, but any ways.... different countries have different (smog) pollution and fuel economy restrictions, so they make air boxes to filter and restrict the (volume) of air allowed to enter the carbs.

Un restricted air flow allows a larger cyclone effect altering the ratio of air entering the CV cavity and overall carb venturi (Mouth). Unrestricted air flows such as pods allow the larger cyclone effect causing, more air, more fuel equaling rich conditions, and by effect altering the VE percentage. The airbox restriction, and exhaust diameter, exhaust length along with engine design and tuning dictate the end VE %. More air in requires more fuel = a larger fuel jet, larger exhaust need...

All countries and manufacturers strive for a VE of 100% which equates to a perfectly tuned and net zero smog rating. Thus a perfectly responsive, low consumption, and clean (no pollution) running engine. This is strived for, but does not exist....yet!

Average engine VE is approx. 70%. some newer engines can and have achieved a modern day VE of 85% and some diesel reaching a 90% with the introduction of fuel injection, catalytic converters, and VVT (variable valve timing), egr valves and turbos. I don't use the phrase lightly, as VE is what has been driving engine designers for decades now in their designs.

Any engine designed from the mid to late 70's to today was designed built and tuned to this vision of power to VE ratio with the two constantly conflicting the other.
So when you have a "stock" engine and you begin removing/replacing parts that were designed to improve the runability and work in unison, expect to see big changes..

Example: most notably the pod filter swap out usually not ending well for most.
mostly due to not having any understanding of the system they removed the part from. Other factors usually not considered are.. altitude, ambient temp, fuel octane to gear ratios to name a few.

So your airbox is to restrict, and clean the incoming air....nothing more altering the allowable volume has a chain reaction of required alterations all the way thorough the engine to the tip of the exhaust. there's a lot more factors and details, but you get the jest...