1970 S: a hole between 2700/3000 rpm

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pierodn

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Hi.
Bike has stock e gine and carbs with Pazon well setted with PVL 6 V coils.
The bike has always run great.
Now has a hole between 2700/3000 rpm over that run great again.
Carbs air pilot cleaned again and float setted both 2mm under the edge.
NGK spark plugs new and new leds.
What i check?
Thank you.
Piero
 
Depends on the throttle opening at those revs when you get the hole, 1/4 and below slide cutaway and pilot (try a 1/4 turn in and then out on the pilot air screw from best position to see if it improves, if in is better then go for richer cutaway, out is better then go leaner cutaway) 1/4 to 3/4 then try different needle slots.
 
L.A.B. said:
pierodn said:
Carbs air pilot cleaned again and float setted both 2mm under the edge.
Click to expand...

Setting the float height is no longer the method recommended by Amal.

http://amalcarb.co.uk/optimising-mark-1 ... uel-levels
Click to expand...

Hi Les,
Amal tuning says:"The correct fuel level for all Mark 1 Concentric carburetters is 0.21" plus or minus 0.040" below the top edge of the float bowl. Thus when the needle valve is being held shut by the tangs of the float, the level of the fuel will be between 0.17" to 0.24" (4.33mm to 6.35mm) from the top of the bowl.".
Please, i have ever known that the setting was 2 mm.
But with 4,5 mm from the top edge seems to me that the float bowl has a very very lower level.
Thank you.
Piero
 
pierodn said:
Please, i have ever known that the setting was 2 mm.
But with 4,5 mm seems to me that the float bowl has a very very lower level.
Click to expand...

The recommended method is to set the FUEL level, not the FLOAT height.

"The correct fuel level for all Mark 1 Concentric carburetters is 0.21" plus or minus 0.040" below the top edge of the float bowl.
Click to expand...
 
L.A.B. said:
pierodn said:
Please, i have ever known that the setting was 2 mm.
But with 4,5 mm seems to me that the float bowl has a very very lower level.
Click to expand...

The recommended method is to set the FUEL level, not the FLOAT height.

"The correct fuel level for all Mark 1 Concentric carburetters is 0.21" plus or minus 0.040" below the top edge of the float bowl.
Click to expand...
Click to expand...

Hi Les,
Amal says : "If your float chamber is fitted with a brass needle valve, you may find the valve sealing under its own weight, before the float has risen far enough to press it shut. Symptoms of this problem can be that the carburetter takes a long time to tickle, hesitates on pickup and does not idle reliably. A Viton tipped aluminium needle valve is now available that overcomes this problem. It is now fitted as standard equipment to all new Mark 1 Concentric carburetters.".
I have brass needle valves and brass seat and my carburetors dont have the drain plug.
If i understand, the float chamber with bowl and viton must have the fuel into; then i measure the fuel level from the top surface of the float chamber edge to the float (above or below?) or to the fuel line? And must be about 4,5 mm. If not i can adjust the brass seat.
Have i understood well, or not?
Thank you.
Piero
 
pierodn said:
so sorry, but i dont understand the differences.
Please, could you kindly explain me what is the way to set the "fuel level".
Click to expand...


It's all described in the Amal instructions. So, now, the recommended procedure is to adjust the float position to set the level of fuel in the float bowl instead of setting the float to a measured distance from the edge of the bowl.
 
L.A.B. said:
pierodn said:
so sorry, but i dont understand the differences.
Please, could you kindly explain me what is the way to set the "fuel level".
Click to expand...


It's all described in the Amal instructions. So, now, the recommended procedure is to adjust the float position to set the level of fuel in the float bowl instead of setting the float to a measured distance from the edge of the bowl.
Click to expand...
Hi Les,
It means that i must measure this height from the top surface of the float chamber edge to the fuel line in the chamber and have about 4,5 mm. If not i can adjust the brass seat (i dont have the stay up black float).
Thank you.
Piero
 
pierodn said:
It means that i must measure this height from the top surface of the float chamber edge to the fuel line in the chamber and have about 4,5 mm. If not i can adjust the brass seat (i dont have the stay up black float).
Click to expand...

Correct.
 
The new ' stay up' floats are much easier to adjust, the tang is metal and bendable. No need to adjust the seat level with new floats. Worth the price.
 
Quick acid test, raise the needles one notch to enrichen the mid range. Test ride, symptom worse? Better? Gone? Report back...
 
As long as the float levels are the same in both carbs, does it really matter ? In the end you jet to the comp. ratio, carb and the inginiton advance anyway. I never take much notice of manufacturers' recommendations regarding jetting - right is right and wrong is wrong. The benchmark is good all-round performance regardless of anything else.
 
