Just up and died on me! Electrical issue and Idle problem.

[Cmackay]

Hey Guys,

First of all, this site is wicked.  Been browsing posts for the past year and it's been an awesome help, and for the most part has helped me sort pretty much all my bike's issues.  So.  The dirty details...

I have a 1981 Honda CB750 Custom.


So the bike didn't run, had been stored for 10 years or so apparently.  Pretty dirty and calcified, and just generally in a state of disrepair.  

What it looks like now...


So - I have redone pretty much the entire front end - new fork seals and boots, drop down bars, head light, turn signals, gauges, brakes clean and changed.  As well - New 72 cb tank refitted to 81 frame, new fuel line, new plugs, air pods (I know, I know - they're being a pain in the ass) engine cleaned, carb dismantled and thoroughly cleaned, exhaust header wrap, frame chopped and welded for flat cafe or brat seat, shortened frame with low profile rear fender with mounted tail light and signals, rear shock, etc.  The wiring has been pretty much completely redone with a custom harness built by Sparck Moto and I've been battling to sort it all out and connect it all with the combination of new parts and stock electrical such as the starter solenoid, cdi's, reg/rec, ignition coils, etc.  

It's been an awesome project so far... and at time's very very frustrating.  But these forums have been a god send.  However, I'm stuck on a few things and would love some input.  The problems I'm having now are...

-New Neutral Switch and wire but still doesn't seem to want to light up on the gauge.  I will be double or triple checking the connections at the back of the gauge and in the top wire cluster again but any other reasons why it might not read?

-Replaced the 68/102 jet combo with 85/110 and put a bit of tape on the pods to restrict air flow.  Seemed to idle well at 1100 but as it warmed up seemed to want to sit around 3k.  Fiddling with the pilots and mix screw but haven't sorted it yet.  Think I'm off on the jets?  Have been looking into the needle shim as well but wasn't sure yet if I'd need them.

-Today something seemed to pop.  Idling high but suddenly it just died.  Lights and everything work but isn't getting any spark at the plugs.  Thinking solenoid or coils because the CDI's were cool and didn't look blown, same with reg/rec, no blown fuse either.  Any ideas?

It's got a temporary lead acid battery in it now but will have an antigravity lithium ion, just happened to have a faulty one that's being warranted.  Otherwise I think the bike is pretty close.  There's still lots of little things I will probably add to it but it's getting close.  Definitely want to swap out the front springs for some progressive springs to get rid of the air pressure requirement, get some gauge bezels, leather wrap the grips, weld some casings for the battery and wiring, etc.

Anyway guys, I've spent hours and hours reading your posts and any help you could give me would be greatly appreciated!

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[Re-run]

OK, well I can point out a few things.
Just fyi on the header wrap. It likes to soak up water. If this water isn't steamed off, it will rot out the pipes fairly quickly. So, keep an eye on that.

Shiny and Slownugly have done extensive work with getting pods to work. If you haven't read their work, you should. Even so, pods aren't going to offer any performance increase over the airbox, only looks. Indeed, the pods suffere other issues sometimes, especially depending on the brand. Cheap emgo pods or some other off brand work poorly, at best. K&N pods would be the way to go. Cross winds can cause things to cut out while riding. Rain can also be a no-no.

The lithium battery is another item. Did you replace the stock regulator with a solid state one? It is a requirement for lithium batteries. I can't remember what type the dohc came with, but it is likely not sensitive enough to handle the requirements of a lithium. Lithium require careful voltage control. They don't like spikes, in that they can burst in to flame. Also, they can't use many of the same chargers that lead acid based or gel batteries can use. Some also require periodic balancing. Just things to be aware of.

Neutral switch, hard to say on that one. Looks like you got aftermarket gauges. Have you hooked it to the old stock unit? I would do so, just to eliminate the new gauge as the issue. It can happen that the bulb in it might be bad. If the stock unit doesn't light up, then you need to check the switch and wires. Check each length of wire to make sure it can carry current. Wires can break inside the insulation and you will never see it. The neutral switch could be bad too, even if it is new. After that, if the wire/switch test good, then the wiring may not be hooked up right. Do you have a diagram for the gauges to check against? It may be different than what was stock on the bike. Very possible actually.

Carb settings and rpm. Ok, here is where I kinda wish I had a bank of these carbs. Your idle is classic of 1 of 2 things. 1: you set the idle for cold and once it warms up, the rpm goes up. My 78 K does this, but the carbs are different. However, I assume you have a fast idle cam built into the carbs that may be actuated by the choke. Mine is anyways. This allows the carbs to be set for warm idle operation while giving a boost in rpm when cold. Check the manual to see if you have this.
2: you have vacuum leaks between the carbs and engine. Quick bursts of starting fluid or carb cleaner at those boots should indicate if you have a leak or not. If rpm changes, then you have a leak.

