YellowBird got a little more love as I continued the march forward today. I installed a new left hand switch from an 09 that I purchased with a bunch of other parts for the bike. Turns out the wire connector for the 04 is different than for the 09. I could either cut and splice the wires or remove the pins from the connectors and swap them. I chose to remove and swap them. It worked out pretty good too. The pins looked slightly different so they were not direct replacements, but I was able to drill out the old connector housing and hot glue the pins into place. Fortunately, the wiring colors remained the same. The 04 had 2 connectors, 1 with the 2 wires for the clutch sensor and the other with the blinker and horn wires. I chose to make a jumper for the clutch connector to remove a possible future failure mode with the clutch kill switch.

After getting the wiring sorted out I put the bike together and went for a ride. Boy is this thing gutless compared to my other 04F (the blue one that sometimes shows up in the pictures). I think it is related to the low compression so I began to investigate that. I decided to do the add a bit of oil to the cylinder trick to see if it would raise the compression. Here are my results:

               Left (psi)               Right (psi)
No Oil        120                         120
5 ml Oil      152                         152     (teaspoon of oil)
10 ml Oil    180                         184      (2 teaspoons of oil)

While the compression did increase, I got to thinking about the amount of oil I was adding in comparison to the size of the combustion chamber. A quick back of the envelope calculation assuming each cylinder is 250cc and has a 9:1 compression ratio. That means the combustion chamber is ~250/9 = 27.8 cc. Adding 5 ml (or 5 cc) reduces the combustion chamber size to 27.5-5= 22.5 which means the compression was increased to ~11:1 ( from 250/22.5) and with 10 ml it raises to 14:1. I assume increasing the compression would increase the psi, the question is would it increase it by the amount of my increase or by less and the oil sealing leaking rings was increasing it more. You notice the increase is directly proportional to the amount of oil added. 5cc increase 30 psi and 10cc increased 60 psi.

While I ponder these findings I plan to check the timing to make sure it isn't just off time a little causing the low compression. I found a post a while back by Addidasguy where he built an engine from components of 4 old engines. It ran, but poorly. He had compression similar to mine (120psi) and he found the timing was out. Once fixed his bike ran great. I'm hoping to find similar. I should have checked to make sure the timing was right on when I checked the valve clearances, but I didn't think to.

Ken

Top Pic
Mismatched connectors.
Next Pic
Removing pins from housings. Pins from old housing came out fine, pins from new housing required a little more persuation.
Next Pic
Connectors together. Note the hot glue on the back and the clutch bypass jumper in the small connector.
Last Pic
Bike as it is today. I purchased a rear cowl off eBay since my bike didn't come with one.

Always trust Adidasguy. Did you (or a previous owner) ever have the timing chain loose or off?

But it could also be a bad vacuum leak or torn diaphragm or something like that causing the slides to stay down, you never get on main jet. I always guess carbs first.

BTW when my bike went under the knife it had about 110 psi one cylinder and 80 the other iirc. After the top end rebuild with 180+ both sides the bike did not have noticeably more power. Now I hadn't really gotten to ride it a lot with low compression because it wouldn't really run when hot but you think I would have noticed the day I picked it up from the shop. And I expected to, but it wasn't different as far as I could tell. Plus all of the other work carb tuning etc that I did since also didn't affect power really, mostly just consistency and idle quality, starting behavior, etc.

FYI.

Quote from: Kenner on February 06, 2018, 11:40:42 AM
If you recall from my earlier post I performed a compression test when the engine was cold and didn't have the carbs installed. The results were:

Left Compression 120 psi       Right Compression 120 psi

According to the Clymer manual the compression should be checked after getting the engine to full operating temperature. Now that I have it running I ran it up for about 10 minutes to heat it up and then redid the compression check.

Left Compression 68 psi       Right Compression 70 psi


WFT! Why would the compression be so much lower with a hot engine?

Then it dawned on me. Even though I was holding the throttle wide open the slide was not lifting since this is a CV carb and just cranking it over doesn't produce enough vacuum to raise the slide. I reached into the airbox and manually raised the slide while holding the throttle wide open and cranking it over. Then I got

Left Compression hot 128 psi       Right Compression hot 129 psi

That's more like it. Interesting to see the difference between hot and cold compression is about 8-9 psi. I didn't have an issue when the engine was cold because the carbs were not installed. Lesson learned.

