Acceleration Misfire

[Saesneg Shaun]

Hi all, I could do with some advice regarding another problem with the K6. When opening the throttle to accelerate the bike momentarily cuts out. Its much more than a flat spot as for a split second the engine completely dies making the forks dive before picking up and accelerating as normal. It only does this when its up to normal temperature and the hotter the bike gets the worse the problem.

I'm running Boyer electronic ignition with the original coils. New plugs and timing checked. Carbs have been cleaned and balanced, new needle valves fitted and float levels checked. Don't know if its related but the bike is (and always has been) a very poor cold starter.

I'm running out of ideas. Coil breaking down maybe?

[Johnwebley]

Does it seem to run lean?

White plugs,

What about R type plugs and resister plugs caps, are you running both?



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[Saesneg Shaun]

Does it seem to run lean?

White plugs,

What about R type plugs and resister plugs caps, are you running both?



Sent from my SM-A546E using Tapatalk

Doesn't seem to be running lean looking at the plug colour. Air screws are about 1 1/8 out which I set during carb balancing procedure. Running NGK resistor caps and D8EA plugs.
Its usually a pig to start from cold but once started it runs fine until its hot.
I've cleaned and balanced the carbs numerous times now. I replaced the pilot with new genuine honda just in case and replaced all the fuel needle valves because 1 leaked. I previously had issues with wear in the point spindle but am now running electronic so I shouldn't be that either.

[Green1]

Are you running an external fuel filter? As that sounds very similar to what my pegaso was doing years ago.

[K2-K6]

Try running it with airscrews turned in 1/4 turn from where they are now (you can set them back if no or poor effect) to assess if that makes a difference in starting and running.

[Skoti]

Carb slide needles in the wrong position?
Set too low and giving too a weak mixture.

[Johnny4428]

Advance mech running freely?

[McCabe-Thiele (Ted)]

I always think poor cold starting indicates a lack of fuel so running a tad on the  lean side. Other reason might be the ignition is a tad retarded.
If your E- ignition has separate adjustments for 1/4 & 2/3 might be worth checking the timing on both, as is the advancer unit if you are using the original mechanical unit.

[Saesneg Shaun]

Thanks all, i'll try turning the screws in to richten it up a bit. I was told too lean and the revs hang when I blip the throttle and too rich revs will bog down then recover. I'm running the stock airbox & filter and the advance mech is replaced with the boyer kit.

[K2-K6]

I always think poor cold starting indicates a lack of fuel so running a tad on the  lean side. Other reason might be the ignition is a tad retarded.
If your E- ignition has separate adjustments for 1/4 & 2/3 might be worth checking the timing on both, as is the advancer unit if you are using the original mechanical unit.

Boyer system has no adjustment between the two sets to be moved. Effectively, the backplate is set up geometrically in manufacture to fix them at exactly 180 degree apart, no seperate spacing needed to cause problems.

In addition, they fire all four plugs at every event of timing ..... at every 180 degree increment that passes the trigger point.

Also, there's no "advance" as such. They set the trigger point at maximum timing point (hence installation notes to check it above specific rpm) then they delay the timing point in software based on engine rpm to give a retarded effect for low crank speed, this detected from pulse count register as you crank it. 

Also facilitates "multi spark" at low rpm firing to try and mitigate plug fouling etc and provide more effective cold start.

Its a pretty comprehensive system solution to replace points with.

[McCabe-Thiele (Ted)]

There is an old post on this problem by Johnwebly? - turned out to be a couple of loose wires on the Boyer unit. I can't post the link using my phone but it's there if you search the term Boyer.

[K2-K6]

Thanks all, i'll try turning the screws in to richten it up a bit. I was told too lean and the revs hang when I blip the throttle and too rich revs will bog down then recover. I'm running the stock airbox & filter and the advance mech is replaced with the boyer kit.

It sounds like the needle and main jet settings are substantially in correct range, as that's more the influence on plug colour from decent running.

If it just gets a little lean as you open the throttle slides, that suggests a deficit in slow speed circuit to stoke it up into response.  The air screw adjustment should show if that's true or not.

In essence, if it does clean it up, then that suggests it's "asking" for a step up in volume of idle jet to bring it in competent range, at which point the airscrew set point would look more normal in comparison to manual.

Interesting to see if that tweak will show any desirable response.

[McCabe-Thiele (Ted)]

It's a long shot this is the link about a Boyer wiring issue.

.http://www.sohc.co.uk/index.php/topic,5861.msg29390.html#msg29390

[Saesneg Shaun]

It's a long shot this is the link about a Boyer wiring issue.

.http://www.sohc.co.uk/index.php/topic,5861.msg29390.html#msg29390

Thanks Ted. I will take a look tomorrow. Unfortunately the predicted monsoon arrived today so I didn't get to play with the bike.

[Martin6]

If it's a 750K6, @Hondaman on the sister US SOHC4 forum, has explained a few times that turning in the idle screw weakens the mixture, as it isn't an air screw, it is metering the flow of already mixed air/fuel. So unscrew to richen.

It still feels alien to me (I'm more used to Amal carbs). But, that's his advice.