Topic: '77 CB750 Revival - Help!

[Radski]

Soooooo... I've picked up a '77 CB750 from a friend of mine and am going through the paces of getting it fired up and back on the road. Admittedly, I AM a newbie and at 40 years old after having a stroke, I'm trying to pull out a bucket list project to check off.

I'd like some help or suggestions as to what to do with one issue I've encountered thus far.

I've adjusted the valve clearances already and checked the tension on the timing chain. However, I'm encountering a weird electrical problem which is stumping myself as well as some slightly more experienced mentors. Im not getting spark on my 2 & 3 spark plugs however I do have spark on 1 & 4. I've checked all continuity and all wires from the points/condensers to the coil connectors and we're good. I've checked the continuity of the wires into the coils and we're good. I actually switched the coil wire connectors (yellow lead to blue coil wire, and blue lead to yellow coil wire) and then I got spark in spark plug number 2 but then didnt in 1& 4. I turned it over and looked at the points and have spark on the 1/4 point but did not see any in the 2/3 point. I checked the timing and its good and the gaps on the points are appropriate and clean flat heads.

What could be the problem? Why no spark? I'm fairly sure the points are worthy but....condensers? Point bad?

Any ideas or suggestions would be great!

[bryanj]

Run a points file through both sets then clean, regap and reset the timing. points can oxidised with standing and stop current flow and its a good idea to do both at same time

[pjlogue]

Do what Bryanj said and if you still don't have a spark on the 2-3 put new condensers in.  I would put new condensers in anyway as a routine tune up.

-P.

[BenelliSEI]

Verify your static timing setting with a 12V test light. If you don’t get a light just as the points start to open you will know the problem is all there. Have you checked to make sure the “trigger wires” t the coils are connected all the way up? I think there is a pair of connectors, just behin the air box? One blue, one yellow wires? Make sure one is not unkooked........
Also, both coils have power when switched on (going from memory, black or bulk/yellow wire?).

[Radski]

Run a points file through both sets then clean, regap and reset the timing. points can oxidised with standing and stop current flow and its a good idea to do both at same time

I did do this and looked at the points which looked pretty darn clean. No pitting and flat.

[BenelliSEI]

Did you try the test light and verify “signal” on both points sets?

[Radski]

Verify your static timing setting with a 12V test light. If you don’t get a light just as the points start to open you will know the problem is all there. Have you checked to make sure the “trigger wires” t the coils are connected all the way up? I think there is a pair of connectors, just behin the air box? One blue, one yellow wires? Make sure one is not unkooked........
Also, both coils have power when switched on (going from memory, black or bulk/yellow wire?).

Timing is all good according to some videos I pulled up on the Tube. The light comes on at the appropriate time every time I hit the "F" mark for both sets. I did check the wires from the points all the way up to just before the coils where they connect and I have continuity all the way. Also have good continuity with the coil wires.

I will try what PJ said and replace the condensers. I have an extra set of everything..points, plate, condensers that are known to be working so perhaps I should switch the whole thing?

[Radski]

Did you try the test light and verify “signal” on both points sets?

Again, I'm really new to all this. I did do something where I checked continuity (I think) to the points. I dont remember exactly now but I did use a multimeter at the points and I did get an Ohm reading.

[BenelliSEI]

Could one coil be bad? Swapthe trigger wires and plug leads over. If the other  pair of plugs go dead, I’d change that coil.....

[Radski]

Could one coil be bad? Swapthe trigger wires and plug leads over. If the other  pair of plugs go dead, I’d change that coil.....

As far as I'm aware, the power (spark) comes from the points > to the coils > to the spark plugs. So if I'm not getting spark at 2/3 point set...isnt that where I need to troubleshoot more? I'm getting all good numbers when checking continuity throughout the wires, points etc. Just no spark.

[BenelliSEI]

I’m just suggesting that if you swap the points wires to the other coil and suddenly you have no spark at 1-4 you can conclude it’s point/condenser (because those points get no spark on either coil). If after the swap points wiresyou STILL get no spark on 2-3, then it’s the coil.......

This ishould be done with your four plugs out, with the hexagonal part of the plug, grounded on the engine, than crank it over on the starter.

[MauiK3]

And after you get spark back check the resistance at the plug connector. They are known to get to high as they age. Read Thoughts of Hondaman. Get his book. Worth every cent.

[bryanj]

You have the order wrong power(+ve) starts at battery via igbition switch to kill switch on black then via black/white to coils then other lt side of coils via yellow or blue to points where it goes to ground until points open then by electrical wizadry a ht spark happens at both end of the ht leads on the appropriate coil.
Now, in order to work the points have to connect properly when closed (zero resistance) and have no connection(infinite resistance) when open which can be knackered by blue or yellow wire shorting to base plate or condenser shorting to baseplate.
On the ht side BOTH plugs, leads and plugcaps on the one coil have to be good or you dont get a spark on either.

Without being rude if you cant understand these points get somebody who does to check out the system.

[Radski]

You have the order wrong power(+ve) starts at battery via igbition switch to kill switch on black then via black/white to coils then other lt side of coils via yellow or blue to points where it goes to ground until points open then by electrical wizadry a ht spark happens at both end of the ht leads on the appropriate coil.
Now, in order to work the points have to connect properly when closed (zero resistance) and have no connection(infinite resistance) when open which can be knackered by blue or yellow wire shorting to base plate or condenser shorting to baseplate.
On the ht side BOTH plugs, leads and plugcaps on the one coil have to be good or you dont get a spark on either.

Without being rude if you cant understand these points get somebody who does to check out the system.

