is there Anyway to Just kill the #4 carb

I've had problems in the past with my #4 carb . It was and is still just spraying gas out of the header straight into the exhaust (4-1) This is Awful.

NOw Its either a float bowl, or A valve thats seized. I dont have the KNowledge or toolsto go rifling through my engine.

I've been running on 3 cyl all last summer It would sometimes not spray , but often did.
Anyway my question is Is there a way to Cut off the gas to the # 4 carb and run on 3 cyl. I've put well over 500$ into this bike and getting tired of it . And the mechanic gave me an estimate of 400-700$ to fix this issue. He thinks its a stuck valve.

maybe cheaper just to swap the engine. or get a new bike .

Losing hope .

 

If your mechanic cant distinguish between engine problems and carb problems it is time to find a new mechanic. The whole stuck valve scenario is a load of crap anyways because if a valve managed to seize and stick open chances are the piston and the valve would hit. If the valve was only partially open then the shim would pop out and turn your top end into swiss cheeze. Not to mention that the sounds the engine would make would make it definately unrideable.

While it would be technically possible to block off gas to the one carb, It would be a very poor choice and running it on 3 cyls can cause serious and permanent damage to the engine. Since you mentioned that you ran it like that all summer, damage may have already occurred.

You will have to rebuild the carbs at minimum and yes it can be costly. Since you do not seem to have the desire to tackle them yourself it may be a good idea to leave that job to a qualified professional. (Not your current mechanic though cause he doesnt sound like he knows his head from his behind)

So your choices are: Spend the money, have the carbs built and tuned on the bike, and pray you didnt already destroy the engine. OR Sell the bike and let the next person worry about its issues. Its as simple as that.

 

If you got a copper or stainless scrubbee pad, or just a small part of it, and stuffed it in the float bowl, it would hold the float up without hurting anything( if done right) then you would have a 3 cylinder XJ ( sounds familiar?)

Meanwhile, I've been seeing racks of XJ carbs going for $50 - $60 SHIPPED on E-Bay. (not to Canada).

Don't give up hope over 1 pesky carb !

 

Yeah but you can not disable a cylinder on an engine and expect it to last for any length of time. The engine is not designed to have to pull the piston and the rod bearings will NOT last.

 

uh. i cant see how it could possibly do extra damage. the rod and main bearings all use common oil and the pressure as such would be the same. i fail to see how it would hurt anything, other than power output.

 

It isn't hard to check the valve clearances. A tight clearance won't allow the valve(s) to seat. Could be a cheap, easy fix.
Just a thought.

 

I just bought a rack of carbs off ebay for $65 + less.than $10 shipping. They are Hitachi's just like the ones on your bike. For less than $75 you would have a set of carbs to rebuild slowly at a comfortable pace. It can cost a little to rebuild them but you could buy the parts as funds become available.

If you rebuild your carbs and your scooter starts running on all four cylinders nobody would be able to beat the grin off your mug with a two by four. It is extremeley exhilarating!

There is a how to in the FAQ section that walks you through the process one step at a time. It even has pictures. These old bikes often have carb issues that once taken care of are easy to keep at bay.

If you have a stuck valve a compression test will tell you in minutes. Borrow, rent for cheap, or buy an inexpensive compression tester and you will know if it's a valve or carb issue.

My money is on the carbs.

Best of luck. I love my 81 650 Maxim.

 

Jonny,
How do you know that #4 is spraying gas??? Are you smelling gas in the exhaust? On a 4-1, you will be getting all of the exhaust out of one muffler, which would confuse the issue. You would have to run the engine with the exhaust headers off to confirm this. It goes without saying that the EGT would be lower on that cylinder as well. You need to do a compression test. Buy/rent/borrow a compression gauge and check out your cylinder pressures. That will tell you if you have a bent valve real quick. The flea-bay carbs sound like a good idea, but bear in mind that you could be buying more problems... Buyer beware! You might just contact Rick-O-Matic about a house call. But first do the compression test!

Switch263, the imbalance the crank would experience if the bike is run up to higher RPMs with 3 operable cylinders can cause parts to bend (cranks, etc) particularly if the engine is under load and fighting the dead cylinder's compression. This could lead to catastrophic failure. I would not run minus a cylinder for very long nor at anything higher than an idle or slightly (1500rpm max) higher. You are correct that the oiling system would function normally (thank heavens). We run our test motors with only one or two cylinders of four operational but I've not heard anything from our engineers as to what problems are encountered. Mayhap I need to make an inquiry with the fellows on Monday. The answer might be of interest to us all...

 

For those wondering how running with a dead cyl can cause damage to the engine:

The piston is supposed to push the rod which turns the crank. When the crankshaft has to pull the piston through the bore several things happen.

