Topic: My CB750/4 is eating Condensers

[Trikeopath]

As the title says, this bike is consuming Condensers quite quickly.
The Motor was built about 10,000 miles (1 year) ago and new points and condensers went in then.
All of a sudden the popping and backing started during a 300 mile journey (in the rain) to the point it would just idle but couldn't be driven.
Bright sparks present on both contacts so got the bike trucked home and fitted new points, condensers (Japanese) and plugs (D8EA).

Bike went great again for about 200-300 miles, until the odd spit got progressively worse over say 30 miles at motorway speeds (70-90) and it was running rough again. Pulled in to re-fuel and 2-3 contacts were sparking again. Borrowed a spare condensor off a friends GS750 and it was still sparking at the points.
Pushed on with the journey, and found it would run ok upto about 45-50mph. Got to the destination (60mile on) and now both contacts are lighting up. Since fitted another set of condensers and they are both sparking now.

Any one got any ideas about why I'm going though these things all of a sudden?

Wiring is basic :-
Dedicated 12V feed from Ign switch, though a fuse to the +ve on the coils. (no signs of a short to the frame)
Blue and yellow from Points plate to -ve on coils. (no signs of a short to the frame)
Coils are showing 4.3 ohms on the primary. (1 year / 10,000 mile old)
Caps are NGK and all show about 5 ohms.

[scottly]

Is this the brand of condensers you are using?

[Don R]

 Scottly may have the answer but also check the engine ground to the chassis/battery. Just a thought from my race car experiences.

[strynboen]

and thek the coils have ground too...loosen the bolts..sandpaper on the metal parts..to get a real good ground..and thek the green ground vire..vho often are mounted close to the coils

[Deltarider]

and thek the coils have ground too...loosen the bolts..sandpaper on the metal parts..to get a real good ground..and thek the green ground vire..vho often are mounted close to the coils

What makes you think the coils core need ground? They're not in any circuit.

[PeWe]

My CB750 got Daichii point plate in the 80's. It lasted at least 10.000 km without misfirings. Arcing points were visible in the dark since bike had a transparent cover.
Except one that broke a point after max 5000 km when riding in France on holiday. Engine suddenly ran on 2 cylinders only. Saw that one point has got the bakelite broken. Rode to a Honda shop that did not have CB750 parts but could repair it with the needed part from another point. It took some km for the bike to stop smoke after 50-70km running on 2 cyl. Daichii can cost if the consequences are summed up.

I was not aware of the bad points then. I had just heard that CB750 eats points/condensers. I should have looked for TEC only if I knew. TEC is in now together with Hondaman ign module so the condensers have an easier life.

[strynboen]

and thek the coils have ground too...loosen the bolts..sandpaper on the metal parts..to get a real good ground..and thek the green ground vire..vho often are mounted close to the coils

What makes you think the coils core need ground? They're not in any circuit.

..just thinking that the metal core in the coils..vill funktion a bit better..if it are groundet.(this is a bit ekstra special problem..so all possib must be tested)..but you are korrekt..the induktive  ground is  to the points..

[Trikeopath]

I think the initial set that did 10,000 miles were daichii brand.
I'm unsure of the make of the set fitted 3 weeks ago but I'll check the bin for the packets. (made in Japan stamped on the case).
Unsure of the GS750 one my mates had in his tool kit.

Last night I pulled the wires out of the Frame and replaced all on the them. I'm all out of spare Honda Condensers now so fitted a pair of KOYO's from a BSA C12. I've done 4 miles to work this morning and I'll do 100 tonight as a tester.

Also, Don R may have been onto something with the bad Ground. The Rear bolt I took that off, did have a job coming out and there was corrosion on the thread. The connection was clean but I had to fit a Helicoil. That cable has been re-fitted with bit of Lithium grease.

I've also covered all bases and ordered a DYNA S.
This Bike needs to stay rolling.

[PeWe]

Electronic ignition is more sensitive about weak groundings.
Dyna coils too? Their 5 ohm coils (black)

[Trikeopath]

Electronic ignition is more sensitive about weak groundings.
Dyna coils too? Their 5 ohm coils (black)

No the Tech guy said my existing set will be fine, at least for now.

I did 94 miles last night, mostly at 80mph and it's still running. Low end is lumpy so I'll have to try a tune that out. Also found the plenum needs a bit of sealing around the rubbers.

BSA condensers, so far so good.

[Trikeopath]

Well it is a good few hundred miles in now with the BSA condensers so I'll call that fixed.

I then went on to fit the Dyna S.
I made it so it can go back on points at the side of the road and made up a travel kit with every tool I'd need to switch it.
Last night I did about 60 miles and the EI system does make it run different. The roll on torque is smoother and a bit quicker plus it showed up a high speed clutch slip which I'd never found before.

I was intending to pull the Clutch to do the oiler mod anyway, so I'll get that off tonight and see how much more cash I can get rid of replacing parts while I'm in there. Our Triumph LSR race bike threw away a bunch of parts on Pendine Sands last weekend so this one deserves some money blown on it too.

[PeWe]

Clutch should not slip! You use motorcycle oil?
I used the best oil I could find in the 80’s thas was a car oil with friction modifiers. Clutch slip at higher speeds. This with 836cc and about 80 rwhp.

If you use motorcycle oil for wet clutch (JASO), make sure that the clutch is properly adjusted. Clutch lever arm at clutch has a free play, clutch lever on handle bar has a play...