Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board Stalling when coming to a stop.

Guys,

I recently upgraded several items on my 1971 trophy. New Pazon ignition, new premier 930 and new 6v coils and wires were installed. The bike starts up and runs fine. After coming to a stop, the bike will die if I dont keep feathering the throttle. This is with the headlight off. I already checked the tank vent which is clear. The charging system is putting 15V into the battery. The battery is new. I did installed the spacer for the carb to keep it cool and it is cold to the touch. I also did carb cleaner around the inlet of the carb and idle did not change.

Any thoughts.

How did you set the idling rpm and mixture?

The mixture screw is about 1-1/2" turns open. The throttle screw is set to run about 1K RMP hot. When I started it, I have to throttle it until warm and then it idles.

So you have not warmed the engine and then tuned the idle mixture for highest speed then ?, so do it next time. The 1.5 turns is a starting point, you need to then do the tune, if the tune sets the idle too high then use the throttle stop to reduce it, 900 to 1100 is a good idle speed. Its a carb not an ECU, a tuned idle on a warm engine gives a reliable warm idle, expect it to be cold blooded until its warm.

I see you have the bike set at 1000rpm when hot on 1 1/2 turns out on the air screw but Kommando is guessing that you didn't do the proper sequence of adjustments. What you have done doesn't make as reliable an idle.

. I had my 67 Trophy set a bit like yours but found that it idled much more smoothly and reliably with the air screw further in. I now do the book style where you lower the throttle slide until the engine is almost stopping, adjust the air screw until it is smoother and faster and repeat. You may find that you need the air screw further out or in depending various factors but I am guessing that your idle is too weak. Does it spit back at all?

Having said all that my bike would usually keep going unless the battery was dead with the headlamp on as I came to stop. If I switched the headlamp off and restarted it would then idle but I couldn't put the headlamp on again until under way.

Dave

I went out and readjusted it. Once warm, I needed to turn out the air mixture screw. The throttle still would slowly drift down until it stalled unless I kept it up around 1600 rpm. Is there any thing else it could be?

When you shut the throttle, rpm being slow to fall can be a sign of a weak idle mixture.

Beat me to it. Snap!!

You need to check the full pilot circuit, even new carbs can have a piece of crud moving around, float height check , fuel flow out of tank, fuel tank breather check.

Were the ignition and carb changes all done during the same period of workshop time?

If so, has the timing been set by strobing? This is important to do before playing with the carb.

Also a new carb cannot be assumed good from the box. It must be dismantled, jet sizes confirmed, and especially the pilot circuit checked to be clear of manufacturing muck.
Effective factory cleaning/flushing cannot be assumed (see numerous threads on this topic). It has come from a dirty place with swarf-making operations, with likely a quick blast with compressed air afterwards. I very much doubt that they spend the time to check that all passages are 100% clear, so you must.

The pilot jet is the most likely culprit for the symptoms you describe, assuming the timing is definitely correct.

...man; you do not need all those check outs; you only need to screw in a bit the throttle stop screws and just that. All other sound right.
With a minimum screw in the engine will not die; but again, is minimum the movement between hesitation and too much rpms. If for any reason the screw in do not work is due to the throttle cable is short.

I did a static timing change and thought the carb needed to be adjusted prior to using the strobe to set it. I did check all the passages already. What is meant by a "weak idle mixture". Does that mean blockage.

Static timing of an EI installation is definitely not good enough to then troubleshoot the carb.
The initial (static) timing of Pazon, Boyer etc is almost always considerably retarded. This will make carb tuning a nonsense, nevermind the potential engine damage.

“Weak mixture” can be blocked pilot jet, it can also be due to many other things.

I suspect you’re referring to TT’s comment, where I think he was thinking of a gradual drop from high rpm after closing the throttle, in which case he is correct in pointing this out.
I interpreted your description to mean that after closing the throttle, it idled for a while and then gradually slowed till it died. Please clarify.

