How far does a PHBH 30mm need to be open to tick over?

[Mickgrundy]

Hi all,
I have just rebuilt a Spanish LI 150 with an RB20 kit, reed valve and 30mm PHBH Delly. It starts with a bit of choke and some throttle, and runs but I cannot get it to tick over without constantly twisting the throttle. I have wound the adjuster on the top of the carb out as much as possible but this isn't enough. Also I have would the large screw on the outside of the carb is as much as possible but the slide needs to be above that. The mixture screw is out by 2.5 turns per AR Rayspeed instructions. I can of course pull the trunnion tighter at the handlebar but this seems wrong as surely I should be able to adjust at the carb end. The choke mechanism is working fine, once it's warmed up I can forget the choke.
Is is the case that it needs a bit more juice as the new setup is very tight and this will bed down when run in?
Any advice gratefully recieved. Thanks! Mick

[missing lynx]

The screws on the side are the tick over and the mixture ( only for pilot mixture adjustment) the screw thing on the top is just for cable tightening once you've fitted the inner. Are you sure you haven't mixed up your mixture and tick over screws? If you lift the slide and screw the tick over screw in you should see the tip moving where the slide moves

[ULC Soulagent]

Need too know the carbs full setup please
The more info you give us will help us help you

[drivera]

If the slide is worn you might have a groove where the tick over screw sits which would make the slide sit lower , hence no tick over ?

[drivera]

If the slide is worn you might have a groove where the tick over screw sits which would make the slide sit lower , hence no tick over ?

Oh and check that the pilot jet isn't blocked as well

[coaster]

Hi all,
........The mixture screw is out by 2.5 turns per AR Rayspeed instructions.

2.5 turns, are you sure about that I thought most carbs should be arounf 3/4 out if you are having to come out that far then maybe you pilot/idle jet is too small or blocked as Drivera mentioned.

Did you do a leak down test when you built the top end? air leaks are common and play havoc with trying to dial the carb in.

[Rich Oswald]

Hi all,
........The mixture screw is out by 2.5 turns per AR Rayspeed instructions.

2.5 turns, are you sure about that I thought most carbs should be arounf 3/4 out if you are having to come out that far then maybe you pilot/idle jet is too small or blocked as Drivera mentioned.

Did you do a leak down test when you built the top end? air leaks are common and play havoc with trying to dial the carb in.

I think the average is about 1.5 turns out. The adjuster on the top is just to take any slack out of the cable. Might be any of those things buy if it is a new build it may need to bed in a bit and settle down.

Rich'

[Mickgrundy]

Hi all, thanks for all of these replies.

To answer some of the points made:

It's a new carb so hopefully the slide isn't worn. The carb is set up per the AF Rayspeed website directions for the engine/carb combo hence the mixture screw can be 2.5 to 3.5 turns out, I went for 2.5 as a start.

No, I haven't got the 2 screws mixed up, I can see that if i screw the larger one in, it contacts the bottom of the slide and pushes it up but not far enough to allow the engine to run unaided.

What is a leak-down test and how do I perform one? Although thinking about it, if I had an air-leak surely this would give me a weaker mixture and I think the mixture is now OK?

[coaster]

Hi all, thanks for all of these replies.......What is a leak-down test and how do I perform one? Although thinking about it, if I had an air-leak surely this would give me a weaker mixture and I think the mixture is now OK?

Its an essential pressure check to make sure you dont have any air leaks. You basically seal off the exhaust stub and then pressuries the top end via the inlet manifold and check that pressure is held. Kits are available but you can get by using a bicycle inner tube and a tire pump. Cut the tube about 12" either side of the valve and slip one end over the exhaust and the other over the inlet manifold. Inflate until the tube swells by a couple of inches and then check for leaks using soapy water. New park plugs nearly alway leak around the threads so a little grease on the thread usually cures that and exhaust flanges are often warped and need filing flat. My recent GT200 build was loosing pressure from both those places and also the reed valve manifold. Others have had problems with mag flange, cylinder head and base joints as well as crankshaft seals etc.

[Mickgrundy]

Thanks Coaster. Sounds like a job for the weekend! I'd assumed that since the whole top end is brand new then everything should fit 100 percent perfectly using gaskets and sealant but thinking about it, that was probably overly optimistic.

Will keep everyone posted of progress.

[coaster]

This has been covered before, I just found the original 'cheap leak down test' thread dating back to 2015

Still relevant

viewtopic.php?f=10&t=140&start=20

[Mickgrundy]

Hi all, thanks again for the responses here. As is often the case, it was quite a simple fix in the end!
The carb was supposed to be set up as per AF Rayspeed website for the RB20 / Dellorto PHBH 30 specs. HOWEVER, the Atomiser installed was actually an AS266 instead of the intended AV266 (this is surely because the writing on the jets is so small no-one of advanced years can read them!). Also, when speaking to one of the technicians at AF, I was told that they have changed the specs for jets due to changes in fuel, so they now recommend an Atomiser AV270, Main Jet 160 and Choke Jet 70. New jets posted off from North Yorkshire and installed and the bike now runs fine.

Next job, get the front brake working properly so it'll stop as well!

[Warkton Tornado No.1]

I'm pleased that you have your carb sorted, though the PH range is not one I would choose personally

However, the atomisers for 'proper' two stroke Dell'Orto's tend to be different for piston port engine & for reed valve engines. For example, the atomisers that I use in VH carburettors on reed valve engines are DP, not DQ as used in piston ported barrels. The differences are the small holes & their positioning in the atomiser sides for fuel pick up.

This note is just one of caution & I would check into it a bit further if I were you. It may be that the AV atomisers are the only type available, in which case.......

[Warkton Tornado No.1]

The differences are in the small holes & their positioning in the atomiser sides for fuel pick up.

Ooops! Of course, atomisers do not always have holes in the sides, though some do.

The fundamental differences between atomisers intended for piston port engines:

a taller protrusion into the venturi (not to be comfused with the 'two stroke' bushing)

& the reed valve engines:

a shorter protrusion

In general, the two stroke carburettor utilises the bushing & protruding atomiser to lean off the lower range. Reed valve engines, being more efficient in this respect, do not require as much leaning off as piston ported.

I hope that might be a bit clearer......