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.

 

Ok Jonny,
You mention the guide is not as clear as you need it to be. Fair enough, I've encountered passages in my Haynes that had me pause and re-read 3 or 4 times before it made any sense. I would wager that you are in a similar spot just now. The cure for me was to invest in several sources of information to help me through the rough parts (between Haynes, the factory manual and the XJCD you can't miss). If you still have issues after covering all available info, you have us. There are a few folks here with the gift of translation (Gamuru, Rick, Blue, Stereo, the list is long but distinguished) who can produce results worthy of any literary work/publisher. Use us.
As for good money after bad, you need to determine if what you have is worth the investment. And right now, my money is on the compression test to tell you that. It will tell you if the valve is involved or the rings. Or it may confirm that the carbs are your singular problem. At this point it is the key to rapidly and inexpensively narrowing down the field and you don't need any special tools (save a compression gauge that can be had cheap from Harbor Freight) or a mechanic to do it (saving yourself at least $100). Just be CERTAIN that you ground out the spark plugs or simply unplug your TCI before you begin. Crack the throttle open full and spin it up (all spark plugs removed to ease cranking). If you would like, I will pm you my # and I'll walk you through it over the phone.
You are not alone in this but you do need to make the investment of a little more time to nail down the issue. We will be able to determine, in a very short period of time, if you have a bad motor or need to rebuild carbs. In this case spending $20 to save $$$$'s.

 

Well on a good note .... The gas that was shooting out of Carb 4 was caused by the Motha flippin MAIN JET that CAME LOOSE and was floating around in the bowl as the needle stayed ..CRAZY!

So I cleaned em up , NOw my bike revs at 7000 rpm when i start it ....Yikes !
I bench sync ed with a red wd 40 tube ... maybe i messed it up .. ?
in other news I noticed my air box has holes and cracks all over the place ... son of a .. So after removing chunks or air box . I just took the entire thing out.
I picked up some POds for 50$ at the performance shop. (i know i'll have to get some larger jets now. )

Could it be the pods that have caused this super high reving?

Should I try and epoxy the air box ?

It did this high rev business the last time I adjusted the carbs.

THE SPRAYING STOPPED! but now Ive other fish to fry... what a world.

 

And I bought a manual for the bike ..the service one from yamaha.

 

Hey Johnny. There are a few competent independant mechanics in Mtl who might be a little more knowledgeable about these old machines. Or at least willing to put a little more effort into a diagnosis. A friend of mine there rides old Suzuki GSs; I'll see if I can get him to recommend someone. In the meantime, where have you been taking your bike and what part of town are you in?

 

Super Motosport in laval.
Im in Laval(chomedy)

 

If all of your carbs are open as far as a WD40 spray tube that could be part of the problem. Back your idle screw out and see if the engine will start and idle slower. Your air filter box needs to be hooked up and no holes on the carb side. All air must go through the filter to get close to the right restriction. I found that out the hard way trying to run my 650 with no carb to air box joints.

 

Don't know those guys, but at least it wasn't Moto International. I recall a couple of shops down in St Henri but that was a few years back. And I think my friend's mentioned a guy up around Mirabel who works on older bikes, maybe a little more convenient for you...

Anyway, I sent him an email and I'll let you know if he has any suggestions.

As for your 7000rpm idle, did you double-check your throttle cable since re-installing your carbs? Sounds like it could be a cable hang-up... And if you still need an airbox in the spring, let me know. I think I have one in a box pf parts that's buried in the back of the garage. Just not very accessible right now.

 

Stay focused.
Don't start doing more than one thing at a time or you will not know what you did to get favorable results.

The Red Tube Bench Sync probably needed you to Open the Butterflys with the Idle Adjustment Rod. Back that Rod off and Bring-down the RPM's.

If the RPM's stay high ... look to see that the Carb Linkage Hook-up is not stuck up inder the Head.
If it is ,,, DONT Pry it or Bend it.
Move the Carbs to free it.

If you need to Pull off the Carbs again ... Bench Sync with a narrow strip of Playing Card ... 3X5 Card ... Business Card. Keep the Flys as close to closed as possible.

Also make sure you didn't reverse the Cables and have the Carbs hooked-up to the Choke ... that will shorten the cable and make the engine race.

 

PM'ed you.

 

psshht.. Copy that rick.

Ill pull the carbs of again tomorrow. And do another carb sync with an old sliver of Visa card. ..
Is it normal that the #3 carb looks closed and the others are a hair open?

As well are the pods Causing too much air to rip through ? What if I put socks over the pods for now?

LIke I said this happened to me before BUt when I synced the carbs with a ... think it was a slice of credit card it fixed the prob.

I checked the cables..they are good..not hung up . and in the right order.
I think the Bflys are open too much. and the Idle screw was not touched...(right=more air ? right?) out closes the flys?

Still cant believe my Main jet and washer have been dancing around in the float bowl.


I know I guy in Miribel...MOto comme fou... thats all he does ( bikes of the 70s and 80s..,but said he would charge me around 300-400$ to tune the bike. I think i can do this. Ill keep trying anyway. If spring rolls around and Im up s**** creek Ill get er done one way or another.

***Edited by Robert, Mind the language please! Thanks!***

 

If you have done the bench sync' properly, the butterflys will all be open exactly the same amount.

 

Have you read the bench sync article?

You place the sliver of card under the #3 butterfly and then adjust #4 so that a similar sliver of card is just grabbed. When you remove the slivers of card but butterflies are closed the same amount and open exactly the same way.

