1981 Yamaha XJ650 Maxim Valve clearance/ carb issues

Alright guys, so I know there's a lot of stuff up already about valves and such, but I am wondering about my bike personally and what the XJ gurus on this forum think. So when I first go my bike it ran... decent, it had to be started with starting fluid and it took me a while to get it started (it didn't like it when I gave it throttle when it first started, also note that this is all happening in freezing weather, between 25-35 degrees) but eventually it would start and after it warmed up it would driving ok. when I gave it gas to ride it sometimes it would rev and other times it would bog down and I'd have to play with the throttle a little before it would rev at all. it did have problems with backfiring a little, but it wasn't terrible and it would idle at about 1.2-3k so it was high, but not ridiculous.

I figured the bogging down was just a carb issue so I took them off and cleaned them, put them back on, and started it (it still didn't start under it's own power), and I started having problems with it idling (it didn't want to at all) and when I did rev it to about 4k it would stay there even after I left off the throttle, eventually it would drop and then sputter to a stop. I tried messing with the choke to drop it back down, but even with the choke all the way off it still would rev high and stay there. When it did idle however it would at about 2k and I would get quite a lot of backfire... So I took the carbs off again and I figured, while I've got the carbs off I could run a compression test (the engine was cold when I did this) and I was getting about.. 30psi across all of the cylinders dry, and about 45-50psi with a wet test. So I figure the rings are still pretty good, not great, but still useable. but those compression readings are probably most of the reason it wont start with the choke on. I was hoping that the camshafts were just a tooth off and all it would take is adjusting them, but when I put the engine at TDC the camshafts are almost perfect, one is just a little bit off, but it's not a whole tooth (still though it has me wondering if I went past the point on one cam then move it one tooth over on the other cam it might actually be a little closer). So I measured the valve clearances. and the results were all pretty close to each other, on the exhaust side they were all about .18mm and all the intake valves were close to .06mm I know they are probably out of specs (not entirely sure where they should be) but they were all really close to each other. maybe +-.01mm. I'm wondering if these readings would cause low compression, and be part of the reason it wont start without starter fluid.

I'm aware that there is a good possibility in order for this bike to run great I'll have to get different shims, but I didn't spend a whole lot on this bike, and I don't want to have to throw lots of money at it. honestly all I really want it to do is run decently. so if you guys think that keeping the valves where they are is possible, and that I might be able to tinker with the carbs to get that idle down and for it to run ok, then that's what I plan on doing, I did mess with the mixture screws so I do need to get a colortune and adjust the mixture. and I did a bench synch so messing with the idle screw might help bring that idle down. I know I also have intake leaks, I believe the rubber boots that connect the air box to the carbs shrunk so they no longer go all the way into the air box (they will go in part way, but there's gaps) and the boots between the engine and carbs are also cracked a lot on the outside, I did inspect the inside of the boots and I didn't notice any cracks, so I think it's just superficial.

I'm sorry this is so long guys! and I really appreciate the time you take to read this and I'd appreciate your input even more. I am a complete novice when it comes to motorcycles. this is my fist bike I've ever really even touched let alone try to diagnose, most of what I do know comes from working on cars haha.
So thanks in advance!!

 

Welcome to the site.

The first thing you need is to get your valves in spec to run a compression test, otherwise you are getting inaccurate readings. Here are the specs:

Exhaust: 0.16~0.20mm
Intake: 0.11~0.15mm

If all your intakes are at .06 that is way tight so replace the shims to get them in spec.

The second thing you will need is to get an accurate reading on your compression test. 30 PSI is way low, even 50psi is really low. I believe this engine should be at least 120 to call it strong.

That is just not going to happen, you will have to spend some money to get your bike running decently otherwise it will be one problem after another. Is like having diabetes and try to fix it by cutting your carb intake in half, it's just not gonna work.

hogfiddles runs a shim pool so all you need is your old ones and a deposit and he will hook you up.

If you have carb intake leaks the bike will not run properly, I have not seen your bike but to me it sounds like you need to take your time and address all the issues that you have mentioned, you can't do something and skip others.

Keep asking questions about how to do things but cutting corners is just not going to get your xj running "ok".

Best wishes.

 

So long as there is some valve clearance they are not the cause of low compression on a (cold) engine. It is possible they've been damaged from being too tight on a hot engine.

While you probably have carb issues, you'll never get a 30-50 PSI engine to idle properly or cold start.

You need to confirm your compression results with a fully charged battery or a boost. Try a different gauge.

