Black 'soot' in carbs, I'm lost!

Yoniboi · Post by **Yoniboi** » Wed Jun 11, 2008 6:54 pm

Hello there,

My low rev gremlins are still there, with a general sensation of unbalance in the motor at any revs. It runs rough as nails when hot below 3000rpm. It runs OK when cold at all revs.

This is the third time I've pulled the carbs to pieces, but the first time ever I ripped them apart, individually, and washed and scrubbed them in hot soapy water.

Each time I take them to pieces there's a considerable (considering they're supposed to be spotless) amount of black grainy soot like dust inside, concentrated above the diaphragms, which appears to be coming in through the breather pipes (the ones that plug into the coils plate).

I don't get it. The area these pipes terminate in is clean, the pipes themselves and the in-line filters are clean (I scrubbed them last time) the fuel going into the carbs is clean, and the airbox and filter are clean. (I know, I've inspected and or dismantled them all).

Where's this black gritty stuff coming from?
I've looked down the inlet manifold (clean, basically) even rubbed my finger around inside and it comes away clean.

I only rebuilt the motor with a 1040 kit 1000km ago, and it ran equally badly before and after. Shit, I thought the rebuild would fix it.

NO, the cam timing isn't out before you ask. Triple checked, at least on my bike, FZR1000 '90, the timing mark isn't a T like it says in the workshop manual, rather there're three lines and I work to the middle one. If that's wrong let me know. Done like that, as a check, the cam lobes at cylinder no 1 are equally displaced relative to the cam cap at TDC.

I've checked the valves three times in the last 3000km, all within spec, not identical, but within spec. Valves were reground 8000km ago and all new shims installed, were re-adjusted after 1000km and haven't needed to be changed since then.

Carb slides are wet with petrol each time I pull the airbox and take a look. Not dripping, but noticeably.
Float heights have been checked umpteen times using Jim's 'Patent Pending' float height tool. Bang on 14mm and haven't moved. Are they normally wet like that?

Any clues???????
Cheers,
John

dragracer1951 · Post by **dragracer1951** » Thu Jun 12, 2008 9:10 am

Here's what I think....
Check the vacuum feed line to the top of the diaphram. Check the O rings there.
Check the seatting of the diaphram. I suspect a vacuum leak that is causing lazy lifting of the slides. That'll make it run rich and I'm still thinking about the grit on top of the diaphrams

creed12r · Post by **creed12r** » Fri Jun 13, 2008 9:06 am

The cam timing marks on the crankshaft look like this

I-I I T

you should be setting your crankshaft at the centre I

then set the cams with the dot lining up in between the 2 lines on each camcap adjacent to it.

Chris

Yoniboi · Post by **Yoniboi** » Fri Jun 13, 2008 9:54 am

I'm not kidding, my crank doesn't have a T on the crank. The dot and the rest on the cam it does, I've had this motor to bits many times now.

Got her fired up this morning (after an 8 hour carb rebuild... I ain't quick but I sure am thorough) and she ran sweet. Now, some 100km later, she's a little rougher but still fine considering she hasn't been properly carb balanced yet.

Considering I haven't a clue where the gritty soot was coming from I'm just keeping my fingers crossed that she keeps running that way.

Noticeably more heat radiating from the engine with the 1040 kit, but the needles in the same place as always riding and climbs stuck in traffic as it always did. The midrange is smooth, but not as eager as I'd have hoped, so I'm wondering if she's now lean on the needle jet. Doesn't hang or anything though. Truthfully, it's been a long time since she ran this good.

Happy from Spain,
John

hotcam · Post by **hotcam** » Sat Jun 14, 2008 12:33 am

Dye used to colour petrol is a dissolved solid and can crystallise out leaving a fine gritty residue, can't think why it might be black though...?

Simonsi · Post by **Simonsi** » Sun Jun 15, 2008 5:44 pm

I had that black thingy in my carbs too.

After an hour of head scratching without any real explanation, i cleaned it all up and put it back together.
Go figure.

RUFtech · Post by **RUFtech** » Mon Jun 16, 2008 6:39 pm

I used to see that black grainy looking stuff in carbs when I worked at a Yamaha dealer. Most of the time it was the diaphragms deteriorating and the grainy stuff was the rubber of the diaphragms. When this happened it made the bike run real rough due to the air now leaking through the diaphragm rubbers. It also caused a loss of power.

Yoniboi · Post by **Yoniboi** » Tue Jun 17, 2008 4:20 pm

BUGGER ME.

That could be it. I don't want that to be it, 'cos they cost a frigggggging fortune each, but that would certainly explain the unexplainable.

Thanks
John

dragracer1951 · Post by **dragracer1951** » Tue Jun 17, 2008 6:24 pm

Time for Flat Slides!!!

Yoniboi · Post by **Yoniboi** » Fri Jun 20, 2008 8:54 am

For the love of Dog, I wanna ride some, not start buggering about jetting a set of FCRs, or FRCs or BBCs or whatever.
I knew I should have bought a (cough) Suzuki

John

hotcam · Post by **hotcam** » Fri Jun 20, 2008 4:43 pm

You could hunt around the wreckers for a set that is already jetted, or even better/cheaper you could hunt around ebay for some cheap diaphragms or original carbs from a bike where the e-tubes have worn out and the rider has replaced the whole bank of carbs and now has the originals left over...

Yoniboi · Post by **Yoniboi** » Sat Jun 21, 2008 2:03 am

That's where the diaphragms it's got now came from. Two of the origunals split!
Finally worked out why she kept farting.
John

silver · Post by **silver** » Sat Jun 21, 2008 6:25 am

dragracer1951 wrote:Time for Flat Slides!!!

FI

Yoniboi wrote:For the love of Dog, I wanna ride some, not start buggering about jetting a set of FCRs, or FRCs or BBCs or whatever.
I knew I should have bought a (cough) Suzuki

I think we've all been there.