Author Topic: 400/4 is popping & banging with poor mpg where to start?  (Read 790 times)

Offline McCabe-Thiele (Ted)

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Re: 400/4 is popping & banging with poor mpg where to start?
« Reply #15 on: June 17, 2022, 04:50:42 PM »
Also get the plugs out and post decent pictures of  them to help identify problem.

Are the 1+3 just wetted with little combustion?

Exactly 1+3 are both clean but slightly wet, 2+4 are virtually identical - if all four were like these I would be happy.

Would a sticking float not shake down from the engine vibration whist I've done the first 114 miles?

I'm thinking bizarre thoughts like can the plug leads break down when the relevant cylinder is under compression. Should I remove the electronic triggers & go back to points I have the back plates?

Honda CB400 four super sport

Offline smoothoperator

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Re: 400/4 is popping & banging with poor mpg where to start?
« Reply #16 on: June 17, 2022, 04:51:01 PM »
Hi Ted, I've attached a link to recent pics of my plugs as I have been going through the process of getting my 400 running after rebuild, as you know. I thought you could compare the look in terms of whether fake or not, as the images can be zoomed in so you get a good look at the plug construction. Pics 1 to 4 show plugs at about 300 miles, and they look lean to me so I've been tweaking airscrews to richen them up. The last image is more recent and shows just one plug, now looking about right, (to me). They all look like that now.

I had 1 cold down pipe, number 2. This was very early on. I suspected carbs, I hadn't really serviced them fully, just a clean and new float valves and o rings. I found an air screw spring missing, and also a lot of gunk came out with carb cleaner spray from all 4 air screw holes. However I suspect the biggest problem was the pilot jets. No 2 was definitely restricted compared to the others. I proved this when using carb cleaner wires on it. OK some will frown but if it's good enough for Alan Millyard it's good enough for me. So pilot jets cleaned, new air screw spring fitted, freebie from Steve Cooper, and No 2 down pipe now hot and running much improved.

https://photos.app.goo.gl/YexezRBYLzAgXvjSA
Steve
2017 Triumph Bonneville T100
1977 Honda 400 Four Restored April 2022

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Re: 400/4 is popping & banging with poor mpg where to start?
« Reply #17 on: June 17, 2022, 05:10:42 PM »
Have you tried swapping round the HT caps Ted? Put 1 on 4 and 2 on 3 etc
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Offline McCabe-Thiele (Ted)

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Re: 400/4 is popping & banging with poor mpg where to start?
« Reply #18 on: June 17, 2022, 05:50:04 PM »
Have you tried swapping round the HT caps Ted? Put 1 on 4 and 2 on 3 etc

I do not have the traditional HT caps Ken just the moulded connectors. I could try swapping leads instead - might have to remove the petrol tank as they are a good fit in the coil end.

That will be next week now no Garage time left today.
« Last Edit: June 17, 2022, 05:52:13 PM by McCabe-Thiele (Ted) »
Honda CB400 four super sport

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Re: 400/4 is popping & banging with poor mpg where to start?
« Reply #19 on: June 17, 2022, 06:29:39 PM »
I'm now wondering if it might be the coils instead now Ted, if they have moulded HT caps then they are not genuine Honda ones, I presume they are something like Dyna coils. I wonder if the primary or secondary circuits are the problem, seems strange it's 2 cylinders acting up and neither are using the same coil.
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Offline McCabe-Thiele (Ted)

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Re: 400/4 is popping & banging with poor mpg where to start?
« Reply #20 on: June 17, 2022, 06:39:50 PM »
I'm now wondering if it might be the coils instead now Ted, if they have moulded HT caps then they are not genuine Honda ones, I presume they are something like Dyna coils. I wonder if the primary or secondary circuits are the problem, seems strange it's 2 cylinders acting up and neither are using the same coil.

Sorry Ken I probably did not mention it in this post - I have the Dynatek electronic ignition kit with their coils - bought new by me in 2020.

