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what to do about carb flooding

Posted: Mon Feb 25, 2013 9:38 am
by droy
Hey guys,

I own a 1970 450 Scrambler. I just had major work done on it by a vintage bike shop. It's been running wonderful (started on first or second kick) until yesterday. Couldn't get it started for some reason. Anyway, I think it's flooded now. Had a strong smell of gas in the garage and gas was leaking out the carb.
What can I do to fix if it is just flooding? Wait a day and try again? Empty the gas out the fuel lines? Check spark plug? HELP!

Thanks David

Re: what to do about carb flooding

Posted: Mon Feb 25, 2013 10:30 am
by Craig in France
Hi David,

It's quite easy to flood a 450 SCR :shock: - I know, I have one too. But it's always a case of 'Operator Error' ... :oops:

By 'flooding', I mean getting too much petrol into the combustion chamber, normally 'cos you've put the choke on when you didn't need to (remember: strictly speaking, it's not a choke, but an enricher). Result is as you describe: normally reliable bike won't start, place stinks of gas.

Very easily cured (I'm gonna assume you've got a standard Dell'Orto VHB 29 carb fitted ...):

1. Take the plug out, give it a clean (e.g. with a brass wire brush) and dry it off.*
2. Pull in the decompression lever and turn the engine over on the kickstart a few times (ignition turned off) - you're getting that excess gas out of the compression chamber, so don't feel obliged to hurry this stage .. :-D.
3. Re-fit plug, DON'T put the choke on, turn on the ignition, open the throttle just a little - and kick as normal. Bike will start.

* Another old trick, in extremis, is to warm the end of the plug with a gas torch or a lighter before putting it back in.

2. There is a different type of flooding. This is when the carb float bowl is over-filling 'cos the float is stuck. Symptoms are bike may not start, place stinks of gas ... and there's fuel running all over the floor. But I don't think this is your situation ... ?

Btw, what is your starting technique? It's quite important to get it right on a 450. What works is:
1. Using the kick start, bring the engine up to compression.

2. Pull in the decompression lever and, still using the kick start, gently ease the piston over compression.

3. Turn on the ignition.

4. If it's cold, put the choke on full.

5. Without opening the throttle, kick the engine over. If properly adjusted, the engine will start. If it doesn't, report above performance. But not too many times. Ducatis are easy starters ... and, as we know, 450s flood easily ;).

6. Once the engine has fired, back off the choke as soon as possible.

7. If the engine is warm, leave the choke alone. Instead, hold the throttle open about a ΒΌ turn and kick the engine over.



Re: what to do about carb flooding

Posted: Mon Feb 25, 2013 10:56 am
by droy
Thanks a lot Craig, I'll try that.

My starting technique is.
Put choke on
Hold compression lever in
push down on kick start
let go of compression lever before kick bottoms out.
When bike is started let out choke.

Usually works.

Re: what to do about carb flooding

Posted: Mon Feb 25, 2013 5:11 pm
by droy
ALRIGHT! Started FIRST kick! Thanks for the advice Craig. Another little trick to know. LOL