The rod bearing has been wearing in a particular way for 26 years. The load has been on one side of the bearing for that time. When the cylinder is dead, the load is placed on the opposite side of the bearing and when it wears slightly knocking can and will result.

Also, when the valves are closed and the piston is pulled down, oil is pulled past the rings and into the combustion chamber. This oil builds up and at minimum will be pumped into the exhaust. It has been known to cause catastrophic failure as oil does not compress like air. It can and will bend/snap the rod.

For those who still dont believe, just cut the fuel to one of the carbs and run it for a few thousand miles. You will have problems. There is a reason why vehicles with multiple displacement systems have specially designed valvetrains which cut compression to the turned off cyls. And not to mention that they are not designed to run on reduced cyls for extended periods.

 

I didn't even think about the effects of compression at higher RPMs, that makes perfect sense.

 

When we have a situation like this one; don't make a recommendation for the Member to do anything that might make the situation worse.

If you don't know what the consequences of your recommendations will do; DON'T MAKE THE RECOMMENDATION.

The Engine won't last very long if the Fuel Supply to the 4-Carb is Cut-off.
Eventually, the strain of having no combustion will lead to Bearing problem or the Connecting Rod separating from metal fatigue.

I agree with those who have recommended the Member find a more competent Mechanic. Certainly, having the 4-Hole Compression Tested and it's Valve Clearances and Operation would be in order.

Although what on-the-surface looks like a Carb Problem; you'd know for sure after having the Compression Tested, the Valve Clearance measured and the Cam Lobe inspected for any possible damage.

Unfortunately, we have arrived at the time when it is going to be exceedingly difficult for you to get a straight answer about what might be wrong with your bike.

Some Dealerships may not want your business. Your Bike, with a myriad of time-consuming problems for a Technician to encounter while performing a Basic Maintenance Job; makes it MORE PROFITABLE for the Tech to NOT work on your machine and successfully accomplish SEVERAL OTHER Work Orders, than to even take-in your Bike for an Oil Change and RISK finding a rounded-off Oil Filter Bolt, or one that's seized.

New Members will COME HERE seeking advice about what to do when they have something not right and don't know what to do ... themselves.

If you know the answer. Help solve the problem.
If you don't know what the problem is because the situation is vaguely stated; get the problem to be less vague before making a recommendation.

Don't tell or even suggest doing anything UNLESS you can INCLUDE possible ramifications of what you have suggested that might happen if they do what you suggest.

One of these days ... somebody is going to do something you heard about and suggested and wind-up being in a deeper hole than they were before they did what you said to try.

 

Well said... as always.

 

without starting a huge debate, i just want to raise one very important point that BUSTS your theory. the pistons are almost ALWAYS being pulled down, because there is almost always vacuum on the intake side. its a very important part of engine braking. the multiple-displacement engines drop valves for another reason, creature comfort. who the heck would buy a car that rumbles the floor boards every time it drops cylinders. other than that they do not have any special bearings.

your theory would be correct on the old Detroit silver 92 engine. but thats because it has a positive displacement supercharger and its diesel, so from cranking rpms to wide open it is always under pressure.

as for sucking oil past the rings......again, what do you think happens when you are cruising down the road under very light load. there is high vacuum sucking oil up. fortunately the rings (when in good condition, as well as cylinder wall) are pretty good at their job and this isnt really an issue.

the rotating assembly was designed to rotate regardless of pressure, be it positive or negative, in the cylinder.

I DO RECOMMEND FIXING THE PROBLEM, but running the cylinder dry would be a rough gutless ride, and would not hurt anything but your fuel mileage and fun factor. i have actually worked on several 2 cylinder industrial engines that have been converted to a "single cylinder engine" with the #2 cylinder used as an air compressor (seperate intake and exhaust manifolds). they work beautifully.

 

In reponse to RickOmatic: Just to clarify in my own mind.


There seem to really be 2 issues here. One issue about which the owner mentioned he has no expertise and 1 that blossomed into a discussion precipitated by the 'what if' should no action be taken.

The troubleshooting techniques offered seemed to be valid and correlate to the advice you gave him. Compression test, valve clearance verification, and carb cleaning. Am I correct so far?

The other issue is what would happen should no diagnostic/repair action be taken. Is this where you take exception? It would seem that this discussion is valid, although probably difficult to understand, and by no means is there an obvious consensus. The end result of the conversation so far seems to be that it would be best to troubleshoot and repair the problem and by doing so eliminate possible catastrophic failure down the road.

