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 .... :shutup:

[husaberg]

Start it cold then .... :shutup:

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.


308343

[Motu]

Starting singles is an art - I started on British singles, and being only 7 stone I had to learn technique as I had nothing else to back me up. Throttle only open a tad was important, just off the freeplay. Conversely, when I worked on stationary engines, they have to be set up to start on wide open throttle.

[jasonu]

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. .?

Those sound like major mods to me.

[FJRider]

T Has a very sooty pipe too ...

The unleaded fuels can cause that ...

[Woodman]

Those sound like major mods to me.

Yeah, granted their are a few tweeks, now if I can only stop the clutch from randomly slipping I will be able to see how she will perform. The coil lead fell off yesterday just shy of 80mph (indicated) but hard to tell if the clutch was slipping or not.


The unleaded fuels can cause that ...

Yeah you are right.

[Grumph]

Saw a similar problem on another pushrod single....it was lack of valve clearance when hot.
Given you've bumped the com up, it's going to run hotter anyway, so allow a tad more clearance.
These things have a weird setup where the oil goes up the pushrods too...

Your clutch problem could well be an indented basket. They're pretty soft. Clean up the slots with a good flat file.

[Woodman]

Ok, back to this.

Got a bunch of jets and new needle and spent a bit of time jetting and set the points to the proper setting and set the ignition timing which was ok.

Bike starts and runs sweet. Pulls like a tractor, but misses at high speeds, maybe 5000rpm? (no tacho). Starts missing a wee bit then gets very bad.
Checked and redone all the connections in the ignition circuit and added another earth for good measure, but still misses. Coil and lead are new.

It has an adjustable main jet and I have experimented with that a fair bit today on the fly so pretty sure the miss isn't fuel related.
My understanding is that if it was the main jet being too small it would just stop revving and not miss? correct?

Magneto? coils? both 40 years old
Any ideas.

[Grumph]

Either points bounce or just plain old age in the windings of the LT mag or coil.

Edit - memory came up with a Ducati mach one a few years back which had the same symptoms. Turned out it had an early points cam in which gave minimal dwell...6v plus modern fuel wasn't a very good combination. Lengthened the dwell by grinding, polished the cam to extend points life and much better.
Find a multimeter with a dwell function and check.

[Woodman]

Chur,

Coils. How do I test them? Anyone in NZ rewind them? any good place that sells them online? looked but can't find although they may be generic small italian ones so just may need to measure and compare to the few that I have seen on the internets.

Also , can the flywheel be remagnetised? have heard this can also be an issue. How do I test for unmagneticness?

cheers

Edit, BTW the clutch is good now. Was the springs. Now replaced.:niceone:

[Grumph]

Chur,

Coils. How do I test them? Anyone in NZ rewind them? any good place that sells them online? looked but can't find although they may be generic small italian ones so just may need to measure and compare to the few that I have seen on the internets.

Also , can the flywheel be remagnetised? have heard this can also be an issue. How do I test for unmagneticness?

More detail needed. If you're referring to the low tension coils under the rotor, shouldn't need a rewind if they've still got continuity and insulation.
If the separate HT coil, something generic with the appropriate primary resistance will work.
Could be right about flywheel magnetism, they do go off with age. I'd ask one of the mag specialists who service the Classic register guys where to get it done.

[Woodman]

More detail needed. If you're referring to the low tension coils under the rotor, shouldn't need a rewind if they've still got continuity and insulation.
If the separate HT coil, something generic with the appropriate primary resistance will work.
Could be right about flywheel magnetism, they do go off with age. I'd ask one of the mag specialists who service the Classic register guys where to get it done.

Yeah sorry, the LT coil. They look fine, but will test. HT coil is new, and apparently right for this bike.

Would be good to find where to remagnetise cheers for the effort.

[Grumph]

Yeah sorry, the LT coil. They look fine, but will test. HT coil is new, and apparently right for this bike.

Would be good to find where to remagnetise cheers for the effort.

I know it can be done - just not who does it now. Used to be a place in ChCh where i had mags remagnetised - big impressive giant "G" clamp shaped lump which hummed and spat sparks....
I'm sure I've seen someone on here report having a rotor remagnetised - just can't remember who.

[Woodman]

Took the flywheel off today. Seems to be pretty magnety and the coils look ok. Points were worn more than first thought so gave them a file. Will test ride soon as in my haste to go for a ride forgot to torque up the flywheel and the key got shorn/shawn/sean/sheared off as it sat there idling in the shed.:( No damage, just need a new key so will have a poke around in the workshop at work tomorrow.

[pete-blen]

Condenser...

[Daffyd]

Take a small dry ice fire extinguisher with yo and give it a blast before you try to start it.

[Banditbandit]

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

Yeah .. this






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.





Yeah - sounds like it's too rich ...


Took it for a longish ride today . ..., but starting was not an issue if I held the throttle open.

yeah .. holding the throttle open leans out the mixture ... it's too rich

[Woodman]

Yeah .. this



Yeah - sounds like it's too rich ...



yeah .. holding the throttle open leans out the mixture ... it's too rich


Funny you should mention this. Just happened to do a cold call on a customer that works on old bikes for a living, and he reckons that my stumbling/missing at high revs sounds like too rich on the main jet. All my jetting has been to fix the starting issues, but I haven't replaced the pilot jet so its a bit odd really, but come to think of it it used to rev ok.

Will have to spend some time doing jetting runs once I get a new key made up for the flywheel.

[Woodman]

Okay, the Benelli is running like a dream, not sure what fixed it, but I rejetted it leaner and fitted a whole new (nos) generator and points that I found in Germany. Its a bit loud but goes real well.

Question regarding brake lights.. Do I need one for the front brake and if so where do they go? Rear is easy, but I heard somewhere that only the rear is required on bikes of this age.

chur