Thank you for clarifying. Clearly I had the order wrong and no offense taken. As I said this is a bucket list project and I'm trying to learn what I can with all the frustration that comes along with it. And I know theres a ton that comes along with it. I'm trying not to resort to paying the local shop $99 an hour to check into this. I'm hoping with the forums people like you all, and some of my mentors, I'll be able to learn and troubleshoot myself and get this bike fired up. Theres more to the story behind the bike which one day soon I'll make a "bike Build" thread to show the progress. But in short, the guy who gave it to me said if I can get it running then the bikes mine otherwise he'll take it back. SO I'm trying to spend as little as I can to get it started ie. taking it to a shop. While I have the time right now I'm open to learning as much as I can to get it back online.

I'm away from the bike until monday ...so it looks like I have some things to check into once I return. Thanks for everyones help! This is such a great community and full of knowledge, humor, and reality checks!

[bryanj]

I am sure most on here will give as much help as we can, electrics is, unfortunately, one of those things that if you are "hands on" can be fixed fairly quickly but are clost to impossible to fix at a distance.

With your points there is a yellow and a blue wire that go along the engine towards the rear then com up and join into the loom usually in a rubber boot where the rear brake light switch wires join in. If you disconnect the blue and yellow wires there, with the ignition and kill switch on, you can ground those wires from the loom(one at a time) and as you remove from ground you should get a spark at the relevant plug lead. If all spark your problem is towards the points, if only one problem is towards the relevant coil.

Hope that helps.

[Radski]

So I return from the weekend to charge the battery which had been dying due to all the starting attempts. Before even ripping into the issue at hand, I take the points cover off, setup the bike for ignition, and low and behold....I HAVE SPARK at that trouble position. Point 2/3. So I take the plugs out of 2 & 3 one at a time, and I'm also getting spark.

Now, I have no idea what changed while I was gone. I have two theories however. Last thing I did was clean the spark plugs for #$%*s and giggles which I know probably has nothing to do with the points. Theory two, the battery was fully charged from the trickle. EITHER WAY, I now have spark at ALL locations which is great.

I took float bowls off the carbs and gave them a clean. Sprayed carb cleaner in all other spots of the carb, put it back on, rigged a small gas can to get fuel in, and the thing fired right up! Fires up on first kick or electric start every time now. I'm both grateful and amazed that this has happened without much other troubleshooting.

Anyway, thank you for all your suggestions as they may help down the line. Now for the bigger project which is swapping (almost) everything over to a '76 frame. Long story behind the reasoning but if anyone wants to know I'd be glad to PM you and bore your eyes out. I'm going to start a build thread and post pictures so hopefully you all can comment and make suggestions along the way.

CHeers!

[BenelliSEI]

Radski...... i’m Working on a 1977 Benelli 750 SEI. It also uses NGK D8EA plugs. What are you using? On two occasions in the past 12 months, I have used a new NGK plug that would fire when laid on the cam cover, but did nothing under compression, in the engine! Eventually it stopped even firing on the cam cover. Threw it out and a new one solved the problem....... if your problem suddenly returns, get new plugs! I buy all my plugs from <clubplug.ca>? When I told them about it, they sent me anew set and confessed their quality control is not what it once was!

[Radski]

Radski...... i’m Working on a 1977 Benelli 750 SEI. It also uses NGK D8EA plugs. What are you using? On two occasions in the past 12 months, I have used a new NGK plug that would fire when laid on the cam cover, but did nothing under compression, in the engine! Eventually it stopped even firing on the cam cover. Threw it out and a new one solved the problem....... if your problem suddenly returns, get new plugs! I buy all my plugs from <clubplug.ca>? When I told them about it, they sent me anew set and confessed their quality control is not what it once was!

Wow thats amazing. Yeah I believe whats in there now are NGK D8EA's. I do also have another brand new set of 4. So it I encounter it again...I'll put the new plugs in.

[Radski]

Hey Bryanj and Benelli,

If you guys can check out my last post I'd really like to see your take on the situation. You guys have been tremendously helpful and full of knowledge so I'm curious what you think about my current predicament.

THanks!

http://forums.sohc4.net/index.php/topic,176948.msg2056774.html#msg2056774

[Radski]

Hello Gents,
Been a while since I've posted in here on my build. BUT....next question...

Have been tirelessly searching the interwebs for ways to clean/de-oxidize/make look pretty again the fins on my head. See a bunch of different ways but wondering what has worked best for you all?

Engine is out but have no intention of taking it apart. I've aircraft stripped it to remove the paint, not so much on the fins, but the rest of the engine. Now just have some very light surface scratches in some areas I'll buff out. BUT the oxidation on my fins (inside on the flat parts) is pretty bad.

What works for you?

[calj737]

Best and easiest thing to use is a stainless steel brush(es). You can find them at the local hardware store, Harbor Freight, Northern Tool in the Welding area. They are about the size of a tooth brush.

Also, grab some Red and Green ScotchBrite pads. You may need to have some flexibility to reach crevices and these work really well.

[Radski]

Best and easiest thing to use is a stainless steel brush(es). You can find them at the local hardware store, Harbor Freight, Northern Tool in the Welding area. They are about the size of a tooth brush.

Also, grab some Red and Green ScotchBrite pads. You may need to have some flexibility to reach crevices and these work really well.

as far as removing oxidation to prep for paint...is it a necessity? The metal is clean from everything else like grime oil etc. but I just want the engine to look better perhaps by giving it a coat or two of new paint. Does the oxidation need to be completely removed??

[calj737]

It does not, but it certainly encourages better adhesion. Some type of primer is always a plus too.