FZR carb conversion

[Walt_M.]

I've never tried the beads. I just got my rear Conti on and balanced yesterday,  took about 40 grams of lead which is about twice what I expected. Do you balance the wheel then add at least that much in beads? Got my old front off but ran out of steam before I got the wheel cleaned up. Tomorrow is another day.

[Walt_M.]

Got the wheel cleaned up and the tire on but it wore me out. Now if the bead will just seat. Monday update, got the tires balanced and the wheels on. Took my test ride and it is good. The handling is much better. It is still running good but with the new tires I was giving it a bit more throttle and I think I need a bit more adjustment. If it isn't the throttle it could be the main jets. I'll have to look at the plugs. Some have suggested it might be a bit rich and I may have to agree as the temperature gauge never got over halfway and it is a warm day.

[Walt_M.]

Found the throttle problem, there is a part of the FZ interconnect that I left on the rear of the rear carb. I left it because I needed the spacer on the throttle shaft and I didn't see it hitting the frame brace. I will be cutting the ear off that and putting it back. The plugs may be a little sooty but I am not changing the jetting yet. I still want 50 pilots so back to jetsrus and I might get some leaner mains too.

[fret not]

Each step is a step closer to the destination.  By the way, how is your knee ?  You must be a pretty tough person to continue wrestling with tires and carburetors with a healing knee.

[Walt_M.]

I wish the knee was coming along as well as the bike. They fixed the main problem which was a torn meniscus. Part of it was getting pinched when I took a step, made me want to fall down and pee. But that doesn't happen any more. I just want it to get better than it is now.

[Kenny]

  Hi Walt,
  You were asking about the weight of or number of beads required to balance your tires , I don't have the paperwork from  the setup I used but I remember a chart that recommended the required amount according to the size of the tire. I believe their web site also has this information. A large truck tire would require more beads to do the balancing than a motorcycle tire assy.
     Cheers Ken S. 
.

[Walt_M.]

I got it back together this afternoon. Have the choke cable connected and the pod filters in the stock air box, still no flapper. It is much easier to start with the remote choke. I was going to try it without the fuel pump but that will come later. I have realized that although I really like the pump, since fuel doesn't flow if it isn't running, if the pump quits the bike stops. That could be very inconvenient, especially in traffic.

[fret not]

Walt, are your float bowls lower than the original ones?  If they are maybe gravity will suffice, but if they are the same height or higher you will need a pump. 

I am planning on using a 12V fuel pump because my 'new' float bowls will be a bit higher than the ones in the original carbs.  Just plain old Gravity would be sooo much easier.

[Walt_M.]

Yes, the float bowls are below the bottom of the tank. You can sort of see it in the photos on post 57.

[Rikugun]

Regarding eliminating the electric fuel pump - if it will work without it I'd say go for it. Simplicity and reliability often go hand in hand. Good to hear you got the remote choke connected. Having owned bikes without that feature I think I prefer to have it on the bars.

[Walt_M.]

If I were doing this mod and did not already have a pump, I would not get one. However as I had it and it works I decided to go ahead and wire it in. I let my bikes set too long between rides and it makes it a hell of a lot easier to start. If the pump fails out on the road I can connect the fuel line around it and ride on.

[fret not]

Walt, you are an inspiration to us all, and thank you for that.

I have not put my tank on in comparison to the position of the carbs yet to see if they are lower than the petcock.  If I can avoid it I will not use a pump, but Reality being what it is, I will take cues from what I see as my 'system' 'falls into place'.

The carbs I have are from a '01 YZF600R Thundercat.  In the Haines manual it is stated that Yamaha went to another induction system because of the expensive carbs on the YZF600R.  So, I don't know if they are better than others or just more expensive.  In the final analysis it is the function, not the cost of carburetors.  Maybe.

[Walt_M.]

I just got back from a very unsatisfactory test ride. I don't think it likes the pod filters. It just seemed to flatten out at 5K. Also had it die on me at the last stop sign before home, had a YICS hose pop off the rear cylinder. Guess I'll have to start clamping them. I haven't looked at the plugs yet but the exhaust pipes are noticeably black. I got 127.5 mains so I am going to try them next but I suspect that may not be enough. I will get it but it just takes time.

