Topic: 550F Tune Up Time *Updated 4/20...please read*

[Scott S]

 I have a '76 550F that I purchased from the original owner. Here's a thread where I got the bike back on the road:

http://forums.sohc4.net/index.php?topic=126113.msg1434228#msg1434228

 For as long as I've owned the bike it's ran rich. Here's a thread that covered that:

http://forums.sohc4.net/index.php?topic=139399.msg1577133#msg1577133

  Recently, I've felt some performance issues. At first, I thought it was because I've been riding my ZRX1100 so much and the 550F is literally HALF the displacement.
 I sold my other 550's so I didn't have another to compare it to. But after riding a 350F and 400F I have at my disposal, it's clear that something isn't right.

 Now that Winter is on it's way I've decided to dig in and give it a good going over and try to get to the bottom of it. I will be doing the full 3,000 mile tune-up, to include:
 
 *oil and filter
 *valve adjustment
 *cam chain adjustment
 *timing check, including advancer operation
 *new NGK D7EA plugs
 *check coils for resistance, etc. I installed new plug caps when I got the bike.

 The bike is stock, other than a Pamco ignition and a UNI foam filter in the stock air box.

 I will also pull the carbs for yet another cleaning and inspection. I occasionally get some fuel from an overflow tube(s) when initially starting the bike. This only seems to happen after I let the bike sit for an extended period, but I will be installing new float valves just to be SURE that it's not having an effect on the float operation/fuel level.
 I also ordered new main jet O-rings and, if needed, some aftermarket 98 main jets (I can't find Keihin mains at the moment).

 I pulled the emulsion tubes and needles a while back, but I will pull at least one to verify the clip position and part #'s. I really don't  think they're worn, as this bike has less than 7K original miles on it.

 I will set the float height at 22 mm and verify that the new float valves work at that height by using the clear tube method.
 Carbs will be bench synced and then vacuum synced once on the bike.

 While the tank is off and the plugs are out, I will do a compression test.

 I'm waiting on parts to show up right now, but I will report back once I dig in. Can anyone else offer ANY suggestions as to what to check or do while I'm in here?

 I noticed yesterday that, if I look in  the spark plug holes, I can see a fair amount of carbon on the piston tops. Would it be OK to use a little bit of SeaFoam down the spark plug holes and let the piston tops soak for a bit?
 

[Scott S]

 Hmmm....reading back through my own post, I see where I replaced the float valves already. No matter, something isn't right and they, along with the float height, will be checked.

 FWIW, the I've put 1,898 miles on the bike sine I've had it. I did the full 3K tune-up when putting it back on the road and the valves/cam chain have been adjusted once during that time.

[78whiteorbs]

Scott did you sync the carbs? Also what is your starting procedure?

[goldarrow]

Look into replacing brass hardware in the carbs. 

[Scott S]

 The carbs were bench and vacuum sync'ed. The bike has never liked full choke. Only partial choke and feather the throttle.

 The only brass parts I've replaced are the float valves. Everything else is genuine Honda/Keihin with lass than 7,000 miles on it. I've put almost 2,000 of those miles on the bike myself. The brass stuff rarely wears out, especially in less then 10K. And all I replaced before were the float valves.

[pamcopete]

Scott,

I would restore the stock air filter to original condition and get rid of the pods and install the original stock jets. I ran into this with my '74 CB750 when I first got it the PO had installed pods that I could never get to work properly. Someone on the forum here told me that the stock air box was the only way to go because the rubbers that connect the carbs to the air box are actually velocity stacks and the carbs will not work properly without them. I got some new OEM velocity stacks, installed stock jets and air filter and the bike suddenly ran perfectly.

I don't know if the 550 has velocity stacks or not, but suffice to say that the air box is more than just a place to put the air filter. The air box and the carbs are designed to work together and you could spend the rest of your natural life trying to get it to run with those pods.

[Scott S]

 It's not running pods. It has the stock air box and stock jets. I'm running a drop-in UNI filter in the stock air box.

[pamcopete]

It's not running pods. It has the stock air box and stock jets. I'm running a drop-in UNI filter in the stock air box.

