79 Cb750L

[Stig]

Hey Guys. Just got this thing the other day and of course like all bike noobs i already have questions.

My main concern is getting this engine running properly.

Right now it is not firing on cylinder 3. I put a brand new spark plug in it and ran the bike to temperature. after removing the plug it looked like that it never even produced a spark. i put it in a different cylinder just to make sure. Now of course it has all the normal signs of a working plug. So my question is what do you think i have. electrical problem with that cylinder or is that carb in need of a rebuild. the wires look brand new.

[LukeM]

Welcome to the forum.  
Step 1:  Go to the home page of this forum, and in the Manuals area, download the Factory Service Manual for your bike.
Step 2:  Go to the Maintenance section of the manual, and check all the systems.
Step 3:  Once you've gone over them, then we can dive into the issue you're reporting with cylinder #3.
Step 4:  Remember that there's nothing better than a good visual inspection.

I'm a big fan of the OSI model in my work (network engineering).  If the lower layers aren't working, nothing in a layer above that will work. The same can be applied to MC repair: It makes sense to get the fundamental stuff checked and working first (compression, timing, etc) before diving into the stuff that relies on the fundamentals (fuel delivery, mixture, modifications, etc).

Your bike is running on 3 out of 4.  This is a good thing. Just need to get the basics checked first, then we can dig into this some more.

Nice looking bike: reminds me of my own 750L (may it rest in pieces/peace).
Luke M

[Re-run]

Try this, move the #3 wire to #2 and the #2 wire to #3 and see if the problem moves. It is most likely a bad connection between the boot and the wire BUT your bike has removable plug wires and so it may not be making contact with the coil terminal properly.

[Stig]

Yea never even thought about that. I got side tracked with the hawks game last night. I'll start giving it a good look at.

[Stig]

well I have spark going to that cylinder. So tonight i pulled the carbs off. diaphragms sound like they got some suction to them. So im guessing they are just really gummed up. going to buy that master carb kit and rejet while im at it. I still have to check compression to all the cylinders. also intake valves look relatively clean. so there is my update :) now the next question. I am over all going to do a 4 into 1 exhaust, probably no baffles and then do the k&n pods. any suggestions on what size jets i should go with? I live in northern IL for the altitude.

[shinyribs]

Ooh,pretty bike! I am familiar with those pipes...they sound goooood!!!Welcome to the forum.Good luck with your plug issues.

[Stig]

lol thanks man. i still cant believe i got such a great deal on it.

[shinyribs]

Stig,I totally zoned out and missed half of the info in your post right above my last post!If you do end up going to a 4-1 setup I would be interested in buying the pipes you have on your bike now.

[Stig]

Well they are not going to be going anywhere for a while unfortunately :p I may be able to jet the carbs but im on a strict budget at the moment. so i needs dem pipes :p also that pipe in the pic has a lil bit of damage on it. apparently it fell off once and a truck ran it over lol.

[shinyribs]

Damage is cool,its drives the price down! LOL Just kidding. I understand a strict budget all too well.. But if you ever do decide to sell keep me in mind,please.


You could always sell your old pipes to help finance a 4-1.....are my high pressure tactics working yet??

[Stig]

lol ill keep you in mind when i decide to sell them. but i would love that 4-1 but right now all the money is tied into trying to just get it back to road worthy status :)

[shinyribs]

Riding is priority #1 !   Accessories can come later!

[Stig]

exactly :) im still in a delema if i wanna go with pods or attempt to throw the stock air box back on after the carbs get rebuilt. I know it would be less painful in the long run to go with the airbox. then i dont have to rejet right away. also My friend who has built a ton of these things tells me that if i go with an exhaust then the carbs will only need to be tweaked and not jetted. It makes sense considering carbs are more influenced by the air going in rather than what comes out of the exhaust valve. and the other good part about the stock box is that all the rubber tubes are still in good shape. So thoughts?  Kinda in a way i guess i wanna make a mild restomod.

[Stig]

Well took apart the cylinder 3 carb tonight and found the issue. the float needle was verrry stuck. took some persuasion but it is out and not being a prick anymore. time to get the carb kits :-D

[Stig]

Its been a looong time since i have posted on here. got busy with work and trying to get parts.

Ended up taking the carbs out and tearing into the bike to see what i needed to get it running.

did the usual compression test and checked under the valve cover. after i got everything back together found out my coils were crack. have those. got into the carbs and they were a mess.

ended up having to drill out one of the tubes and easy out the other 3. got them cleaned up all pretty and upon assembly one of the emulsion tubes....the one that holds the main jet....decided to disintegrate on me.

So I managed to find a set of carbs on ebay for 70 bucks and just got those. so now waiting on them showing up. But at least I have another 4 chances to get a good tube. And its nice i have a couple spare parts.

So here they are so far after all the cleaning and drilling lol

[Stig]

The bike is running! however I have fuel leaking out of the bowls. not sure why yet. wonder if the gaskets i put in there are not sealing properly. letting it sit overnight to see if the gaskets swell up a little bit and seal it. I do have a couple of possibilities. But I am happy that it is running on all 4 cylinders and it is sounding mean :)

[alehman]

Is it leaking from the gasket area or from the overflow?

[Stig]

It was from both but then the overflow stopped. been gone all weekend so have not had a chance to rip back into it. One of my friends was going to check on it when i was gone to see if the gaskets just were not set quite yet or something. Ill find out in the am. But hey at least it is one step closer :)

[alehman]

A gasket leak is pretty straightforward... if it's leaking from the overflow then you either have sticky floats that can't move freely or the float's needle valve isn't seating correctly. This can be caused by gas varnishing on the seat. You can lap those seats with a q-tip and chrome cleaner or toothepaste, which has a very fine abrasive.

[Stig]

checked the gaskets after this weekend and it seems they are ballooning up and sealing. all three are good but one. so it may need a bit of time. I guess it is normal for these types of gaskets. Ill know more in a day or two.

But onto the next big question. I desperately need tires. Can anyone help me with some choices and I am assuming these tires have tubes in them to. I am not looking to spend a rediculous amount of money for tires since the season is kind of in its down swing. But I do want to ride it until it snows.

any help is appreciated.