low compression in #2, maybe another problem?

So, I bench synced my carbs. Then I synced them with vaccuum guages and YICS tool I got from Chacal. Then I colortuned and got the pilot air mixture screws adjusted pretty well. When I tried to tune out the missing in the idle I could not tune it out, so I did a compression test. My number 2 cylinder is averaging 20 psi less than the other 3 cylinders. Also, when using an infra-red thermometer on the exhaust pipes, the pipe from the number 2 cylinder is reading around 40 degrees F cooler than all the others. I am still getting some soot on the plugs at higher RPMs, but that's rather uniform and not just affecting #2. I have ridden a few hundred miles since I got the bike, and I know the PO rode it at least that as well before I bought it. Not sure how long it sat before then. The PO claimed to have done a top half rebuild just before I bought it, but who knows how true that is. My question is: Is there anything else I should test or try to do to correct this problem before I go and tear the whole engine apart? I've already spent more trying to repair this bike than I bought it for and it's becoming much more of a pain than it is a joy, seeing that I've only been on 1 ride outside of town since I bought the thing. Any suggestions would be great. I'm going to buy some Marvel Mystery Oil and try that tomorrow, I read on here that dumping a few TBSP into the plug sockets can help. Thanks in Advance.

 

Can you do a leak down test? If your valve isn't seating fully it could well explain your temps and psi loss. Check the valve clearances as well. A tight valve will imitate a cracked seat.

 

check the comp' on #2 "wet"

 

I'd like to do a leak down test, but haven't found any instructions to find TDC for that cylinder. I'll reread through the haynes manual and see if I can find anything in there that will help. If it is indeed a valve not being seated correctly, is that an easy fix? Is there a thread anyone knows of that would have this info so I can just read about it? I did some searches but couldn't find much on finding TDC for a leak down test. I'll ride it to work today and see what I can find. Hopefully it won't cause any damage to the bike. I'll do a wet compression test today too. I wasn't sure if it was ok to do wet tests on a small engine so I only did dry yesterday and came up with 100-80-100-100 psi on my cylinders. I'll post my findings when I get home from work this evening. Thanks again.

 

I can't find anywhere explaining how to find TDC on each cylinder. I can do it on a car, but not sure how to do it on a motorcycle engine. Anyone have any ideas?

 

Pop the valve cover, the ignition rotor cover and all the spark plugs.
Rotate (counter-clockwise) the engine using the flats on the ignition rotor and line up the cam lobes on the cylinder in question to where the intake valve (the ones toward the back of the bike) has just closed.
This is the tricky part. I use a 10" philips head screwdriver (use whatever you have that has a cylindrical round shape) and slip it into the spark plug hole, using care that I don't drop it in or score the threads of the head. I then gently continue to rotate the engine with my other hand holding the screwdriver handle and feel for when the screwdriver crests the compression apex. This is where you will need to be very careful as the rising piston can wedge the screwdriver shaft in the sparkplug hole so it is best to keep it straight up and down in the hole. With a little patience, you can get the piston to TDC +/- 1/2 a degree which should be fine for your purposes.
Good luck and sing out if you run into problems.

 

I did a wet compression test today at work. They came back 130-115-120-120. So my number 2 cylinder is pretty close, although slightly lower than the others. Still, I can disconnect the boot from the plug with the bike running on that cylinder and won't notice any difference in how it is running unless I bring the RPM's up to 3k+. Any other plug being disconnected and the bike dies immediately whether or not #2 is plugged in. I live at about 5500 feet, so I don't know if that affects the compression or not. The main reason I'm checking all of this in the first place is because I have very little power off the line, and often times barely make it through intersections before I get the RPMs up to 3k or higher and it goes like hell. I can't think of anything else to do to the carbs that I haven't already done. So I am assuming it must be in the engine. I am at my wits end lately with this bike, which sucks because I really really like it. I just can't ride it more than a mile before I am left sputtering my way through each intersection with a line of cars honking at me

 

i thought the standard comp should be 156 psi?
what does your #2 plug look like?