If the issue is buying a set of carbs on ebay to rebuild if necessary this advice also seems valid. Having a set of carbs to rebuild at leisure with no need to finish them in a hurry seems like a good way for a person with limited experience to do the job right. I am certain that my wife, who has no desire or technical ability, could rebuild the carbs from your write up in the FAQ section, although I don't anticipate her doing the rebuild for me. (Nuts) Just looking for clarification.

WAMAXIM

 

Robert



Robert,
first I noticed that my fuel milage is horrible, I smelled gas .I took the Headers off , and started it, and believe me it sprays like 2ft off the block. And back into my air box as well. So I will try something tomprrow. I will try switching my plug wires 1&2 to 3&4 and see what happens. That is if they will reach...
Next I will check the float heights. And clean the carbs ...again.
If this does not work . I will look into buying a compression gauge, and figuring out how to do it.

I ve heard of people Running on 3 cyl . of course not as powerful as all 4

These posts are starting to confuse me. Believe me I love this Bike .It being my first, the time Ive invested in it has already been teaching me alot along with this forum.
The last thing I want to do is Ditch it, and buy a new bike . As convienient as it would be to buy new and maintain it. Having bought a used and maybe abused bike is requiring me restore and SPEND money on what seems to be a serious issue.
Being somewhat new to this world of bikes (1yr) I am a hands on guy with tools but not special tools. And very tired of Having my wallet raped by a garage I find myself at a stand still. Do I keep spending . Or put that money into a new bike?

What I am lacking is a step by step . My guide is so vague. I think I am capable of fixing this. I'm searching a trouble shoot guide , to avoid buying unnessesary parts. do I start with the carbs, coils,valves? Close off the float untill I have the funds to rebuild the carb? and buy all these tools I will use once or twice? Im not one to give up , but this issue is stressing me.

If I may add at some point at the end of the riding season it stopped spraying and my gas mi9lage was far better . I start it every couple of days, and just recently it started spraying again.

 

Get this Factory Workshop Manual.
Find a competent Small Engine Mechanic or a recent graduate from an Automotive Technical School.
Become friends.

http://www.yamahapubs.com/html/itemsear ... del=XJ650K

 

Just the way Rick said it. First things to do.

--- what on-the-surface looks like a Carb Problem; you'd know for sure after having the Compression Tested, the Valve Clearance measured and the Cam Lobe inspected for any possible damage

 

Johnny,

Don't give up. I've been there. It may sound complicated and confusing now, but there are step-by-step instructions on the XJ CD ( see XJ CD ) and here in the forums for just about anything you'd need. Plus there are extremely knowledgeable people just waiting to answer your questions.

My advice is to fix it. You can do it. It probably isn't as serious as it seems. Take it one step at a time. As you eliminate or fix possible problems, it helps to narrow down what might be your primary problem.

Get a compression gauge to start with and check your compression.

If the compression is off, adjust the valves (good instructions are in the service manual from the XJ CD). If you can get the compression close to spec that should eliminate the valves as your problem.

Still problems? Attack the carbs. It may be a stuck float valve - seems to be a common problem. Fantastic how-to instructions are in the forums Clean your own carbs. Check out the other writeups in XJ FAQ Suggestions. The first time getting the carbs ZESTFully cleaned / tuned / synced took me a weekend because I had to keep double checking stuff, plus they were fairly dirty and needed extra attention, but it wasn't hard. Now I can clean them and get them back on the bike in an afternoon.

Still problems? Put up another post. Someone's bound to have had similar problems and probably a solution.

Just my .02,
Dan

 

RickCoMatic,
I believe you are the xj guru no question . I did not post to start a debate. I do not question your credibility . I appriciate your patience . Im just discovering more and more problems, and it becoming a pain in the ass. It has to come to an end .

Ill do more FAQ searching before I post .

Just wanted to say thanks to everyone for their help.
Jon

 

I know how you feel.
When you step-back and look at the bike you know there's something just not quite right.
That's all. But, what is it.
Not 9 out of 10 times ... but, 99.99 out of 100 times its Carbs or something related to getting the gas from the underground tank at the filling station into the Combustion Chambers of your Engine.
Something along the way is out-of-whack.

With gasoline flowing all-over out of the 4-Carb ... It wouldn't be too hard to say that the Float is stuck OPEN and flooding you out.
We need to determine what is by having you do what we'd do if we had the bike.

I'd test to see if the Float was stuck open.
Put a piece of Vinyl hose on the Bowl Test Nipple and tape the free end up on the Fuel Tank.
Start the Bike and Open the Number-4 Float Bowl Drain Screw until Gas appears in the Hose.
If the Gas that comes out of the Fuel Bowl into the Vinyl Hose rises above the
Top of the Fuel Bowl where it attaches to the Carb Body ... you'll know where all that extra gas is coming from ...

If the Drain Screw is Seized ... Don't bugger it up.