Yamaha Grizzly 350 quad running rich

[Guineafowl]

Belongs to a neighbour who says it’ll start without the choke in any weather, and it does smell rich. Plug is sooty. 15,000 miles (or hours? It doesn’t say).

Mikuni CV carb - I’ve given it the usual stripdown and blowout. Nothing unusual, other than:

- Slight wear patch high up on the jet needle.
- Idle mix screw was 2 3/8 turns out, which seems a lot. He hasn’t fiddled with it. Many variants so I’m struggling to find the right factory setting.

Float intact and seems to work and be set about right.
I’ve managed to pinch the throttle cable disconnecting it, so I’ll need another one of those.

He wants it running right for sale, so, carb kit? Or is the modern way to buy a Chinese copy carb and save the hassle?

 

[roofman]

Belongs to a neighbour who says it’ll start without the choke in any weather, and it does smell rich. Plug is sooty. 15,000 miles (or hours? It doesn’t say).

Mikuni CV carb - I’ve given it the usual stripdown and blowout. Nothing unusual, other than:

- Slight wear patch high up on the jet needle.
- Idle mix screw was 2 3/8 turns out, which seems a lot. He hasn’t fiddled with it. Many variants so I’m struggling to find the right factory setting.

Float intact and seems to work and be set about right.
I’ve managed to pinch the throttle cable disconnecting it, so I’ll need another one of those.

He wants it running right for sale, so, carb kit? Or is the modern way to buy a Chinese copy carb and save the hassle?

Try dropping the needle a notch to drop the taper into the main jet.

 

[addjunkie]

Too much fuel….not enough air. Is it the same from cold with no air filter

 

[Nomad]

I had a big Kawasaki bike with similar symptoms, all bits checked and within factory spec.
Chap at my local bike shop told me to adjust the carb float so fuel level was at at the lowest factory limit.
It was a massive improvement, after that the bike needed choke to start, when warm it ran very sharp and crisp.

Chap explained on older engines everything is a little bit worn, nothing is broken but add up all the "not ideal" items and it's running very rich.
Dropping the fuel level in the float chamber affects fuelling at all revs rather than playing with 1 item (main jet, idle screw, etc).

 

[roofman]

I had a big Kawasaki bike with similar symptoms, all bits checked and within factory spec.
Chap at my local bike shop told me to adjust the carb float so fuel level was at at the lowest factory limit.
It was a massive improvement, after that the bike needed choke to start, when warm it ran very sharp and crisp.

Chap explained on older engines everything is a little bit worn, nothing is broken but add up all the "not ideal" items and it's running very rich.
Dropping the fuel level in the float chamber affects fuelling at all revs rather than playing with 1 item (main jet, idle screw, etc).

Good point made, what i will add is fuel to low in the bowl can cause starvation at high RPM also, so its a fine balance.

 

[Guineafowl]

Thanks all. I’m more used to lean-running slide carbs, dying on throttle and popping on overrun. Plus, this is a little sod as you can’t get to the idle mixture screw when it’s fitted. I think the problem is somehow sorted by the cleanout - it doesn’t stink of fuel now and the plug is a nice colour. Doesn’t idle very well.

But… the owner wants to sell it on, and asked me to put in a carb kit, so that’s what I’d better do. Ordered from quad bikes Wales. Last CV carb I played with, I spent days trying to make it behave.

 

[Guineafowl]

Carb kit in, new main jet was smaller than the one fitted, so someone might have been jetting it up a bit. Mix screw set at factory 1.5 turns and seems to start and run fine. Set float level to about 14mm. Mind you, on a baking day like this, anything will start and run well…

Charged him £30 labour, plus £50 parts, hopefully not too far adrift. Also might have found him a buyer for it.