Topic: Now that the idle hover is fixed....help me tune the carbs

[TwoTired]

I guess my problem is all related to fuel level issue(s). Got home last night and there was a puddle of fuel under the bike. ...

... What gets me is that the problem is intermittent. The bike ran great Monday afternoon. Yesterday, it didn't want to idle when I first cranked it. Full choke, half choke, no choke...made no difference. The idle problem is different, too. At one stop, it may hang at 2-3K rpm, the next stop, it's fine. The next it will hang a little high but then drop to normal idle.

Fuel contamination can cause this with particles intermittently catching between the float needle and seat.

This is the #3 carb. See the corrosion on the jet holder? The o-ring is past that, but could this be an issue?

It looks like the oring is past the corrosion.  But, the corrosion left a sharp edge to cut the oring.  A nicked oring may not seal.  Check the oring for deformity.

The parts jets are marked with a slanted star looking emblem and "40".

The "slanted star" is a Keihin symbol.  That's the company who made the carbs for Honda, and what is normally found in the stock carbs.

What do you make of this? What difference would the length of the body and the lay out of the holes make? Which ones would you use?

Well, you previously told us that all the parts except the mains were stock Honda.  And now we see that was not the case.  So now I question what other parts in the carbs aren't Honda supplied, as well.  In particular, the emulsion tubes and slide needles.

The jet length determines how deep into the fuel supply the tube reaches.  The shorter tubes will "starve" at a higher fuel level than the long ones that Keihin intended to be used.

The cross hole's size and number control the amount of air premixed with the fuel before passage to the carb throat.  Those holes are interactive with the air screw setting.  It's no wonder your previous air screw manipulation didn't behave as expected.

I'd use the jets from Keihin.

Cheers,

[Scott S]

 THOROUGHLY cleaned those Keihin slow jets today and installed them.
 I'm soaking the Keihin mains that came out of the same carbs. I'll see if they're usable or not.

 The floats may not have been monkeyed with too much, but I'm not sure they're 100% correct, either. I don't trust my measurements (and it's hard to do by yourself), so I'm going to a buddy's house tonight. He's a 2-stroke guy and has lots of carb experience. He's going to help me check/set the floats.

 The #1 carb had some similar corrosion but, again, only at the tip. I pulled the main from the #3 carb and had to give it a good tug to get it out.  I measured 4.5mm from the edge to the bottom. The seat is a good 3.5-4.0 mm from any corrosion. I actually had to rub a little motor oil on the o-ring just so I good push it back in. It's snug and I don't feel like they're leaking.

 #1 corrosion pics.



 Depth of seat on #3.


 Seat is 4.5mm from edge. That's a 4.5mm gap on the calipers. Should seal fine, don't you think?

[Scott S]

Well, you previously told us that all the parts except the mains were stock Honda.  And now we see that was not the case.  So now I question what other parts in the carbs aren't Honda supplied, as well.  In particular, the emulsion tubes and slide needles.

 I said that because that's what I believed. No intention to deceive.

 The slide needles are #272304. I'm trusting you when you told me that is a stock Honda number. I cannot say for sure about the emulsion tubes. I do know that I did NOT use the tubes that came with the rebuild kit.

 I also pulled an idle mixture screw from the parts carb and compared it to what's in my carbs; they were identical, so I'm assuming they're stock and will leave them in.

[Deltarider]

O-ring in the pic looks healthy to me. If they're all like that and the jets go in snug, no problem with sucking excess fuel. Stamped number on your needle indicates they're the right ones. So I would assume emulsion tubes are genuine too.
Checking float heights is very simple indeed (they are always right, unless PO has messed with them). I fear too many in this forum are tempted to "adjust" them. Anyway, with carbs in place you can do it after removal of the float chamber. BTW, you can easily cut your own 22mm check gauge from something like a business card.
Check float needles for free movement, without sticking.
I'm pretty sure the standard clip position for the needle is 3^rd , but I can't judge for you, as you have altered intake and exhaust.

[TwoTired]

I said that because that's what I believed. No intention to deceive.

I never meant to imply deceit.  It's just that we have to use the data you give us to formulate advise.

I'm reminded of an old saying in the computer industry:  Garbage in = Garbage out.  Doesn't matter how well the computer works.

The slide needles are #272304. I'm trusting you when you told me that is a stock Honda number. I cannot say for sure about the emulsion tubes. I do know that I did NOT use the tubes that came with the rebuild kit.

The needle number matches what I found in my 627B carb sets.
I think you need to measure the emulsion tube holes, as you have already found parts in the carbs that were aftermarket.  How can you have faith that those are correct?

One of the things I was going to suggest earlier was to drill those holes larger or add some to make the mid-range leaner.  But, it kind of depends on what you have currently.  If you currently have 550F emulsion tubes now, changing them to the correct part might be all you need to do for midrange improvement.

Cheers,

[Spanner 1]

Further to Deltarider's post.... float 'tab' bending to adjust float height is a little more difficult to achieve IMO as the 'new' setting requires the tab to be nicely horizontal to the valve and the tab to valve surface smooth... ( I polish mine ). A crooked tab, while achieving the correct fuel level will 'cant' the valve to the side as it moves upward to shut-off the fuel often causing no shut-off and carb overflow.... just something ( else !! ) to think about

[Scott S]

 Well, I had a friend help me set the floats tonight. He's a heck of a mechanic AND a 2-stroke guy. Apparently, 2-strokes are very sensitive to carb tuning and he's got a feel for what I'm going through.
 I personally watched him set the floats to 22mm.

 I also cleaned and installed the Keihin slow jets. Carbs will go back on the bike tomorrow and I'll see what she does.

