Prim cutting out when idling to halt

Hi running rebuilt engine in, and it is cutting out after a few miles if I idle to a halt at lights etc (when I am changing down to stop in neutral)

I have been told this is a commen symptom of a badly seated choke. The choke on the PHBH carb has been replaced with a flip choke. The bike has all new cables, new carb etc. Tickover seems fine when bike is cold.

How do i check the seating of the choke, also could the seating on a flip choke be bad as there is no cable flex etc?

Cheers

jim

Yep 24 carb.

The choke is a flip up as opposed to cable operated, so I am presuming that it will HAVE to go up and down correctly as there is no cable flex. The handle at the top will ensure it goes up and down. is that all there is to seating it?

carb seems to be set up right, taffspeed jetted it and the fella that rebuilt the engine set tickover, which is beautiful when the bike is cold, just seems to be when it gets warm that it cuts out when idling (to a halt)

Cheers

Jim

Will check plug and see what it is like.

Jim

Check how many turns out your air screw is. Air screw and pilot have effects on tickover and pulling off up to one quarter throttle. Also your clip on the needle jet may be set really low down (hence the bogging). Don’t make any serious alterations till you are run in though.

You may find the pilot, slide atomiser, needle and mainjet all need changing once you are run in but you will need to post their sizes once you take a look in the carb.

Its easy to rich on the bottom end lean in the top range and vice versa. so mark your throttle with dots representing eigth,quarter,three quarter slide openings and do some plug chop tests - when setting your carb up.

What size is the carb? I thought PHBH was 28mm and 30mm

Don’t know what the jet size is, taffy jetted it to suit the whole setup.

Fuel pipe is good, carb is on the inside of the frame so fuel pipe is just really long enough to take the tank out of the frame, as far as it bogging in throttle positions, I’m still running in so haven’t really given it any amount of throttle, and have been short changing. Not noticed anything though, it seems to be quite keen in all gears.

As far as I can tell the choke is not sticking, with a flip it’s either on or off, isn’t it?

From the advice that I have solicited I’m starting to think it’s more carb mixture than anything else, does this sound reasonable?

It has been suggested that I get it run in and then get it dynoed? Anyone’s thoughts please?

Mike - I would send you some pictures of it now it is done, but it doesn’t look any different to when I got it from you, apart from a couple of chrome finishing touches, new tyres and a new seat, but it has had the works.

Polini 130, 24 carb, upgear kit, leo vince exhaust etc etc. MOT was no problem at all either!

Cheers

Jim

Ok I assume its 25mm then. Take the carb of the manifold and look at the bell mouth. You will need a torch. Follow the line of the choke plunger to a small hole in the bell mouth. You should see the brass choke plunger blocking the hole. By pulling the cable you should see it rise as well. Once you are satisfied the choke is seated okthen you can set the rest of the carb up

Ok a shop will always jet a bike on the rich side. This is wise as they don’t want to be responsible for engines going bang. You could start off by adjusting the mixture/air screw. First you need to establish whether it is an air screw or a mixture screw. If the screw is before the throttle slide it is an air screw.Screwing this in richens the mixture, screwing out weakens. If the screw is after the slide ie. nearest the manifold it is a mixture screw. screwing in weakens the mixture,screwing out richens.
Warm the bike up and adjust the screw whichever it is so that you weaken it off and see whether you can get it to tick over. You may have to screw the tickover screw in a bit to achieve this. If still no joy you will have to look at a smaller idle jet.
Hope this is of some help

Sorry PHBL.

Cheers

Jim

how big is your pilot jet. I currently use a 48 in my polini 130 and even thats a bit rich. my airscrew is 1.5 turns out.

Does your fuel pipe follow a sensible gravity fed route (as best as possible/ Are you running the carb coming out of the frame ?

Does it bog down at all at any given throttle positions. Flip choke uses a rod instead of a cable so any sticking of the plunger should be obvious.

Is the plug really fouled when u check it after a ride ?

just a few considerations [:roll:]

Get it run in get it dynoed then watch it blow up! Only joking but don’t rely on a dyno to set your jetting. Its not real world. Best way? long stretch of road down hill (slightly) one way, uphill the other, a few jets either side and lots of paitence.

Checked plug (1st opportunity, sorry) and it is spot on, nice biscuity colour.

Have only been riding gently though as running in - no full throttle etc.

Cheers

jim

Original von Avenger (Mike A565): Check how many turns out your air screw is. Air screw and pilot have effects on tickover and pulling off up to one quarter throttle. Also your clip on the needle jet may be set really low down (hence the bogging). Don't make any serious alterations till you are run in though.

You may find the pilot, slide atomiser, needle and mainjet all need changing once you are run in but you will need to post their sizes once you take a look in the carb.

Its easy to rich on the bottom end lean in the top range and vice versa. so mark your throttle with dots representing eigth,quarter,three quarter slide openings and do some plug chop tests - when setting your carb up.

Su scala ridotta

All excellent advice