Oh... Maybe I'll just take the rest of the day off...

[Duanob]

Look into replacing brass hardware in the carbs.

Funny you mention that. My 550F always had a low RPM stumbling issue no matter what i did. The warmer it got the worse it got. I finally just decided to replace the pilot jets with new. When I took the old ones out I noticed two different sizes! Two were after market although they still were Keihins, they were shorter than OEM. After a new set of pilots the bike ran perfect.

BTW Scott s SWEET BIKE! I miss mine and wished I hadn't sold it.

[Scott S]

 These are genuine Keihin pilot jets. I know what you're talking about....had an issue with those shorter jets in a CB500 once.

 There's not so much a stumble as simply a lack of power or "Oomph". The bike just doesn't have the ass that it should have. Plus the fact that it's running very rich.

 What about pouring a little SeaFoam down the spark plug holes? To loosen the carbon? Maybe do that, run it to blow it out and then change the oil?

[goldarrow]

The reason I bring up about the brass hardware issue is that on my troubled bike, same symptoms as yours, I swapped out the carb and put in my known good working carbs from well running bike, problems magically disappeared.

[Scott S]

 Well, the first step has begun. I warmed up the bike today (very hard to get started, BTW.....it's been a little hard to crank the last couple of times I rode it. Usually, it's been sitting for at LEAST a week between starts).
 Took some compression test readings. The good news is that they all seem to be OK. I have two different compression testers; one that screws in and one you hold over the spark plug hole.
 



 While the readings were different from each gauge, but they correlated. With the thread in gauge, I got:

 #1)  125 psi
 #2)  115 psi
 #3)  110 psi
 #4)  110 psi

 And with the press on gauge, I got:

 #1)  170 psi
 #2)  150 psi
 #3)  150 psi
 #4)  150 psi

 The plugs were, surprisingly, not bad looking....except for #4.




 The carbon on top of #4 psiton seems wet or oily compared to the others, too. This leads me to believe that there's possibly a problem with #4 carb or float height, maybe?

 I'll let the bike sit overnight and start the 3K mile tune-up. I'll also pull the carbs and put my eyeballs on everything one more time, including doing the clear tube method on float height, especially for #4.

 Thoughts?

[KiefRichards]

#4 burning oil?

[Scott S]

   Except that there's never any oil smoke or usage. Any smoke is black, unburned fuel type smoke. Only when you get down on it pretty hard.

 If compression is OK on that cylinder, where would the oil be coming from? Valve guide or stem seal, maybe?

[KiefRichards]

I only mentioned it because my plugs look EXACTLY the same, all clean with #4 black.
I stuck a borescope into #4 and found the cyl wall is pitted.
My bike uses less than a quart in between 2k mile oil changes, and I've never seen in smoke. But guys I ride with say it does when I really get on it.
May not be whats going no with yours, but...

Oh, compression #4 on my bike is within 10% of the others, so its in spec in that regard

Are any deposits on the plug crusty or ashy?

[Scott S]

 Hmmm......very interesting. I wish I had a boroscope. What kind of mileage are you getting?

 I've ridden behind this bike many, many times. I've never, ever seen any white smoke. Only black, gassy smelling smoke when the rider rolls onto it really hard.
 It's always gotten poor mileage since I've owned it; about 26 mpg with a best of just under 30 on a long highway trip.

[KiefRichards]

Yeah, rings or cyl wall damage will often make blue smoke under WOT.
As far as mileage goes, mine's a k4 750. So, apples to oranges, I get around 40mpg, a little over 50mpg on my best tank during a recent road trip.
26 sound really low...

[Scott S]

 Ok... reviving this one.

 I did the complete tune up but didn't do the clear tube on the float level.
 
 With a tune up and fresh plugs, it ran great.....for about two tanks of gas.
 It still occasionally pees out of one of the carb overflow tubes (can't determine which one) and eventually fouls the #4 plug. It's a dry, fuzzy carbon fouling.
 Power just slowly drops off. I haven't checked mileage.

