Project 3LN1 Restoration

OK, so a nice mix of bits you you have there, give praise to the previous owner and their complete lack of attention to the essential details - given that they are 3LN3/ carbs, IF the internal (not visible) jets have been changed for equivalent 3LN3/5 bits - then aim for 3LN3/5 carb settings all through, you already have 3LN3/5 starter jets

Check this page

https://www.2fiftycc.com/index.php?...8-26mm-carb-settings-specs-3ln-3yx-zeal.9787/

You want to see if you have the correct pilot air jet - check it's # and check for the correct pilot jet, check it's # AND type bleed or non bleed

Definitely 97.5 in the centre - and choose which of the outers gets 100 and 102.5 by flipping a coin - you will need another #100

You bend the small metal tang, the other piece you see there is on the back of the rubber needle to keep it from falling out when trying to assemble that lot - use the needle through the hole trick which @my67xr suggested.

You are aiming for a float height of 14.7-14.9mm which will yield a 10.5mm fuel height

Yes, it's normally quite a large flat blade so that it fits snug in the slot and gives you adequate torque and doesn't mangle the slot in the jet as an added bonus.

I would leave the jet housings in place for now as unless the emulsion tubes are visibly worn, which is rare, but not impossible, it's very difficult to detect by eye...

If you however have the irresistible urge to remove them, the housings don't come off by twisting - there's a locating dimple, so the emulsion tubes have to be pushed in and the jet housing slid off - some may slide off easily, others - stubborn AND if when you remove them, some of the slide housings may lift, not an issue, however when you reinstall the slide housings, you push the slide housing down and tighten the hollowed nut on the end, you don't tighten the hollowed nut to pull the slide housing into place - the nuts are fragile and break very easily.

We should also check your jet needles, but get the above part sorted first.

 

Ok so a couple of points to clarify.

Regarding the fuel level, the main reason I gave up on attempting the float height measurement in the first place was that due to the angle that the carb has to be placed at for correct measurement, I found that it was extremely difficult to get the float needle to make contact with the valve seat and keep it there.

For a correct measurement to be taken the valve must be seated and the spring just on the cusp of being compressed.

I found that due to the inverted angle, the needle tended to slide down the tube in the float making correct measurement extremely difficult. It became almost a three handed operation. At the time I found it difficult to describe in words so made a short video of the problem (see link underneath).

https://drive.google.com/open?id=0B-6LVdXzRTTGcTNmQVNnZmN0b1U


Some people have the knack for it, I know @my67xr swears by it, and he has a real good feel for it, but I just couldn't get it to work for me.

As an aside, and I'm just thinking out loud here, but from working with vertical carbs on my current project (1976 Yamaha XS650) the float height is an absolute breeze to set on these, literally turn the carbs upside down take the weight off the valve, and measure the height with a ruler.



So would it be feasable to get the float height measurements from a bike that has already had the fuel level correctly set, and then place the carb upside down on the diaphragm caps and measure what the float height is from there?? Just thinking in my head but could this be an easier way to do it?? and it would at least get you in the ball park anyway.

I do think that my way of doing it has some merit, in that it ensures a correct level with fuel in the bowls and with the needle valves under fuel pump pressure. If you're still having carb problems after that, then there can be no doubt about either the level of the fuel or the integrity of the float valves so it can rule some stuff out when troubleshooting.

I will concede that it is more time consuming to do, the constant filling and draining of all 4 carbs was annoying (though having 4 tubes and an empty cola bottle helps).

 

One more thing. If it was me, I absolutely would remove the jet blocks. The reason being when I first got my bike it had was fitted with what appeared to be 3ln-3 carbs but it actually had one of the outer carbs replaced with an entire 3ln-1 carb body!! Seeing your 102 jet in there is bringing back some awful memories and removing the jet block is the easiest way to know.

Definitely remove all the jets first and ensure you have what you're supposed to have. And remember to be EXTREMELY careful undoing that 6mm nut that holds on the jet block. Give it moderate force and if it doesnt move, spray it, put the socket over it and gently tap it with a hammer and add heat but whatever you do.......... DONT force it, it's incredibly easy to strip.

 

OK @beano - now I can why you were having difficulties measuring float height

Check this post
https://2fiftycc.com/index.php?threads/my-fizzer.872/page-32#post-15537

Those carbs are off of the bike, and inverted, sitting on the diaphragm covers and held in place at that angle so that the float is dangling and the needle slides into the seat easily

This was why I cutout that card, because trying to maintain the correct angle and get an accurate measurement with verniers or just a steel ruler wasn't simple - that cut out card goes easily into place and provided a great visual of the actual height, whereas a ruler held in place very much depends on where your eye is for the actual measurement

I'm seeing the picture now - that must have been challenging

Check the post I linked above - I had set and checked the fuel level, before flipping the carbs to take that float height measurement - the outcome was that if you have a target fuel level, subtract it from 25.2.-25-4 mm and you will now the target float height - the same calculation also works in reverse, if you've got a known, but incorrect fuel height, very likely you can subtract that amount from 25.2-25.4mm and Ill make a firm bet that will be your measured float height

Remember - adjusting a float height for the FZR250 is only a step to getting a correct as measured fuel height which is the final measurement which matters

 

You went on better than me with that gauge - great work and I see you also made a wooden stand for your carbs - Sounds like we need a Team Fizzer Carb Adjustment Club

 

Ah I see, yes that makes a whole lot of sense Mr. Ruckusman. I must remember this thread next time I'm at the fizzer. That gauge is also great idea, @my67xr If I'm getting this right, you insert the float into the gauge, seat the needle valve, then adjust the tang till its on the cusp of compressing the spring? Very nicely done I must admit!!

 

OK, so I've measured the angle the carb angles - they're 16 degrees off of horizontal on my bike - it's got a different rear shock R6 and now ZXR260 forks, however that angle should be close enough for a baseline reading of the fuel level

Now turning the carbs over to measure the float height with the float bowl surface at 39 degrees the floats dangle correctly, the diaphragm surface is at 28-29 degrees - there's an 10 actual measured 10 degree difference between those two surfaces off of parallel

So I'd say if you make one cut to put the carb throat at 16 degrees off horizontal for measuring the fuel level, and the other cut at 29 degrees to put them upside down on their lids to do the float height you should be accurate enough

I'll just go and measure one more thing to confirm something else

 

Not that I want to through cold water on this discussion, but aren't we over-complicating the fuel height issue?
Performance is not that overly sensitive to the fuel height. Provided it is within sensible limits (not flooding or running dry).
At least this is certainly my experience.

 

OK, I just did a really quick paper mock up - 1 picture = 1000 words, 2 pictures 1,000,000 words

From memory the spacing was a bit of a PITA because of the ends interfering with float bowls

 

It's a yes and it's a no, because the FZR's wear the emulsion tubes and run like crap when they do, so being certain of the one controllable variable fuel height, that then allows you to know for sure if the tubes are worn or not.
Unless they are totally kaput, it's difficult to actually tell be eye

Past that $200 for carb kits would be silly if it was the fuel height all along, and @camarda's carbs have been messed with with supposedly new parts, so it pays to get the fuel height correct

 

If anyone in your suburb has tossed anything wooden onto the street, that will suffice

I figure 45 minutes at most spent getting the stand right is probably better than 3 or 4 refits onto the bike after adjusting the float levels to check fuel height

 

@my67xr I am assuming that you ended up at about 14.7-14.9mm float height to get a 10.5mm fuel height, if indeed that's where you ended up finally after all of the testing

 

Fantastic - that confirms that the sum of those two elements is 25.2mm for both the 3LN1 & 3LN3/5