This damn carb....

[madcow]

As some of you know, I recently swapped in a Z400 carb, it was perfect for a while, but it seemed like it needed rejetting. I put in a 145, then went back to a 147.5 main and now it will barely go past idle. With the choke on, it'll go to about half throttle, then sputter and miss as if it's not getting enough gas. With the choke off it won't go past 1/4 throttle before it does this. The float height is fine now, it was way off before I adjusted it. I can't seem to figure out what the hell is wrong. I blew out all the jets and the places they thread into with an air compressor, that helped a bit,but it still sputters. It idles perfectly except when the revs come down, then it idles lower for a bit and returns to normal.

 

[yamarider]

Did you check for air leaks? When you're doing a lot of trial and error like this, constantly taking the carb off and putting it back on, it's likely that you managed to put a crack in the intake manifold.

 

[madcow]

I don't think it can be an air leak, if there was it would idle erratically, plus I don't take the carb off when rejetting it, I just loosen the clamp and spin it, but I will check that out just in case.

 

[97warriorrider]

mine kinda of pops around 1/4 throttle..I asked on here and Jason told me to adjust my fuel screw..He said that the main doesnt really affect anything under 3/4 throttle..check out the thread in the General section

 

[madcow]

Yea he gave me that speech too. It's actually after I get past 1/4 throttle.

But anyway, I changed the gas, and I can't believe I didn't notice this earlier, because it was really yellow. I also realized that this problem goes away after I put a load on the motor, so I have to get it moving without using more than 1/4 throttle, then after a few seconds I can open it up more and more. Damn this this is temperamental, either it barely works at all, or it works perfectly.

I went up to a 150 main, which helped alot, but also didn't let it rev as high as it should. But now it pulls like hell, I broke the tires loose in 4th on slightly icy gravel, I stil don't have enough grip to do a wheelie. I'm starting to think that there's a leak somewhere in the vacuum slide system, so the slide doesn't so up as much as it should and therefore doesn't give enough gas.

 

[madcow]

Well I stripped one of the screws that holds the top cover in place when I was inspecting it for damage, I was too lazy to get my dremel out and slot it so I just left it. Once again laziness has screwed me over.

 

[madcow]

But where would I find them? Hardware stores don't have any.

 

[madcow]

Never even heard of them, maybe they're a USA only chain.

 

[yamarider]

You should have a freakin hardware store somewhere that has metric screws, it's not an uncommon thing. I worked at a little hole in the wall ACE hardware store and even we had all the metric screws. Any of the big home improvement places should have them too.

 

[madcow]

They do have metric screws, but nothing that small. They're all M6 and above.

It's really weird how canada, an officially metric country has more SAE sized hardware than metric.

 

[madcow]

Update, I opened the top, and the diaphragm looks fine, no holes but it did has a kink on the outer edge in 1 spot. The diaphragm on the side looks fine too, so now I'm confused again.

 

[madcow]

What holes do you mean by that? Yea the slide moves fine as far as I know, I have nothing to compare it to though.

 

[madcow]

I first had the 147.5, then switched to 145, then switched back to 147.5, that's when it happened. I went up to 150 and it still happens, but it's not as bad. I'll try the blocking thing tomorrow, and yes it does make a whoosh noise when I more the slide. The needle is fixed to the slide, but I can push it up a millimetre or 2.

What I noticed is that if there's no load on the motor it will barely go past 1/4 throttle, once I get moving it goes away mostly. I need to get it moving using almost no throttle, then go easy for a while, then WOT and it would barely miss later. Really annoying when it misses while moving because the motor nearly stops and it just jerks me forwards, I almost hit the bars when that happened in 2nd gear.

 

[madcow]

Was that posted in the wrong topic? I already knew all that and I didn't ask about the specs. I'm confused. :-/

 

[madcow]

Yea I'm getting tired too, spent the whole weekend trying to figure this damn thing out.

 

[darebee]

Mad Cow

There are lots of Fastenal (and similar industrial suppliers in Canada).
Here is your TO locations http://www.fastenal.com/web/locations.ex?action=search&zip=toronto&state=ON
The only caveat for you non-industrial customers is that you have to take a whole box.
You need 4pcs M4 screws and you gotta buy 100.

You want to drive to Stratford I'll give you the cap screws you need ;-)

 

[madcow]

Yea I don't need 100 screws. And driving all the way to stratford for some screws is just a waste IMO, and my dremel-slotted screws are doing fine for now.

 

[madcow]

Well I'm even more confused now. There are 2 large holes in the filter side of the carb leading to the space below the diaphragm in the same chamber. If I block them nothing happens. There are 2 holes on the bottom of the slide though, I block those and it has trouble moving, and air comes out of the 2 holes on the filter side. From what I understand, the slide shouldn't move at all if those 2 holes on the bottom of the slide are blocked, correct?

From what I understand, air comes through the carb, some goes into those 2 holes and pushes the slide up. Is that pretty close to what happens?

 

[madcow]

The slow speed enricher looks fine, and the holes are on the bottom of the slide, on either side of the needle. I forgot about the main jet holder, maybe something's screwed up there.

 

[madcow]

Well my diaphragm isn't stretched or anything, fits in perfectly. Maybe the hole in the bottom of the slide is too big or too small?