Trouble starting hot?

[Woodman]

Just recently got my old bike running and rideable. Its a 73 Benelli 250ss. No major mods except its overbored to suit an xr280 piston, and some porting work and the compression has been raised to about 10.5:1. Running standard delorto UB24 with adjustable main jet.

Starts and runs and idles and everything when its cold, but once it warms up it is a real bitch to start. Also eats spark plugs. Standard is a bp7s, and have tried a bp6s today to see if a hotter plug will help, but no difference.

Bloody annoying cos I can't stop anywhere when I go for a ride cos it just won't start for a few hours at least.

Any clues anyone.?

[pete376403]

Weak coil or condenser (I assume its points ignition). or heat soak to the carb - is there an insulating block of any sort between the carb and manifold?

[Woodman]

Weak coil or condenser (I assume its points ignition). or heat soak to the carb - is there an insulating block of any sort between the carb and manifold?

Aaaah, coil is new, condensor is original I think.How do you test them? Insulating block is there.

[Motu]

Battery or mag for ignition - does it need the battery to start? The mags are pretty weak at starting revs, double check the plug gap, it'll be a lot closer than we are used to today...I'd pull it down to about 20 thou for starting. The Stornello eats plugs too...and I don't remember what heat range it used to take, it's not in the listings anymore.

Also it'll be either rich or lean on the hot start - if it starts with full throttle it's too rich.

[FJRider]

Start it cold then ....

[husaberg]

Start it cold then ....

Pilot and idle too rich, will make starting hard when hot. The 7 plug is also likely too hot for a hotted up engine, my 2 cents. Neat bike those.
remember seeing one about 24 years ago at tommy McLeary's in chch

[FJRider]

Pilot and idle too rich, will make starting hard when hot. The 7 plug is also likely too hot for a hotted up engine, my 2 cents. Neat bike those.
remember seeing one about 24 years ago at tommy McLeary's in chch

A lot of bikes overheat when the oil level is low. Or oil flow around the motor is slow. The fuel vaporizes before it gets into the cylinders. On modified engines it seems worse.

[Grumph]

Aaaah, coil is new, condensor is original I think.How do you test them? Insulating block is there.

From memory they're 6V. Is the coil a 6V? Could be condenser too. See what your local repco/supercheap has that will fit, don't worry about rating, bigger is better. Generator is crank mounted, when it's running put a voltmeter on the battery and check voltage running vs not running to see if it's charging.
Feels like electrical to me...

[Woodman]

Battery or mag for ignition - does it need the battery to start? The mags are pretty weak at starting revs, double check the plug gap, it'll be a lot closer than we are used to today...I'd pull it down to about 20 thou for starting. The Stornello eats plugs too...and I don't remember what heat range it used to take, it's not in the listings anymore.

Also it'll be either rich or lean on the hot start - if it starts with full throttle it's too rich.

Won't start without the battery, but will run without it. I,d say the Stornello probarbly has the exact same electrics.

Pilot and idle too rich, will make starting hard when hot. The 7 plug is also likely too hot for a hotted up engine, my 2 cents. Neat bike those.
remember seeing one about 24 years ago at tommy McLeary's in chch

Just emembered that I had raised the needle the other day and it wasn't having those issues then. This bike has basically been in boxes since 1991ish. Bought it in Greymouth in 1982ish for $125 and rode it round their for a couple of years. Was bloody fun at the Taylorville kart track till they kicked us off.

A lot of bikes overheat when the oil level is low. Or oil flow around the motor is slow. The fuel vaporizes before it gets into the cylinders. On modified engines it seems worse.

It does run pretty hot. Food for thought.

From memory they're 6V. Is the coil a 6V? Could be condenser too. See what your local repco/supercheap has that will fit, don't worry about rating, bigger is better. Generator is crank mounted, when it's running put a voltmeter on the battery and check voltage running vs not running to see if it's charging.
Feels like electrical to me...

Coil is 6 volt, Last time I checked it was charging well, but will get a condensor. Someone told me they deteriorate if sitting for too long?

great info guys, cheers

[Voltaire]

Ignition timing? maybe retarded?
I have found in the past with unknown old bikes its the parts you assumed were ok that usually the problem, ht lead, plug, blocked carb, even once a partially blocked exhaust, would start run but then stop.

[Woodman]

Ignition timing? maybe retarded?
I have found in the past with unknown old bikes its the parts you assumed were ok that usually the problem, ht lead, plug, blocked carb, even once a partially blocked exhaust, would start run but then stop.

Carby has been overhauled with a few new bits. Exhaust is definitely not blocked, HT lead is new. Timing was done by my eye, when I put it together last week, so will set more accurater with a bulb etc, but I usually get it pretty spot on by eye.

It goes like a rocket once it starts.

[husaberg]

Won't start without the battery, but will run without it. I,d say the Stornello probarbly has the exact same electrics.



Just emembered that I had raised the needle the other day and it wasn't having those issues then. This bike has basically been in boxes since 1991ish. Bought it in Greymouth in 1982ish for $125 and rode it round their for a couple of years. Was bloody fun at the Taylorville kart track till they kicked us off.



It does run pretty hot. Food for thought.



Coil is 6 volt, Last time I checked it was charging well, but will get a condensor. Someone told me they deteriorate if sitting for too long?

great info guys, cheers

has it got a square slide delloto cause they can be put in backwards.........

[Woodman]

has it got a square slide delloto cause they can be put in backwards.........

Na round down draft dell.

[Motu]

Battery ign should have a good spark, you should see a good crack booting it over. Again - hot start issues are usually mixture. There are only 3 mixture options - rich, lean or spot on.

[Woodman]

Took it for a longish ride today . Coil lead fell off twice, but starting was not an issue if I held the throttle open. My brain tells me to have no throttle when kickstarting a single after owning an xl600 for a while. So Motu you may be right in that its too rich. Has a very sooty pipe too, although the spark plug is a perfect tan colour.

Picture attached for those who require visual stimulation.