If you still have low results you need a leak down test to see where the compression is escaping.

 

+1.

If it ran at all, the compression test was faulty. Re-do as above. If you want good numbers, get the valves in spec first.

If your valves are out of spec, it's not a "possibility" that you'll need to replace some shims, it's a certainty. Job one. And every 5K miles, learn it.

You DO have carb issues; and once properly serviced, the valves will need to be in spec to set the carbs up properly.

If you want to properly recommission and ride this bike, you're looking at around $600 ~ $800 if you do the work. You'll need a service manual and be prepared to sink some man-hours into it. If you truly do know anything about working on cars, then you CAN do it; but you'll have to get a service manual and get serious or you'll just fail repeatedly.

It CAN be done; personally I've done two XJs so far. I love 'em. But a lot of work was involved; and the above budget is inescapable.

 

kc,

Welcome to the club. Bad news...I'm not one of the gurus. Good news...Fitz is. More good news...the advice and information given by Eco is as sound as any of the gurus. More bad news, sorry...Everything you've described is not the makings of a "decent" running 650. 28* here in Nashville. Rolled her out the garage, half choke, hit the starter...Varoom! Great news...you've come to the right place. Providing you have a good plant (engine) and you do the necessary work to bring your bike back I can assure you will not be disappointed. XJ series bikes are very strong, durable and well built bikes. Keep this thread going. As you dive deeper into the re-commissioning process use this thread as your Q & A thread. At the time you will have learned and done many of the things many of us have you can read your first post and tell for yourself how far "out" and "off" your bike truly is (was). Good Luck.

Roc

 

what fitz said...

CN

 

The soundest advice you'll get from anyone is this:

Buy a Genuine Yamaha Factory Service Manual specific to your Bike.

Having a "Factory Book" gives you the ability to illicit help from any Small Engine Tech, Automotive Expert Tech, and anyone else with Mechanical Skills.

Having "The Book" takes all the mystery out of how to do anything from changing a light-bulb to rebuilding the Plant from scratch.

You can place an ad on a Technical / Vocational School's bulletin board and get someone to help you.

Having the Factory Book answers all the questions.

 

Wow, Thanks for all the replies guys!! I wasn't expecting so may people to read this haha. So after posting this I did realized that it would be pretty stupid to try to keep the valves the same and not mess with the shims.. so I am already planning to replace the intake shims, but it seems like the exhaust valves are within spec. I do have a Haynes manual for the bike, it was one of the first things I did after purchasing it. it is the electronic version however, so it takes a little bit of navigating. I plan on getting a hard copy soon though . BigFitz, thanks for the comment, I can tell you just by looking at this bike that there is A LOT of work. I plan on doing most (if not all) the work myself, but I'm not really in a position to spend hundreds of dollars on it to get it running perfect. I know it seems like I'm trying to find short cuts, and to be completely honest I am hahaha, that's why I'm trying to do everything that cost's as little money as possible first before I start throwing money at it (even if it does improve overall performance). I do understand that things like replacing the shims which will cost some money is a necessity and can be damaging to the engine if not addressed. Sorry if I'm sounding like a cheapo, but my situation wont allow me to be so giving with my money haha I hope you understand...

I was a little uneasy about the compression test as well when I was getting those results.. I was honestly surprised that an engine could run on such low compression like that, so I'll try to get another tester and see if the results change. As far as the power goes (I have ridden it) when the carbs would work with me it accelerated quite nicely! it didn't feel down on power at all!!

MiCarl, thanks for taking the time to read all of this! I think Fitz is right, those readings were probably off, but when I bought it, it would actually idle. granted it was about 1-200 rpm higher than it should have been and it was rough, but it still idled. At least it would before I cleaned the carbs the second time and messed with the mixture screws, that's why I think I might be able to get it to idle if I tinker with the carbs . and I am aware of the possibility that the valves were damaged, I'm crossing my fingers that they aren't though!!

Also quick question about how my engine would rev high even though I was off the throttle, could my float levels be causing too much gas to be entering the engine by any chance? and if they do do you guys have any way of removing seized float bowl drain plugs? two of them are stuck in there really good haha.

Thanks for all the support everyone, I really do appreciate it!! and I apologize if I sound like I'm one of those people who wants their transportation to get from point A to point B and doesn't care about taking care of their motorcycle at all. I promise I'm not, but there's only so much I can do... Thanks again!

 

Courtesy of Chacal

- A lean air-fuel mixture condition, which can be caused by a variety of problems......vacuum leaks, plugged or too-small fuel jets, etc. Old or "stale" gas may also cause a lean fuel-air mixture to occur temporarily (until the fuel is used up!).

