Author Topic: New guy with a ton of questions (Read 2216 times)

dr.seiss · « **on:** December 04, 2011, 11:08:45 PM »

Picked up a CB750k4 recently and it's gonna take a bit to get it in the condition I want. I could use a little guidance. In what order would you address the following issues?

1. Squeaking, grabby front brakes.
2. Spark arcing to case.
3. After riding for approx 30 minutes, the idle hovers around 2000.
4. The oil tank breather hose drips oil after a ride. This is the one atthe to of the tank. The lower one is connected properly to the tranny area.
5. The starter makes an odd noise when throttle is twisted. I have a video of this that I need to figure out how to upload.
6. Oil weeping from several spots. The tach cable, the head gasket(very little), bottom of oil tank at main hoses.
7. When the choke is applied, the engine dies.
8. Occasionally when shifting from 5th to 4th it will not engage.
9. The carbs (I think it's #1 or #2) will leak from overflow tubes if the petcock is left open.

I'll post a vid or two when I figure out how. Thanks!

Nicky

dave500 · « **Reply #1 on:** December 05, 2011, 01:27:28 AM »

gday and welcome,id look at both front and rear brakes first,id also if the fork oil is an unknown age id see about changing it,,dont believe anything the seller told you,,you have to make sure for your self.

grcamna2 · « **Reply #2 on:** December 05, 2011, 03:27:31 AM »

I'd deal w/ under the tank "arcing spark" issue & the oil line leak.

Toxic · « **Reply #3 on:** December 05, 2011, 03:40:33 AM »

ummm you have a spark and leaking gas.... I'd worry about that first. Then brakes.

Welcome and post pics.

dr.seiss · « **Reply #4 on:** December 05, 2011, 12:24:00 PM »

Thanks for the responses. I'm going to order some new spark plug caps and an oil seal for the tach drive today. That should clear up the arcing and leakage around the valve cover area. Next is a carb cleaning to unstick whatevers making the fuel come out the overflow tube.

bollingball · « **Reply #5 on:** December 05, 2011, 12:31:46 PM »

I think most people are saying fix safety items first. Fire brakes and so on.

fishslayeryo · « **Reply #6 on:** December 05, 2011, 01:38:03 PM »

Welcome aboard, i'm with ya, just picked up my first cb750 about 3 weeks ago. Guys are right the leak/spark first. My front brakes are sticking. First thing you can try is guitar string in the release hole in your master cylinder res...it's plugs up and won't release pressure to your front caliper. The other issue could be your front piston in your caliper is stuck. I just tore mine all apart lastnight..caliper and master cylinder to do a rebuild on all of it with OEM parts, minus the stainless brake lines I just got in today from slingshot cycles:) Here's the best link I could find on the front caliper cleanup before new caliper seal. Good luck and congrats on the new ride!

http://forums.sohc4.net/index.php?topic=99152.msg1105890#msg1105890

~Yo Han

MCRider · « **Reply #7 on:** December 05, 2011, 02:04:32 PM »

While you need to fix the leak from the overflows, I'll take this opportunity to fill you in assuming you don't know this point.

On bikes like ours that do not have the more modern vacuum operated petcocks, it is standard operating procedure to turn the gas off every time you stop the bike. Every bike made since you were of driving age has a vacuum operated petcock. So its not an issue. All bikes of the 1970s era do not.

Some will shortcut this to everytime the bike will be parked for long time periods. This is a safety issue as you've already experienced these bikes can stick a float for any one of a number of reasons. This can result in a leak onto the garage floor and a fire when sparked.

This is not an old wives tale, its in the operators manual if you have one.

I would NEVER leave one of these bikes overnight without turning off the petcock. Whether you think you've got the carbs fixed or not.

Following this protocol will invariably result in you riding away from a parked period, with the gas turned off. usually its just a laughable situation, but can be dangerous in itself. Its the lesser of two evils.

CrankyOldGuy · « **Reply #8 on:** December 05, 2011, 05:47:37 PM »

+1 MCRider

I always turn the petcock off when parked for any length of time especially when using the side stand. I have had a few of the laughable situations but after turning the petcock on engine response was almost instantaneous. No worse than traveling down the road and having to switch to the reserve position (fortunately never had to when I was passing on a busy 2-lane highway

).

The brakes would be first in my mind. If you get it running properly the urge for a quick spin may overcome the thought to fix the brakes. JMO.

Harry O.

Stev-o · « **Reply #9 on:** December 05, 2011, 05:59:41 PM »

Safety first, change the caps and don't forget to clip the spark plug wires a quarter inch before installing the new. +2...turn the petcock off!
Squeaky brakes are fairly common, new pads/shoes may be in order. And address disc/drum.
Your idle may be high due to leaky carb boots?
Take care of these few things and check back.

