TV175 PHBH26

[greenfingers]

The bike goes like the clappers at full throttle but is as boggy as hell a tick over or weaving through traffic. I get the sensation its gonna stall at any point. Whats going on here…? Every time I take it out the carb has to come off, jets out and blown through. The fuel is fresh. Its from the same garage I've used for years. I'm fairly certain the problem isn't electronic but I do have a variatronic set up and replaced the stator last year.Drive side oil seal at the same time too!! But she is still dreadful to start!!! I'm confused about the mixture screw and the air screw. I've screwed the air screw right in and then come out one and a half turns - and I can see how this slightly lifts and then lowers the slide - but I'm guessing this only matters at tick over as opposed to open throttle.Could this be the problem!!!??? Do I need to screw it right in and lift the slide slightly??? If so - why wasn't this a problem before???
The choke seems to be seated properly too - turn on the choke and it lifts straight away….
Could this be a mixture problem…? in terms of the mixture screw I mean as opposed to getting the ration right at the petrol pump…But, while I'm on the subject - does this ration have to be down to the last millilitre!!!!????
So - can the mixture screw move with time!!?? it appears to be completely screwed in but I have to confess I'm not sure if turning one way or the over means that it comes out of or goes further into the body of the carb. If I'm honest - I'm nervous about touching it.
The scooter was tuned before I bought it with the variatronic kit. It ran like the clappers and I've changed nothing - so I'm happy its jetted correctly.
But why so boggy!!!??? Why so difficult to start!!!???…….Ideas gratefully received…

Martin

[Toddy]

How old is the carb is the slide / needle worn it may require a smaller pilot jet if it's only boggy when it's up to 1/4 throttle

[greenfingers]

Hi Toddy - brand new I think. Its absolutely immaculate….

I'm starting to convince myself that I've over done the oil to fuel ratio. I was told it should be 3% - and at risk of sounding like an idiot - 1% one be 45 ml per gallon wouldn't it, so 3% must be just under 150ml - in other words one and a half jugs of oil every time I put a gallon in. Sometimes I've topped up with less than a gallon - say just under 3 litres of fuel. So - doing some mental arithmetic at the petrol station - I'd simply add 100ml of oil. Seriously - does the mixture have to be absolutely measured down to the last ml!!!??? genuine question…..but surely not when its pouring down with wind and blowing a gale!

I'll drain the tank and try some fresh fuel and measure it out microscopically.

Have I got the right plug? its a mugello 186 barrel and runs on an N4C plug - again the plug that was in it when I bought it. It used to be a perfect biscuit colour believe it or not - but its often black and wet when I take it out when it won't start. I reckon its running rich - but I've made no adjustments and its only done a couple of thousand miles…..can it start to run rich??? plus me over doing the oil ration…? And intact - I remember reading that adding too much oil has the opposite effect in that it actually mms less petrol and therefore a weaker mix….o why the think black oily plug.

I'm happy I'm not burning oil - seal replaced last yea and a couple of hundred miles since.

If it is a problem with air:fuel mixture which way do i turn the mixture screw to adjust one way or the other? How does it work…?



WTF!!!!

[Rich Oswald]

I agree with Toddy, it could just be that the pilot jet needs reducing also check that your spark plug gap isn't too wide. Not sure what an N4C is, is it a Champion, but i'd be using an NGK B8 for general use with a Mugello kit.

Rich'

[Scooter Paul]

Ok, if I'm reading your original post correctly I think you are confusing your tick over screw with the air screw. The tick over screw alters the revs at tick over and it does this by raising the carb slide. So your description seems to refer to this not the air screw which alters the air to fuel ration at tick over up to about 1/4 throttle. It should not be screwed in normally about 1/2 to 1 1/2 turns out but this does vary and is best fine tuned with a running engine at slightly high tick over. Screw the air screw in or out until the engine sounds sweet usually when it's at its fastest tick over. The bogging at low revs could be entirely down to this airscrew being wound in. I haven't done the maths on your fuel mixture.

Paul

[greenfingers]

Rich - what should the gap be on the plug you suggested…??.I'll get one this weekend.

Paul - yes I've not made it clear at all. I understand the difference in the 2 screws - one is the filter side of the carb and lifts or lowers the slide height, the other (to the left of this when looked at whilst on the engine) doesn't sit proud - its almost like a grub screw and sits flush more or less with the surface. I'm guessing this is the mixture screw though. So how does it affect the mixture if screwed in further or out….?? genuine question - less air when its screwed in or more???