Ken

128 psi is good, it will run with near 100 psi cold and 110 hot - I know that for a fact, I ran one to there and it still ran well. Down on power compared to a higher compression motor but ran fine enough.
Cool.
Buddha.

Quote from: mr72 on February 10, 2018, 07:08:50 AM
Always trust Adidasguy. Did you (or a previous owner) ever have the timing chain loose or off?

I've never had the head off myself, but I did notice some pry marks (can be seen in the earlier photos showing the exhaust studs) making me think the head has been off before. The ODO shows about 19,600 miles but I have no idea whether that is accurate. The guy I bought it from owned it for about 5 years but only put 350 miles on it (according to the title). I am inclined to believe that is true too because it had last been registered in 2014 so it sat for about 4 years before I bought it. The kid was pretty young and lived at home with his dad. It looks like it was a project bike that never got finished (unfortunately his idea of project was to cut and remove things like the muffler and stock airbox just looking for more noise I guess).

I did check the valve clearances again since I've had it running (albeit poorly) for a bit and they were all within spec. I verified the timing was correct as well and as far as I can tell it appears OK. The 1 and 3 marks were correctly pointing at the chain when the cam grooves were pointing at each other and  they were 18 pins apart. They did seem off a tad but way less than 1 tooth on the sprocket which might indicate a stretched chain.

I already redid the carbs with all new O-rings and eliminated many of the vacuum lines so I hope I eliminated any potential vacuum leaks. I inspected the diaphragms when I had the carbs apart and did not see any tears or pinholes. I ordered some new O-rings for the intake boots because I did not replace those. I do have the nice running blue bike and I am tempted to swap carbs and see if it runs better with those to see if the carbs are the problem. I will do that when my new O-rings come in and I pull the carbs to install them.

Ken

I did a bit more work on Yellow Bird today. I pulled the airbox off and started her up. I was able to see that the slides would move up and down when I revved the engine hopefully indicating that my diaphragms are OK.  I took my son on a little ride just to get the bike warmed up enough that it would idle without the choke.

Once it had a stable idle I sprayed a little starting fluid around the carbs listening for any engine rev increases. I noticed a slight increase when fluid was sprayed around the right intake boot. I have new O-rings on order so I will replace those when they come in. I also bought a lunchbox filter and larger jets from a seller in the "for sale" section so I plan to put those in to richen it up to match the increased airflow.

I am still dealing with a serious lack of power. The vacuum leak that I found seemed quite small because when I sprayed a bit of fluid there the rpm increase was very slight, barely registering on the tachometer. Would such a small change really be the cause of my missing power?

Ken

Another small trick to share is when working on the engine, if the fuel lines are long enough you can place a small sawhorse next to the bike and strap the fuel tank to it while doing some maintenance eliminating the need to unhook the fuel lines. I was able to check the timing, valve clearances, and compression with the tank situated like in the picture below.

Handy diagnosis tool is a laser thermometer. Mark a point on the exhaust where the temps should be the same and take readings there. Any differences will show up really well. And you can do it ant any revs ( and if you have a dyno any load).

My new carb intake boot O-rings arrived today. I removed the old, flat, crusty ones and replaced them with the new flexible rings. Unfortunately, it did not improve the running of the bike. It still has almost no power when under load. It also does not idle as it should. When the choke is engaged it does not rev up to 3-4k rpms like my other bike. I plan to swap the known good working carbs from the other bike onto this one to see if they are the problem. I hope it is, but in the back of my mind I kind of hope it is not since I already went through the carbs cleaning them and replacing the O-rings. If it is the carbs it still means I have much to learn about performing a carb cleaning/overhaul (edit: both sets of carbs work fine so it looks like my cleaning and overhaul procedure is sound...nothing like having others critique your work to make you doubt yourself).

Wish me luck!

Ken

You are ruling out the potential issues, that's a good thing. You have to make educated guesses. Swapping for known working carbs will certainly be a helpful way to isolate whether the problem is with the carbs or not.

To be low on power requires either bad compression or inadequate fuel (and air ... but in a CV carb they are necessarily related). Swapping the carbs will tell you whether the compression is at fault. And as a bonus, if it turns out it is the carbs, then you already have them off the bike!

