Is there a doctor in the house?

My VF750F needs one. Riding along just great. Stopped at a light, pulled away and looked in my mirrors. It looked like I was flying a crop duster! Grey smoke billowing out of my tailpipe. A new "clickety-clickety" rattle from the engine. The two rear jugs seem to be ornamental at this point; they have ignition spark, but the rear headers are only warm to the touch while the engine is running.

This is weird. Cam chain tensioner failed? I did not hear the sound of a piston slamming into a valve, though. I will buy a compression tester and check that out. However, very soon I will run out of ideas as I am not a skilled mechanic. I could take it to a shop, but I do not want to spend large sums of money on a bike this old. Maybe time for that new Fifth Generation VFR?

 

Hey some times even some of the best skilled mechanic end up at a loss for anwsers when it happens to me i walk away and clear my head and when i return most of the time it is stairing me in the face.
when you take off, the oil all runs to the rear of the motor and with the rear head not hot maybe it has a hole in a piston or rings ? first run a compression test and see what you come up with ? how do the rear plugs look ? ( speed )

 

Rear plugs look clean, but were damp. The ceramic on each was slightly discolored (orangey brown).

A compression test is next, but I have to buy a tester that fits. Nuts!

These symptoms are weird. Both rear cylinders are out of commission, so I would normally think CDI or coil. But I have spark to both. Maybe the spark is too weak to ignite the mixture or the spark is mis-timed. But then, why the increased clatter? Maybe a certain amount of extra clatter occurs when the rear valve train isn't powered? How about a blown head gasket? The smoke didn't really smell sweet to me, but I have never smelled hot coolant before - not even in my errant teenage years!

I need to run the compression test and go from there. I had a beer, and feel better. I am committed to this bike one way or another. You can see it in my gallery - I think it looks good enough to keep.

 

when the bike takes off ether coolent or oil runs to the rear of the engine, i dont see no spark couseing a bad smoke problem it would foul the plugs and not fire, the coolent is a full system so coolent is all ways at the rear of the head,if it was coolent it would smoke all the time,oil is a wet sump system and would run to the rear of the engine,maybe the air box is full of oil due to blow bye and runs to the rear carbs when you take off ? let me know what the compression test is (speed)

 

Ok what color was the smoke? Have you checked the oil in the motor..What color is it? If you had blown the head gasket the oil will be gray and full of oil and coolant. Check and see how much coolant is in the rad. Take the cap off and inspect is it down? The noise in the motor does it come from the top of the motor or more to the middle? I will do my best to help as work on bikes for many years at Honda and yamaha and a proud Onwer of a 91 VFR750.

 

Thanks. The smoke was a grey color. It smelled like unburnt gasoline more than sweet coolant, but I don't have much experience with diagnosis.

The oil looks great - clean as it was when I put it in - but I didn't ride the bike more than a couple of blocks after the engine began running only on the front jugs.

No perceptible loss of coolant, but again, I only rode the bike a short distance after the problem started.

It was like throwing a switch. The bike was pulling hard on all four cylinders one second, and the next it was a parallel twin crop duster!

I have some MP3s of the smoke and the clackety noise if you're interested. Or you all can wait for the compression test results. It's a mystery . . . .

 

Sounds to me like the cam lobes may have departed this life. I hope I'm wrong, for your sake. Good luck.

 

I will agree that back in 84 Honda did have some bad cam lobes and they were replaced as a service bulletin as did a few back then. An easy way to tell is remove the valve cover and on the rear bank and look at the lobes you will see meatl in a lot of places and the lobes will be almost round as the were soft and would loose there shape. Most would notice a decrease in power on take off and poor fuel mileage. I have had any smoke form this. You say it smells like raw gas. I would do as one said is open the air box up and look dow the carbs to see if some thing has got sucked in..Good luck hope this helps..Chris

 

The plot thickens! Cannot see any coolant in the radiator (although the reserve tank shows perfect level). No coolant is showing up in the crancase oil. And a blown head gasket doesn't explain the clatter, which sounds like the cam chain to me.

Well, after the compression test I'll know more. Or not. I might not know anything until I dig into the engine. In the meantime, I am bikeless! I am seriously considering immediately buying a '98-'01 or a Ducati Multi while I putz around with the VF750F.

 

The hose to the coolant overflow is bad and has been for some time. This means that when the coolant heats up and gets pushed over to the overflow bottle, it goes through except for a few drops that get out through the crack in the hose, and burn off before you know it. But when the coolant cools and shrinks, it can't pull the coolant back from the overflow bottle, it just pulls air through the crack in the hose. This means the coolant overflow has the right amount, but the radiator has air in it.

They all do that sir. The crack in the hose is probably right at the top of the arc, where it goes over the airbox. You'll want to replace this hose.

I doubt this is your only problem, but it's one of 'em.

 

elizilla, thanks. That makes perfect sense. I'll replace that hose. Still have the matter of 2 and 4 out of commission and that clickety noise . . . .

 

An update -

The threaded insert for the compression tester is in the mail. I am sure the head gasket has failed, though. The starter wouldn't turn the engine over until I removed the rear plugs, which were wet. The radiator took about 250 ml top it off.

Something else may be amiss as well. That "clickety-clickety" noise is disturbing.

The deal is, I do not relish the idea of pulling the engine and getting in over my head trying to fix this problem. The top end looks fairly complicated, what with the cam chain and tensioner. I am a lawyer, not a mechanic! But who wants to spend a ton of $$$ taking an old bike to a mechanic?!!

 

If you can pull the carbs and adjust the valves, you just did 2/3 of the job. Contact me if you need help. I just did the FRONT AND THE BACK headgaskets on my VF700F.

 

Mason, can the rear head gasket be replaced without pulling the engine?

 

No - at least not for the '82-'85 VF750F/VF700F Ceptor.

 

Another update - the bike is scheduled for a compression test and a leak down test next week at a shop.

I am going to fix it myself. There are some parts of the job I am nervous about, but what better bike to learn to wrench on than this one? Also, I definitely won't pay a mechanic to fix it. I have the cash, but it's the principle. The bike just isn't worth a $800 mechanic bill at this point in its life.

So, I may be shouting for advice later on.