- A vacuum leak somewhere in the intake system.....intake boots, internal o-ring seals, etc.

- Mixture screws not properly set or adjusted.

- Vacuum piston sticking or stuck in a partially raised position.

- Idle speed screw set too high, or set to create a "proper" idle speed when the engine was cold (and thus results in a "high idle" once the engine reaches operating temps). The idle speed when the engine is cold should be modulated via the use of the choke (enrichment) control system.

- Butterfly valves opened too far; synch screws out of adjustment.

- Throttle cable wear, adjustment, or throttle lever brackets installed incorrectly or interfering with other nearby objects (cylinder head fins, etc.).

- Choke (enrichment) circuit is stuck "open"....this can occur even if the choke lever is rotated to the fully closed position, if for some reasons the choke plungers are not fully closing (cable wear, cable adjustment, bent finger brackets, or installation problems). In addition, even if the choke plungers are "closing" fully, if the choke plunger valve face or its seat are worn or scarred, this will allow fuel to leak part the plunger and richen the mixture even if the plungers are closed.



Why your engine seems to be schizoid:

A hanging idle---one that stays high and slowly comes down when decelerating---is a sign of lean mixture. The opposite case, where the idle drops dangerously low then rises, is a sign of rich mixture.

A bike that runs better when hot is probably lean, and a bike that runs better when cold is probably rich.

But sometimes a bike that can be adjusted "just right" when cool, but actually starts exhibiting signs of running lean (hanging idle) as it warms up. And if the idle speed is then re-adjusted while the engine is warm, but eventually falls and the bike dies (especially when sitting at a stop light). Or if the pilot screws are adjusted, then it's too rich when cold---all in direct contradiction of the above observations.

Experience shows that this is a sign of worn throttle shaft seals.....the aluminum carb bodies expand with the heat, but the steel throttle shafts---resting comfortably in a nice cool airflow---don't heat up and therefore don't expand. Once the shaft seals get old and hard, they no longer are able to flex and fill the gap.....so the carb starts drawing air around the shafts, leaning it out.

Drain screws:

http://www.xjbikes.com/Forums/viewtopic/t=4281.html

 

-Shortcuts don't work.

-"Tinkering" doesn't work.

Break the carbs down and properly service them. In the Haynes, this section begins on page 119. Float levels are covered on page 126 and 127; plus there's good advice here: http://www.xj4ever.com/setting%20fuel%20levels.pdf

-Then once the carbs have been properly cleaned, serviced and adjusted, and your valve clearances are in spec, then you can synchronize them and get rid of the "hanging idle."

Once the motor's running, we need to talk about those 30+ year old brakes.

 

A hanging idle can be caused by a number of things. Most of them carb related.

Low compression can also cause it. You need about 60PSI to make the engine run. But, it takes some time for the gas (not gasoline) to leak out so when the engine is running you have more compression than that. The more RPMs the less the leak affects the combustion.

Now imagine you've got the thing running at about 2,500 rpm and trying to adjust the idle down. As you get to about 2,000 one of the cylinders leaks badly enough it doesn't keep firing and the RPM suddenly drops. Now the other 3 are in trouble too and it quits. This is why you can never get a leaky engine to idle properly.

Get your compression sorted out. If you have some valve clearance and it's that leaky you're probably looking at a major expenditure. As long as you have ANY valve clearance the valves are closing and I wouldn't spend a penny on shims yet.

 

Compression test 101 (if you didn't know)
- All 4 plugs out
- Fully charged battery, on a booster, or jumped to a non-running car
- Throttles jacked open
- unplug ignition black box, or cross the solenoid, key "off"
. . . (never fire the coils without the plugs)
- crank for around 8 "hits", or until the needle stops moving.

+1 on brakes & tires, and all the other great advise.

 

With the Bike being three decades old, ... servicing the Carbs to bring them back to a "Like-new" condition is a MUST.

Fortunately, the Carbs being Aluminum, Brass and Bronze allows for the rack to be rehabilitated to such conditions.

Carb "Kits" are available to make the Float Valves, Gaskets and Mixture Screw Micro-Orings NEW.

After 30 years, ... the Bores for the Diaphragm Pistons should be Scrubbed and Polished to allow for absolutely un-impeded movement of the Diaphragm Piston.

Scrubbing with ScotchBrite Medium (Gray) and dressing with ScotchBrite Fine (White) will restore the Bore and rid the Cylinder of an oxide coating which develops after many years.

