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Cruiser 80 timing and carb

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Cruiser 80 timing and carb

Post  slinkymalinky on Sat Apr 15, 2017 8:31 am

Hi everyone,
First post here after reading a great deal of incredibly useful info.

I recently bought myself a Cruiser 80 after the previous owner got it about 90% finished and I'm struggling to get it running. It will rarely start and, on the occasions it does, it seems to run very rich for a few seconds before dying. It spits back loudly through the carb as well.

I've lowered the needle to the first notch but are there some base settings for the two carb screws that I use as a starting point to get it set up?

I was also wondering if there's a good method of setting the timing without having to remove the head to measure the 1/4" BTDC? The angle of the plug hole has got me stumped on how to measure this.
Thanks in advance.

slinkymalinky

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Timing

Post  Bigjim on Sat Apr 15, 2017 9:11 am

slinkymalinky wrote:Hi everyone,
First post here after reading a great deal of incredibly useful info.

I recently bought myself a Cruiser 80 after the previous owner got it about 90% finished and I'm struggling to get it running. It will rarely start and, on the occasions it does, it seems to run very rich for a few seconds before dying. It spits back loudly through the carb as well.

I've lowered the needle to the first notch but are there some base settings for the two carb screws that I use as a starting point to get it set up?

I was also wondering if there's a good method of setting the timing without having to remove the head to measure the 1/4" BTDC? The angle of the plug hole has got me stumped on how to measure this.
Thanks in advance.
You have checked that the AMAL carb has all the correct jets?  Go to the AMAL web site, they have hints & tips as to how to set up their carburetors. The larger headed screw (throttle stop) adjust the tick over & smaller one adjusts the pilot jet mixture.  AMALs usually use the middle notch for the needle settings as base start point.
The next bit is best done with a warm engine.  You may have to re do some of the settings once the bike is warm and running evenly.
Essentially, screw in the pilot air screw (the smaller one) until it stops, then unscrew 1˝turns. Next, unscrew the throttle stop (the larger headed one) until the throttle can FULLY close.  Open the the twist throttle a bit and start the bike. set the throttle stop to keep it running at a fast tickover, when you let go of the twist grip.  Now lower the throttle stop a small amount, the engine will slow down, as it gets to the "faltering" point screw in or out the pilot air screw to speed the engine up. Lower the throttle stop AGAIN until the engine slows down, again adjust the pilot air screw to get a clean tickover.  to test if the mixture is correct, give teh twist grip a quick blip, if the engine falters or stops, then the mixture is too weak.  Carb spitting suggest a too weak mixture.
One more thing, do you have a "choke" on the carburetor?  either manual via a lever or a disk on the mouth of the carb?  This is used to aid cold starting.  

The timing & electrics is the same as the AMC lightweight 250s.  All wipac.  Are the points clean, are they set to the correct gap, is the capacitor (condenser in old money) OK?  Is the battery in good order?  Make sure that the card sits firmly against the barrel and that the gasket/O ring is good.  Sometimes the carb flange gets distorted over time, heavy handed mechanics.  Check it with a steel rule, if slightly warped, you can flat it own on a piece of glass or similar flat surface, using very fine emery/wet & dry.  clean thoroughly after doing.
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Carburettor

Post  kerabo on Sat Apr 15, 2017 11:49 am

Well said Big Jim

Can I just add that if you use modern oils with a lean mix your fuel is thinner and goes through the jets faster. On My 87 I want down a fraction in all jet sizes and dropped the needle one notch. Another thing that is critical on the Monoblock is fuel height . The Pip in the word Amal on the float chamber cover is the correct level. Any higher you will need lots of flooding to start. I drilled an old casting out on that spot.

Ken
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Re: Cruiser 80 timing and carb

Post  Bigjim on Sat Apr 15, 2017 12:38 pm

kerabo wrote:Well said Big Jim

Can I just add that if you use modern oils with a lean mix your fuel is thinner and goes through the jets faster. On My 87 I want down a fraction in all jet sizes and dropped the needle one notch. Another thing that is critical on the Monoblock is fuel height . The Pip in the word Amal on the float chamber cover is the correct level. Any higher you will need lots of flooding to start. I drilled an old casting out on that spot.

Ken
I have seen perspex covers made with the line marked on, as test.
There is a good article in the East Anglian Autoclycle club's recent magazine, on the effects of the 10% ethanol. Which reduces the RON rating for unleaded petrol. This then reduces the power, which is crucial for mopeds, especially as they have so little power to start wit It suggests adding 10% paraffin, or heating oil or even diesel at 3% to improve the burn factor of the petrol.
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Re: Cruiser 80 timing and carb

Post  slinkymalinky on Sat Apr 15, 2017 3:33 pm

Thanks guys.

