Cota 247C Amal carb issue....I think?

[iconic558]

Montesa 247C with Amal mk2 Concentric.

Now the bike starts n rides fine but for this odd issue.

Even when hot, stop the bike, restart after say a minute and ride off, just off idle and she dies after 10 yards....keep the gas up for say 30 secs longer and ride her on just off idle and she gets thru this and is ok again and will be...until stopped again.

It's annoying as it means I either keep her running in the queue for a section or restart her and give her some beans before the section to get over this 'blip'....not good if you have any mechanical sympathy.

Now from what I read Amals can be a little quirky. My thoughts are she is running slightly weak but I should add idles good when hot on 2 turns out of air screw....saying that idle speed creeps up as she gets hotter, not by lots though but enough to notice.

Worn throttle needle and seat....but wouldn't this cause a rich condition?

It's as if she cools down in 30 secs

At this point I have not touched the carb', just asking the question.

Cheers guys

Edited May 27, 2017 by iconic558

[feetupfun]

Sounds like something stopping the flow of fuel to the float bowl when there is no motor vibration.

When you stop a hot motor, fuel evaporates from the float bowl. This fuel is usually replaced through the float valve, but sometimes a float valve requires vibration from the motor running to keep it working properly. This can deplete the fuel level in the bowl, causing a lean stall after you start it. By giving it a good rev when you start it you are causing lots of vibration.

Another possible cause is that you might have a vapour (or air) lock in the fuel line or fuel tap, which can cause similar symptoms.

As for the idle RPM increasing as it warms up, that may be perfectly normal or may indicate an air leak, or may be the fuel level going low - need more information.

The standard AMAL faults of worn needle jet and worn jet needle have no effect on idle, they just detract from the pleasure of riding what would otherwise be lovely smooth engine performance by making the motor run lumpy and causing premature sparkplug fouling.

[iconic558]

[keychange]

I had similar issues years ago took me 3 months to fix  - revs would climb and she would  run lean and get hot then impossible to restart.  After checking all else it was the timing  so check your timing - it is critical. 21 degrees over flywheel.  I gad tried setting the timing countless times with light etc - eventually just printed out a timing disc and set it with that ...fixed!

As feetup says it could be air leak but it sounds very similar to my issue.

As for other common things to get wrong -  

• check your plug gap as the Monty spark is not strong and the gap is small so has to be on spec manual says 0,4mm -
• not a bad idea to change the condensor ( just cut wire on old one and fit new one under the tank metal on metal).
• right side engine seal
• if you have a non spec muffler - get a new replica one it made heaps of difference to my performance

 

 

[iconic558]

Cheers