Carb trouble

[Teglease]

Hi
' I have an LI 150 fitted with a 185 barrel & a dellorto phbh carb, the scooter starts & runs fine, but the problem is it spits out a lot of fuel, It runs without a filter as it seems to need a lot of air consequently the fuel is everywhere, can anyone help,

[Teglease]

Anyone

[Storkfoot]

Very hard to give any diagnosis without carb type and jets, ignition type and timing, exhaust and also what 185 barrel. But, as the engine seems to crave more air, perhaps the jetting is set too rich.

[Warkton Tornado No.1]

I run a conservatively tuned Rapido (Ø71 Suzuki TS piston) that was tamed by the 61 mm stroke, but even that creates the mess you get, probably more noticeable by not having a hole in the panel & a big flap of baggy trouser material to soak up the petroil mist like in the 70's

That’s the main reason I’ve had to doctor up an elbow from an old air-cool VW on to the carb. A standard GP bellow just wouldn’t allow it to breathe.

From what’s said on this Forum, a ‘Breathe-sweet’ elbow & filter should work well, but alternatives such as Polini are available.

[68Sxandy]

I have exactly the same problem on my Mugello 186 kitted SX. Tried the remote filter but it just caught all the oil/petrol and wouldn't start or run. I use one of the MB panel filters and wash it out fairly regularly, still makes a mess of the panel and floor boards.

[roli150lam]

Make a small hole in the bottom of the bellows tube,fit a frain tube(a la mr.innocenti).Should start and run like that.

[johnnyXS]

I am assuming that you have checked your timing is correct ? what timing are you running do you know ?
Is the engine fitted with reed valves and have you checked them?
have you done a compression test ? or a leak down test ?


You're never going to be able to get your carb tuned properly for roiad use running with no air filter.

it might be ok for racing but its useless for setting up your carb for the road . Its impossible to regulate a consistant and stable air flow and consequently your fuel mix will be all over the place at any given throttle position.

You need to set up your carb by working through it systematically . its not just a question of chucking a particular needle or main jet combination in and a miracle performance is going to occur.

Mark up your throttle into 4 equal divisions to find out exactly which jets and carb components need tuning /replacing. . I usually use some masking tape and a felt tip.
Then do some testing at 1/4 thottle half throttle 3/4 and WOT and see exactly which part of the rev band is giving problems and tackle one section at a time. Blip the throttle from idle and guage your off idle pickup response. Does it bog ? or splutter and threaten to stall ? or is there a sharp immediate pickup ?

Personally I always start with the idle settings because the pilot jet and air mixture screw setting have an effect on the carbs performance right up to 3/4 throttle .Plus its easier testing an engine that will tick over nicely without keep cutting out.

[Teglease]

Thanks very much for all the responses,
Johnny XS there's a lot more to this than i thought

[bluebob]

You're never going to be able to get your carb tuned properly for roiad use running with no air filter.(johnny xs)
not sure the above statement is correct.plenty of people run scooters perfectly with no filter,(normally the bigger carbs)i prefer to use one simply to protect against grit being sucked in.although on my cast 200 I bought a 26mm delly jetted for a 200,which ran shite with my ramair type filter on(too rich)and as I was in a rush ,instead of rejetting I took the filter off,runs great.like yours it is messy,spits plenty out but runs fine.if you decide to use an elbow and ramair /breathe sweet type don't be lazy like me ,take the time to slowly downjet it as if you don't you will get fuel pooling in the elbow.if you prefer the open carb,maybe try running as lean as you can get away with.both setups will work,matter of choice

[johnnyXS]

You're never going to be able to get your carb tuned properly for roiad use running with no air filter.(johnny xs)
not sure the above statement is correct.plenty of people run scooters perfectly with no filter,(normally the bigger carbs)i prefer to use one simply to protect against grit being sucked in.although on my cast 200 I bought a 26mm delly jetted for a 200,which ran shite with my ramair type filter on(too rich)and as I was in a rush ,instead of rejetting I took the filter off,runs great.like yours it is messy,spits plenty out but runs fine.if you decide to use an elbow and ramair /breathe sweet type don't be lazy like me ,take the time to slowly downjet it as if you don't you will get fuel pooling in the elbow.if you prefer the open carb,maybe try running as lean as you can get away with.both setups will work,matter of choice

Not looking for an argument bluebob but you're answer is not really addressing the issue that Teglease posted about is it ?

quote 'Hi
' I have an LI 150 fitted with a 185 barrel & a dellorto phbh carb, the scooter starts & runs fine, but the problem is it spits out a lot of fuel, It runs without a filter as it seems to need a lot of air consequently the fuel is everywhere, can anyone help,

His situation is the same as yours but teglease clearly doesn't think that way of running his scoot is fine.

Its not just the rough idle and low speed surging and all the filthy mess thats the main issue when running with no air filter.
Its all the damage that is constantly being done to your expensive engine. Why anyone would knowingly damage such an expensive precision bit of kit is beyond me. ?

