Topic: 400/4 No spark -Update

[MDW]

I just rebuilt the carb and prior to that number 4 cylinder wasn't firing. Now I don't have spark going to 1 or 4. What I have done:

 - Tested the capacitors - both appear good
 - Tested the coils for resistance - both at factory spec
 - Replaced the points for 1 & 4 with a new set
 - I swopped the plug caps and that made no difference i.e. caps appear to be fine

What I still need to do:

 - The  timing may be out (using a test light it stays on for the whole cycle of the engine) but the engine was running prior to the carb rebuild (2 weeks ago)
 - The carbs need syncing

I thought tracking down the issue would be simple but so far I have not found it. Any thoughts on what I could try?
Thanks

[mca2]

Check plugs are good, check for 12v at the feeding side of the primary circuit. Check for 12V and the cables going to the breakers with points open. Check for 0V with points closed.

[Deltarider]

Check plugs are good, check for 12v at the feeding side of the primary circuit. Check for 12V and the cables going to the breakers with points open. Check for 0V with points closed.

Don't expect to see 12V at the points. It will be more like 10 - 11V.

[MDW]

Thanks both. I will have a closer look at this today. I saw that I had about 10 volts going into the coil. Hope at is as it should be?

[MDW]

I checked the voltage at the coil and I have 9.8v in the black/white wire, the same at the yellow but 1.3 at the blue. At the condenser/points on cylinders 2/3 I have 9.8v and  on 1/4 1.6v. I looked for obvious signs of problems in the wiring in different places but saw nothing. Any suggestions where I might look or how best to track down the issue (electrics are not my  strong point!). Thanks

[Deltarider]

Clean the surface of points 1+4 very lightly (4 strokes is enough) with a little file as you may find in your nailclipper. You may need some aceton or alcohol. Do not clean with paper like business cards! Repeat measurement. You should read less than 1V across the points when they're closed and around 10V when opened. It takes very little to hamper the points switching. Paper will fill up the little crater and even after having had a plastic card between them for temporary isolating (to prevent frying the coil), you will need to clean them.

[MDW]

Thanks Deltarider I will try this but I isn't the problem related to not having enough voltage going into the 1/4 coil? I read 10 volts at the black wire and yellow but about 1 volt at the blue which goes to the 1/4 coil. The black/white is the live wire as I understand it but if I also have 10 volts on the yellow (2/3 cylinders). Shouldn't I have the same at the blue wire going into the coil?

[MauiK3]

I'm stuck back where you mention the test light staying on, this may indicate a points wire is involved.

[MDW]

Yes, I cannot explain that unless I have something not connected properly. Please see the attached photo. Everything looks right to me, but maybe a more experienced eye will notice something?

[scottly]

Put a piece of paper between the 1/4 points contacts. Do you still read 1.3 v?

[MDW]

Responding to Deltarider and scottly  - I got voltage readings at the points circled in the photo. So for 1/4:

Breakers/points fully closed - 10v at the blue wire and <1 volt at the points
Breakers/points fully open  - 10v at the blue wire and <1 volt at the points
Breakers/points just open - 10v at blue wire and 10v at the points

I got the same results for 2/3 except when the points were fully closed I got <1v at the wire and <1v at the points. It was quite tricky to get stable readings on both 1/4 and 2/3. At one stage on 2/3 I was getting 10v at both places even if the breakers were wide open. I got that a couple of times then the next reading seemed to be in line with what I listed above for 1/4. Could there be an intermittent fault? I may need to test this again but the readings for 1/4 seem to be correct.

Also I took readings with a piece of paper between the 1/4 points when they were closed. At the points on one side of the paper I got a reading <1v and the other side 10v which still confuses me!

Can you draw any conclusions from this? Thanks

[scottly]

Does the spring have the insulating washer between it and the tab on the points plate? It sort of looks like it's missing or miss-installed, which is why I suggested putting the paper between the points. Compare the 2/3 points for reference.

[MDW]

Do you mean the spring on the on the points mechanism whether it connects to the points plate in the lower red circle on the photo?

[scottly]

Yes.

[MauiK3]

A common problem

[Don R]

 The thing to remember is the connecting screw, the condenser wire and points wire need to be isolated from ground until the points close.

[MDW]

Scottly, Deltarider etc. Please see the photos. As far as I can see the insulation washers etc. are correctly installed. It looks like I can only post one photo at a time so will add the others in separate posts

[MDW]

#2/3

[MDW]

#4/5

[scottly]

Yes, the insulators now look correct, but look at the side view of 1/4, image 5038. See how the blue condenser wire is connected with the end pointing down, close to the points plate? It looks like there is clearance now, but it should be flipped over like the 2/3 side in image 5039. This wouldn't be the first time this is happened, but it's been quite a while, and I wouldn't have caught it without the last pics.

[Deltarider]

There is also a rare risk that the smallest insulator inside the breakerpoints ia misaligned. See pics for the correct assembly order.

[MauiK3]

Additionally, I had the same issue with worn points plate screw heads, I got new ones, at either Partzilla, Z1 Enterprise or Common Motors, they are M5 x 12 (I think)

[MDW]

Thanks everyone. I will flip blue condenser wire over and start her up to see if 1/4 now fire and I will get back to you with an update!
I also saw Partzilla carries those screws but never got round to ordering them yet

[MDW]

Deltarider, in the photo of the assembly order of the washers/insulators etc, where (which side of the plate mount) does the smallest insulator go? Is it with just one of the larger insulator washers or on the side with the nut etc.? I am not sure mine even has them, or where I would find them if it doesn't. Is there a work around?

Also I flipped the blue condenser wire. I haven't tried to run the engine yet but when checking the timing with a 12 volt bulb I notice the bulb is lit for almost the entire cycle of the engine. It goes out a good way before 1/4 is supposed to fire. Obviously this is not right but what are the consequences? The engine was running before when it also had this issue. Thanks

[scottly]

The smallest insulator goes inside the hole in the plate. It keeps the screw from grounding out on the plate.
The light should turn on when the points open at the F mark; the spark happens when the points open. The light should go out when the crankshaft rotates approximately 1/2 turn, or 180 degrees, when the points close. The time when the points are closed is called "dwell", and is also approximately 180 degrees of crankshaft rotation. During this time, the ignition coil is charging up, getting ready for the next spark when the points open. If the point gap is too big, it will shorten the amout of time the points are closed, giving the coil less time to recharge, which can affect the strength of the spark at higher RPM. Since the light is turning off and on now, it looks like the original problem is fixed. Like Maui suggested, you should get new screws, because yours look pretty buggered up.
The lower screw that holds the main points plate to the engine is missing a plain washer like the other 2 screws have.