Reverb does have a point about throttle cable free play. While troubleshooting this issue, ensure that there is plenty of slack in the throttle cable when the slide is completely at the bottom of its travel (when the stop screw is unwound/removed).
If the slide is hanging on the cable, you will never make any sense of the idle adjustment.

koan58 - the stalling occurs when coming to a stop. The idle drops to between 1.5-2K and then gradually slows until is dies.

Hi Brian, Exactly which 930 do you have? A normal 930 or Premier?

Did you check/adjust float level? It is important to know on new AMAL, normal or Premier float level is higher than the old days. Now they need/want just above bowl gasket surface which will make top of float horizontal with gasket surface. This is per AMAL instruction sheet. I find if you lower it, carb will run lean overall. Still mine idled fine when I lowered float level thinking of the old .080" lower.

Also if Premier you must use .019 pilot jet. This larger than the .017 pressed in jet on old carb. I've experienced your dying on new Premier with .017 jet. Many sellers sell carb with .017 jet. Unscrew pilot jet & look at silver nose. 3 rings = 019 jet # 622/502-19. 2 rings is .019. Many changes in new carbs even though they look similar.

Here's link to size chart: https://www.britishmotorcycleparts.co.nz/amal-premier-pilot-jets

As was stated strobe timing is imperative. I tend to find the motor runs better 2deg retarded. That would put line on rotor about 3/64" in front of pointer, meaning line is closer to front wheel that much. You can experiment. Depends on your fuel. Always use highest octane you can get even if it has ethanol & lower octane doesn't. Higher is still better.

I do just rough mixture & idle adjustments after riding 3-4 miles. Then fully warm motor for 15 miles or so & that is more the real operating temperature.

Generally when mixture & idle rpm are correct motor will run lean cold & you'll have to hold throttle on some until bike is warmed. About 4-5 miles or so depending on how cold the day is. If the motor idles cold, it's usually too rich & idle will be uncomfortably high warmed. 1000 rpm is a good hot idle in my mind. Reduces stalling with prolonged idling in heavy traffic & will not be too slow at bottom of long down hills on cold day. A side effect is a little higher oil pressure hot at idle & it is said a little more oil flinging on cams etc.
Don

Original post:

"I recently upgraded several items on my 1971 trophy. New Pazon ignition, new premier 930 and new 6v coils and wires were installed."

I'd still say do the strobing, as it doesn't seem to have been done yet, then go from there.

"I did a static timing change and thought the carb needed to be adjusted prior to using the strobe to set it."

This is arse about face, IMHO.

Brian- How did the bike idle before the electrics upgrade?

Dave

By weak, I mean not enough fuel in the fuel/air mixture. I should probably have said “lean” to someone from a Southern state.

The idle mixture screw being too far out makes it lean/weak when the throttle is shut. So does an air leak into the manifold.

If the carbs float level hasn’t been touch since new I have found that none of the premiers (Carbs with stay up float as standard - as all new carbs have stay up floats) have required adjusting.... I’ve fitted and sold quite a few.

I didn't see an answer to the question "How did it run before the EI conversion?".

Before all else, strobe-time the engine. Ignition timing is not affected by carburetor adjustments. Retarded timing can cause stalling at idle.

I have seen clapped-out carburetors cause an engine to slow down and stall when warm. Theory is, the carb body expands and causes a sloppy fit on the throttle slide to become sloppier, leaking air around the slide. Push the slide(s) back and forth in the bore(s) with your finger; look for excessive play.

Another thing that can cause stalling, especially after a quick drop to idle, is a voltage drop. You said that the charging system is supplying 15V to the battery; that's too high. If it's been that way for any length of time, you may have ruined the battery. Check battery and charging system health. Over-voltage charging points to the voltage regulator (zener diode or aftermarket rectifier/regulator?). Breaker point ignition will tolerate a voltage drop; an EI will not.

15v seems high as charge voltage. My own bike puts out 14.5v max.

Yes, 15V is high, as noted in my previous post.