Piero, that is a wierd place to have a misfire.

My only idea to explain you misfire is perhaps your needle jets have finally worn out to the point where your mixture is now too rich at the 2700- 3000 rpm range. Lifting the slides a little more above 3000 rpm allows a little more air in and corrects the mixture enough to allow the bike to run well again. (That's my guess)

Like Concours, I think changing the position of the needle will tell you if your issue is caused by the needle jet and needle interaction. Concours thinks you should move the needle up to richen the midrange... but I think you should move the needle down to lean out the midrange because of a worn needle jet. I believe as the brass needle jet wears out, the mixture gets more rich, so I think that perhaps your needle jet has worn to the point where it's too rich in that 2700- 3000 rpm range.

If adjusting the needles down helps, then order new needles and needle jets and assemble them in the recommended positions and your old performance should return. Good luck!

** I should also mention that if the carb's slide body wears excessively, the mixture does get leaner, which is opposite to the effect of worn needle jets, so if Concours's suggestion works to fix the problem then you may need to address worn carb bodies.
 
o0norton0o said:
Piero, that is a wierd place to have a misfire.

My only idea to explain you misfire is perhaps your needle jets have finally worn out to the point where your mixture is now too rich at the 2700- 3000 rpm range. Lifting the slides a little more above 3000 rpm allows a little more air in and corrects the mixture enough to allow the bike to run well again. (That's my guess)

Like Concours, I think changing the position of the needle will tell you if your issue is caused by the needle jet and needle interaction. Concours thinks you should move the needle up to richen the midrange... but I think you should move the needle down to lean out the midrange because of a worn needle jet. I believe as the brass needle jet wears out, the mixture gets more rich, so I think that perhaps your needle jet has worn to the point where it's too rich in that 2700- 3000 rpm range.

If adjusting the needles down helps, then order new needles and needle jets and assemble them in the recommended positions and your old performance should return. Good luck!

** I should also mention that if the carb's slide body wears excessively, the mixture does get leaner, which is opposite to the effect of worn needle jets, so if Concours's suggestion works to fix the problem then you may need to address worn carb bodies.
Click to expand...

When he talks about "a hole at 2700-3000", I interpret that as a (what we here would call) "flat spot", where, the power is less than it was just before, and after that, RPM wise. Perhaps piero can clarify for us.
And yes, "spitballing" by simple tests can include what I call going too far THE OTHER WAY, just for reference.
Enrichening the idle (as a test) could also let us know if we are hunting in the right forest.
I expect an air leak or electrical problem will shake out.
 
Do you do most of your riding at 2700-3000 rpm? If so try a new set of needles and needle jets. On my '70 it seems like I change them more often than spark plugs ( a little exaggeration, but...).

Greg
 
hi,pierodn you really need to know at what throttle position your problem is happening unless its an electrical problem ,i once had my triumph t140 e missfire at around 3500 rpm every time, below and above those revs it was fine it turned out to be corrosion on one of the lucas rita bullet connectors from the pickup, did the problem start suddenly?
 
Hi.
The bike has 3000 km fom complete restoration.
The bike has always runs very great.
Bike has two PVL 6 V coils and Pazon I.E. Sure fire setted 31 degree to 5000 RPM.
NGK spark plug with a perfect brown color both and no smoke from exhaust.
The stock Amal 930 overhaull with new hard hanodized sliders and all other prts new (all parts!).
The bike starts to the first kick, has idle hold to 1.000 rpm, and run perfect until 2.900 rpm, then stop to go over and then it starts sobbing.
To day i have cleaned the air pilot way (but was clean and the cleaner spray came away from all the holes), setted the fuel level 4,5 mm from the top of the float chamber edge (the previous setting was the float bowl two mm under the top edge) and changed both the 106 with new one.
Wires are all well tighten.
On monday i will ride for a chek.
Double bah!
Piero
 
If it always occurs at the same throttle opening then it's likely to be fuel/carb related, if the throttle position has no effect then it's likely electrical.
 
The comment about raising the needles one notch is probably the correct answer. That hesitation might the 'cough' I often mention - probably due to lean-ness in the mid-range jetting. It is a good situation to be in, if the miss is due to that, - because when the jetting is just rich enough for the motor to run smoothly, that is usually best power.
 
kommando said:
If it always occurs at the same throttle opening then it's likely to be fuel/carb related, if the throttle position has no effect then it's likely electrical.
Click to expand...
Hi.
In case, electrical what?
Piero
 
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