yamaha only runs with choke on

[The Artist]

hello everyone.

I have a yamaha quad bike but i figure almost the same as a conventional bike so im gonna ask this question anywayz.

Its 350cc 4 stroke. Only runs with the choke on, if i turn it off it bogs down and dies. It idles ok when choke is on but when revved it pops and bangs. Doesn't backfire, just pops like fuel is getting into exhaust.

The carb has a weird diaphram thing i have never seen before but thats fine, no leaks in that. Carb was stripped and cleaned twice with a compressor and carb cleaner. Its spotless now.
Spark plug has not been removed because its a strange size and none of my 5 different spark plug sockets fit it and its right down in the block and not accesable with anything else.

There is no silencer fitted at the moment. I put one from a 125cc moped on but thats too small so I removed it.

Now, does anyone know what I need to do, is this likely to be caused by a bad plug?
Does it need a silencer although 4 strokes shouldnt.

HALP! please

oh and before I got hold of it, it had been stood in a shed covered in mud for about 1 year.

[hmmmnz]

have you got the airbox and filter on??
to a certain degree you need the silencer, for back pressure, it will cause it to run slightly lean, nothing compared to not having a filter on though,
the diaphragm lifts the slide, but if you have no holes or tears in that, then it'll be sweet,
____________________
the humans are dead
I kick arse for the lord
Wiring Diagrams BIDNIP it bitches

[Timmeh]

Trying to run an engine without an exhaust will make a right mess of the air/fuel ratio. It's running massively lean, and only when you put the choke on does it just about give the engine enough fuel to run properly (at idle)

It's a bad idea, very quickly you'll run the risk of the engine cold seizing (where the piston overheats, expands and welds itself to the inside of the cylinder.) This will of course, wreck the engine.


____________________
GSXR400 x2 | '94 RVF400 | '93 TZR125 4DL (again)
20:22:30 BLUEX5: i would love to be forced to undergo a**l plugging with different sizes
20:48:18 Temeluchus: comp you hunk of smouldering homos3x you

[The Artist]

ok, but i tried with a 125cc silencer and it made it no better. same problem plus more, when i revved it bogged down, even with choke on!! I will avoid running it till i get a silencer!!

can someone remind me rich and lean? rich is too much fuel, air or what now?
any other ideas?

[Timmeh]

rich = too much fuel
lean = too much air

If you had a standard sparkplug I'd say get a colortune, but that won't help in this case.

Is the air filter all present and correct?
____________________
GSXR400 x2 | '94 RVF400 | '93 TZR125 4DL (again)
20:22:30 BLUEX5: i would love to be forced to undergo a**l plugging with different sizes
20:48:18 Temeluchus: comp you hunk of smouldering homos3x you

[The Artist]

yes, although if there is a leak in the air pipe, will this be a major problem. I havent removed the air box or cleaned the foam but i know it there cus i put my finger in lol.
I will give it a clean.

oh and occasionally when revving it may blow air back through the air intake, i can feel it because the intake points at my face!!

[Timmeh]

yeah.

Air leak in the inlet tract will cause this exact problem.

Air coming back at you might indicate a timing or valvetrain problem, or it could just be the crankcase breather. Does the engine stutter when it happens?
____________________
GSXR400 x2 | '94 RVF400 | '93 TZR125 4DL (again)
20:22:30 BLUEX5: i would love to be forced to undergo a**l plugging with different sizes
20:48:18 Temeluchus: comp you hunk of smouldering homos3x you

[The Artist]

ok, i will double check the air pipes etc.

it kind of sputters all the time and pops and bangs. air back at me occasionally although didnt do it much today. I was only running for 2 mins at a time going up and down my driveway! It did get really hot.

I really want to get a new plug in put cant get old one out! I need to find a socket or weld my own one together. ive tried clamping something to the end of plug but dont want to break the ceramic.

[Timmeh]

Backfires tend to get caused by air leaking past the carb's inlet manifold (it certainly was the case with my CBR) so it might be worth checking to see if the rubber's in one piece and the clips not loose.

Oh look at me creating tons of work for you.
____________________
GSXR400 x2 | '94 RVF400 | '93 TZR125 4DL (again)
20:22:30 BLUEX5: i would love to be forced to undergo a**l plugging with different sizes
20:48:18 Temeluchus: comp you hunk of smouldering homos3x you

[The Artist]

ok, ill run over all the air pipes and rubber seals. im used to simple 2 strokes

i got the quad for £100 so its a bit of fun.

[Timmeh]

for a hundred notes you can't go wrong, really.


____________________
GSXR400 x2 | '94 RVF400 | '93 TZR125 4DL (again)
20:22:30 BLUEX5: i would love to be forced to undergo a**l plugging with different sizes
20:48:18 Temeluchus: comp you hunk of smouldering homos3x you

[The Artist]

i should have taken a picture of it when i first got it 3 days ago. No plastics, 1 inch thick in mud. frame bent at front. front suspension jammed down, every single wire you could find on the quad was cut at either end, 2 punctured tyres, all were flat, no brakes at the moment, no lights.

I think they call it a SUMMER PROJECT! Gonna take me a while but it'll be worth it!

thanks for your help btw