The bike was very difficult to start when I got it and the seller told me that he hadn't gotten round to rebuilding the carb so that's where I began. I used an Amal stay up kit with a 320 main, a 105 needle and 30cc pilot. Points are new and gapped to 15 thou, battery is new and fully charged and I'm getting a healthy spark (possibly not at the right time!).,

I have had some trouble with fuel pouring out of the bell mouth so I also bought a new seat for the fuel valve which seems to have cured the issue. It may well be that the fuel level isn't correct so I'll see if I can knock up a perspex cover to check that's right.

Interesting tip regarding the thinner mixture with modern oils Kerabo, I'll bear that in mind.

I'll have another go using Big Jim's suggestions for the pilot air screw and throttle stop screw but I suspect that the engine hasn't been timed accurately either so if none of the suggestions bear fruit I may well whip the head off to try and get that done properly with an accurate BTDC measurement.

Will I definitely need a new head gasket if I do, or will I get away with recycling the old one?

slinkymalinky

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head gasket

Post  Bigjim on Sat Apr 15, 2017 3:41 pm

If it's the solid copper type, then clean it, wait until the other half is shopping, then if you have a gas stove, heat it up until it is very hot and let cool. It's called annealing. Or use a blow torch.
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Re: Cruiser 80 timing and carb

Post  banjo boy on Sat Apr 15, 2017 3:56 pm

When I built my carb For my 87 I was having flooding issues I took kerabo(ken) advice went down a size on standard size run with silkoleen fully synthetic made sure everything was spotless clean and took all the advice as given here, that was 2 year ago and never had flooding since and runs very well,once you get to stop flooding if bike still won't fire up then move onto timing,hope you get sorted soon, it is so frustrating when you are trying to get to the root of the matter.but rewarding when you do sort it.

Regards
Laurence
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annealing copper

Post  piston 197 on Sat Apr 15, 2017 4:11 pm

To anneal a copper head gasket , heat till red hot then quench suddenly in cold water,
With hardened steel allow to cool slowly, with sprockets I put them in the woodburner over night and take them out in the morning when the fire is cold
Copper works the other way round and needs to be cooled quickly to anneal

JH
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Re: Cruiser 80 timing and carb

Post  slinkymalinky on Mon Apr 17, 2017 12:26 pm

I can report back that I've had a successful bout of carb fiddling and now have a nicely running engine. I managed to to get a slightly lumpy and hesitant tickover, used a judicial amount of guess work and luck to get it timed then went back to the carb settings which seems to have worked wonders. It now starts easily and settles into a steady tickover after using the suggestions here.

Thanks for the tips and help all. Now, onto the oil leaks, intermittent lighting and slipping clutch!

slinkymalinky

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AMC engine gaskets

Post  FB vincent on Mon Apr 17, 2017 4:57 pm

Bigjim wrote:If it's the solid copper type, then clean it, wait until the other half is shopping, then if you have a gas stove, heat it up until it is very hot and let cool.  It's called annealing.  Or use a blow torch.

AMC originally specified a very thick insulating cylinder head gasket for the 17T/20T and 25T engines, probably made of compressed asbestos fibre. This was clearly a feature of the Piatti design, since the 49cc Sturmey Archer engine (actually made by BSA) as fitted to the Raleigh Mopeds RM1 and RM2 have similar porting and head gasket. Obviously Piatti intended that heat from the cylinder head should not pass to the cylinder (or vice versa). This is the complete opposite of Villiers who used thin aluminium cylinder head gaskets in their later engines, and in some cases (early 2F's) there was no gasket at all. Whether the seizures that AMC engines are prone to is the result of this gasket is a subject for discussion! Sandy Ross

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Piatti

Post  piston 197 on Mon Apr 17, 2017 5:14 pm

It would seem Mr Piatti was a persuasive man and managed to persuade maufacturers of the merit's of his design which also appeared in Trojan mini motor engines, it would also seem that he managed to con people into the fact that his design was more efficient and the way forward ??

nearly everybody else used the dissipation of heat from the alloy cylinder head via a finned cooling area to keep everything col, Mr Piatti chose to insulate his head from the cylinder with an asbestos gasket, but then again so did Honda ! albeit on fourstrokes ??

I think he was trying to stop heat from the cylinder which would run hot happily enough from getting to the head which was used to get heat away from the combustion chamber to prevent pinking ??

JH
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Signor Piatti

Post  FB vincent on Mon Apr 17, 2017 6:37 pm

Perhaps Signor Piatti realised he had a problem with cylinder distortion, in that the earlier 25T has a large exhaust nut while the later 17T/20T has a push in exhaust pipe with no nut. It would be really interesting to know more about the development of these engines, but I fear that any contemporary knowledge is now lost. Sandy Ross

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Re: Cruiser 80 timing and carb

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