Tuning carb low end issue

[gaz73]

Hi all I have a Dellorto PHVA 12mm carb and after fitting new piston rings it now runs very lean (bogs when applying power but doesnt stall)

I raised the carb needle clip to maximum height and the mid to top range is good but the low end is sluggish until I get to 20mph.

Ive read that I must keep the clip in the middle of the needle when running in and get a bigger main jet, another source said change the float height, another source said get a bigger pilot jet.

I was looking for more ideas basically lol im not sure which road to pick here. Again theres no manual for this bike anymore, been looking for 2 years, I only have the service manual and the carb manual are nowhere near detailed enough for tuning.

Thanks.

[Tango]

Sounds like a pilot jet issue........

[soll]

sounds like a job for our resident youtube mechanic.....Someone call Tamsen

[gaz73]

I will get a new pilot jet, and a new main jet, throttle valve sleeve and probably a new needle, that's where this is going I think, from what im reading you need to change a few things when dealing with low to mid range.

Today it was back to boggy but only when cold, it was slightly more pokey when warm but not much, also strong smell of petrol i think the float is too high, does the needle height affect the float level? Im amazed I need to do all this just after new rings its mental, I guess when you get a new top end you've gotta cross your fingers and hope you don't need to buy several sizes of each part.

[Mr Fro]

The best thing. Absolutely the best thing you can do is spend £30ish on a dyno run. That'll tell you what's going on with your fuelling.

The next best thing is to read THIS. Be prepared to have the carb off and on a few times before you get it right (ish).

That being said, I'm assuming your bike is a 2-stroke so might need to run a bit rich on the midrange a bit to start off with if it's a premix. Someone who knows more about 2-strokes than me (cough, cough, Joeman, cough, cough) might be able to advise better.

[gaz73]

The best thing. Absolutely the best thing you can do is spend £30ish on a dyno run. That'll tell you what's going on with your fuelling.

The next best thing is to read THIS. Be prepared to have the carb off and on a few times before you get it right (ish).

That being said, I'm assuming your bike is a 2-stroke so might need to run a bit rich on the midrange a bit to start off with if it's a premix. Someone who knows more about 2-strokes than me (cough, cough, Joeman, cough, cough) might be able to advise better.

 

Thanks guys, yes its a 2 stroke 50cc scooter, auto choke and auto belt transmission etc and tutorials I find on tuning are only for manual gears/choke bikes so I cant do the tuning tests they talk about.

I will look into the dyno run, sounds cheaper than I expected.

Ive fitted a new main jet thats a few sizes bigger, slight improvement when I get to 20mph but it doesnt make sense, that means im running lean but im not getting lean spark plug readings or lean symptoms.

Im about to try a gadget I have thats basically a glass spark plug so you change the mix until you get a blue flame, it sounds to me like a very accurate way of getting a perfect tune up.

[gaz73]

OK I fitted a new pilot jet and main jet:

pilot was 36 now 40

main was 55 now 60

and theres no real difference in power, I tried the gunson colourtone and saw a nice blue flame but when i turn the screw lean it stayed blue and when I turned it rich i got the slightest flicker of orange every few seconds but never a constant orange. Does that mean the pilot is now too lean? it contradicts the increase in pilot jet. It seems like with pilot jet you need to go up or down 1 step not 5 like with main jet.