 

it was looking fine, a nice brown and not sooty. as of today all of my plugs are showing too rich and I'm guessing this oily wet substance is going to be oil on them. This can't be any good.

 

Are you doing the Test with a Fully Charged Battery and the Throttles WIDE OPEN?

Making sure the Throttles are Wide Open is essential for getting the right compression values.

Pull the Cam Cover and get the Valve Clearances.
Maybe you DO have a tight Valve or two.

But, your "Wet Test" Numbers should have come up higher than they did for you; so I'm suspecting that you didn't have the Throttles Wide Open.

Try it again with the Throttles Wide if you didn't before.

 

Originally I didn't open the throttles at all. For the wet test I turned the throttle to full open while turning the engine over. Looks like I'll be pulling the Cam Cover tomorrow and checking valve clearance. I'll do another compression test as well, use a little more oil than I did today, and make sure the throttles are completely open. I'll do a search and find a guide for checking valve clearances. I have all the tools to do them for cars, so I'll just assume those will work for a motorcycle as well. There is a tinny knock while the engine is running, sounds like it's coming from the left side of the bike. It's hard to tell for sure tho. I've mentioned it to some other people I ride with and they claim it's normal. This is my first 4 stroke or street bike so I'm not accustomed to the noises they make. If it were a 2 stroke motocross bike life would be much much easier.

 

Reading the Valve Clearances are a Piece-O-Cake.
Pop the Cover.
Pop the Crankcase Cover on the Left Side.
Use the Square Flats on the Ignition Rotor to rotate the Engine.
Measure the Clearances with the Cam Lobe fully opposite the Valve Bucket.
See what you got!

 

If your doing your valve clearances then this is a good time to do a leak check on #2. With #2 at TDC get a rag and a duster gun connected to shop air. Stick the nozzle of the duster gun into the #2 spark plug hole and seal around it with the rag. With air pumping get a friend to check if there's anything comming out the exhaust or with the air filter removed the carb intake. Either spells respective valve leakage.

 

If I'm having issues with bogging down when accelerating at low RPMs, especially from a stop, could that be anything other than a carb issue? I'm wondering if I should rejet my carb for the 5000+ foot altitude. I'm not sure where the PO bought the bike, so I'm muling over any options I should consider. Also, I am no longer fouling plugs while idling, but I do get soot on all 4 plugs at higher RPMs, any ideas on what that could be from?

 

Sounds just like the Pilot Mixtures are too Rich.
Classic.

Start tweaking the Pilot Mixtures lean until you get good coloration and no bogging-down.

 

I've been working on that for the last few days. I just don't want to lean them out too much. I have a "pop-poppity-pop" sound already which makes me think I might be a bit too lean on the mixtures. I tried to tune that out all day yesterday but could not find any adjustment to the pilot mixture screws that affected that sound. I have a colortune plug, but it seems to burn blue even if I turn the screws all the way in. I synced the carbs using a single gauge with an attached hose that had the small red nozzle attachment hose from a can of carb cleaner that I epoxied into a vacuum hose connector and added a medium sized fuel filter for a chamber to. I didn't get very reliable readings from it, but adjusted them to match the maximum vacuum pressure of the lowest pulling carb.

 

You should have Synced them to all be the same Vacuum as you get on Number-3.

Colortune:

The Colortune Blue is the Ideal set for Idle.
But, the Bike requires more Richness than just for Idle.
You also need a Supplemental Richness to achieve no hesitation upon opening the Throttles.

When I Colortune ... I start Lean and bring the Screw OUT until I get the Blue.
Then, I continue bringing the Screw OUT until the Blue fades-out due to the Increased Richness.
Once I get there ... I micro-adjust it Back to the Blue (on the Rich side) and then go back OUT just until that Blue starts to fad-out from being a tad too Rich.

That seems like a good spot to be.
The final test is the opening of the Throttles to see if there is any hesitation.
If not, I leave them there and let the Plug Coloration tell the story.

