19mm carb trouble shooting

zxtimmy · #1 (**permalink**) 05-07-2009, 10:56 PM

Been having some troubles with my carb today on my w/c blata rep. Not sure if its a coincidence but it came about after doing a decent burn out on an old tire.

It's a replica 19mm carb.

The engine is flooding... big time... to the point where fuel was pouring out from the exhaust.

Fiddled around with the float, seeing if it was stuck or something. Didn't appear to be. We've played with the little metal bracket which seems to adjust where the float rises and lowers to.

So far all we seem to be able to achieve is either flooding it majorly, or starving it of fuel.

We've managed to get it started, but only after pouring some fuel into the cylinder to give it a bit of a kick and get it turning over.

Then adjusted the idle and the other screw (which we are assuming is giving the engine some fuel with the throttle shut off?), which it seemed to work well, but it did have a bit of trouble idling, especially after giving it some throttle, where it would settle down and then die.

Which indicates to me that it's being starved of fuel. Revving it out is emptying the bowl and it can't refuel fast enough? BUT, changing the float so that it refuels faster leads to more flooding.

Anyone have some advice, or tips/tricks on setting up a replica 19mm carb for a watercooled blata replica?

I'd like to go all out and buy a genuine dellorto/wallbro but I'm not too keen on the idea of forking out over $170 on the legit option.

MortysMiniMotos · #2 (**permalink**) 05-07-2009, 10:59 PM

one tip for blatas using 19mm

use a fuel tap.

zxtimmy · #3 (**permalink**) 05-07-2009, 11:45 PM

Quote:

Originally Posted by MortysMiniMotos

one tip for blatas using 19mm

use a fuel tap.

That is a good idea actually. If I manage to get it running properly again I'll fit one!

TheClaw70 · #4 (**permalink**) 06-07-2009, 09:11 PM

Is it getting enough spark? Maybe you need to rejet it a bit. How much oil is in the fuel? What colour is the ceramic in the spark plug?

All these questions and more can be answered right here!

<for a price, of course...hehehe>

No only kidding, about the price, that is

zxtimmy · #5 (**permalink**) 06-07-2009, 09:56 PM

Spark is fantastic. Very strong and bright. And the plug looks pretty good. However it has had a tendancy recently to foul the plug prior to all this happening.

The fuel mix is 25:1

We've managed to get it running by putting a bit of fuel directly into the cylinder and firing it up, but, after giving it some decent handful of revs it then would bog down and die. Which to me seems like it's sucking up all the fuel currently in the bowl, and the carby isn't refuelling fast enough. But, when I adjust the little metal tab which determines how far the float will rise and fall, to fill up the bowl faster. It then just floods!

TheClaw70 · #6 (**permalink**) 06-07-2009, 10:14 PM

Go to 50-1 and stay there. You wont have any problems this way. at 25-1 you run the risk of leaning out <there is less fuel to burn as the oil doesn't...think about it>although more oil doesnt hurt, more fuel is better..

zxtimmy · #7 (**permalink**) 06-07-2009, 10:45 PM

I'm thinking about it. But it doesn't make sense to me? 50 parts fuel vs 1 part oil, is a leaner mix, i.e, more likely to lean out than 25-1?

Either way, if I could get the thing to start and run nice then I'll play around with my mixes some more!

TheClaw70 · #8 (**permalink**) 06-07-2009, 10:56 PM

Quote:

Originally Posted by zxtimmy

I'm thinking about it. But it doesn't make sense to me? 50 parts fuel vs 1 part oil, is a leaner mix, i.e, more likely to lean out than 25-1?

Either way, if I could get the thing to start and run nice then I'll play around with my mixes some more!

Whilst i am no expert on this <feel free to interject, more experienced folk>, my understandidg is that the more oil you have, the less fuel there is to burn. At 25-1 you have twice as much oil in the mix to interfere with combustion. Whereas with 50-1 there is more fuel to burn which gives a more stable burn and less gunk in your motor.

This isn't neccasarily your problem, though. You might just find the carb is way too big for your motor and its flooding the crap out of it. 19mm on a 40cc is quite large. With a 14mm rep carb i was still getting a tonne of overflow in my b1 rep. Is your motor stock?

zxtimmy · #9 (**permalink**) 06-07-2009, 11:08 PM

Aside from a 2 shoe clutch and an NGK plug, pretty much stock. The bike was running great, had plenty of grunt, wanting to lift the front under power. And it had no problems sending me for a highside last sunday...

It was an all of a sudden thing it started flooding it, and I mean REALLY flooding it. To the point where fuel was literally pouring out the exhaust. And this was only after a stonking great burnout.

All signs seem to point to float problem but it is pretty touchy with the adjustments. I'll give it another go tomorrow after work. Bend the little metal part in, to slightly take away a bit of flow, turn in the airflow screw fully in, then 1 3/4 turns out. With any luck the fuel which has flooded will have evaporated, and she'll start.

I'll post up the progress.

rover · #10 (**permalink**) 06-07-2009, 11:58 PM

Spot on Claw
Too much oil= leans out the mixture...oil is a contaminate " for want of a better word" in the fuel.Oil is only there to lube bearings and likes...Fuel makes the bang...50 to 1 is good with a good quality oil.

19mm carb trouble shooting

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