Author Topic: CB 750 Project 1 - Rides Well but a few tweaks needed (Read 131727 times)

maduncle · « **Reply #675 on:** October 30, 2016, 01:18:14 AM »

Hi Tim,

I bought the Joker Machine oil pressure gauge and adaptor mount, its a good gauge and easy to read from the riding position.

http://www.jokermachine.com/products/cb750-oil-pressure-gauge-assembly.html

Terry in Australia · « **Reply #676 on:** October 30, 2016, 01:41:41 AM »

That gauge looks great, if I didn't already have one, I'd buy it myself!

timbo750 · « **Reply #677 on:** November 01, 2016, 10:16:35 PM »

Rear brake parts arrived so that is now all sorted. Found out though that the exhaust is resting against one of the sump bolts. Its hard to know much extra clearance I need, so I am going to change the socket cap acrew for a hex head bolts which should give me about 1mm. I will also put a little bit of heat on the collector and push it a bit. I don't want to distort the exhaust or weaken it.

Also can someone tell me which kick starter is the correct one.

timbo750 · « **Reply #678 on:** November 01, 2016, 11:00:32 PM »

Terry and Clif. I did look at the Joker guage and it is very neat but I went with a different option with the oil pressure guage. I found out on another build thread that there is available an adapter to replave the factory plug and gives a 1/8 npt female thread. I also got a Marshall guage ordered direct for $66 delivered.

Terry in Australia · « **Reply #679 on:** November 01, 2016, 11:31:54 PM »

No worries Timbo, I've got a Marshall gauge on mine.

timbo750 · « **Reply #680 on:** November 02, 2016, 12:00:41 AM »

It would be nice if there was a local dealer here in Australia. There doesn't seem to be anything of quality available here.

Terry in Australia · « **Reply #681 on:** November 02, 2016, 12:42:10 AM »

Quote from: timbo750 on November 02, 2016, 12:00:41 AM

It would be nice if there was a local dealer here in Australia. There doesn't seem to be anything of quality available here.

There was back in the 70's and 80's mate, when our bikes were new, you could buy just about anything for a CB750 back then, and I did, but nowadays there's not enough demand in Oz, that's why ebay is your friend.

timbo750 · « **Reply #682 on:** November 02, 2016, 12:20:12 PM »

Thanks Cal, great idea

timbo750 · « **Reply #683 on:** November 04, 2016, 11:02:57 PM »

Just tried my first test start, no luck. Carbs aren't leaking so that good. The engine turns over fine as well. All I got was one back fire, so I am going to check that the timing is right first. I also haven't fitted the bottom of the air box which I know would affect how it runs but should still start.

timbo750 · « **Reply #684 on:** November 04, 2016, 11:44:25 PM »

The points were way out, thought I set all of that when I installed it. But I cant seem to set the static timing right. The Clymer manual says the points should be just opening at the F mark but they opening for 1-4 at least 5 degrees before.

Terry in Australia · « **Reply #685 on:** November 04, 2016, 11:48:27 PM »

Yeah, don't worry about the airbox mate, your bike will start fine without it. Drop one of your float bowls off and see if there's fuel in it, if not you might have a blockage. Pull a plug lead off and shove a spare plug (any heat range) and give it a crank and see if you've got spark, and lastly, make sure you've got the right set of points connected to the right coil, or else your timing will be 180 degrees out. Cheers, Terry.

timbo750 · « **Reply #686 on:** November 04, 2016, 11:52:48 PM »

I know I have fuel to #4 as the drain plug wasn't tight and it leaked a bit. Don't think I have a spare plug but will have a look. And I traced the wires from the points to the coils, blue for 1-4 and yellow for 2-3.

timbo750 · « **Reply #687 on:** November 05, 2016, 12:21:21 AM »

Can't find a spare spark plug hanging around so will go and get one tomorrow morning. I checked the idle air screws and they were way out more than they should, I am getting more back fire but not sounding like it wants to run. Will start a fresh tomorrow.

disco · « **Reply #688 on:** November 05, 2016, 01:58:24 AM »