If a carburetter cannot be tuned to run correctly with an air filter fitted then there is something seriously wrong !.... either it is the wrong carb for the engine (probably too large) or its not been correctly jetted and set up or there is something wrong with the engine.

I run a standard LiS150cc engine on a Jetex 22mm carb . It has an adequate fuel supply, air supply and is correctly jetted and set up. It cruises all day long at 50+mph with a top speed approaching 60mph.
No body is going to convince me that a 186cc engine needs a 30mm carb ......its too big ! Its been a commonly held myth since Stevensons Rocket that bigger is better ...its not. Its a proven fact borne out by extensive testing.
My Motorbike is a 650cc it has two 34mm carbs and has a top speed of 115mph . I cannot see how any 186cc cylinder is going to need a 30cc carb .

I would switch to a 26mm and get it jetted and tuned professionally on a dyno with an air filter fitted.
rant over

[bluebob]

apologies to op ,just a quick reply to johnnyxs.
the only thing I disagreed with was your statement to teglease that" a road going scoot cannot have its carb tuned without a filter".Me,teglease or nobody else mentions 30mm carbs or that big carbs are best!

[johnnyXS]

well lets agree to disagree ok ? I don't wish to take this thread off topic .We can start another thread to discuss filters

The op asked if anyone could advise on reducing the spitback and messy petrol/oil mix smothering his scoot .
I seem to remember a 30mm carb being mentioned somewhere but apologies if I'm wrong. If it is a 30mm my advice would still be to change the 30mm carb for a 26mm to cure the problem and get more reliable performance.

[burnside]

No body is going to convince me that a 186cc engine needs a 30mm carb ......its too big ! Its been a commonly held myth since Stevensons Rocket that bigger is better ...its not. Its a proven fact borne out by extensive testing.
My Motorbike is a 650cc it has two 34mm carbs and has a top speed of 115mph . I cannot see how any 186cc cylinder is going to need a 30cc carb .

I run my GT186 (Franspeed Race) with a 30mm Dellorto and no filter, setup as recommended by Richard Taylor, runs spot in. Maybe someone should tell Richard that he's got it wrong

I do however run my Mugello 186 with a 26mm and air filter.

I do get some spit back on both though, with the Muggy and filer I just made a small hole in the bottom of the bellows for it to drain out, and with the GT I have a pad on the inside of the side panel that soaks up oil & petrol (but not water). If the spit back is excessive though then the carb jetting needs to be looked at.

Do we even know what carb the OP is running?

[johnnyXS]

Do we even know what carb the OP is running?

it seems we do not

Teglease was posting last year about starting and running problems with a Dellortto 28mm fitted .
quote
by Teglease » Mon Aug 24, 2015 5:52 pm
Help' I've just rebuilt my lammy engine with new 12v ignition to replace the old 12v one. the problem is it will only start on full throttle but won't rev, I've checked the timing all ok it's running a 28mm delorto carb, It was running ok on this set up for 1500 miles before it broke down which is why I fitted new electrics, the crank has only done about 1500 miles,
Anyone have any ideas please'

There is no indication whether or not this problem was solved by fitting a new 12v electronic ignition system !....

As he specifically mentions a 28mm Delly I assume that is what is still fitted so i should have checked . It looks like the scoot was running fine with the original carb for 1500 miles so I should have thought it unlikely to be the source of this problem but if there is no fuel or air filter fitted and its not been cleaned and reset for a year who knows ?

[Teglease]

Oh dear ,,, I seem to have opened a can of worms here sorry. the original problem (Mon Aug 24, 2015 5:52 pm) turned out to be a doggy stator plate, everything was fine until I recently fitted the new barrel 185cc (removing the 200 small block) the carb remains the same 28

[johnnyXS]

off topic I know but how do you find the 186cc performance compared to the 200cc ?

Going back to your carb problem . if it was running fine without spitback from your 200 barrel setup and all you changed was the barrel, piston and head I would suggest the problem is likely to rest with one of those three components or something you did when changing the engine.

I think a compression test and a leak down test would be an excellent starting point just to confirm that there are no isssues with the new engine installation. Was the barrel new ?

[Teglease]

Yes I only changed the barrel, head & piston as the 200 barrel was poor quality and the inlet manifold wouldn't tighten down even after re-tapping the barrel, saying that it was a lot quicker that this 186cc stage 4

[johnnyXS]

Yes I only changed the barrel, head & piston as the 200 barrel was poor quality and the inlet manifold wouldn't tighten down even after re-tapping the barrel, saying that it was a lot quicker that this 186cc stage 4

thanks TG thats good to hear. Glad you got the problem sorted anyway

i have an Indian 200cc small block kit ready to fit to my spare crankcase and I was curious to know how much difference there might be in performance.
The only fly in the ointment is a mismatch of the inlet port to the inlet manifold.
The Indian grasp of consistancy and quality control is a complete mystery