The loud pop, hard to say. Usually only fuses pop like that. I assume you checked those just to be sure.
The manual details how to check coils and such. I would look into that. Also, maybe Shiny will see this and clean up the info I have tried to relay.

Only other thing I would add is to put on a fork brace. It might look cool without it, but these forks are not very strong and they like to twist. You can drill the rivets from the fender and just use that brace if you want. Shoot it with some black and it will blend in.

Oh and you should totally drop in some cb900 cams.

[Cmackay]

Wow awesome!  Thanks for all the info man.

Well I feel like a bit of a jackass on the popping and not starting front.  After tracing my way from the battery up and checking every component, I found that I had actually pinched the wires coming from the starter controls between the base of the triple tree steering column and the nub that prevents you from turning the front end 360 degrees.  So cut out the crushed wires and spliced back together and everything worked fine.  Felt like an idiot but pretty fortunate on that point.

As far as the pods, they're coming around a bit.  I definitely have to track down some of those other threads on the subject but steps in the right direction for sure.  Tossed some tape on them to restrict the air flow and with the larger jets and pilots almost all the way in was able to get the hot idle down to around 2k... still not where I want it but trying to figure it out.  Ripped it around the block for a bit and wasn't awful, definitely a bit slow off the hop but alright power once I got going.  Little boggy though.  As far as vacuum leaks... I'm going to try again with something a little more combustable than wd40 just to be sure because nothing was sucking in.  Haven't checked about the fast idle cam yet since I haven't had time but I'll give that a little gander hopefully at some point tomorrow.

Thanks for the recommend on the fork brace too.  Definitely going to pick one up.  I'm located up in Vancouver, Canada and sounds like I might get nabbed for not having a front fender on so I'll ride it until I get caught and told otherwise but figured if need be I could attach a low profile fender and mount it somehow onto the fork brace.

For the last thing - the lithium battery upgrade.  I'm not 100% on the reg/rec but since you mentioned that I did toss a volt meter on the battery while running and never really got a reading higher than 13.7 volts... so I would hope that means it wouldn't change and over charge the lithium.

I bought the bike for $300 not running and not together.  I have owned a motorcycle before, years ago but this is my first undertaking of a project like this.  Definitely still learning a ton through these forums, manuals and youtube.  So really do appreciate the info.

[Re-run]

Crushed wire, I could see that causing a loud pop if the insulation was broken. Lucky you didn't wipe out something else. That is also when a lithium battery doesn't play nice. They don't like shorts very much.

Does your idle knob do anything?
On my v45, it has cv carbs, different configuration though. However, when it was running very lean, it would run a high idle like this. The idle circuit/jets were partially clogged and caused a lean condition. So make sure those are clean.

I think I have the same law about a fender. Ride in the rain once, you'll appreciated it!

Well, I don't know if a voltmeter would detect voltage spikes on a stationary bike. Hard to say, just make sure your reg/rec are in good shape and monitor things for a bit if you decide to do a lithium. Also, rev the bike over 2000 rpm and see what your voltage is. 13.7 is ok, 14.5 should be about max.

[Cmackay]

I've been playing with the idle knob a bit but it doesn't seem to do a bunch.  It's been pouring rain here the last few days so haven't been back fiddling with it.  I'm starting to think there's some vacuum leak I'm not finding though, because the pods are pretty taped up and it's still high idle.  Would opening the pilot screws lower the idle rpm by balancing out the fuel / air mix? Or does it only really affect riding performance?
I mean, I guess the other option could be to toss in some bigger jets but I'm already running 85/110's, only others I have are some 120's.

Yeah I really like the clean look without the front fender but I'm sure i'll have to bite the bullet at some point.  Plus I do live in a generally very rainy city so probably not the worst idea.

Thanks again for the info.

[Cmackay]

Okay so it seems to be idling alright now but a new problem.  After ripping around it's got no power on the low end of any gears.  Once it gets up to speed in each gear it seems alright but otherwise it's super boggy and no get up and go. Would this be one or both of the jets being too large?  If it's running alright at the top end of each gear does that mean that the one jet is good and the other is too big?  Definitely a novice at the jetting stuff and having trouble tracking down specific information about it.  Any help would be greatly appreciated!
Also is it pretty normal to get a fair bit of heat and smoke coming out of the crankcase filter now that the airbox is gone.  Seems hot to me but not sure if that's just something normal with the airbox gone.

[Re-run]

You definitely have low end mix issues. Easiest way to tell if you are lean or rich would be to get the bike to operating temp, then change the plugs to new ones. Then ride around at low rpm, below 4000, for a few minutes. Kill the engine and check out the plugs. Look at the insulator inside the plug and see what color it is. You should look for a light tan or so. White is too lean, brown or black is too rich. The fuel screw can adjust this, to an extent. Out is richer, in is leaner.

I can't say about the filter as I still have my airbox.