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Discussion Starter #1
Hi, sorry I'm at wits end here. The details :

I cannot get the main circuit setup on the QBcarbon ramair box. I've gone from the 152.5 main in the jet kit to a 162.5 main jet and I cannot get a reading higher than .024 mv (even with the mixture screws 4 turns out. (Jerking and very high EG and engine temp means there's no sensor error.)

Why is it so lean ? Can a blocked passage in one carb cause this ?

I've just put the stock box back with the last known settings and it's fine !

What's going no here ?

What's the symptoms of an air leak and loosing pressure in the box - running rich ? I would think that this extermely lean condition might've been caused by a leak between the carms and the intake manifold, but the stock setup performance proved this not the case.

Any ideas ?
 

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Blue is best
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When you are referring to .024mv, do you have an on-board o2 sensor?
 

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Discussion Starter #3
Yes, a heated Bosch sensor and digital gauge, plus two EGT probes in #1 & #3 header pipe with same gauge.

It is suppose to make it dead easy to tune - and it was with the stock airbox.

I'm obviously missing something with the ramair setup, but what ?
 

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There is something wrong with your o2 sensor, it possibly may be fouled, check it out.

A quick setup for the qb box would be:

1) 150 - 152.5 mj
2) block main air correctors
3) use stock needles
4) mixture screws 3.5 turns out
5) run the float bowl and diaphram vents into the funnel on the dirty air side of the filter. This will create the proper pressure differential that the carbs require at speed.

Your Bosch sensor should give you approx. .900mv at full throttle for an a/f ratio of 13:1. This is the setup I have and it works perfectly.

Let us know how you make out.
 

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Discussion Starter #6
Thanks for the replies !

Yamaguy - according to the instructions the vents should not be rerouted if you're using a full aftermarket exhaust. I have full Akrapovic installed. Do you still want me to route them ?

martinc - I've used a foam weather strip to seal it and the silicone on the adapters. Wouldn't loss of pressure cause an extremely rich setup ?

I'm on to something at present and will let you know. I overtightened one of the mixture screws - turn it in all the way and then 3.5 turns out. The tip broke off and stayed in the fully turned in position, causing one carb to be extremely lean.

Although the FlowCommander is set closed, I suspect that the internal balancing mechanism then causes all carbs to get the same mixture - extremely lean.

I sure hope this is the answer !

Now all I have to do is get hold of the nice guys at Carbureter Warehouse and wait about 6 days for a replacement t arrive.
 

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Sandman said:
Thanks for the replies !

Yamaguy - according to the instructions the vents should not be rerouted if you're using a full aftermarket exhaust. I have full Akrapovic installed. Do you still want me to route them ?

The vents HAVE to be routed into the box or they will not pressurize properly at speed. There are 2 schools of thought on where to reroute them, but after studying stock ram air systems (like on a Kawasaki) I routed mine into the highest pressure point in the box ie. in front of the air filter, into the airstream if possible. Doing this ensures that the correct differential will remain in the system to cause the fuel to flow up out of the bowls at speed. If you dont do this, the bike will carburete very poorly if it runs at all. If the box pressurizes and the vents remain at atmospheric pressure, the fuel will not rise up the emulsion (needle) tube into the carb venturis at the correct rate resulting in a lean mixture.

This may expain why your o2 sensor read extremly lean when you were doing your test runs.
 

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Discussion Starter #9
Hi, I went back and read the instructions carefully and .......

There's two issues here - 1) Float Chamber Vent Tubes, and 2) Vacuum Slide Vents.

Attached are the scans of the instructions for these two parts. Although the Vacuum part is very explicit about the need to use it only for std or slip-on, there no such mention for the Float Chamber part !

I originally read it to apply to both sections, but now it does make sense and I'll try the Float Chambers first.

martinc, I followed your thread when you tested the routing of the vent tubes. In my case, I think I'll have to route at least the Float vents to prove or disprove this.

How do you seal the two tubes sticking up into the box ?
 

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I drilled the holes,that stuck round pieces of foam about 1 mm smaller than the tubes themselves to the box floor,than slide the tubes through them;they have to be stuck real well to keep the carbs from sucking them in!

Oh...use longer tubes......55mm is way too short.
have then stick out at least 3 inches over the carbs.
 

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Sandman, you can try routing the tubes into the box on the CLEAN air side of the filter first. The bike will run better than not routing them into the box at all. If the system is balanced, it will just require selecting the proper main jet and plugging the main air jets to get it to work. If you are still having trouble, route the vents into the funnel where they will "see" the most pressure. I believe that there is enough of a pressure drop across the air filter to cause the vents to "lag" slightly giving you a lean mixture.

This what I have discovered through testing. Again, if the system is balanced, all you have to do is select the main jet and plug the main air correctors. Keep this in mind.
 

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Discussion Starter #14
Hi, my mistake has become quite obvious and I will route the float bowl tubes, but I'll try and route them to the clean air side first. I'm not keen on letting them sit on the dirty side with all the dust and sand we're driving in.

I'll update later tonight.

Thanks for the help.
 

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Discussion Starter #15
Hi, firstly HAPPINESS :jump with the float bowl tubes on the clean side it now runs - hard.

Thanks for the replies and help !

I still have a lean condition that I need to get out though. Everything is perfect up to 6,000 RPM in top gear. If I accelerate from this point, it goes way lean and only recovers with the throttle full open.

What controls this area of the carbutation ? Needle and or float level ?

I suspect that the air/fuel ratio is fine, but the amount delivered at this point is too little hence these two areas.
 

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I still have a lean condition that I need to get out though. Everything is perfect up to 6,000 RPM in top gear. If I accelerate from this point, it goes way lean and only recovers with the throttle full open.

Are you sure you have a lean condition? You have an O2 sensor which will tell you whether you do or not. Lean would be anything under .900mv and rich would be over .920 (give or take). If it is lean you need to plug your main air correctors, this will richen the mixture through entire range. If you have already done this you can try raising your needles one notch (or 1/2) to start.
 
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