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Bike stored for 29 years - tips welcomed on engine oil flush and prep before startup

lockeed

lockeed

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I bought a 1977 CB750K about two weeks ago. Couldn't be happier, bike is 100% original with only 12,500 miles. It's been in storage since 1988.

I started by removing the carbs, spent the last 2 days cleaning them, they were very dirty and gunked up.

Next step was to change the oil and filter, but I was wondering if I should flush the engine or if there's something better suited for a bike that's been stored for so long.

Anything specific I should pay attention to? Put a little lubricant on top on pistons before startup etc...?

Thanks
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I pour oil into the oil galley at the plug on the right side. I've used a rubber hose or an oil pressure gauge fitting and pipe fittings and even tried an auto AC oil tank, I put a quart in using air pressure through the AC tank and can even turn the oil pressure light off for a minute. I'd add a little marvel or WD40 to the cylinders but not too much, it can bend the rings if you overfill that. I squirt some into the top of the motor too through the rocker cover holes.
 
Quick update on the progress ad some questions for the pros. Today, it came back to life after a 30 year break. :)

Started this morning by changing the oil. I replaced the oil cooler line that was leaking towards the bottom. Flushed the oil tank. Cleaned the gaz tank and petcock. Sprayed a tiny bit of WD-40 in the plug holes and put new plugs in.

Bike started up but I had to remove the choke and give it some throttle to come alive. It wasn't turning as it should. Oil light quickly switched off though. I let it rev at low rpm for about 10 seconds and shut it off.

Started to diagnose what could be wrong. I ended up cutting about 1/4" of my plug wires and reset them tight. A little fuel had come off from one of the drain screws on carb #4, so I worked the screw a little and it stopped. I ended up checking and resetting the other drain screw and found that carb #2 was barely dripping fuel when the screw was open. Telling me that the float needle was possibly stuck or something... I used a rubber hammer to knock on the carburetor a little... It probably worked as I was working on some other stuff, I finally got a good flow coming out of the drain spout on #2....

I restarted the bike, it felt much better, but still had problems idling. I was able to stabilise it at 2000rpm or so. Gong under that it would eventually die within 10 seconds. Keep in mind I'm still waiting on my carb sync gauges to arrive so that needs to be done. side note, I did bench sync them though.

Couple things I noticed:

1) I barely had any exhaust fumes coming off from #2 cylinder/exhaust. I had more "air" coming out of the small drain hole than from the main exhaust hole... I ultimately*found the culprit = looks like insulation from the exhaust... don't know how that could bundle up like that and clog the exhaust, maybe mice? Anyway, I took it off, so that's solved.
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2) This is where I need you're help / Bike seems to rev on all four when you're past 4000rpm or so, but starting from a 2K idle, twisting the handle quick will make it sputter. It takes a second to rev, which makes me lean towards an accelerator pump issue... Maybe tied to or directly related to the stuck float needle and barely draining fuel issue noted earlier on carb #2...

also, like a dumda**, I just realised that the slow jets on the K7 are removable, somehow I had in my head that they were pressed in... Don't ask me why. They were cleaned and I ran plenty of comp;ressed air trough them, but I did not take them out. Could this be an issue as well? I'm attaching a picture of the plug on #2. Feels very dry to me. Note that the cylinder #2 also backfired a couple times under rev.

Sorry for such a long ass text! I just don't want to mess anything up - I've been careful with the bike from the start... And learning a lot as I go. Never worked on this generation.

Thanks!
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Carbs still not clean enough, many say yes but the only one you listen to is the bike, it will tell you truly by running right.
 
Thanks AMC. I did take the carbs off yesterday and cleaned the slow jets. They were dirty. I also caught a mistake I did; while cleaning carb #1, I took out the needle and throttle valve to clean each of them and for some reason, I reinstalled #1 incorrectly. On the air box side, the bottom of the valve are beveled, I put that bevel the other way around on #1... Don't ask me why. Now everything looks good and I know the accel pump works, I sprayed some gaz in my eyes :eek:

Should be able to try it on later today. Tips welcomed here, would it hurt if I didn't put on the air box just for a couple engine run today?
 
Non CV carbs should run fine airbox-less if the carbs are in jam-up mechanical shape, I run my 550 all the time on short startups and running to keep it loose and goosey. I have custom made by me short 3 inch long pods to fit but the bike sits and the pods tend to rot if you oil them and let them sit so saving the set for possible days on much more running.

