Difficulty starting when hot

Could be worth while getting the carb ultrasonically cleaned and clean the air filter too. You can get a good ultrasonic cleaner from Maplins for about £100. I've already cleaned 4 carbs plus odds and sods so it's already paid for itself. Brings carbs up like new. It's well worth using the fruit extract cleaning solution too,

Simon

I've got a 750 Combat with a Mikuni conversion (Allen's standard VM34 conversion kit), Denso IW22 (5307) spark plugs and Boyer ignition. The bikes been sat a long time but today I rode around 70 miles on two 35 mile trips with a 2 hour gap in between.

On the outward journey I stopped to adjust the idle speed, the engine stopped and wouldn't re-start. After 3 or 4 minutes of kicking it restarted and I continued without problem.

On the way back I had to stop rarther abruplty (nothing serious), the bike stalled and again took some minutes to restart.

In between the sweaty kick starting the bike sang along merrily.

Any thoughts?

Much appreciated.

Dave

Hello well your first problem is the Mikuni Vm34mm Cabs tend to run lean have you any bluing on the exhaust pipes , a clean sign of lean mixture from a very hot flame witch sends the pipes blue, there are out the SU carb conversions these tend to be a lot better , and Have you looked at the new Self Generating electronic ignition systems By Electrexworld.co.uk for Norton twin you need STK-102D this runs your lights and ignition in one and you don't need a battery . but you can still have one to dump over load in to it , it all fits in place of your alternator and comes with a timing plate and every thing you need in a kit, cost less than Parzon or Boyer ,or Rita Electronic kits, , and the beauty of this one is NO need of a Battery, So give it it a look at, Yours Anna J

The Electrexworld kit only produces 50w, which does not sound like enough to run CDI and lights. I would wonder about starting without battery support. You can fit a battery, but according to instructions that will reduce output even further.

Hard starting from hot - most probably lack of fuel rich mixture. Richen the mixture and and retry.

In a mechanically good engine without faults it should run, as we all know, when the fuel mixture is adequate, too rich and it should start but be lumpy and may even cut out, at the extreme it will also not start, too weak and it will be hard to start and if it does, the revs may rise before stopping due to lack of fuel. Carburation is a complex subject, but working back from the what the engine needs to run along with a plug condition check helps a lot with diagnosis of carburation faults.

Hope you get it sorted.

If it starts well from cold its not likely to be lack of fuel ,,rich mixture does cause hard hot starting.I would set up with a colour tune plug when warmed up.

1. 'Stopping abruptly and stalling' = weak mixture when throttle shut off.

2. 'Adjusted tickover', does not say which way, I bet down - maybe high revs experienced due to already being lean = lower the revs thus insufficent fuel lift for the given speed of air through the carb at the lower setting.

3. Good starting from cold just confirms the cold starting (choke / temperature compensation device) capability is functioning.

I have much the same problem on my Mikuni converted 72 Combat. Starts from cold fine, Needs a minite or two with the cold start on then runs beautifuly. When warm i occationaly have to flick the cold start on for a couple of prods then off again and away she goes. However dont touch the throttle from cold or warm. Works for me and i am reluctant to mess with the carb because she runs like a dream.

Mark