 

Ok, so do you guys think I should address the shims first? or try to get accurate compression results? I haven't tested it when it was hot, so it's very possible that could yield different results. And ya big fitz, I can tell just by looking at the front brakes I'll have to rebuild the caliper.. one pad is worn almost down to the metal and the other still has quite a bit left. haven't gotten to the rear brakes yet, but from what I've read there's a pretty good chance I'll have to replace those too haha. Thanks for the posts guys!!

 

Your front brake pads are wedge shaped. One is narrow at front, the other narrow at back. They're like that because the caliper pivots rather than sliding.

They're not worn out until the wedge shape is gone.

 

ok, I'll take a look at the bakes again to see if I can understand them a little better. Also quick question, do you guys think if I replace all four rubber joints from the airbox to the carb, I'll get rid of that intake leak? I think the old ones just shrunk a little, just enough to make it too short to reach the airbox. Is there anyway to reuse the old ones and stretch them out a little without them trying to shrink back to a smaller size?

 

can you put up a picture of the carb/airbox boots on the bike?
i can't imagine them shrinking that much in length without shrinking in diameter. then they wouldn't even fit on the carbs and they'd be loose in the airbox. maybe their the wrong ones

 

Yes, you should get the valves in spec and then run a compression test, otherwise you will just be chasing your tail.

 

Ok, so I just ordered the valve shim removal tool, so hopefully I'll be able to pull them out and get new ones soon. I've got the engine mounts out in order to remove the valve cover, so as soon as I get it all put back together, I'll take some pics of the intake boots. Thanks for the comments guys!!

 

Here is a video on how to do it without the tool.

http://www.youtube.com/watch?v=V3gxT57eoDE

Check out some of the videos this guy posted about working on his xj550. some of the procedures will be the same as your 650.

http://www.youtube.com/watch?v=e3pLqVZXGLw

 

Thanks for the links! I've actually already seen quite a few of his videos, They're great!!! I missed the valve shim one though, so thanks for putting it up, I'm probably going to wait for the valve shim removal too, but everything else seems good.

 

That's not supposed to be necessary, altho it was recently suggested to a TURBO guy.

 

Shouldn't be. On my 650 Max I only had to remove the horn.

 

hmm.. well for some reason I couldn't get if off without removing them. the bar that goes right across the frame right behind the horn I think, was about.. half an inch directly over the front screw for the valve cover. I had to remove the mounts in order to even loosen the screw, so maybe there's something else wrong?

 

kc,

Possible frame mod?

Roc

 

it's possible.. not likely but possible.. who would intentionally put a bar across the frame right about the valve cover though? although, the previous owner did cut off the mufflers.. so I guess anything's possible haha

 

Let's see some pics.

Space is a bit tight on the 550 but you can still get right to the bolts...

 

I'll try to post some pics soon, but my valve cover is different, it doesn't have the screws that go in the middle of the valve cover. They go around the edge I think there is about.. 12 screw all together. They're smaller hex screws if that helps any.

 

I'll work on getting some pics of my bike in general up possible tomorrow or Wednesday

 

kc,

Sounds like you don't have a XJ or you have one with a non-XJ plant. Like Fitz said...let's see some pics.

Roc

 

Alrighty, Here are some pics guys!! I know it looks rough, but I wanted a project bike, and I've got one

So far I've re-upholstered the seat (my first time ever doing it, and I think it came out pretty good). It's got new mufflers because I want it street legal. previous owner chopped handlebars and didn't do an amazing job welding them.. so i replaced them with similar lower profile handlebars (I personally like the look). And I put side view mirrors that mount on the side of the handlebars. So in theory, this should be street legal, now I just have to make it run right!!

 

It's a pre-YICS 650 Maxim and you probably just needed an allen wrench with a shorter "elbow."

The bike in the pic I posted has a YICS motor, so yes the cover hold-down bolts are different.

Your motor is definitely a 4H7. Now let's see what the full VIN on the frame (on the side of the steering head) says.

 

I've looked it up before using vin decoders and other things like that and from what I understand its a 1981 Yamaha XJ650H maxim. The full vin is: JYA4H7008BA115456

 

also I could not for the life of me get an allen in it, even one with a shorter elbow.. I had literally half an inch max between the frame and that screw. it was kind of annoying.. hahaha. I was actually tempted to try to use pliers to unscrew it (good thing I didn't, it was tight and I would have messed it up quite a lot). even it I had managed to loosen it though, there was no way I could remove that screw with such minimal clearance.. that's when I removed the engine mounts...