[Scott S]

I think you need to measure the emulsion tube holes, as you have already found parts in the carbs that were aftermarket.  How can you have faith that those are correct?

One of the things I was going to suggest earlier was to drill those holes larger or add some to make the mid-range leaner.  But, it kind of depends on what you have currently.  If you currently have 550F emulsion tubes now, changing them to the correct part might be all you need to do for midrange improvement

 I didn't pull the emulsion tubes tonight, but 100% of my problems are low end. Idle to just off idle. Once she gets moving, she runs great and pulls hard.
 If these changes fix my current problems and I THEN have mid-range problems, I'll research the emulsion tubes. Maybe a stupid move on my part, but again...part throttle up to full throttle runs great.

 Looking back at all this, I kinda feel like somebody long ago put in some slow and mains and called the carbs "rebuilt". Nearly 30 years later, I'm stuck with putting together the pieces.

[Deltarider]

Further to Deltarider's post.... float 'tab' bending to adjust float height is a little more difficult to achieve IMO as the 'new' setting requires the tab to be nicely horizontal to the valve and the tab to valve surface smooth... ( I polish mine ). A crooked tab, while achieving the correct fuel level will 'cant' the valve to the side as it moves upward to shut-off the fuel often causing no shut-off and carb overflow.... just something ( else !! ) to think about

Checking the float height in it self is simple. Adjusting is difficult and I strongly advise not to bend tabs at all, exactly to avoid the effects Spanner describes rightly.
As for needles and their emulsion tubes. If the needles are genuine (and 272304 is correct for all 500s) I think it safe to assume the emulsion tubes are genuine too.

I also cleaned and installed the Keihin slow jets.

When you had the slow jets out, have you also sprayed carb cleaner in the carbhouse holes where the slow jets sit? And when sprayed, did it come out of the tiny little holes in the carb mouths (engine side)?

[Scott S]

Checking the float height in it self is simple. Adjusting is difficult and I strongly advise not to bend tabs at all, exactly to avoid the effects Spanner describes rightly.

 Then how do you adjust float height if you don't bend the tabs?

 (And how do you guys do multiple quotes in a reply!? LOL)

[Scott S]

When you had the slow jets out, have you also sprayed carb cleaner in the carbhouse holes where the slow jets sit? And when sprayed, did it come out of the tiny little holes in the carb mouths (engine side)?

 I didn't do it yesterday, but previously, all jets and passages were checked with carb cleaner and compressed air.

[Deltarider]

MY experience is that floats never have to be adjusted, so tabs never have to be bent. But... if a PO has bent a tab nevertheless, you can carefully bend it back. That's the only adjusting floats can need, to correct somebody's mistake, but that's my view. Checking float heights is not even in the maintenance schedule. That tells you.

[Deltarider]

Further, a old factory Honda "pocket-size" service spec book I have here says the standard needle position is "4th groove from top".

Kevin, can you inform us somewhat more about this spec book. How 'Honda' is it? Did it copy the mistake on p 165 of the Honda Shop Manual (see above) by any chance?

[Deltarider]

Scott, having read this thread over, I just can't share your conclusion that the engine is running too rich. Symptoms - rpm staying a bit high and not returning to idle - indicate running lean. Have you checked for airleaks by spraying carbcleaner (or WD-40) around the carb to engine boots? Are O-rings behind the manifold in order? Exhaust gaskets in place?

[Scott S]

Scott, having read this thread over, I just can't share your conclusion that the engine is running to rich. Symptoms - rpm staying a bit high and not returning to idle - indicates running lean. Have you checked for airleaks by spraying carbcleaner (or WD-40) around the carb to engine boots? Are O-rings behind the manifold in order? Exhaust gaskets in place?

 New O-rings on the manifolds as well as new boots on both sides of the carbs. New exhaust gaskets.
 NO vacuum leaks found anywhere.

 The bike smells rich at idle. When trying to leave from a stop, I have to clear out the carbs.
 I'll have them back on the bike in a couple of hours and, hopefully, have a good report later today.

[Deltarider]

 

The bike smells rich at idle.

So does mine. It stinks.

[Scott S]

 Well, I hesitate to declare it fixed.....I need to put some miles on it and get some heat in the engine.

 BUT, there is an immediate and very noticeable difference. There's power from idle to 3,000 rpm that wasn't there before. The whole powerband feels better and smoother and stronger. It hasn't hung up again YET.
 I can even pull off in 3rd gear from a near stop at only 2,500 rpm. That would have been impossible before.

 There's a whole new powerband below 4,000 that I didn't have before! Yay!

 Mixture screws set at 1 turn out, idle is between 1,000-1,100 rpm. Starts right up, especially with the Pamco ignition. I don't even have to give it gas when it's warm, just touch the starter button.

 Ride report later today.

[Spanner 1]

Glad to hear it  .... so after 41 posts back and forward, the problem was cured by setting the correct float height on the 4 carbs... and really that was all that was wrong in the end ?

[Scott S]

 I think it was a combination of float height (which I thought was set correctly before, and the slow jets.

 There is a HUGE difference between the Keihin jets and the aftermarket stuff. Remember, this bike had been sitting for over 28 years! I wrongly assumed that the slow jets that were in it were stock. It wasn't until I stumbled across the genuine Kehins that I could see the difference.

 I think the holes in the aftermarket jets were just too small and too few to let in the proper amount of air. Add to that a little extra fuel from the floats being off it damn near had me whooped!

[Old Scrambler]

Did I hear you were buying beers for everyone!?

Good Job! Now you can talk smart(er) like some others on here!

[Scott S]

Did I hear you were buying beers for everyone!?

Good Job! Now you can talk smart(er) like some others on here!

 Next time you're in the Charlotte metro area, beer's on me!