Timbo,
The kick starter on the RH in the pic is the correct one for an early 'K'.
Try some starting fluid, that will quickly tell you if you've got a carb/fuel issue or its spark related.

timbo750 · « **Reply #689 on:** November 05, 2016, 04:58:10 PM »

Well I have spark, so that's 1 thing eliminated. Unfortunately I won't have much more time today to continue checking as I have family duties. I am guessing it may the carbies. I rebuilt them a while ago and judging by the way the idle screws were way out I am guessing something else is too. I will check the valve timing as well in case I got that way wrong.

timbo750 · « **Reply #690 on:** November 06, 2016, 12:38:24 AM »

Check the valve timing. Number 1 inlet starts to open just after tdc for 1-4. Its a stock cam so no minor adjustment available or required. So at the moment it all points to a fuel issue. Tomorrow I will get some aero start and try that before I pull the carbies off.

timbo750 · « **Reply #691 on:** November 06, 2016, 11:35:41 AM »

I did a bit of reading (which I know sometimes I shouldn't ), the back fire seems to be in the inlet and I read that it will most likely be too lean. Can anyone agree or deny this?

timbo750 · « **Reply #692 on:** November 07, 2016, 01:16:37 AM »

The aerostart didn't make a lot if difference except for more back firing. I removed the air box ready to remove the carbies, I was not expecting what I saw and I am not sure what it means.
Carby 1

Carby 2

Carby 3

Carby 4

It looks to me that pistons 1-3 are pushing some fuel back. Could the valve timing be out? Or is there ignition whilst the inlet valve is open?

timbo750 · « **Reply #693 on:** November 07, 2016, 12:04:31 PM »

I have done some more logic processing about where things are where they should be. At the moment I am thinking I have 2 problems to sort out, one being the carbies and I think that I will have to remove them and reset all the adjustments.

The other is the timing, I am almost certain that the timing is wrong and it is firing too late. this late fire and the redundant spark is causing a backfire through the carbies. It's been 20yrs + since I have worked on an ignition system so I am a bit rusty on the fine tuning.

timbo750 · « **Reply #694 on:** November 08, 2016, 05:16:16 PM »

I am confident now that I have the timing right. After doing some more reading I used the ohm meter method and although not 100% it is close enough to get it started.

I also checked the cam timing again, at TDC for 1-4 the exhaust is just closing and the inlet just opening.

It still wont start but backfires. So thag leaves the carbies. I will remove this weekend and and reset everything.

seanbarney41 · « **Reply #695 on:** November 09, 2016, 01:50:56 AM »

Timbo, did you have the advancer apart? It is possible to re-assemble the advancer cam 180 degrees out...I would double check that before messing with the carbs.

b52bombardier1 · « **Reply #696 on:** November 09, 2016, 04:47:58 AM »

Yea, putting the advancer back together 180 degrees out will drive a Honda mechanic insane. Don't ask me how I know. I said a lot of bad words and drank a lot of beer that weekend.

Rick

Sent from my SAMSUNG-SM-N900A using Tapatalk

timbo750 · « **Reply #697 on:** November 09, 2016, 10:19:56 AM »

Sean and Rick, you guys are life savers. How do I tell?
Or is it obvious when you are looking for it?

b52bombardier1 · « **Reply #698 on:** November 09, 2016, 12:58:13 PM »

Somebody will come along here with instructions for noting the best markings on the advancer to avoid this problem.

For today, after learning (badly) of this on a 90 cc Honda engine 5-6 years ago - I put black Sharpie marker alignment marks on the advancer before disassembly.

Rick

Sent from my SAMSUNG-SM-N900A using Tapatalk

seanbarney41 · « **Reply #699 on:** November 09, 2016, 02:16:06 PM »

There is a tiny dot (so tiny that it sometimes has worn away) on the shaft that needs to align with something...unfortunately I can't remember what. There are pictures somewhere here. Plus I think hondaman covers it in his book. I will dig around in some stuff and try and figure it out, but it may take me a while. I am pretty sure there are only two ways to do it...so maybe just take it apart and try it the other way

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Author Topic: CB 750 Project 1 - Rides Well but a few tweaks needed (Read 131727 times)