Then you sync #1 to #2 and then sync #2 to #3.

When you are all done you adjust the idle screw for a sliver of light through all carbs and all of them should look identical.

Read read read read and then after you understand what you have read you go do it.

 

main jets falling off is a HUGE problem with the mikuni carbs used on a lot of the honda's at the track. i assume you are working on hitachis though?

 

#3 is the static (non dynamic) carb, all other carbs should be synced to it.
If it is showing more closed than the others, get them to mimic #3.
Turn the sync screws, not the idle screw to adjust each butterfly valve.
The idle will rise when you turn the idle screw clockwise.

 

Halfcentury (
Read read read read and then after you understand what you have read you go do it.)

Id be insulted ..if you were not right...
sometimes I feel like a complete TARD. Reading it is one thing applying it is another . Its easy to get distracted when there are surprises . Especially when the invisible gas fumes are right under my nose on the bench.

Its coming together.

Alright so I bench syncd again , this time with a card. runs much smoother. With the engine warm it Idles at 2000 rpm minimum ie with the idle screw all the way out(NOt completely unscrewed, but out untill there is no change) and the engine does not stall...probably because the Flys are adjusted a smiggin too open.

I guess that means the whole rack 1,2&4 are off ever so little . And the throttle sticks now.... hmmm

I guess I should Turn the screws out just a few mm out . Or.. take em off and but them back on the bench and do it there.

Maybe oil the cables is a good idea as well ..

I know the throttle body is the problem now as there is still a little slack in the cable.
When I give it just a little it sticks reving high 5000rpm. If I give it a quick shot on the throttle or to it seems to simmer down. if I take my finger and physiclly push down on the throttle body ever so little it idles down .

I do not see anything obstructing the throttle body ...may be its the boots off the block rubbing ?

anyway I know the Idle screw Is slightly off. I just need to bring it down 500rpm , and find out what is not letting my throttle body depress all the way.

Where should the Idle screw be when its on the bench ...?turned in just enough so it shows light cracking through or Closed.

Ill be back.

 

NO ! don't touch anything else. . . it's time for a RUNNING sync !
That's your next step.
Search topic- - MANOMETER
You can easily make a 2 tube Manometer, and get the sync perfect.

THEN, you start fine-tuning the 4 pilot jets.

 

It is possible to have no adjustment left on the thumb screw, when bench syncing have the 'throttle stop' thumb screw set so there is some thread left to back off.

 

This has been one of the best threads I've read in this forum. Tons of information and hints being passed down the line. I still haven't gotten to my ebay carbs but not in such a huge hurry until this thread plays out and johnnymaritimes xj is lifting the front wheel between the 2- 3 shift.

Keep at it JohnnyM! It sounds like you are ever so close!

 

All right . so now That Ive Cleaned my carbs for 3 hrs and polished the cylinder bores+ bench synced again .. now backed the idle screw out nearly all the way I have her idleing at 1200-1500rpm ....
As well she likes to stay reving high for a few seconds untill I really give'er a snap on the throttle and she simmers down to 1200-1500rpm . Could this be because of the PODS? is it possible the pressure is off becasue of them . Or is it the butterflys sticking open ?

Ive checked the spring...its ok
nothing is stopping the rod
cables are not mixed up

 

Sounds like it just needs a good running sync.

 

hanging idle could be lean pilot settings

 

Another thought is the throttle shaft seals...

 

as it is all my pilots are turned in all the way (tight) thats how they were when I dissasembled them . I tried to turn them in to count how far out they are , but they were In already and stuck. I shaved a flat head screwdriver to fit in perfectly and applied a little heat with a mini torch and it let go (2 were stuck).

Are the shaft seals the rubber on the side of the carb, where they are all connected?

 

"Are the shaft seals the rubber on the side of the carb, where they are all connected?" i think you have the right spot

you could try the un-lit propane torch trick to find any vac. leaks, including the shaft seals. move the torch around and see if the engine revs up (or stalls out). when it does, you found a vac leak. dont be fooled by the propane being sucked into the pods.

 

Ill try that tomorrow.
thanks Zookie

 

ok i got a vacume gage. I hooked it up to #4 and the gage needle is dancing everywhere.? when I give throttle to 3000rpm it stays at 5hg

 

have you got a fuel filter & a restrictor in the line?

 

I have an aquarium air valve in my vacuum gauge line. Works great

 

I have no Idea how this thing works., And there is no instructions found in the forum...
What should it read on the manometerand what is "cm hg"? At the moment it idles at 2000+- rpm on my tach.

 

Well its tuned , I have it idle at 1100 rpm, throttle response is good, a little boggy but better than ever. I took it for a very short 1 km road run on the dry and frozen street ....ZOOM! holy SHITE! I cant believe I Whatr ive been missing.

1 .Now the new problem Ive discovered is After the run the throttle sticks and sloooowly goes back down to 1100 rpm, Unless I push down on the throttle adjustment screw, which has brought ne to the conclusion that the #3 and 4 screws are not the originals and have much less resistance..Ill replace those for some harder ones... Guess I can find them at a hardware store.

2. Now Ive noticed that I have alot of Exhaust or BLOW Bye coming out of the crankcase hose end.. Almost burning smell .

Maybe im running too lean with the pods? Where can I channel this blow bye ? As the original case captured it and sucked it back into the engine now its fumey stank is just venting under my arse.