You probably have too large a Fuel Filter in the line for Syncing.
All you need is one to act as a baffle to soften the fluctuations.
Too big and you just draw the air out of the Filter and get an unsatisfactory reading on the Guage.

You might even try it without the Filter in there and see what happens.

 

Rick can you specify the filter size that works best? One like we use on the bikes or a larger one?

Mine is probably 2 inches. I get "good readings" around the 40 mark that vibrate say 36 to 42 or a bit less at idle. Does that sound reasonable? I was tuning using the max reading

 

I use a little Fram Filter.

My guess is that it doesn't change the reading all that much.
One guy has already told me: "Depends on the Gauge!"

 

Still haven't had a chance to pull the valve covers off, been really busy with work/school and volunteering at siggraph this year. I managed to drill a hole through my float bowl today trying to extract a screw. So far nothing I have done to this bike has fixed the problem I have had since the day I got it. Guess I'm narrowing it down pretty quickly tho. Only things left I can imagine would cause these problems are float heights and valves, both of which I plan to do (once the new float bowl arrives anyhow). It's pretty difficult to work on in a parking lot tho, so the valves are going to be tricky. I can't exactly leave the bike in the middle of a bay at work for 3 or 4 days while I try to figure out the valves. So we'll see what happens.

 

Shad:

Where are you located?

 

Denver Colorado

 

OK, checked all my valve clearances today, all are in spec. I took the carbs off, checked the floats, bench synced again, synced with vacuum gauge again, put in new plugs as specified in the haynes manual, colortuned again, and still turn my plugs black within a mile of riding. When I was colortuning, I would get it just into the nice blue and just out of the orange, then once I touched the throttle, it was bright orange again and I would have to tune it in again, this happened every time I touched the throttle after getting it into the "bunsun burner blue" color. At first my number 2 cyclinder wasn't even getting fuel for some reason, it had spark, though. I had to adjust the mixture screw to get it to burn at all. I also still have no power when taking off, and still barely make it through intersections. I have to play the clutch for the first 50 feet after the bike warms up to not bog way down. I really don't know what else to check. I think I must have bought a cursed bike or something. The only place I know that I would trust to take it after the last bike mechanic ripped me off 600 bucks is the yamaha dealership here in Denver, and they want 150 bucks an hour to diagnose it, and then 150 an hour plus parts to fix it once they figure it out. I already put more into this bike than I could ever hope to sell it for, so dumping a few thousand into it to have the dealership do it isn't an option for me. Anyone have any ideas that I may have missed or could try?

 

I beginning to think your Valve Seals are shot ... or, you have a Compression issue that's letting some Oil get-in with the Fuel Mixture.

Have you been needing to add Oil to the Engine regularly?
Do yo have the results of Compression Test?

 

Wet compression test results 130-115-120-120. Haven't had to add any oil since my last oil change, but haven't ridden much since I last changed it, and for all I know the lost oil would be replaced by fuel in the oil. I do get pretty awful gas mileage.

 

Rick, the bogging and lousy fuel mileage makes me wonder if there isn't the possiblility of a blocked intake or plugged exhaust. Any feelings toward that direction?

 

May help somewhat:



I'm thinking altitude may be a big issue for ya. Check those jet sizes against what it should be stock.

 

I'm not sure where the PO got this bike. It could have been from low elevation. Anyone know what proper jetting is for 5000+ feet? I'd be willing to try just about anything at this point. As for the exhaust or intake being clogged, I have a new air filter. The temp on exhaust for my number 2 cylinder is lower than the others, this is also the cylinder with lower compression. When I went to colortune it yesterday, I had spark but no fuel getting into the cylinder until I adjusted the pilot mixture screws out a bit. Today all of my plugs were pitch black again. I put maybe 3 miles on it last night to charge up the battery some after all the starting and shutting down I did yesterday.

 

After reading the whole Thread again; I'm beginning to think the problem is less with Mixture and more toward Oil Fouling the Plugs.

