Carbs == head asplode

[xwhatsit]

It never ends. Just as I get the thing running perfectly, fueling spot on, ignition system producing a spark, it all turns to shit.

Decided to swap 125 main for 122 recently. Did that, but the shit-house Keyster carb rebuild kit's float bowl rubber seal swelled to a huge size and wouldn't fit back in. Won't be buying anything from Keyster again. Managed to stuff it back in, but part of the seal was pinched and weeped a little bit.

Decided to fix that today. Pulled a float bowl rubber out of another carb I had, moved the jet needle from pos#4 to pos#3 (one setting leaner). Put everything back together, now 100% fuel tight. However the bitch doesn't like to start, or idle. With pilot screw set at 1.66666 turns out, it misses at idle very frequently. It's very slow to return to idle when revved. Things improve a lot when the pilot screw is turned out many turns (it's almost falling out), but it's nowhere how it was before (and why should this be screwed out so far?). When opening the throttle it often stalls. What do these symptoms suggest? Surely changing jet needle height one notch shouldn't cause this. Have I mangled the float height? Bent the needle? Grrr.

As GiJoe1313 told me, `if it ain't broke don't fix it'. I am dumbarse.

[Grub]

I think the answer is pretty clear. Richen it up again. Those computers at th factory might just know a thing or two you think?

Long term effects of over-leaning are piston damabge and ultimate failure along with possible overheating of all sorts of bits. GiJoe him plenty savvy fella him be.

[tri boy]

Grubs right mate. Better to be slightly rich, than lean.
The pilot jet and needle height work together in a sort of cross over fueling graph.
By leaning the needle, you have to some extent also leaned the idle/just off idle part of the fuel system. Thats why you need the idle mix wound out so far.
Google carbs for some great reference material.
I've got some sites logged. I'll see what I can find.

[xwhatsit]

No, it's not like that. When I was trying to sort the original hard starting/idling, I richened it up a lot in an effort to stop it eating spark plugs. It wasn't really eating spark plugs, it was just the ignition system was piss weak. Ignition system fixed, I wanted to make it leaner again so it wouldn't drink fuel etc. Plus the 125 main (stock is 122) was causing a slight bog at wide open throttle.

The stock needle position is at #2. So by going from #4 to #3 it's still somewhat richer than stock.

I'm guessing by pulling it apart and putting it back together I've broken something or fucked something up. At least I'm pretty sure I got the slide around the right way this time!

[tri boy]

Here's some reading.
www.pianoperson.com/bike/TriumphCarbBook.pdf

Oh well, tear the top off a cold one, and start the age old ritual of fault finding.(you know you secretly enjoy it).

[xwhatsit]

I should also mention it's a round-slide with a pumper, not a CV/SU job.

[The Pastor]

going up a jet size = more petrol goes in? do you have enough air going in?

[xwhatsit]

going up a jet size = more petrol goes in? do you have enough air going in?

Down a jet size. Back to standard. Works fine with open throttle, just small openings is where it fucks around.

Perhaps I've blocked the pilot passageways. Take to it with a can of carb cleaner tomorrow, after giving it a good wind up in the morning.

[xwhatsit]

Anybody got any tips on setting (EDIT: measuring) the float height? I've read so many different articles on it, but they all (including my Haynes manual) confuse me. 90 degrees from standard orientation...? Which way?

I've got a pair of fairly accurate digital vernier calipers.

[xwhatsit]

Well I figured out what the problem was, after stripping it down and rebuilding it all over again, with copious amounts of carb cleaner. Intake manifold is leaking around where it interfaces to the cylinder head.

Sprayed some carb cleaner at the join between the manifold and head, engine just stopped. Tried it again with open throttle, engine died for a second until it finished chewing on the carb cleaner and then fired up again.

So in taking off the manifold and putting it back together again, I've somehow munched the seal. Have just called up Econohonda and ordered a new O-ring, but has anybody got any tips on sealing it up? Blue loctite goop OK? It seals up oil OK.

Cheers. Happy now I know what it is. Fits with the symptoms, too -- having to unscrew pilot mixture way out, fucking about at half throttle, but running OK at high revs and open throttle.

[tri boy]

Good for you. The "spray the mating surfaces" trick had totally slipped my mind Must need to eat more brain food.

If I remember correctly, the manifold is alloy base, with a O-Ring.
Pays to "Face off" the alloy with some fine wet n dry sand paper on a flat piece of glass, as they occasionally warped due to over tightening.
The new O-ring could be easily found around town if the bike shops havn't got one. (It just needs to sit Proud of the surface to guarantee a good seal. Use a bit of Vaseline, or O-ring grease on it at installation.

[xwhatsit]

Oh cool, I'll try that `facing off' thing. Econohonda will get me this new O-ring hopefully by tomorrow morning (I love those guys ). The current O-ring does not sit proud of the surface at all. It's a bit squashed.

Would some blue loctite goo hurt, though? Is the grease to make sure it sits in its groove without getting scratched by the bits that pinch it in, or is it for sealing as well?

Thanks.

Was slightly put off when I read that the carb cleaner getting sucked in should make the idle smooth out and run better, whereas my engine died. I'm assuming this is because I practically unscrewed the pilot mixture screw, making it very rich, and the addition of carb cleaner makes it too rich to run at all.

[tri boy]

Yep, a light smear of grease helps the O-ring "settle" in the groove while the manifold is tightened and it acts like a tacky retainer so it doesn't fall out of said groove during installation.
You could use a light smear of gasket sealant on the two surfaces if you like. But the new O-ring will do 99.9999999% of the sealing duties.

Over time, the heat from the cylinder head causes the O-rings to harden and fail. A common cause of rough idle, and fueling faults.
Well done Sherlock.

[xwhatsit]

Yay! Econohonda managed to get that O-ring to my door at about 7.30am today. Love those guys. Pulled old O-ring out (it was flat and square, lol), cleaned up the face as much as possible, new O-ring in with some grease, torque the bolts up. Set pilot screw to normal factory setting.

Kick once, `ticka ticka ticka ticka ticka'. Warmed it up, went for a ride around the block, back to its normal self. Squirted some carb cleaner on the manifold joins and nothing happened. Still started with a pussy-weak sitting-down kick from hot.

The idle seems a bit high and I can't get it down (idle screw not even touching the lever). I've possibly done something silly with the cables, but there still seems to be some slack. Perhaps the throttle spindle. Who knows. It's not very high, sounds like 1200-1400 instead of normal 1100-1300, so I won't be too fussed unless it bothers me.

Thanks guys.