I'll try the plug and gap as Rich suggested - after that I'll have a look at the needle and jet. Are they likely to have altered or worn in 2 years though??? Again - genuine question….

Thank you lads….

Martin

[Toddy]

I'll try the plug and gap as Rich suggested - after that I'll have a look at the needle and jet. Are they likely to have altered or worn in 2 years though??? Again - genuine question….

Thank you lads….

Martin[/quote]


Yes

[dylansdad]

My take on the maths for fuel/oil:

For a 3% mixture, 3% of the total (fuel and oil together) should be oil. So, as fuel is now measured in litres, in 5l (5000ml) 3% should be oil - 150ml - and the remaining 4850ml (4.85l from the pump) should be petrol. I'm not sure how critical this is but as 1 gallon is approx 4.5l, then 150ml of oil in 4.5l would be a little over 3%. The experts will tell you if that matters

[greenfingers]

Yes -
I'm not sure everyone stands there with the jug up to the light measuring the last drop - but, hey! maybe that's partly where I'm going wrong.

How does the gap in the plug affect the running of the engine - can it make it boggy/smokey…?

[Storkfoot]

Do you have an air filter? If so, what type and have you cleaned it?

[greenfingers]

Hi - remote filter - foam……seems clean enough….

[Storkfoot]

All filters need cleaning quite regularly. Otherwise they get clogged up, reduce the amount of air they let through which gives you a rich mixture.

Mugellos do seem to have a propensity to display the symptoms you talk about. Perhaps very hit and miss port timings

[greenfingers]

I'll try a replacement. Thank you….

[MickYork]

what is your carb set up Pilot, needle (which clip), main jet, atomiser, etc

[rossclark]

There's a difference between a mixture screw and an air screw. it depends which side of the slide it's on.

You can tell if a carb has an air screw or a mixture screw by it's location on the carb. An air screw will be on the intake side of the carb while a mixture screw will be on the engine side of the carb.

They work opposite one another. An air screw adjusts how much air is being delivered through the pilot circuit: in is rich (less air) and out is lean (more air). A mixture screw adjust how much fuel (or air/fuel mixture) is being delivered from the pilot circuit. In is lean (less fuel) and out is rich (more fuel).

For 2 stroke PHBH it's a mixture screw.

[greenfingers]

Thanks lads - I honestly think this is a minor problem wit the carb set up - wear or adjustment. I'll take it off later strip it down and get the information……

appreciated

Martin

[greenfingers]

Morning..

Right - Dellorto PHBH26
Needle X7 - 3rd clip
AV260
main jet 102
pilot 53
Slide 40

I've checked the air screw (the engine side of the carb as opposed to the screw that lifts the slide) and its 2 and a half turns out.

I've took out the float needle which has the red tip and appears all ok.

Martin

[Storkfoot]

I have no experience of the 26mm PHBH although I do of the 30mm variant. Are you sure that it is an AV260? That appears quite lean to me with an X7.
I'm going to ask a few questions:
Have you now cleaned the filter with petrol, or soap and water?
Have you checked for air leaks especially around the exhaust and inlet manifolds?
How many miles have you done on this engine?
When was the top end last off?
You say it goes like the clappers but was does it fell like when you accelerate gently. Are they any flat spots as you acclerate?

[greenfingers]

Def AV260….

Haven't cleaned the filter yet but will do tomorrow

I'll check for air leaks - had air leak problem before with the outlet manifold on my series 2 and it was noticeable straight away. I don't think I have any but will check.

I've done about 1500 miles on it - stripped it down last year (summer time) because it was running badly. Replaced the drive side seal and stator as the wiring was rubbish..vey brittle with far too many repairs for my liking. Ran well after that.

It runs well on full throttle but doesn't like it being opened up quickly - likes to build up. Feels like fuel starvation a bit.

I noticed yesterday far too many air bubbles in the fuel pipe than I ever want to see….I wasn't sure if this was because I was hovering around half a tank at first with the fuel tap not switched to reserve. I filled her up but got the same flat spots - but sporadic on the mile or so back home. I re tightened the banjo clips to make sure no leakages. I'll double check the pin hole in the fuel cap in the morning - and sure its not obstructed by the rubber seal.

Martin

[greenfingers]

Sorry!!!! slipped finger…AV266!!!!!!!