[fret not]

Smooth 'laminar' air flow is important for the intake.  I recall Treedragon stating he got better power when he lengthened the stock inlet "horns" on the carbs.  The carbs I have came with fairly long plastic "horns"(factory issue) to smooth the air flow. 

The factories have gone to significant lengths to develop air boxes for the intake.  Pod filters have not been recommended for the stock carbs because of lesser performance,  so maybe I see a correlation  between pods and your new carbs.  The pods keep debris from entering the carbs but don't seem to help smooth the air flow.

I ordered some mild steel mandrel bends to make 'manifolds' for my 'new' carbs.  I will be making a file of pics to document the process, and will try to put it all together in another thread when it happens.

[Walt_M.]

Mike, you are probably right about the air flow and I will go back to the stock filter and air horns. I just need to get it sealed better than I had it. Probably go to the 127.5 mains as I did think it was rich last time. I will keep posting. 

[Prophet Of Doom]

The XZ400 comes with two different length velocity stack - about an inch longer and a bit curved on the front.  Generally speaking longer gives better low down power, shorter, up top I've read, so perhaps an attempt at getting both?  The XZ does something similar with valve cams also with different on front and rear.


There are calculators on the web about how long to make velocity stacks for a given RPM and carb diameter. 



Given that RPM changes all the time I was musing a while back about the idea of building a servo driven velocity stack for the XZ that would always be the optimum length.  The R1 does this I think.

[Walt_M.]

Got my test ride in this morning and it is a lot better but now it is rich down low. I had it to 8K which is actually fast enough for the street but it is sluggish below 4K. I think I will go back to the 60 starter jet as I am not exactly sure where it comes into play. The needle jet is not notched but it does have a washer under it so I might drop the needle too. And,  Mike, FWIW, you might want to just try the stock FZR jetting in your Keihins first. It might be pretty close. I am starting to get some money invested in jets that I may never need. At $7.50 apiece it adds up.

[ChrisV]

Sounds like you might want to do a couple of these.
http://www.ebay.com/itm/like/262404550401?lpid=82&chn=ps&ul_noapp=true
some of the smallest ones could be drilled out to larger than 125 if needed,
Just an idea

[fret not]

Chris, generally it is not a good idea to drill jets unless you are in a tight spot and it is the only way out.  Jets are very carefully machined so they have no burrs or irregular surfaces to disturb their ability to flow fluids.  Even pushing a wire through a jet can scratch it and change it's flow rate.  Now, since Walt is a machinist I am sure he is aware of this and may well be able to manage altering jets, but then they need to be marked as to their new capacity.  Tiny jets are rather difficult to read the numbers let alone re-marking them to another value.  It's better to have factory marked jets so you can make informed adjustments.

Getting old kinda sucks sometimes.

Walt, I had figured to start with factory jetting, hoping it will be close, but I know that changes may well be required.

My mandrel bends arrived today, so cutting and fitting will soon begin.  But before that I will be helping my brother get his slat flats bike prepared to run Sept. 10 - 13. (Suzuki T500 Partial Streamlined/ Fuel)

[Rikugun]

I agree with all the warnings regarding jet drilling but have gone ahead and done it anyway on more than one occasion with good results. Jets can be quite pricey and it's unlikely you'll have every size and style available so drilling can be a viable option and sometimes necessary in a practical real world sense.

Jets I've drilled are kept in a separate plastic bin since I don't try to mark them. Prior to drilling I use the drills as go/no-go gages to establish a baseline size. You can use the same technique on unmolested jets of different sizes to then compare against drilled ones to roughly gage it's size.

One of the pitfalls is drilling too much. The first time this happened I soldered the jet closed and redrilled. This was admittedly an act of desperation as I was stuck with no immediate options but it worked very well. I employed this technique again this past winter on my snow thrower. I foolishly tried to jet a problem away that I sensed had nothing to do with carburation. Since I had gaged the sizes prior to drilling I was able to return them nearly to their factory state after fixing the real problem. I say "nearly" because it has fixed jets and always ran a bit lean. Well it doesn't anymore and now runs better than it ever has. Don't tell the EPA.