1948 Iron 4G Coil Ignition

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brenton.roy
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Re: 1948 Iron 4G Coil Ignition

Postby brenton.roy » Sun Aug 11, 2019 2:27 pm

According to the manual in the club library, full choke.
'...The direct effect of pulling out the plunger control of the “Bi-Starter” is to move the lever M to the position shown in the illustration. This causes the disc valve G to rotate until the primary hole F coincides with the passage entering the throttle chamber immediately above the throttle butterfly C.
'51,'56 Squares, '48 VH, '27 Model C, R67/2, Mk IV Le Mans, '06 Super Duke and Ariel projects.

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Re: 1948 Iron 4G Coil Ignition & Solex

Postby chris.matthews » Thu Aug 15, 2019 1:43 am

Hello everyone,
Many thanks for all the suggestions, but the frustration grows.
I set up the Solex off the bike are took the float chamber off - when I turned the fuel on it duly poured out of the two hoes in the float needle assembly. I refitted the carb to the bike and had the two float retaining bolts loose, and I got leakage from the float chamber.
I 'm sure fuel is getting into the float chamber.
I have stripped and cleaned everything several times, in my own mind the carb is fine.
But it will not start - not a glimmer.
Even after 20 or 25 lusty kicks the plugs are bone dry.
Tappets are OK; Compression Test gives between 3.2 and 3.5kg/cm2.
When I did the engine it was a refurbish - not a full rebuild. It is already +60 and bores looked OK, so nothing was done in this regard.
I did New Cams and Followers and bottom end bearings and most importantly cleared sludge traps and oil ways.
Valves were ground and new valve springs fitted.

Valves seemed to be OK in their guides - so new guides were not fitted.
Yesterday with the carb off I turned over the engine (plugs in) with the KS and put my hand over the inlet manifold.
There is vacuum but its not like a big single - with the slow speed of the KS I thought it was OK - but the local Brains Trust feel its not enough.
They have high enthusiasm for me to pull the head and fit new valve guides - if its essential than I will go this way.
What's the consensus ?

But I keep thinking that it was running great a few months back and has done almost no running since.
Rocker Box cover is off - could this be allowing too much leakage at guides ??

So I am very open to suggestions.
With very best regards from a very hot Tokyo (35 C)

Chris

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Re: 1948 Iron 4G Coil Ignition

Postby john.whiting » Thu Aug 15, 2019 1:56 am

My first step with a no start /plenty of spark is to use some spray start..."start ya bastard" is the local brand -25% ether.........a lot safer than spray bottles of petrol.........if there is any spark at all the ether will light,if the spray doesnt kick ,then there is no spark.......other suggestion is to squirt heavy oil into the intake valve springs and stems ,which will seal any air leakage............is there any way you can check intake manifold vacuum?....even sticking your hand over the carby intake while its kicked over......but I ask again.....is there a strong blue white spark?........any supressed components?

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Re: 1948 Iron 4G Coil Ignition

Postby nevhunter » Thu Aug 15, 2019 3:43 am

That type of carburetter choke requires the throttle to be at idle for it to work effectively. it's a bypass setup. Nev

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Re: 1948 Iron 4G Coil Ignition

Postby john.whiting » Thu Aug 15, 2019 5:05 am

Yes,something fundamentally wrong with the bi starter.......might be better blocking it off entirely ,and trying to get going .On a warm day a petrol engine should be able to run after a few seconds without any mixture enrichment ,and a bit of rag over the intake just to get it going.

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Re: 1948 Iron 4G Coil Ignition

Postby Paul_Linden » Thu Aug 15, 2019 10:06 am

The compression test of 50 psi sounds all right. If it was running all right before you refurbished the engine then the same guides should not be causing a problem now.

Regarding the carb - have you checked that the float is not leaking, and too much petrol is getting through preventing it from starting? I have had two brass SU floats develop a small leak (probably due to ethanol) so that the carb floods, enough to prevent starting, but not so much that petrol leaks out of the carb. Just a thought.
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Re: 1948 Iron 4G Coil Ignition

Postby chris.matthews » Thu Aug 15, 2019 12:17 pm

Hello and greetings from a Hot Tokyo (35C) where we await Typhoon #10,

A few comments as my day winds down.
I never ran the bike when I got it -I was scared of the sludge traps - justifiably so, as they were packed solid.
My running was after I rebuilt the bike - it was OK, over 100 miles of illicit (non-shaken / MOT runs) but now is driving me nuts.
I'm very happy to see the 50psi might be enough - YouTube suggests about 100psi on more modern bikes.
I'm due to revisit this tomorrow with some of the local brains trust.
I established there was some vacuum by putting my hand over the inlet (with carb off), but nothing quantified.
I still have doubts about the BiStarter and will try starting in all 3 positions (Full; Half and Closed).
But the most basic concern is bone dry plugs, surely its not about to roar into life until the plugs see petrol.
That's it from here for today, many thanks for constructive thoughts.

Float seems ok, no fuel inside it.
If it did, surely it would be flooding = plugs are bone dry.
Now that David Jones has retired does anyone know where I can get Solex Parts ?

Best regards,
Chris
38 Velocette MSS; 39 VB; 48 4G and 52 BSA B31 and workshop full.

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Re: 1948 Iron 4G Coil Ignition

Postby paul.jameson » Thu Aug 15, 2019 8:14 pm

This still sounds like a carb problem to me, although I did have some spectacular problems with the coil ignition on my own 1948 4G from time to time. As one last check on the Solex carb, have you undone the 4 screws which hold the float chamber section to the rest of the carb? This joint is vertical. (I don't have a bi-starter carb here at present so that description is from memory). When you remove these 4 screws, you should be able to see the passage which takes fuel into the bi-starter. There is a hole in the gasket corresponding to this passage. Could the gasket be fitted such as to block this passage? I do emphasise that I am working from memory here, but it is worth a quick check. Presumably the errant silicone could also have got into this passage?

If we have no joy with the carb, we can go through the coil ignition issues but I will need a good description of the coil conversion to be able to help.

Changing valve guides, etc., at this point is most unlikely to solve the problem, in my humble opinion.
Paul Jameson
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Re: 1948 Iron 4G Coil Ignition

Postby john.whiting » Fri Aug 16, 2019 3:37 am

I would definitely give it a go with spray.........but one more point that I hesitate to say.......are you sure the spark leads are in correct firing order. and the cap isnt carbon tracked.

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Re: 1948 Iron 4G Coil Ignition

Postby brenton.roy » Fri Aug 16, 2019 10:02 am

I agree with Paul, it sounds like a carb problem - particularly if the float bowl is full and the plugs are dry after lots of kicks.
Do you have a version of Aerostart or some ether based spray available in Japan?
'51,'56 Squares, '48 VH, '27 Model C, R67/2, Mk IV Le Mans, '06 Super Duke and Ariel projects.


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