Topic: First time starting new engine, 2 & 3 not as hot

[Bankerdanny]

When I experienced symptoms like yours the issue was ignition. On my old 550 it was a failing electronic ignition. On my 750 it only went away when I disassembled my 2-3 points, dressed the surface of the points with a file and made sure that all insulator washers and sleeves were properly installed.

[jakec]

I have checked the insulator washers, as well as cleaning the points with fine sand paper. It is entirely possible that it is the points,since this problem seemed exist the same before rebuild.. But checking points over and over I don't see anything wrong with them.

[jakec]

I just ran it again after adjusting air screws, checking points, ensuring fuel flow, new plugs on 2 & 3.

Ugh!

[Deltarider]

Have you checked the 2+3 plugcaps (resistance)?
You can check them like this. Start with checking the total resistance from one plugcap via the coil to the other plugcap. Realise that new resistor plugcaps are around 5kΩ each. The coils secundary itself is around 14-15kΩ, so with both plugcaps attached, you should read 24-30kΩ in total. When you read over 30kΩ in total, unscrew both plugcaps to be tested individually. Over time the plugcaps resistance tends to increase. When over 8kΩ, replace. Do not run and resistor caps and resistor plugs. When you have the choice, I'd prefer resistor caps over resistor plugs. Verify plugcaps are firmly connected to the wires.
Is by accident condenser 2+3's forked connector on the wrong side of the brown insulator ring? Any arcing at the 2+3 breakerpoints? Here's a vid showing a good and a bad condenser.

Condenser 1+4 is bad, 2+3 is good.

[jakec]

Thanks for the response. The spark plug caps are new, would testing them also be testing the coils? Coils are stock and I am using NGK 5 ohm resistance coils. I am not sure what type of plugs they are, they just the manual specified D8ea plugs.

I watched the bike run with points cover off yesterday and it seemed that the points weren't arcing at all, or maybe just a little (like right side 2.3 in the video). When I was setting the timing the 1.4 was arcing a bit too much but that was corrected when I set the points gap and cleaned the contacts with sand paper. I will check the condenser fork asap.

I am considering buying new coils and an electronic ignition, as well as taking out carbs to inspect while I wait for parts to arrive. There is a ride on the 28th I would like to attend.

[Deltarider]

A little sparking at the breakerpoints is normal. 'Buying stuff' is not the solution (its a serious addiction in some societies), diagnosing is! The coils are rarely the problem!

[jakec]

I agree, I'm not in a big hurry to spend $200 although I feel like I'm exhausting my options.

I just checked and both condensers are connected the same way, with washers separating the forks from the post that connects to the points plate.

[Deltarider]

The plugs are the D8EA type which is good, the 2nd from the right might have its electrode bent too close to the center electrode. I'd check that. The gap should be 0,7 mm.
Without having read all the above, have you tried swapping the coils to see if the problem follows?

[jakec]

I don't have any extra coils, and the leads aren't long enough to swap the 2.3 into the 1.4 position. Although that would be a great idea.

Is it possible that a bad coil can fire some of the time?

[Robbo]

Have you tried swapping the condensers?  If the problem moves from 2-3 to 1-4, I would replace the bad condenser.
If the problem remains with the 2-3, at least you have eliminated a bad condenser as a possibility.


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[jakec]

I had already tested the condensers separately and they behaved the same. I could certainly swap them but they aren't looking anything like the bad one in the video.

[Robbo]

I had already tested the condensers separately and they behaved the same. I could certainly swap them but they aren't looking anything like the bad one in the video.

It’s something I would do personally and it is a quick and easy task.  I’d also re-check my valve clearances and do a compression test.

Regarding the carb air screw setting, I have my 350f carbs at 1 turn out from lightly seated.  I believe you said yours are set at 1 3/4 turns.  I would be worried that they might be set too lean.  Have you tried them at other settings?  Turning them in will make it richer.  I would be tempted to try setting them at 1 1/2 or at 1 1/4 turns out from lightly seated.


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[jakec]

Just removed carbs, all had plenty of gas in the bowl and once they were drained I looked inside. Nothing to note inside except 3 & 4 float height is a little higher because the springs inside the needle valves are weak. They weren’t leaking though. I also confirmed the jet sizes and that they aren’t clogged. Finally I checked the bench sync which seems adequate. I think I can rule out a problem with the carbs.

[jakec]

I also removed the points and advancer, which both look fine. The advancer shaft does not appear bent and neither does the bolt that holds in. The advance springs are strong and the arms snap back nicely.

[scottly]

I just rebuilt carbs and corrected float level. Unless you mean to do the clear tube method.

Ignition can't carbon foul spark plugs; you have a carburetor problem. Verify the fuel levels in the float bowls as Alan suggested, using the clear tube method. This can be done with the carbs mounted on the bike.

[jakec]

I thought that maybe the fouling occurred if the cylinders were only sparking correctly say 1/2 the time.. then each combustion would have double fuel. I did buy clear tube and plan to do a tube test while the carbs are out.

[Scott S]

I would like to do that now but there are two things stopping me, 1. don't have a single line long enough, and 2. it's pretty much impossible to install a line on the carbs when in frame.

  Now that the carbs are out again, install the proper 5.5mm fuel line in the correct length and get rid of the external filter. Fit the line to the carbs BEFORE installation and then attach it to the petcock, not vice versa.

[Alan F.]

Could this now be a matter of independently setting air screw positions for each carb?

Or is that too off the wall and will add to the confusion?

[Deltarider]

Could this now be a matter of independently setting air screw positions for each carb?
Or is that too off the wall and will add to the confusion?

Good question. According to p.95 in the Honda Shop Manual the CB400F air screw openings are supposed to be at 2±¹/₂ turns out. http://www.honda4fun.com/pdf_man_officina/pdf_manuali/CB350-400/CB350-400_09.pdf

[jakec]

Yeah I had installed all lines before inserting the carbs, including vents and drains. 4into1 Is all out of 5.5mm ID hose so I got some 5.3mm. I also ordrered new coils and ignition. I have some clear tube for the carbs now. So I'll try and sort out the carbs before the other stuff gets here.

[jakec]

I think I will also replace the main jet O rings while I can, they seem fine but I just read a post from mark saying if you have bad O rings gas can slip by on the outside dumping tons of gas into the mixture.. sounds familiar. Anyone know the hardware store O ring #?

[Alan F.]

The Harbor Freight metric o-ring kit is handy for things like this. It's about $8 and they are fuel resistant.

[jakec]

We don't have a harbor freight here, it's a blessing and a curse!

[bryanj]

Those O rings are a none standard bastard size that not even a lot of hydraulic people keep.
Somewhere on here is a post with all the carb O ring sizes in it i wrote some time ago. My books aint handy so i cant redo them

[jakec]

This is on the site:

http://www.sohc4.net/carb-o-ring

Also found this (minimum order 10):

https://www.theoringstore.com/store/index.php?main_page=product_info&cPath=368_12_603&products_id=20659