running like a dog part III

[paulbaker1954]

right now completely at a loss what to do next about this

Ht leads checked
Plugs checked
Plug caps checked
carbs as clean as a bloody operating theatre
float levels ok
no fuel starvation
Head completely overhauled by machine shop (valves checked, lapped in and head skimmed)
Boyer system tested at Boyer and no issues
All wiring to Boyer system checked and all connectors replaced
Have run with Boyer system connected direct to battery and with spare leads from stator plate (ie all loom connections taken out of the equation)

Still getting this afterfire on 1 and 2 and quite frankly I am running out of ideas

It is intermittent, seems to get worse as engine warms and often in initial start get a really loud afterfire

I am sure this is something stupid and obvious but I cannot trace this damn fault

All ideas (however crazy) welcome

[Erny]

Paul said to hear this... fully understand your frustration!
Hope you'll find root cause soon

[paulbaker1954]

Paul said to hear this... fully understand your frustration!
Hope you'll find root cause soon

Me 2
Further thought are there any members near me that would be willing to come and have a listen/spare a couple of hours !!!!

[K2-K6]

Offbeat thought,  can you check that the TDC position you are using for cam timing is exactly at TDC by correlation to the piston?

I'm unfamiliar with what you've got to indicate that with Boyer system.

[Nurse Julie]

Partially blocked / occluded #1 & #2 downpipes and or silencers. You did say even 'crazy' ideas 😊😊😊

[Laverda Dave]

Paul, you say you have checked the spark plugs. Given the circumstances I would renew the plugs as these appear to be the only thing you haven't tested. I assume you've tested them for a spark but they can break down under compression and as another thread I think pointed out recently, the porcelain core of modern plugs are no longer glazed. If ethanol is present in the fuel the moisture that ethanol attracts could be getting into the ceramic of the plug causing a missfire. I've had a similar problem years ago on a speedway bike. The last thing I did was buy a new plug and the problem disappeared! Four new plugs from M&P will cost £12 and free postage!
Good luck and hope you solve it.

[Erny]

Or, just swap 1&2 by 3&4 - quickest option

[philward]

Don't know whether this has been suggested before Paul but what about putting the original points system back on? Although Boyer has tested the system, there may be some interaction between the Boyer system and the electrical characteristics on your bike. I know this is a long shot but you are at that stage. Thinking this with it being on 1 & 2 and as has been said previously that is normally associated with one ignition circuit.

[Seabeowner]

Beat me to it Phil, was about to post:
Post your video clip again to remind us. It sure sounded like a misfire caused by spark at wrong time. Still like to see it tested with points.
Does it disappear when the bike is revved?
You could try the exhaust system that came with the bike or has that gone in the bin. And was it you who had a failed exhaust on your pattern replacements?

[Rob62]

I can’t believe that this saga will turn out to be a faulty spark plug....the first thing you change whenever you have a running issue 😳😳

[K2-K6]

http://www.sohc.co.uk/index.php/topic,14377.msg116537.html#msg116537

This thread makes me wonder if the timing marks are compliant with what you now have spec wise.

There can be a notable timing difference from the different iteration of mech.

[paulbaker1954]

Did some more testing today, first I ran the Boyer system off a separate battery. This way I can run with the Honda ignition system off i.e. there is no charging of the Honda battery.
Reasoning being was wondering if I was getting some stray AC out of the rectifier interfering with the Boyer box. That said I did check the rectifier diodes a week or so ago and all were ok. Result no change.

Then swapped plugs from 1 and 2 with 3 and 4 (already did this as part of initial checks) but this time seemed to sort the problem. Go figure.......... That said only had chance to run the bike for 5 mins but sounded smoother and no backfiring.

Here is where I confess to possible stupidity in that I may have not been pushing the plug caps fully home on the plugs on 1 and 2 all the time. I am guessing that if the caps are not fully home on the plugs this would for sure cause intermittent firing resulting in unburnt fuel in the exhausts
That said I did take bike to professional mechanic who claimed he had adjusted plug gaps so he clearly didn’t put em back properly either!!!

Doesn’t make much sense as I had done all this before but don’t care if the issue is sorted.

If this turns out to be the cause I will feel REALLY STUPID as I know that in my early days of cars with no other knowledge first thing ever was to wiggle the plug caps!!!!! Maybe sometimes knowledge is dangerous as you sometimes simply forget the basics!!!!!!!

Will be doing some more testing over next week or so and may still not be out of the woods but feeling more optimistic that I have finally tracked this issue.

Good news is out of all this......

I have a fully overhauled head (skimmed to fix the original oil leak from around the timing chain area), with reground valves, fully reconditioned carbs, new inlet rubbers and when running now is ticking over smooth as anything.

I have learnt a lot through this frustrating process that will stand me in good stead so I am ok with all the stuff I have done

[K2-K6]

Well hopefully you've got it now,  so fingers crossed to hear further positive outcome.

As you say, to get experience like this is invaluable however it's acquired really.  It all serves to help running them longer term and been quite a walk through of all the various functions and testing that may help others too.

[Laverda Dave]

Good news Paul, sounds like you may have cracked it.
The first thing I always do now with a missfire is change the plugs, cheap and easy fix.
Now go and thrash it before the weather gets bad 👍.

[philward]

Great news Paul! Hope that's it sorted
PS - Ref my previous suggestion - misread your post prior to my suggestion as if misfire was on 1 - 4 (hence same ignition circuit) - yet another senior moment! (becoming ever more frequent!