#3 #4 Plugs completely black after 1 mile

[CA]

I think I figured it out!!!!!!

Ok so heres the deal, I used my brothers air compressor and put it up to the vent hose for the good carbs...1&2; air flowed freely out the hole opposite the air jet in the air bell...put the compressed air into the vent hose in 3&4 and there was immediate resistance and it tried to push the nozzle out...there was some air flow from the holes in the air bell but not as strong!!

So my conclusion is that air flow is obviously being restricted somewhere...

My next test was to take off the float bowls on 1&4. I felt where the air would come out on #1 the good carb, it was a steady stream on about the middle of my hand, felt like it was coming from a hole or a jet, just couldnt find where...when I did the same with 4 (through the vent hose) the air was not coming out the same at all, and there was a different sound...the air did not come out a steady stream where it did on #1; it felt like it was just finding any hole to go through...

Now I slid off number 4 carb to check the T-fitting and the T fitting and vent hose seem to be fine, they are not restricting air at all...

So I guess air is getting restricted inside somewhere, and I just dont know the innerworkings of the air flow within the carbs to now which brass jet to check , or holes to clean...that where you guys come in...

What now???

PS - THe out-sides of my brass floats are sucked in...are they gonna work still, thought that was weird, maybe just cause they are dry...

[John]

And last but not least, when you cleaned your carbs did you make sure to clean the little jet in the bottom of the bowls? If you strip the paper off a bread tie the wire works nicely for cleaning it out. It's the little hole in the bottom of the bowl. If you stick the tube on a can of carb cleaner in that hole and pull the trigger you should get a nice energetic atomized stream coming out of one of the holes on the flange. Make sure it's pointed away from you when you do it - carb cleaner in the eyes REALLY hurts .

That small hole on the bottom of the bowl is actually the fuel supply for the enrichener (choke) circuit. The thin brass tube sits in this hole in the side of the bowl. The pilot (idle) circuit has it's own jet, located in tower next to the main jet. As stated, cylinders 1 & 4, and 2 & 3 are fired by the same coil, so if a coil is bad, it would show up that way. Either of those pairs misfiring, but #3 & 4 being affected would lead me to think the problem is fuel related, as #1 & 2 share the same fuel supply, as does #3 & 4. Check the routing of the hose on the carbs. As was mentioned earlier, the lower set of hose (those closest to the float bowl) are the fuel supply, and the upper set is the float bowl air vent. If the vent is restricted, then the carbs will be rich, maybe too rich, and they will fuel foul.

[CA]

See above...

i guess my above post wasn't there when you started writing...

[DGXSER]

Hmmm...Well...it does sound like we are on to the source of the problem. Now...I honestly do not know the small details of the inner workings on these carbs that well. I would try blowing the air the opposite direction to blow the gunk back out the vent opening. Keep working at it with small wire, carb cleaner, and compressed air. One of the carb gurus will chime in soon enough and know alot more.

Yeah, John probably did not see your last post. He knows these things REALLY well.

[bikerphil]

If you blew compressed air thru the vent tubes while the bowls were still on, that will damage (collapse) your brass floats every time.

[CA]

oops...

See its these things that I do not know...dang it. So I guess I need new floats?? Can I just check to see if they still float??

What in the world is constricting air flow....

Can I un-collapse them? Anyone have some I could buy? Or know where the cheapest are...I just looked them up and they are expensive..

...frustrated...

[dbeardslee]

CA - Whoooooooaaaa! Don't put compressed air on those lines with the bowls attached!!!!! That will definitely crimp your floats.

There's some wierd physics that go on inside those carbs. You can put your finger over the vent line and turn the fuel on and gas will pour out of the carbs. Take it off and it will stop. I'm thinking a partial restriction could result in a rich condition.

My thinking on the exhaust was this - If you have a 4/2 that would also segment your carbs #1 #2, and #3 #4. If you have a restriction it should result in less airflow and a rich condition. JAT

Sorry for the redundency in the first line - you guys type too fast for me .

Check the floats first before you chuck 'em. If they aren't leaking you may still be able to use 'em, but they may need to be slightly higher. Mine were pinched and I had 'em set at 27mm, and they worked OK. I replaced mine with plastic floats from MikesXS - $12 ea. - so I could quit thinking about them .

[DGXSER]

How long did your bike sit before you got it?? That vent tube is just open to the air filter box, so any critter can crawl up in that tube and make a home. Spiders could have babies running all over your carbs down into the tubes and dying from the fuel and then you got "gunk" in your vent system. I always figure out the way it came in is easy path. I would use the carb cleaner and or PB Blaster down the vent T/path. Then compressed air back the other way to force the chit out the tube it came in from. There is a post here somwhere from TC with a color coded diagram of the paths in these carbs. try to find it, very informative. May shed some light on your air path issue.

[CA]

hmm

Well i guess I will just keep blowing on all the avenues to get the crap out of there...without my floats in...and ill check the floats...so I should raise them to 27mm??

[bikerphil]

The correct float height is 25.7mm, upside down, with bowl gaskets removed. If the carbs are squeaky clean, you should have no problem running at that height. Now those dented floats may or may not cause a problem. You can get new ones if needed from Mikesxs.com for $12 apiece, P/N 20-6500. I'm 90% sure these are the correct ones, mabye someone who knows for sure will chime in.

[gscbertrand]

You could try lowering your main jet needle 1 notch to give the system less fuel and check them all before moving anything. Are you working with a shop manual? It sounds to me like your pilot or mid range fuel systems are giving you trouble also check to see how the spring in the tops are sitting they have been known to get bent.

[dbeardslee]

P/N 20-6500. I'm 90% sure these are the correct ones, mabye someone who knows for sure will chime in.

Those are for a TX and are way too wide for an XS. The ones you want are the Part #20-6502 (plastic). That 10% will get you every time .

4 more posts Phil - You're almost there .

[bikerphil]

Those are for a TX and are way too wide for an XS.

Thanks for checkin' that, DB. I kinda figured they might work 'cause the 5 digit Yamaha P/N (14985) was the same. 3 more to go.

[dbeardslee]

I thought the same thing, and ordered one just to see. That's how I know .

[CA]

still float

So I put all the floats in near boiling water and they all floated, the only thing was two seemed to float a little higher...and one looked to have a tiny hole in it but it didnt have bubbles coming out, just one little one sitting there...again they all floated...

Those I can replace if need be, but the issue still remains, why air flow is being restricted to #3#4 carbs. I would think such pressure going through would clear everything that may be temporarily blocking it out....still lost...