You just have to be logical about it. If it's the carbs, then it means either:
- adequate fuel is not getting added when the throttle is opened
  - the slide is not coming up and the needles are still blocking the main jet -- you verified the slides move up when you open the throttle, so this is not it
  - fuel is not getting to the main jet when the slides come up and the needles are out  -- this is maybe low floats, sticking float needle valve, clogged float valve, clogged passageway in the main jet fuel supply
- air is being added in bulk past the point of the jets so it is not mixed with fuel
  - it could be a bulk air leak, which you began to rule out with the big o-ring swap, or some other major air leak somewhere else like a completely missing o-ring or vacuum cap gone

We're not talking about tuning but gross diagnosis of a big failure. It sounds like it's just not ever running on the main jet so I suspect fuel supply especially if the slides are clearly moving all the way up when you open the throttle. But it could be that vacuum is sufficient to pull the slides up but also air is being sucked in somewhere past the jets keeping it very lean when the slides are up.

Is there any chance the wrong jet is installed? Maybe the mid and main jets are swapped? Or the wrong main jet is installed? Should be pretty obvious, right? Don't the Mk2 carbs have a pretty big main jet, over 1mm? You can eyeball that.

I can't count the number of times I had my carbs apart trying to sort them out before finally discovering it was bent valves all along. That includes two sets of carbs! And several times I tore them down and found mistakes I had made putting them together the previous time.

When you cleaned the carbs if you check the emulsion holes in the sides of the main jet holder/emulsion tube. They are extremely tiny and block with almost anything. If they are blocked they will stop the needle and mainjet working properly. They are also very hard to clean properly. They are also the first thing to suffer from alcohol fuel because they are so tiny and in a air/fuel mix environment. Unlikely to the the alky problem but I have seen it, especially on bikes that have sat for a long time with fuel in the bowel. Usually there is a lot  white corrosion inside the bowls when you open them. If there was lots when you first opened the carbs they MAY be unsavable.
Mine was a VERY stuffed bike when I bought it and it had been sitting for ages. I ended up cleaning the carbs 3 times before I managed to get them running properly,then they were fine. Replaced the needle and seats, because it's a Suzuki, and i could NOT clean one of the pilots without stuffing it. Nothing would get the grunge out of one of the jets. Clogged solid. Bought new pilots, and both mains, which fixed them, but the galleries were full of junk.

Agreed. I used a guitar string to clean mine. And cleaning a 0.4mm jet is a fools errand when they are 5 dollars each.

My pilot jet wouldn't even unclog with a guitar string. It was seriously grunged...

Yeah, no kidding. I would always just replace the pilot jet. It's too small to try and clean anyway and the fact is just a tiny amount of gunk would cause a serious impediment. Those Mk2 carbs especially, with a 0.2mm pilot jet... that's smaller than a 0.010" guitar string! Think about that. An ordinary piece of copy paper is about 0.08mm thick... over 1/3 of the entire size of the pilot jet. To "clean" a pilot jet like that would require using a 0.2mm drill bit, which nobody has because that's unbelievably tiny.

But you can clean the fuel orifice under the pilot jet with a guitar string... it doesn't have to be a precise diameter. But it does have to be not-clogged. I used a piece of a 0.013" and a 0.018" guitar string to clean mine, dunno about the Mk2, probably need smaller, and smaller than 0.013" is not rigid enough to use for cleaning.

Better still is to strip the carb down to only aluminum parts and then put it in an ultrasonic cleaner.

I use 8-40 or 42 srings on my Tele ( heavier on the Strat 10-46). That's .2mm and 10's are .22mm.
The problem with using guitar strings is they can scratch the inside of the jet oriface. This can and does cause flow disturbance through the jet. This is especially true if the string has been cut with side cutters. As the end is wider than the original string and much sharper.

wow, those are pretty tiny strings. Smallest I have are 0.010s. Good point about scratching the brass jet. All the more reason to just replace.

mr72 and Gregjet,

Thanks for the replies and suggestions. I haven't had much time to work on the Yellow Bird lately, but I have appreciated your insights.

This weekend was spent at my friend's cabin which is at 7000' near Bear Lake, UT. We got 24 inches of snow on Saturday night while we were there. It was amazing! I have 3 little kids ( ages 4, 8, & 10 .... there were 12 kids total at the cabin) and we had so much fun playing in the snow, sledding, and building snow forts. The snow is really good for us here in UT too because this year has been super dry and unseasonably warm.

Now that a cold front has moved in I am reluctant to do much work in my unheated garage. Call me a wuss, but I prefer to feel my fingers . I have a couple of space heaters that I'll probably pull out in a day or two. For now I have to finish unpacking from our weekend trip.