You DO have low Compression numbers. Maybe not so low that they are at the point where there isn't enough Compression energy to fail having the Cylinder fire. But, I'm inclined to think that Oil Fouling has something to do with the whole picture.

What's the condition of the "Shelf" inside the Airbox ... just beyond the Air Filter?
Do you have evidence in there that would indicate that there is a good deal of "Blow-by" gases being drawn-up to the Airbox?

Beyond that ... What chance is there that the 4 Pilot Mixture Screws aren't the ones that came with the Carbs?

 

I'll check the air filter shelf in the morning. As far as the pilot air mixture screws being different than the ones that shipped with the bike, it's definitely possible, I know nothing of the bike's history. To add to the oil fouling the plugs theory, I had noticed a little bit of oil on the plugs at idle when I first began trying to tune it up. I haven't noticed oil being on the plugs lately, but I suppose I could have it tuned to burn that oil up and just leave soot. What could I check to see if it's indeed getting oil into the plugs? Is this something I can repair myself, or will I be better off selling the bike for a huge loss and moving on?

 

I don't think you are quite ready for cardboard and Magic Marker sign; yet!
I think we have to do some further shakin'-down.

I don't think we have pulled-out all the stops getting you fixed.
I don't know what's next. I have a guy coming-in this Sunday.

Once that's done I going to be trying to figure this out somehow.

 

Sounds like a plan. I'll keep trolling the xj forums and trying anything I can think of tomorrow at work. I'll check that air filter for sure, and see if I get any oil on the plugs at different RPMs for a while, that should kill an hour or 2. I checked my floats by using the clear tube method on all four bowls, but I think I'd like to pull them and check the correct height with a very accurate little ruler I have at work. I read that it should be 17.5mm from the mating surface on the carb bowl to the mold line on the floats, so I'll be checking that for accuracy too. I really need to get my hands on some mercury vacuum gauges, but no funds for that right now. Might as well throw in another oil change tomorrow while I'm at it. I'll post anything I discover. Thanks for helping me out with this.

 

Rick, would you rule out a crack in the head?

 

well, today i tore the carbs off the bike...8 times. I made every precise adjustment I could to them. Followed every post and manual I could dig up to make sure I did everything correctly. Reset the floats perfectly, resynced perfectly, put in another set of new plugs. Changed the oil again. Cleaned out the gastank of rust. put on a new fuel filter. Checked everything over again and again. I spent a total of 9.5 hours tearing it apart and making sure it was all correct. I rode it 3.5 miles before the bike was running so poorly I thought I could only be on 2 cylinders tops. As soon as the bike heats up to a normal running temp it's unrideable. There is no visible smoke coming out the exhaust when it's running. The #2, 3, and 4 plugs were pitch black after that short of a ride. There was no indication of oil on them. The air filter is brand new and unobstructed. There was no indication of andy "blow by" gases in the air filter housing. I know the valves are all within spec. I didn't notice as much carbon build up when it is idling, they stayed relatively clean compared to riding it anywhere. I'm still tearing through gas too, I can smell it strongly through the exhaust even with the mixtures screws out only enough to keep the bike running. I can still unplug the number 2 cylinder from the wire and hear no change in the condition of the bike once it's hot. If I unplug 1,3, or 4, and then unplug #2 I can hear a little difference, and it dies quickly thereafter. I've put more into the bike than I paid for it now, which totals more than 3 times what they go for on craigslist. This sucks.

 

Pull the tank.
Look at where the Coils are attached to the frame.
Undo the fasteners and take the Ground Wire Terminal Eyelet and clean it to bare metal.
Likewise, where the Eyelet touches the frame. Sand the contact spot down until its bare metal.
Make sure that there is no resistance in that spot what-so-ever.

Get a set of Spark Plug Wire "Splices"
Splice-in new wires from the Coils to the Plug Caps.
You can get high quality performance wires for a buck-each at a Junk Yard. Just yank a Spark Plug Wire off any German Car.
If the Plug Caps are molded-on the wires ... leave them on.