There is a massive spark at No 1 Cylinder when I attach  a spare plug to it.
« Last Edit: June 17, 2022, 07:03:05 PM by McCabe-Thiele (Ted) »
Honda CB400 four super sport

Offline McCabe-Thiele (Ted)

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Re: 400/4 is popping & banging with poor mpg where to start?
« Reply #21 on: June 17, 2022, 07:11:49 PM »
I think I will need to do a compression test just to eliminate a possible head gasket issue.
Honda CB400 four super sport

Offline Bryanj

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Re: 400/4 is popping & banging with poor mpg where to start?
« Reply #22 on: June 17, 2022, 09:49:16 PM »
The US site keep talking about dyna systems peeing about

Offline McCabe-Thiele (Ted)

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Re: 400/4 is popping & banging with poor mpg where to start?
« Reply #23 on: June 17, 2022, 10:27:31 PM »
The US site keep talking about dyna systems peeing about
I was recommended the Dyna Kit by my BiL he has fitted them to most of his bikes over the years he rates them. Can you post me a link to the article(s). I've only tested for spark on No1 cylinder using a spare plug on the engine casing. It was a very good spark. I can switch the leads for 1& 2 and see if the problem moves to a different cylinder? I have the option to fit the points again to eliminate the electronic points.
Honda CB400 four super sport

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Re: 400/4 is popping & banging with poor mpg where to start?
« Reply #24 on: June 17, 2022, 10:54:27 PM »
It does look like that originally fitted plug may be suspect Ted, especially as you've got decent spark with substitute. New set I'd try first to take that out of equation easily.

The carbon corded HT leads I think are fine (I seem to be in a motoring minority on this, but used them for years on cars very successfully) mostly they'd fail from people pulling the lead rather than cap to get them disconnected and fracturing the connection there,  but the NGK on wire leads are similarly vulnerable if treated the same way.

Often the crimping goes through the insulation to connect but when the centre is paired back like wire stripping and bent outside the insulation to be fully captured by the crimp they seem very competent in my experience. That's if you need to remake an end connection.

If they are the Dyna leads to their spec I'd encourage the continued use as the resistance can affect switching on these system.

I'll be careful taking about that topic, may attract the attention of the Dutch resistance police  ;D careless talk costs sparks an all that   :)

Offline McCabe-Thiele (Ted)

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Re: 400/4 is popping & banging with poor mpg where to start?
« Reply #25 on: June 18, 2022, 12:50:16 AM »
I'm going stir crazy in my head regarding the plug leads is it possible that I have them connected up wrongly firing order wise?

At present the left side coil has two HT outputs I have one connected  to number 1 cylinder & the other to number 2 cylinder.
The right hand coil has two HT outlets one is fitted to cylinder 3 the other to cylinder 4.

Is this the right firing order?

When I bought the bike there was only one plug lead lead on each side hanging by a thread - one of the coils was also cracked. Hence why I went for the Dyna S system on the advice of my B-i-L.

If I have the leads fitted correctly then I can eliminate the Dyna S magnetic switching system by re-fitting the original base plate, rotor ponits & condensers. (I will do a compression test first).

The Dyna coils are 3 Ohm is that likely to cause a problem if I return to a CB points based system for the test ?



 
Honda CB400 four super sport

Offline cbxman

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Re: 400/4 is popping & banging with poor mpg where to start?
« Reply #26 on: June 18, 2022, 06:41:49 AM »
Ted,

1 and 4 on one coil.  2 and 3 on the other. (CB750). Almost certainly all the fours will be like this.

Jerry
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Offline Bryanj

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Re: 400/4 is popping & banging with poor mpg where to start?
« Reply #27 on: June 18, 2022, 07:13:26 AM »
Yes you have the coils wrong, also 3 ohm coils draw more power which means you can not afford to poodle about as you will need at least 3000 rpm for the bike to charge.
There was no individual link to the us site but quire a few individual reports of failures and i can never post links anyway on my dumfone same as i cant watch videos linked for some reason

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Re: 400/4 is popping & banging with poor mpg where to start?
« Reply #28 on: June 18, 2022, 08:48:39 AM »
Ted,

1 and 4 on one coil.  2 and 3 on the other. (CB750). Almost certainly all the fours will be like this.

Jerry

Well spotted Jerry, yes you're correct and I think for all the Japanese fours ever made which all do this.

Ted, you'll not be the first as many others have done this over the years too including my local bike shop years ago. They asked me to look with them at a problem bike that they could not sort, they'd done exactly this,  :-[ all round.

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Re: 400/4 is popping & banging with poor mpg where to start?
« Reply #29 on: June 18, 2022, 08:53:55 AM »
Yes you have the coils wrong, also 3 ohm coils draw more power which means you can not afford to poodle about as you will need at least 3000 rpm for the bike to charge.

Yes definitely Bryan if using 3ohm with points ignition.

With most fully electronic electronic triggering they normally go to fixed dwell time that doesn't over saturate the coils at low speed as I understand them. That aspect taken out, should make them no more demanding than conventional as the "wasted" dwell time won't be there to heat the coil unnecessarily. 

 

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