MCRider · « **Reply #10 on:** December 05, 2011, 06:12:18 PM »

Also, since the carbs have been overflowing, you may have experienced one of the other things that happens when the petcock is left on. Fuel will flow down the intake throat and past the valves into the cylinder, where it washes down the oil film on the cylinder and pollutes the oil in the crankcase. You should change your oil first thing, and after any other episode of leaky carburetors.

It may not be raw fuel that's flowing. it may be fuel vapors, from the overflow, that condense on the cold cylinder walls.

I've seen this many times back in my shop days. We'd dump the oil on a 450 to do a tuneup and get 1/2 quart too much. Definitely fuel pollution. ASk the owner, nope hadn't been shutting off the gas.

Acccelerates wear on everything, esp valve gear.

chewbacca5000 · « **Reply #11 on:** December 05, 2011, 06:17:35 PM »

+1 MCRider you beat me to it! I was about to say the same thing. Had it happen to my K3 before.

MCRider · « **Reply #12 on:** December 05, 2011, 06:23:18 PM »

Quote from: chewbacca5000 on December 05, 2011, 06:17:35 PM

+1 MCRider you beat me to it! I was about to say the same thing. Had it happen to my K3 before.

Yup!

dr.seiss · « **Reply #13 on:** December 05, 2011, 09:32:35 PM »

Thanks for all the replies guys! I am in the habit of shutting the petcock off, but I've forgotton twice and woken up to an empty tank. All the time I had my old CL450 I never for got once! Looks like it's time for an oil change too.

dr.seiss · « **Reply #14 on:** December 05, 2011, 09:33:35 PM »

Also, does the annoying captcha thing ever go away?

dave500 · « **Reply #15 on:** December 05, 2011, 10:40:33 PM »

signed in?it might be a post count thing?just unscramble this first,,,fnjsucteb r5$%:JDae

70CB750 · « **Reply #16 on:** December 06, 2011, 03:55:01 AM »

The choke should kill the engine - if it works properly.

+1 on the fuel off, I do it every time I put her on stand, OK, not at the gas station, but if I have to walk away from her, the petcock goes to off. She is good in keeping her bottom dry but I always done it that way. I actually never had bike with vacuum operated cock, hmmm, maybe the CBX750 had it? Not sure now.

dr.seiss · « **Reply #17 on:** December 06, 2011, 09:14:42 PM »

Quote from: 70CB750 on December 06, 2011, 03:55:01 AM

The choke should kill the engine - if it works properly.

I've heard this several times now and I understand that cutting off the air killls the motor, but I'm confused why the manual says to use it. At any rate, having the choke lever in any position other than fully up doesn't seem to do anything at all.

Danno · « **Reply #18 on:** December 06, 2011, 09:22:37 PM »

the leak out the over flows is usually caused by dirty needles and seats the seats can be polished with a matchstick in the carbs and the needles can be removed and polished

the other cause of a leak out the overflow tube aside from rust in the tank is a hairline cracked overflow tube they can be cleaned and soldered or replaced i believe they can still be gotten depending on which carb set you have

dr.seiss · « **Reply #19 on:** December 06, 2011, 09:49:21 PM »

Quote from: Danno on December 06, 2011, 09:22:37 PM

the leak out the over flows is usually caused by dirty needles and seats the seats can be polished with a matchstick in the carbs and the needles can be removed and polished

the other cause of a leak out the overflow tube aside from rust in the tank is a hairline cracked overflow tube they can be cleaned and soldered or replaced i believe they can still be gotten depending on which carb set you have

Great info! Is there a step by step carb cleaning how-to? Also, how do I know what carb set I have?

70CB750 · « **Reply #20 on:** December 07, 2011, 04:03:05 AM »

Quote from: dr.seiss on December 06, 2011, 09:14:42 PM

Quote from: 70CB750 on December 06, 2011, 03:55:01 AM
The choke should kill the engine - if it works properly.

I've heard this several times now and I understand that cutting off the air killls the motor, but I'm confused why the manual says to use it. At any rate, having the choke lever in any position other than fully up doesn't seem to do anything at all.

I use the choke for cold starts - closed - to get more fuel to the combustion chamber(s) When it starts I alternate to 2/3 or 1/2 - depends on how she runs. If I am in a hurry, I keep the choke at 1/3 when I take off and open it fully at the first stop sign.

Just my experience

fishslayeryo · « **Reply #21 on:** December 07, 2011, 08:24:23 AM »

Here's all the manuals you could ask for:)
http://forums.sohc4.net/index.php?topic=17788.0

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Author Topic: New guy with a ton of questions (Read 2216 times)

bollingball