FPL won't runwithout choke

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Chris B
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Re: FPL won't runwithout choke

Post by Chris B » Sat Jan 04, 2020 6:07 pm

Well, you certainly seem to have been pretty thorough.

However, your report of "an incredible bright blue-white spark at both the points and the plug" makes me suspicious.

An "incredible blue-white spark" is exactly what you need at the plug, but you shouldn't be getting a powerful spark at the points. A faint spark at the points is fine and normal, but a powerful spark across the points is often an indication of a failed or failing condenser.

You say: "Right now, with the original #3 needle in place (which was meant for a 10:1 mix) it runs perfectly on the 25"1 mix."

Sure it does - but it'll only run perfectly with 25:1 if you use the wrong needle. It's trying to tell you something is wrong. As explained in my earlier post in this thread, the underlying problem is still there. I'm trying to point you towards a possibility and, despite your reportedly impressive sparks and an understandable reluctance to accept that the issue might be electrical, the problem may yet be hiding in the ignition system. You should not for instance, be getting bright sparking at the points. And whilst your spark plug might be giving you what looks like a beefy spark at atmospheric pressure, who knows what it's doing under compression?

A failing condenser can cause the symptoms you've described, and a failing condenser (properly termed a capacitor) can also simulate various other faults too - including making an engine behave as if it's running lean. As an example - although nothing to do with Seagulls - I've seen an ancient Austin 7 (I don't know if you've got any of those in Florida) that would only run on choke because the condenser was failing.

So - as I'm sure you're aware, and regardless of the location of the root of the problem - installation of the incorrect needle is only disguising the fundamental fault. And, as noted earlier, your report of strong sparks at the points make me suspicious!

C
Last edited by Chris B on Sat Jan 04, 2020 7:18 pm, edited 1 time in total.

mrlmd
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Re: FPL won't runwithout choke

Post by mrlmd » Sat Jan 04, 2020 7:18 pm

The spark at the points was observed in the dark as I spun the engine using a power drill, and the spark at the plug was considerably brighter than that at the points. Both seemed the appropriate brightness to me but I have no way of quantifying them. All I know is that the motor starts within one or two turns of the first cord pull and that it runs great.
And as I said, one of these days I'll take the carb apart again and make sure the air passage in the center cylinder is totally clean but I don't think I can get it any cleaner. The jet is absolutely clean and the rest of the carb is spotless, going through the ultrasonic cleaner with a variety of chemicals numerous times.
I hear all you comments but I have been over this thing many times and cannot find anything to alter or improve the current situation.

Chris B
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Re: FPL won't runwithout choke

Post by Chris B » Sat Jan 04, 2020 7:29 pm

"The spark at the points was observed in the dark as I spun the engine using a power drill, and the spark at the plug was considerably brighter than that at the points. "

Oh okay, thanks for that. We're on the same page now.

So it was in the dark, and possibly not quite the "incredible blue-white spark at both the points and the plug," that made me suspicious.

Hey ho...

Back to square one then.

C

Chris B
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Re: FPL won't runwithout choke

Post by Chris B » Tue Jan 07, 2020 3:47 am

Marc -

I've just revisited this thread and noticed you say that you used WD40 to check for an air leak at the carb / block joint. Presumably you're referring to the old "Mark 1 Ear Test Method", where you start the engine and then squirt WD40 (some people use propane) at the outside of the joint you're testing, while carefully listening for a change in the engine sound / rpm.

If that's the test method you used, did you apply the same test to the throttle cable entry point at the top of the carburettor? You may well already be aware of the problem I'm about to describe, but I'll mention it anyway for the benefit of others who don't. Years of engine use eventually cause the throttle piston to become a less than snug fit in its barrel. In fact I've seen a few that were downright rattly. As the wear progresses and the clearance slowly increases, air begins to get sucked in through the throttle cable entry orifice, pulled down past the throttle piston and thence into the choke tube airflow, where it leans out the mixture.

The wear problem and related air leakage tends to appear earlier and be more pronounced if the carburettor body has been cast from "Mazac" (an inexpensive zinc / magnesium alloy, similar in appearance to aluminium and much favoured by carb makers) because the casting is much softer than the throttle piston. Whilst I'm not sure what alloy Villers used for their Seagull carbs, I do know that Amal used Mazac for thousands of carburettors that were factory fitted to Seagulls.

So if you haven't done so already - and especially if your throttle piston isn't a nice snug fit in its barrel - it might be worth firing her up and then generously hosing the throttle cable entry point with WD40. If WD40 isn't available then you can use anything that's suitably volatile. In the days before WD40 many of the old timers used a gas torch for this task (although obviously not lit, and preferably not indoors either!).

Anyway, if you try the WD40 test at the location mentioned and the engine sound / rpm changes, then that's where at least a part of your mystery problem lies. If so, then a rubber boot packed with grease and fitted at the throttle cable entry might serve as a temporary remedy. Not forgetting, of course, that you'd also need to change the needle back to the correct one for your 25:1 mix.

Just a thought.

C

Chris B
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Re: FPL won't runwithout choke

Post by Chris B » Thu Jan 09, 2020 5:23 am

BTW - just to be clear, it's not simply air leaking in past the throttle assembly that causes the lean mixture. To be pedantic about it, the air leakage reduces the vacuum in the venturi, which in turn prevents the metering jet from delivering sufficient fuel. Same thing happens when there's an air leak at the carb / inlet port joint.

mrlmd
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Re: FPL won't runwithout choke

Post by mrlmd » Fri Jan 10, 2020 5:31 pm

Thanks for that, I'll check that out too.
My piston slide does seem like a pretty snug fit though, no excessive slop in it's movement up and down.

Chris B
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Re: FPL won't runwithout choke

Post by Chris B » Mon Jan 13, 2020 5:22 pm

It's excessive wear across the diameter of the slide and bore that causes the problem I've described. Small capacity 2-stroke engines seem to be more sensitive to this leakage than 4-strokes and larger engines. The related lean running due to partial loss of vacuum tends to be more noticeable at low rpm (hence difficulty with starting).

C

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Charles uk
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Re: FPL won't runwithout choke

Post by Charles uk » Mon Jan 13, 2020 5:50 pm

Not a problem I've ever come across on a Seagull, perhaps because the throttle slide moves so little & the primary compression is relatively low, unlike a motor scooter that spends it's life driving around town.
Make it idiot proof and someone will make a better idiot.

Chris B
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Re: FPL won't runwithout choke

Post by Chris B » Mon Jan 13, 2020 6:42 pm

It's a problem I've encountered on elderly motorcycles. I recall that one was an ancient BSA D1 125 and another was a friend's Greeves, which - apropos nothing at all - I think had an Anzani engine.

Possibly encountered less frequently with outboard motors because they generally run in a much cleaner environment than bikes - fewer abrasive particulates in the air. And, as Charles points out, an outboard throttle receives far less use than that of a motorbike.

C

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Collector Inspector
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Re: FPL won't runwithout choke

Post by Collector Inspector » Mon Jan 20, 2020 9:37 am

So now there are sparks at the points?

Condenser and or terminations that one.

No indication yet that there is the washer/seal in place under the carb jet holder to carb body. Part #V107X3

Do you have the correct ID compensator fitted?

What is the float height?

Can we have some pics please?

We just love pics aye.

BnC
A chicken is one egg's way of becoming others

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