Carb or ignition problem

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dart6

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Recently i imported a Combat from the USA. When i picked it up from the shippers it started 1st kick, idled well but did not run well.
It has a later aftermarket Norvil fibreglass tank that looks like it had an epoxy coating applied at a later stage. The coating has become brittle and flakes off easily so i was able to remove the majority of it. The original fibreglass appears fine
It has a Boyer MK3

I had the amal 932 carbs ultra-sonic cleaned and reinstalled them but there was no change.
I swapped the 12V coils [wired in series] for 6V coils [wired in series], the HT leads and plugs and still no change.

It still starts 1st kick and idles well when cold and battery has charge.

Before i change the carbs i would like to know - if the boyer was crook would it still start 1st kick and idle well even when cold?

Thx Brett
 
Yes with Boyer it needs a fully charge i.e. good condition battery. Will start and run but won't run well if battery is not "fully charged" i.e. they are fussy. It can lead you to feel it has fuel starvation.
obvious other areas to look at, plugs, float level and blocked jets.
Sounds like the tank may well need to be lined with Caswells or similar.
 
I think the more recent fibreglass applications are impervious to todays gas
 
Can you define does "not run well"? There are a lot of degrees of this condition. I don't think a bad Boyer box would act like this but they do like a good solid 12V at speed to work good. Do revs rise smoothly in neutral? When idling smoothly, try the headlight, does the engine keep smoothly keepin' on or does it falter some? The stock charging system is not all that so if a battery is not really topped up charge-wise, it can give fits to a Boyer. As an example: Several years ago my Boyer equipped MK3 actually started to miss at regular intervals when slowing for a turn. It was a lowish battery. The extra voltage used to run the turn signals, coupled with the low revs (and subsequently low charge rate) at the corner caused the Boyer to sign off with each flash.
 
dart6,
Are the chokes fitted and if so are you using them?

Dave
 
Can you define does "not run well"?
Click to expand...

Valid question, other than you none of us are there so describe the problem with more detail, is the bike running on the road or are you just opening the throttle on an unloaded engine, what revs and what throttle openings are good and which are bad, both pipes hot or one or both cold etc etc.
 
dart6 said:
no chokes
Click to expand...

Without chokes it'll run like a pig until it warms up, and it shouldn't tick-over too well while cold.

Dave
 
Have you checked for correct jetting in the carbs when you had them off to be cleaned? Are you running air cleaners? What type?
 
You can easily tell if the motor is starving for fuel. When it is cold and the chokes are off, it should spit back through the carbs. Put the choke on and warm it up. Then it should rum smoothly without spitting back or missing. If you wind the throttle on when it is warmed up and you get a gasp, the motor is being starved of fuel. The least detectable problem is a blocked tank breather.
 
Thanks all I appreciate all the feedback. We don't need chokes down here in NZ. As stated previous the bike idles good after a few seconds cold, no faltering. It's slow to rev and uneven but idles nice after sitting.

I've ordered the Pazon Altaire as i've never liked the boyers, they've only ever given me trouble in the past.
As for carbs i have the PWKs from Jim i was going to use on another build .
I plan on fitting the carbs first
 
A couple easy checks. Put a voltmeter on the Boyer and see what you have for voltage as you rev it up. Check the advance with a timing light.

Have you checked the screens on the fuel taps to be sure they are not clogged with degraded fibreglass resin ?

Greg
 
I have this very technical technique and a very expensive diagnositic device that most people have, but don't know it....

Let me help you.... so follow my directions..

1) start the bike

2) let it warm up for at least 2 minutes.

3) SPIT on each exhaust pipe.

4) END TEST, see diagnosing results below:

DIAGNOSING RESULTS

1) Both pipes are hot enough to boil the spit instantaneously : Bike is firing both cylinders

2) One pipe boils the spit instanteously with a puff of smoke, but the other is just HOT and the spit runs down the pipe with maybe some slight smoking: This is a bike running with only one cylinder firing. The other cylinder's exhaust is hot because it's pumping compressed air which heats up, but it's not firing because if it was the pipe would instantly boil the spit into a puff of smoke...

In the past, I've assumed because an exhaust pipe was "hot" that the cylinder was firing. If it's not hot enough to boil spit at the header pipe, it's not firing...

IF both pipes smoke when spit on, I would then check spark timing, then carburation, then valve clearances...
 
Kind of sounds like timing could be off to me. And no not all newer fiberglass is impervious to ethanol and your Norvell tank is probably too old anyway and would need to be coated with Caswell's . Ultrasonic cleaning wouldn't necessarily clean out your cards and less you completely disassembled them and sprayed cleaner through all of the orifices. That's the only way you will know if they were clean.
 
I have seen quite a few Commandoes with cleaned and correctly set Mk 1 Amals that will just not run properly for no good reason. the pilot jet system is particularly poor and difficult to clean properly. Some of these bikes I have seen have had "new" carbs. I'm not talking about Premiers here I have no first hand experience with those. Most go to single Mikuni for hassle free running as there are less and less of us prepared to persevere with the old Mk1 Amals when they play up.
 
Thanks again all. I'm in process of swapping out the carbs but ran into a hiccup as the manifold flange is thicker than the original so a longer thread is needed.
Can someone tell me the thread and size please

Brett
 
dart6 said:
I'm in process of swapping out the carbs but ran into a hiccup as the manifold flange is thicker than the original so a longer thread is needed.
Can someone tell me the thread and size please
Click to expand...

Do you mean the manifold to head Allen screws/bolts? In which case they are 5/16" x 18 Whitworth (although you may get 5/16" x 18 UNC even if you order "Whitworth").

Or do you mean the manifold to carb studs, which are 5/16" x 24 UNF.
 
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