LCGB Forums

Thanks for all the help with VHSH carb rubber topic think/hope that is sorted, but got some jetting issues so thought I'd best start anew thread.
Ok once I managed to get the carb to stay on had a good run out on Sunday and it ran ok once I applied some throttle, the problem seems to be at the lower end i.e pulling away and up to mid way in 2nd to 3rd sort of anything below 25 - 30 mph, its quite spluttery as though its missing or too much choke.( choke not on )
The other thing that occurred which could be unrelated after running at around 50mph for a couple of miles when I shut down approaching a junction the engine died and cut out and had to bump it on the fly.
Set up is this :
IMOLA 185
IMOLA reed valve
30mm VHSH Dellorto carb ( Jetting unknown going to take the carb off later )
MB REVtour exhaust
using 3% mix
Going to take the carb off later once I've done my homework and read up to find where all the jets and needles are
As you can probably tell this is a bit of a learning curve for me so any pointers would be much appreciated.
Thanks

Pilot jet maybe too large,check the size
Needle clip could be too low,try moving it up

ok set up is this:
main jet 135
choke 60
pilot 60
atomizer DQ262
needle K23 3rd clip down
slide 40
idle screw 2 and a qtr turns out
mixture screw 2 and a qtr turns out
thanks

Pilot seems a bit large
Should be maybe 50 to 55
Try moving the clip up to second top,this will help
The small screw at the fuel pipe will set your idle
The large screw on the spring will set your mixture
Try it out a bit and see if it helps

Thanks Mark tried moving the clip and turned both Idle screw and mixture screw in half a turn seems slightly better going to order some pilot jets tomorrow a 50,52,55 before I tinker anymore !! What do you think about the main do you think that should be a bit smaller, say between 125 and 130 ?
Thanks

Try turning the mixture screw out 2.5 to 3 turns
See how that feels
The main jet won't be in play at 25-30 mph so I doubt it's that
I'm not sure what the main should be for an imola but there may be some info in the carb set ups pages
Btw try it on the top clip,and possibly order a half clip washer with the jets as the clip position does make a difference low down in the range ,try this before ordering jets as the pilots for they carbs are expensive I think

Thanks Mark going to give it a go tomorrow i've also ordered a few pilot jets 50, 53,56 so going to see if I can sort it for the weekend.

Any luck with this??

what jetting did you use in the end?

gazza wrote: the problem seems to be at the lower end i.e pulling away and up to mid way in 2nd to 3rd sort of anything below 25 - 30 mph, its quite spluttery as though its missing or too much choke.( choke not on )
The other thing that occurred which could be unrelated after running at around 50mph for a couple of miles when I shut down approaching a junction the engine died and cut out and had to bump it on the fly.
s

both these problems relate to your pilot circuit.

If your engine dies when closing the throttle on over run then thats a sign of an incorrect idle mixture, its probably too rich.if you think about it ,...when your throttle is closed no matter what speed your scoot is goin what is it that your engine is running on ? the idle or pilot circuit !...
You need to get your idle correct because the pilot jet, slide and pilot mixture screw are all responsible for both the idle and pickup off off idle at low revs

Here's one then, 3 VHSH 30's on different motors and none of them need choke to start after being stood for a few days and all three running different idle jets. Obviously the choke plungers are all fully seated but each motor 4 strokes with the throttle just open and on the overrun.

Wack wrote:Here's one then, 3 VHSH 30's on different motors and none of them need choke to start after being stood for a few days and all three running different idle jets. Obviously the choke plungers are all fully seated but each motor 4 strokes with the throttle just open and on the overrun.

well the stock answer to 4 stroking on a 2 stroke engine is that the mixture is too rich at that throttle position On a 30mm Delortto VHSH it is recommended to try a weaker slide.

You tell us nothing about any of the engines and I know next to nothing about jetting and tuning that particular carb so I'm not really in a position to even speculate but I'm sure there will be plenty that will know.
I'd look to the Kart racing fraternity for guidance if it were me as that is apparently a popular carb for karting.

Yes the carbs were made for karts but they're a different kettle of fish compared to a scooter, mainly being flat out all the time and a pumped system with big idle jets. The slides are 50 as standard and are expensive to buy , then find out it's not the problem. I'm currently on a 42 idle on a 250 motor and it's still too rich, the other motors are a RB 20 and a Vespa Ml200 Smallframe.

Perhaps I've missed it but have you mentioned the pilot's emulsifier tube yet? It is common to run a big pilot, like yours, with a 'sized' emulsifer tube to act as a restriction to pilot circuit.

To check this you need to remove the pilot jet and then use a fine bladed slot head screwdriver to remove the brass emulsifer tube that sits in the body. The generic emulsifer tube is a CD1, which can then be used with a sized pilot jet, e.g. 40 (common range for VHSH carbs is 38-45 with CD1).

Note that changing the pilot with a restrictive emulsifier tube may do nothing to influence the pilot mix as you could fit a 100 pilot jet if the emulsifier is only a B38!

Determine what you have in the way of emulsifier, then assess pilot requirement.

Adam

Yes I've played about with the emulsion tube(s) and ended up without one as even with the CD1 the idle was too rich with a 37 pilot. Eurocarb were unable to offer much advice but did say that they are aware some motors do need the emulsion tube removing .

CD1 should always be fitted as this is simply a generously sized blank that allows the pilot jet of your choosing to be the determining feature. That said, 'never say never with Lambretta.'

Adam

Idle emulsifier
by Wack » Fri Jul 08, 2016 10:26 pm

As can be seen, the topic was discussed recently.

Perhaps there may be feedback available that may help you.