 

I have NGK plug wires that are newly spliced in on the bike now. I took a wire brush and some fine grit sandpaper and shined up the ground eyelets and anything that was possible for them to touch today. No improvements from any of those things. I did discover a vacuum leak on the carbs today. I sprayed starting fluid all around to see if I had a leaking boot on the carbs. It turns out that the throttle valve is sucking air through the side of the #4 carb. Would that cause a rich condition on the plugs? Either way it's something I'll be fixing as soon as I get the cash for it. Anything else I should replace if I'm going through the trouble of replacing seals and whatnot for the throttle valve? (the rod passing through all 4 carbs that the butterflies pivot on is called the throttle valve isn't it?).

 

You're in for a long day in Camp!
That's for sure.

If they come apart without a fight and this is your first time Overhauling a Rack; you could be all day.

Bottom line.
Separate the Carbs from the Rack.
Remove the Throttle Butterfly Plates.
Pull-out the Shaft. Pry out the old Seals.
Insert the new Seals.
Put them back together again.

 

I would think if you have a vacuum leak it should make that cylinder lean. Shaft seals may just need alittle lube to get it to seal up again. You might want to try that first and see if your vacuum leak goes away.

 

Yeah, I was kinda thinking that would cause a lean condition as well. But I definitely have a very rich condition going. I'm still not finding any oil on my plugs. Do you think I should try different jets? I'm at 5300 feet, not sure where this bike came from originally. Would altitude affect the mixture from the jets that much? I tried to find a thread on jet sizes for altitude, but I couldn't find anything.

 

well, it's barely running now. I put an infrared temp gauge all over the exhaust system. My number 2 cylinder has spark, but is not igniting. I'm guessing it doesn't have enough compression to do anything. I can grab ahold of the exhaust pipe where it exits the block and hold right on. It tops out around 97 degrees, even when the other pipes are over 140 degrees. When I pulled that plug, it was wet with gasoline. The #3 and #4 plugs are still black after less than a mile of riding too. #1 plug seems fine still. There is still no smoke coming out of the exhaust, and no apparent oil leaks. No matter what I do to the carb on #2 it makes no difference. It seems like the closer I get to having it tuned correctly and everything I can check in spec, the worse the thing runs. Anyone have any advice? (Thanks to everyone who has offered advice and ideas so far as well, I really appreciate your help. I don't know what I'd be doing without you guys.)

 

There is a loud knocking sound whenever I start up the bike for the first time after it cools down for a few hours. It's the loudest behind the cover plate that says Yamaha on it under the heads. I'm assuming this is the access panel to the cam advancement, but I'm not sure. Could it be a timing issue? The PO claimed to have rebuilt the top end of then engine, and the valves all being in spec lead me to believe he may actually have done that. How much play should there be in the cam chain too? Think I could have bad pistons/rings or bad valve seals? Any tests you can think of that I haven't done, I'd be more than willing to try.

 

Anyone know what size jets (main and pilot) are recommended at 5000+ feet altitude?

 

don't run the bike until you have stripped the head down and found out what is going on, I still don't rule out a cracked head.

 

Have you ensured that none of your exhaust is blocked perchance? Mice build nests in the weirdest places (so do mud daubers, atmospheric vents in a Carter AFB on my 66 GTO, go figure). I've had problems with a blocked exhaust on an old Honda of mine and it was the muffler batting that caused it.

 

I checked the exhaust pipes, no blockage. I rented a garage today to work on the bike. I'm going to do a full tear down. I've decided I most likely need new rings at the least, maybe need a bore job too. I figure there isn't enough compression in #2 to get any burn, and since everything else on the bike is in pretty good condition and i'm still fouling plugs, I'm going to assume it's oil getting into the cylinders and maybe should do a valve seal job while I'm in there. Hopefully I won't need a bore, but who knows what I'll find when I open it up. Anyone know of a good how-to for doing the rings?

 

Shad - first good luck with your tear down. If you can, pictures will greatly aid those who have to follow you. Thanks