Spit back standard carb

[Chewyboy]

Hi everyone
Would appreciate some help please.
Nearly finished S3 Li 125/150 restoration. Dellorto 18mm standard carb with new jets in to suit 150cc new cylinder and piston. When warm difficult to start. Remove air filter and rubbers and starts ok. Fair bit of petrol in bottom of rubber, so suspecting drawing in too much fuel because of spit back in there. I have saved the original rubber with the valve and tube coming out of it. Would I be better off putting this on to drain spit back fuel away. What causes the excessive spit back and can I do anything about that rather than drip fuel out through the original fitting.
Thanks in anticipation.
Paul

[Warkton Tornado No.1]

Presumably you’ve done the usual check to ensure that the choke is fully off.

Presumably you’ve also checked that your air filter is not restrictive.

What do you have in the carburettor as far as slide, atomiser & jets?

Are the new jets genuine Dell’Orto?

[Chewyboy]

Yeah, new air filter and no blockages, choke seems to be operating OK as when warm and ticking over if you operate choke it tries to die and returns to normal when choke is off. All new jets and slide, got them from local scooter shop so not sure what make they are.
Thanks for the interest having another go now.

[Warkton Tornado No.1]

As everybody on this Forum will have witnessed, time & again, we can all get tricked into thinking that the choke is fully ‘off’ when it isn’t.

You wouldn’t be the first & certainly not the last.

As for jets & slide, I hope they are genuine Dell’Orto with the diamond logo as Jetex can vary.

Check the float & needle as well. Ensure your float needle is the red tipped.....

[MickYork]

The sticking or not fully returning choke is a good call.

I'd also check the jets and see what size they are ? post on here with your settings and see what everyone thinks...... maybe drop a size on the pilot ?

[CHRIS in MARGATE]

Piston facing right way round ?

[Chewyboy]

Thanks everyone

MickYork- jetted it up as per standard 150 Li in Sticky's manual.
Slide 5914-2
Atomiser 5899-1
Main 105
Pilot 45 but did revert back to original 125 pilot which was 42 and smaller as you suggested
Starter 50

Warkton- float and needle seem OK red tipped and shutting fuel off.

Chris in Margate - yes arrow on piston pointing correct way.

However, more symptoms if this helps.
From cold, does not want to start with no throttle and choke operated. Will start with a good few kicks with no choke and throttle open. Also starts better with air bellows off.

With the air bellows off looking through the choke aperture I can see the choke rising to clear the hole and returning to fill the hole. I have adjusted it so it doesn't quite clear the hole when raised so that when it is down there is a bit of slack in the cable to make sure it is fully down when lowered.
Is there any way to know that it is fully closing other than what I have done?
Once again thanks for the interest.

[Meds]

I had similar problems which I never bottomed, just learned to live with it.
Some things I did
strobe the timing and set it correctly when running, it helped a bit.
Used an air hose with a drain, it helped a bit.
Kept it running with the fuel off when stopping to make it easier to start, it helped a lot.
One thing I never tried (and should have) was a known good carb from another scoot to confirm That the carb was/wasn't the fault, as I suspect it was a bit worn

[CHRIS in MARGATE]

True story: fixed a non engine fault for a guy last year; new kickstart shaft in series 3 150. Wouldn't start. Rang the guy and asked if he'd had starting problems. He said "yes it's a bitch". Obviously why kickstart shaft snapped. Once started it ran nicely. It had a 20mm carb on. Took an old 18mm out of the drawer, connected it and it started immediately and ran spot on.
Right definitely carb so stripped, cleaned, blew it through, correct jetting. Wouldn't start !! Sold him my 18mm and perfect.
Loaned that 20mm to a guy rebuilding a TV200 and the carb would not start. Internal obstruction somewhere !

Try another carb.

[a.lo]

trying to get to the bottom of spitback myself on a newly built untuned engine, always associate this being a too rich sympton but internet searchs mainly on cars or bikes all state it as being too weak. anybody know better?

[MickYork]

besides the carb' it could be port timings causing the issue. Also the piston may be a factor.

Some of the Indian 175 alli' barrels can be a nightmare...

[Warkton Tornado No.1]

With regards to the choke, the soft alloy of the body is prone to distorting easily if knocked.

So I would suggest disconnecting the cable & reinserting the brass plunger. It may be that the rubber pad is worn or missing. Doh! I just thought of that! Turn it so that it seats fully down. Turn it with a screwdriver. Place spring & threaded cap back in (obviously without cable) then try…..

At least you will have eliminated one possibility….