 Since compression tested good, coils and plug caps tested good and a tune up was done, I'm learning towards a carb issue. Definitely#4, and maybe another....if that's the one that's pissing fuel.

 I picked up an NOS Honda needle and emulsion tube. Kinda hard to find for the F model. I'll replace those on the #4 carb and find a way to do the clear tube method on all the floats. If that doesn't fix it.....Well....anyone wanna buy a 550F?!

[Deltarider]

Look into replacing brass hardware in the carbs.

Don't. The original brass parts hardly wear. Cleaning is another thing, however.

[Scott S]

 I got around to trying the clear tube method today and it was good news/bad news.

 The good news is that the fuel level seems to be perfect. The bad news is, I was sorta hoping for a smoking gun!
 I only checked #4, because that's the only cylinder fouling the plug.




  I also tried messing with the mixture screw on that carb and it does NOTHING. The other three have an effect. I screwed the one on #4 all the way in...hell, I even REMOVED it and sat in on the ground. No change at all. What does that mean?
 I sprayed carb cleaner in the hole while I had it out (not with the bike running) and I could hear it coming out of the throat of the carb into the plenum/air box.

 Unless ya'll can tell me what might be going on with the mixture screw circuit, and if that would be causing the issues I described earlier in this thread, my only other option is to try changing the emulsion tube & needle for the NOS one I picked up.

[flybox1]

Your mixture screw meters air as its on the carb side of the slide. 
(Lets call them air screws so we are reminded what they control)
All they way out and its circuit should be wide open, allowing max air in when at idle.
Have you tried leaning out the #4 idle circuit (nearly) all the way (out) and doing an idle circuit plug chop?
Does nothing?  fuel is getting in somehow. 
bent needle?  worn needle seat?  cracked jet seat?  bad jet o-ring?

[Deltarider]

Your mixture screw meters air as its on the carb side of the slide. 
(Lets call them air screws so we are reminded what they control)

Just in time Flybox, just in time 
Check that the little O-ring around the main jet seals well and is not deteriorated.
Why is it always #4 seems to be the blackest? My experience.

[Scott S]

Have you tried leaning out the #4 idle circuit (nearly) all the way (out) and doing an idle circuit plug chop?

 I can say that I cleaned the carbs myself when I got the bike. I sprayed carb cleaner both ways through all the passages. Then, when I continued to have carb problems, I took them to Rick at Old Skool Carbs and he ultrasonically cleaned them. Any time I've had them off, I've checked them out.

 Most of the other air/mixtures screws are at ~1 3/4 turns.....whatever gives me best sound/idle. So, maybe set this one at 2-2.5 turns and see what happens? I'd didn't change the idle at all when I removed it COMPLETELY.

 How do I do a chop on the air circuit? Fresh plug, ride around at 1/4 throttle and kill it?
 And the bike still smokes (fuel smoke...not oil) when I get down on it hard. It should be well off that circuit by then, right?
 I'm just trying to understand.

[Scott S]

Your mixture screw meters air as its on the carb side of the slide. 
(Lets call them air screws so we are reminded what they control)

Just in time Flybox, just in time 
Check that the little O-ring around the main jet seals well and is not deteriorated.
Why is it always #4 seems to be the blackest? My experience.

 Checked the O-rings last time I had the carbs off. They've been replaced and are a tight fit. Even takes a little pressure to get it on the jet holder post.

[flybox1]

Your mixture screw meters air as its on the carb side of the slide. 
(Lets call them air screws so we are reminded what they control)

Just in time Flybox, just in time 
Check that the little O-ring around the main jet seals well and is not deteriorated.
Why is it always #4 seems to be the blackest? My experience.

Checked the O-rings last time I had the carbs off. They've been replaced and are a tight fit. Even takes a little pressure to get it on the jet holder post.

haha Delta....mom always said 'check your work!" 
idle chop - warm up your bike with old plugs.  make your air screw adjustment, new plugs in on #1(for comparison) and #4.
let it idle (under a fan, no riding) for 4-5 minutes. cut it, and compare #1/4 plugs.
I might even go as far as disconnecting the headlight to save the battery.