Ken

Kenner, It has been over 45deg C (113F) in my shed. Maybe I should send you some of the extra heat for your workshop. Sometimes too hot to breath in there.

Quick update. I haven't made headway with the Yellow's poorly running engine, but I did do some work earlier that I failed to mention. I added some bar risers and some new handlebars. The handlebars on the bike were bent and rebent multiple times so they looked awful when I got it. I had a spare set from a DRZ400 lying around so I put them on. I also purchased some fairly cheap eBay risers. I much prefer the more upright seating position now, but the bars are a bit wider than the stock ones which makes turning feel a little odd at full chicken (edit. I originally put the other word for rooster here and it got updated to chicken (does the forum have some words it automatically changes?)...funny!). I am deciding if I want to cut them a 1/2 inch narrower on either side. I realize I should have taken the picture further back to show the whole bars, but I was more focused on the risers at the time.

The risers I ordered were: https://www.ebay.com/itm/Pair-1-1-8-7-8-Universal-Bar-Clamp-Riser-Taper-Handlebar-fit-Dirt-Bike-22-28mm/332422420831?ssPageName=STRK%3AMEBIDX%3AIT&var=541452464351&_trksid=p2060353.m2749.l2649

They were only $15 and  I am pleased with the quality. The only drawback is the spacers that they use which go inside so it can mount either 7/8 inch or 1 1/8 inch bars. They were a little squirrelly to install. Once tightened down they feel fine.

Ken

I had a chance to do the carb swap today. Good news. Its is not the carbs. Bad news, it is not the carbs.

I put the carb bank from the Blue 04F on Yellow Bird and it ran just about the same. It was hard to start and it had almost no power under load. Just to double check Yellow's carbs, I put them on the Blue machine and it ran like a top. Both sets of carbs were just overhauled by me and they both work fine.

Now on to what could be causing Yellow's lack of power. The trifecta of an internal combustion engine is fuel, fire, and compression.

I know it is getting fuel (at least I know the carb bank is good).

The compression is low, but others have ran their bikes with less.

That just leaves fire. I already installed new spark plugs. I plan to check to coil resistance and also check the timing with a timing gun. I have already mechanically verified the timing by pulling the head and checking the timing marks on the cams with the mark on the ignition.

What do you think?

What should I troubleshoot next?

Ken

I'd be doing the same you are.  Eagerly waiting for your findings!

Quote from: Kenner on February 21, 2018, 07:01:34 PM
The trifecta of an internal combustion engine is fuel, fire, and compression.

I know it is getting fuel (at least I know the carb bank is good).

The compression is low, but others have ran their bikes with less.

That just leaves fire. I already installed new spark plugs. I plan to check to coil resistance and also check the timing with a timing gun. I have already mechanically verified the timing by pulling the head and checking the timing marks on the cams with the mark on the ignition.

What do you think?

I think you're barking up the wrong tree with ignition. But hopefully I'm wrong. At least it's easy enough to check the same way you did with the carbs: swap the coils and CDI from the working bike over to the bad one.

Now, you could have the ignition timing way wrong, you could have the valve timing somewhat wrong. So I suppose it's worthwhile to double-check that, maybe even do a comparison with the working bike just to be sure your procedure is good.

But in the end, IME anyway, with electronic ignition, they fail in a binary fashion: either it fires or not. You don't get low power due to poor ignition. This is not a 1950s VW with points. So you might be running on one cylinder (bad coil, wiring) , or you might be running on one cylinder only when it gets hot (bad hall sensor in the signal generator, bad coil). Maybe check by pulling one plug wire at a time when it's acting up and see if pulling one has no effect (that's the bad side) or pulling one kills the engine entirely (only good side). Likely not the CDI/ignitor because it would just die. Likely not the signal gen, again usually they get hot and fail completely, bike dies when hot. Likely not bad wiring, that would not cause it to run bad only at high revs/load.

It could be resistance in the wiring in series with the coil causing the coil charge/discharge rate to slow so that it can't keep up at high revs. Unlikely though. You can ohm that out easily enough and rule it out. So if you're really convinced it's maybe ignition I'd start with chasing the wiring with an ohmmeter and make sure it's all good, then swap coils bike to bike or do the plug-pull check (or both), and once you rule out ignition then you know what the problem is.

My money's on compression. I hope I lose