 

You aren't the only one with clearance issues, kc. I haven't put a wrench on my '81 650 (which is exactly the same engine style you got there) in a long time but if I recall correctly yeah its a tight fit like you've discovered but I was able to work an allen key into from the underneath tank side ~ directly on top of the valve cover. I have several spare allen hex wrenches with different elbow lengths with the same metric size heads because of this. Next time you go to an auction or garage sale with tools for sale, pay attention and you'll pick up extra tools like this just to make your life easier. Guess I was fortunate my father had several sets of tools in the garage when I grew up; don't tell him I put a few spare tools in my own toolkit!

 

Alrighty guys! So I got the valve shim removal tool in the mail today and took a look at all the intake shims, and measured the clearances the best I could. Final measurements are:

Cylinder 1:
clearance: .08mm
Shim size: 285

Cylinder 2:
Clearance: .04mm
Shim size: . 280

Cylinder 3:
Clearance: .05mm
Shim size: 285

Cylinder 4:
Clearance: .05
Shim size: 285

So if my math is correct the size shims I need for each cylinder are as followed.

Cylinder 1: 280
Cylinder 2: 270
Cylinder 3: 270
Cylinder 4: 270

What do you guys think?

 

What about the exhausts? They go out of spec more drastically because of the higher temps.

Cylinder one: .08 plus one size smaller would put you at .13, in spec. Correct.
Cylinder two: .04 would need two sizes smaller to get you to .14, in spec. Right again.
Cylinder three: You only need TWO sizes smaller (a 275) to get you to .15 and in spec. OOPS!
Cylinder 4: Again, a 275 will bring you to .15 and in spec. A 270 is three sizes smaller. OOPS!

NOW: Do the exhausts. Then see what shims you can swap around before you buy replacements. Or, contact member HogFiddles, who runs a "shim pool." Personally, I don't re-use shims; but I'm in a minority.

Oh, and good catch. Ya gots some right tight valves there. Let's see the exhaust numbers.

 

Oops! hahaha thanks for catching those! That could have been bad if I ordered the wrong ones... I though I had put the exhaust clearances up before, but maybe I forgot to. I don't remember what each individual one was But I know they were all extremely close to .18mm give or take .01mm. either way I'm pretty sure they were all within spec (.15-.20)

 

Exhaust spec is .16mm ~ .20mm; if they're all around .18mm you're good.

 

Haha thanks again, I just realized I was off a little! But ya, they seem to be in spec. So for cylinder one, I can use cylinder two's shim (280) to get that in spec. and I need to get (1)270, and (2)(275). Where would you suggest I get new ones from, and about how much to they cost?

 

Or, since I'm on a budget, should I just contact Hogfiddles and go that route?

 

http://xjbikes.com/Forums/viewtopic/t=45368.html
download that spreadsheet and you'll never go wrong
print the .pdf and save a lot of time, there's a intake and exhaust ready to measure every 180 deg.

 

yeah Dave (hogfiddles) will be glad to help you with the shim-pool swap. I've dealt with him plenty of times

 

It's up to you. I'm personally obsessed about doing everything by the book; virtually everyone else re-uses shims, especially within the same motor. I'm probably being overly cautious, go for it.

You don't need a spreadsheet to figure out shim sizes; one size smaller shim adds .05mm to your measured clearance; two sizes adds .10mm and so forth. You can do them in your head. There's no math involving the actual size really necessary other than "does it need to be one size, or two sizes or maybe three sizes smaller?" (or larger in rare cases.) So if adding .05 to ANY clearance brings you back in spec, then all you need to know is "one size smaller" than what's in there. No complex math.

 

Yup! I know the math is easy, I just did it wrong haha. Not going to lie, I think the spreadsheet is harder to understand hahaha! but it doesn't really matter. between all of us here we got the right sizes . I did PM hogfiddles, so hopefully within the next week or so I can get those shims installed and get a good compression reading! that does make me wonder though, with the smaller clearances between the intake shim and camshaft, that would actually cause the intake valve to be open longer! that is probably why I've got backfire through the carbs and low compression maybe.

 

Quite probably. When they're tight, not only are they open longer, they open too soon and close too late.

 

this guy has the best price I have found for new shims.

http://www.ebay.com/itm/29mm-Diameter-V ... 5d4447cef3

http://www.ebay.com/sch/m.html?_odkw=&i ... &_from=R40

CN

 

You better keep looking

 

You better keep looking

 

care to elaborate?

CN