Honda CB750 K2 - back on the road Ep.3 Spark & compression tests
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- Опубликовано: 20 окт 2024
- So why is this engine so hard to start from cold & cylinder #2 only firing once the engine has warmed up? Time to do some diagnostics...
Andy
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Thanks for all your support, until next time...
Andy
You provide perhaps the best step-by-step processes for maintaining and diagnosing the aches and pains of vintage Honda motorcycles on RUclips....I particularly like the way you walk the viewer through your diagnosis thinking and what you are considering as options. Introducing us to helpful tools that sharpen the choices is really helpful. This time, you also very helpfully shared with viewers the procedures set out in the manual (even showing the actual pages...). You're helping the old-timers who want to preserve these machines and training a new generation of garage amateurs who want to learn....Many thanks!
I really like that you don't skip or fast forward through parts. I hate when people do that, I can't learn anything that way.
Correct :-)
Guys say the throttle should be held full open when checking compression. Thanks for the video. Nice bike. You know your stuff. Looks like those points are aftermarket. On TEC points the plate has those little marks all over like your base plate does.
Hi Andy, here is something about compression that you might find amusing , I bought a 49 Matchless G80 500 , it ran reasonably well , but leaked oil real bad from a split pushrod tube and seals , anyway after removing the head I found the piston ½ inch down the bore at TDC ! Off came the barrel , and then I found all three ring gaps at 3mm ! I calculated the comp at 4.1:1 , it started and ran ok 👍.
Wow! Lol
Andy....I just recently saw a restoration on a Yamaha RD 400 2 stroke from the same era. There are replacement coils out there that will work. Also....there are electronic ignition kits that can replace the points and condensers and will provide much better spark. Mainly just wanted to let you know that part is doable. Looks like you may need new rings on the bike as well, as long as the cylinders aren't damaged or out of spec.
Andy i have a cb550k from 1977, the same ignition system and a wasted spark.
Every year before riding it i have to clean the points a little with a bit of fine wet and dry sandpaper, if you measure the voltage across the points when they are closed you can measure the resistance of the point surfaces, they should be at least the same and when you clean one set first observe the difference it makes.
Doing this makes a big difference in how the bike starts ( less voltage for the coils when the starter is engaged ).
My old bike starts immediately when the start button is pushed unlike my brand new cb1000r which has to figure out when to fire before it's happy with just a crank sensor, i finally got the idle mixture screws dialed in correctly after all those years.
Also connected four plastic hoses to the float chambers through the drain screws and found that the breather holes above the fuel level needed unblocking........
For some reason the points deteriorate when not in use.
i have a set of new spare points but still use the original ones because they still work after 60.000 km. and capacitors, the capacitors still have about the same capacity when i tested them last so no reason to change.
Nice to see a classic back on the road again, well done, cheers.
I want to jump in and say open the throttle for a true compression reading ! but I'm only half way through the video ..hope you notice ..we'll see ..👍🏻☮❤
Engine should be warmed up to get the rings expanded for best result.
Andy, so would I be correct in thinking it’s possible that if the spark hasn’t been strong enough for a while it’s caused the valves to coke up (maybe) so they’re not closing properly and leading to the poor compression? The compression improving a bit in all cylinders with the addition of oil - you’re thinking the cylinders/rings are contributing to the poor compression also?
Should have the companion cylinder spark lead grounded through plug to check spark
Put oil in cylinder 2 then do the compression test to see if it's the rings or the valves I think its a sticking exhaust valve
bit of a shame . wen was the last time the valve clearance where done
Andy Change your overhead lighting to LED I did HUGE DIFFERENCE ..