LI 150 Series 3 poor running ideas please?

[jonalabaster]

Hi, I have a 1962 LI150 that I have just restored. Is all standard and I have replaced the piston (with standard 150) and rings. Currently running in. Have cleaned out Carb (standard) cleaned jets etc and checked no gunk in float chamber. Have checked earth connections as well. This is a 4 pole stator plate DC with battery to power brake light and side light. She starts with no problem has a good spark and after running the plug is a nice chocolate brown colour. Have a new spark plug and HT lead. Runs perfectly for about 15 mins and then starts missing occasionally. Have tonight replaced the coil and the performance was better but still went lumpy after about 15 mins. She ticks over with no problem. All electrics seem to work fine and all is original 6V AC. Have checked flow of fuel which works to half a pint per minute. The tank looks cleanish and have checked there is no blockage in Carb. Filter appears clean as does the float bowl. I'm thinking it may be a condenser problem but before I take her all apart I wondered if there may be a simple solution I have not considered. Thanks in advance for your help

[johnnyXS]

are you sure about the flow rate ?

1/2 pint in 60 seconds is way too little.
you ought to get more than that through a drinking straw.....

I would remove the petrol tap from the tank and carefully check the feed tube to make sure it hasn't been blocked or crushed.
You might find some very fine rust particles have formed a sediment in the petrol tank if it hasn't been used in a while and then filled to the brim.

I agree about the condensor... it does sound like a condensor breaking down when hot.

Next time it coughs and splutters when you are riding it try putting on the choke and see if the running improves.

[HxPaul]

If the OP is using a standard tap,the flow is about right,standard taps flow roughly 1/2 pint in one minute.Before doing anything else,remove the filler cap and run the engine again. If the engine carries on running the vent hole may be blocked in the fuel cap.

[jonalabaster]

Thanks both, have cleaned and unblocked the breather tube in the filler cap previously, but will drain tank and check the main filter again. Cheers

[Knowledge]

If these don't work for you, then I would return to the idea of the condenser failing as it warms-up. However, worth checking flow rates and petrol tap gunk options first.

[grandpa]

Hi jonalabaster
Compression low when warm
Air box bellows collapsing when warm
Faulty spark plug when warm
Air leak when warm
Good luck

Grandpa

[jonalabaster]

Thanks All

Have a list to work through then will do each this weekend

Thanks again

[johnnyXS]

If the OP is using a standard tap,the flow is about right,standard taps flow roughly 1/2 pint in one minute.Before doing anything else,remove the filler cap and run the engine again. If the engine carries on running the vent hole may be blocked in the fuel cap.

very good suggestion about the vent Paul, I didn't think of that. Just riding around with the cap off for 20 minutes should prove if it is the cap vent.
I hadn't realised that the original tap had such a small flow rate. Another possibility that occurred to me is that a fuel flow restriction could be at the fuel bowl needle jet . I know some larger 22mm cabs need the needle jet enlarged to increase the fuel flow to the fuel bowl so that the main jet is always covered.

Might be an interesting test to remove the fuel bowl and measure the flow rate from the carbs needle jet into a catch vessel like a bowl .

[jonalabaster]

Thanks again, fairly sure it is gunk in the tank. Have drained the fuel and filtered through kitchen towel and there is a fine residue which is either rust or sand. Have not ordered some rust clear off internet and will start again. After filtering a number of times she ran much better for longer. So will continue to explore this before replacing condenser. Also have checked points and firing point and that all looks excellent.

Cheers