CVs will work fine at pure idle with no airbox but not work right as soon as you go higher up because the slides won't function right.
 
When it comes to carbs look into the mirror and say "I have found the enemy and he is ME'. The way 99% of it works out. You just gotta be able to critique your own work to pull the rabbit out of the hat there and it's clear you did that.
 
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Thanks again for your inputs - carbs went back in the bike today- feels like 1977 all over again compared to last Friday :) Very smooth now.

Two things prevent me from saying that the bike runs perfectly now:

1) Says in the manual the bike should idle @ 1K rpm +/-, mine idles great at 1400rpm (tach reading) and this is with the air box out. If I go lower and drop it at 1.1 or 1.2K it tends to drop in RPM and stall after maybe 10 seconds. Other than that, engine runs smooth at 1.4 to 1.5K idle.

2) Twisting the throttle quickly from idle, it'll stall for a second before it picks up. If I do it quickly but more gradually, it seems to work just fine. No backfire anymore though and engine feels strong.

Tips welcomed.
 
It can be perfectly normal for a whopping amount of sudden throttle on direct lift carbs to make the engine choke for a second, why CV carbs were invented. The idle speed not necessarily exact either, the DOHCs are supposed to be at 1000 but they too are more comfortable at 1000+, say 1200. May get better after motor has a real chance to figure out it is running again. Whatever is comfortable to you. Fine tuning the idle mixture screws may help that too. All 4 screws should have the ability to individually pretty much kill their respective cylinders to drag down the rest of the motor when they get cut off. Sync will help lowering the last bit too. Might try a bit richer on the mix, if ethanol in your gas, the mix by the book may be a bit lean. Ethanol leans slightly depending on how much in the gas. PCM controlled cars adjust that out instantly but old school like bikes don't. The accel pump must work instantly with no lag as compared to throttle movement. On the DOHCs they call for a slight amount of slack to the lever, I take that out to move instantly. You still have lag built in because the check valve is getting shut with the first thousandths of pump lever movement and the passages have to purge too.
 
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Thanks again for chiming in. I adjusted the accelerator pump per manual, but I'll just eliminate the play.

I'm at 1.5 turn now on the idle mix screws... I'll try to fine tune when I get my carb sync gauge latter this week. With the idle screws, should I fine tune until I get the highest RPM as some suggested?
 
The DOHC says 1000 in manual too but I generally used 1100-1200 and fine all day long.

One other thing the slightly faster idle does is to level out primary drive noise to be quieter.
 
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I bought the same bike last week. But it had only been stored in a shed for the last 11 years, not 29! Ive also managed to fire it up without the airbox installed but it runs rough. I did not change the oil/filter yet. This should be my next step Im guessing?
 
TeamFast said:
I bought the same bike last week. But it had only been stored in a shed for the last 11 years, not 29! Ive also managed to fire it up without the airbox installed but it runs rough. I did not change the oil/filter yet. This should be my next step Im guessing?
Click to expand...

Change oil with a low cost one, run it for 5-10 minutes at low rpm. Flush that oil and put some good oil in it. Then clean the carbs carefully, sync the carbs and you'll be close to having a good running bike.
 
I wouldn't touch it for now, just do a 10 minute oil warm up and swap, then switch to good oil and new filter + new spark plugs of course. But if the bike was stored for 11 years, take those carbs off and dissemblable them. They'll need a good clean, there's a good write-up on it here on the forum.
 
So ive been trying to get the bike running and its been intermittent. Ive cleaned the carb three times now, however I just realized ive been testing it without the airbox on. No airbox, no pods, just straight carbs. So I was only really able to get it to idle and any throttle application stalled it. A few times I could rev it, ever so slowly to get it up to 4K.
So ive cleaned the airbox and will attempt it again. I'm hopeful this is why it wasn't running well.
There is a vent hose that comes from top of engine and connects to airbox. This is in pieces. is this critical or are people bypassing this crankcase vent?
Wish me luck!
 
If its a dohc yes the air box will make a huge difference, if its a sohc it will make little if no difference. Need some more info on what bike you have. No matter what bike you have the crank vent is critical, do not bypass it, go get some hose from auto parts store.
 
If I had to guess, I'd say you're carbs aren't properly cleaned and synchronized. Did you remove and clean the accel pump? Did you remove all the jets? Idle jet included? Did you sync the carb using #2 as reference? Did you set up the air screws where they're supposed to be?

Did you follow the PDF instructions found on this forum?
 

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