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Just finished building an engine and the set up I've got is a mugello 225 with a 28mm PHBH. It's running fine except when I'm starting to pull away a on a hill and it just bogs down. I have to back off the throttle and let it settle for a second then try again. I think it could be too rich but carbs baffle me. This is what I've got in the carb.
Pilot. 55
Atomiser. aV266
Needle X7 2nd clip from the top
Main 112

Any ideas what to try

Thanks

You don't say what exhaust you have on there, some expansions don't give much torque low down so you will need more revs pulling away. Same goes for some top end tunes although I believe the Mugello is fairly mild. The jetting doesn't seem far out btw.

The main looks way too small (this won't affect your posting problem though) i'd bang a 125 in straight away and take it from there.

Regards the pulling away problem, What gearbox is in it ? (and front and rear gears) could be too tall also what's your timing set at ? too far retarded and it could cause the problem. Sometimes an auto advance/retard unit can help pulling away issues.

The initial fuel and air mix for up to 1'4 throttle for accelerating away from idle is governed by your slide, your pilot jet and the air mix screw.
Your main jet and needle have virtually no effect until nearly half throttle so I'd put those factors aside for now until you get the slide, air mix screw and pilot jet sorted.


Provided that your timing and spark is ok and you have checked and definitely haven't got a slight airleak around the inlet area then you should concentrate on getting the slide, air mix screw and pilotjet correct first .

Get the engine up to temperature then adjust the idle speed to a fairly quick idle around 1000rpm which will be a bit higher than you'd normally be comfortable with.

Adjust your air mix screw in to weaken the idle mix and out to richen. Small 1/4 turn increments at a time and allow 5-10 seconds for the engine to stabilise at each step. I usually give the throttle a couple of revs and then let the idle steady .

If the idle tends to rise and fall by itself the idle mixture is too weak and if it starts to cough and splutter the idle mixture is too rich.
Gradually adjust the idle speed in steps to reduce the idle speed down to where you want it at each step fine tune the air idle screw.
If you need to screw the idle mix screw in until its less than 1x turn out or screw it out more than 2.5 turns then you will need to change your pilot jet.

Once you have the idle stable try revving the engine from idle a few times to make sure that you get an immediate throttle response and the engine doesn't cough and splutter (too rich) or bog down (too weak)
Then with the engine at idle put half choke on and note what happens to the engine .
Does the revs rise immediately ? (too weak ) or does the engine bog and threaten to cut out as it should do (too rich )
Try increasing the throttle more slowly...do the revs die ? that might indicate that your slide is too lean ie too large a cutaway on the slide. Conversley if the revs now pick up you probably need a richer slide. I believe they are stamped 30-60 (weak to rich) The slide has a big effect on your initial throttle from 1/8th to 1/4



Your 55 pilot jet is quite rich but we don't know yet if your idle to 1/4 throttle mix is too rich or too weak.
What is the number on your slide ? this is important . Your slide could be the problem or that together with a too rich pilot jet . Then again your inlet could well have a slight air leak making the mixture too weak. Try spraying something volatile around the rubber stub like carb cleaner or WD40 etc and see what happens to the idle speed . If there is any change you have a leak.

Hope this is helpful. If you let us know what happens when you make the changes suggested we can better advise you on solving this .

Thanks for the replies, it gives me something to work on. It's a sterling exhaust

Omega 7 wrote:......It's a sterling exhaust

I think you might have found the problem, not used one but my understanding is that they are similar=r to the ScootRs pipes which are quite revvy and suffer from a lack of low down grunt. A JL3 or similar would be better for pull away.

Trev, I agree with Coaster. I had a PM, which the sterling is a copy of, on a mugello 186 years ago. That was the same. Change the exhaust, mate.

Please dont change the exhaust! (yet)

While it's true another exhaust may be better, depending on your gearing etc, pulling away as you have described is more likely to be your jetting and as already mentioned you need to first look at the slide/air mix screw / pilot first!

Johnnyxs above has given a very thorough reply however I had the same problem last year with a 225 Mugello and a 55 pilot on a 30phbh. Just dropped the pilot to a 52 cured it perfectly.

Rich'