Mirror Image Carb?

[lakehouse]

This morning, just to satisfy my own mind, I got a fresh can of spray carb cleaner and shot every opening and passage available. And as I had expected, all the ports, tubes, openings, flowed freely with no restrictions. Cleaner dripped or sprayed out the terminating opening readily.

Just for a FYI - In a previously mailing, Mousewheels said that he wasn't familiar with the model carb like I have that had a "rubber" jumper on the outside of the main body, where the adjusting screws are located at. This appears to be nothing more that a vent connection from the bistarter cavity back to the top of the fuel stored in the fuel bowl. I assume that is to prevent a vapor lock when filling that chamber with fuel, as well as when the fuel contained in it is used. (See attached photo.)

I am currently, and have always been, using the OEM bistarter on the carb. The new one that came on the carb that I had ordered online fit way too loose. (More of that wonderful Chinese quality stuff!) The new bistarter itself measured 0.008" in diameter smaller than the OEM unit, and I seriously doubt that the puny "O" ring that is supposed to seal it would do its job.

I have a coffee can that I silver soldered a copper tube at the bottom, to use as a temporary fuel source when working with the old British carbs years ago. In the past weeks, I had connected it to the carb, and eliminated using the bike's gas tank, fuel strainer, shut off valve, and fuel and vacuum lines, although all the components are new. It had no effect on the running conditions at all.

I still have it stuck in my head that the problem could possibly lie in a low fuel level in the carb's bowl. But since the plastic float, along with its stops, are molded together, I cannot see where there would be any provisions for adjustments. I DON'T want to grind down the needle, for obvious reasons. This is the first time I have run across a non-adjustable float in a carb of any kind. And your thoughts would be......?? If there is no adjustment, why is the spec given in the service manual?

My plan of attack right now (unless you have an idea for adjusting the float level) is to reassemble and install the carb, hookup a secondary vacuum source to keep the fuel valve open (hand vacuum pump), and seal off the vacuum port on the carb itself. Then I'll start the motor up, and see how long it will run at an idle (if it will). I can monitor the vacuum, as there is a gage on the pump. I'll post the results here when I get them.

As an additional FYI, I have read every article in the Wiki, and the carb sections two or three times. What a fantastic collection that is. BIG KUDOS to all that were/are involved with it! That's just what us tinkerers need who love to work on our bikes ourselves. Let alone those who want to try and squeeze all the power we can get out of them. GOOD JOB!!

Later my friends!

Andy

[lakehouse]

Upon reassembling the carburetor, I decided to do a little measuring to try to see where the fuel level is when the bowl is full, and where exactly does the main jet sit in relationship to it. Follow my path and train of thought to see if I am overlooking something, or have something wrong:
From the mating surface of the carb body (where it mates to the bowl), to the lowest edge of the tower that the jet and the emulsifier is contained in is 0.940". (Sorry, I still use the inch system vs. the metric.) And that is holding the carb upright in its normal mounting position.
From the bowl's mating surface where it bolts up to the carb body on the inside of the bowl itself where the fuel is stored is 1.155".
That leaves a difference of 0.215" to the tower. (Or a gap between the tower and the bottom of the inside of the fuel bowl. The opening edge of the main jet when installed in the tower is recessed by 0.065".
Overall, the very inside bottom of the fuel bowl to the opening edge of the jet totals out to be 0.280". In my previous examination of the fully assembled carb, with fuel in it when the engine dies, measured out to be between 1/2" (or 0.500") and 5/8" (or 0.625"). That would indicate that the opening edge of the jet has between 0.220" and 0.345" of fuel at a HIGHER level than it is. In other words, the jet is completely submerged in fuel at that point. And that does not take into consideration, the amount of fuel that is displaced by the float itself. I would guess that you could add at least another 0.050" to 0.100" of fuel that is higher than the jet is. I no longer feel that an improper float level is my culprit.

After reading the Wiki and a super close examination of the carb itself, I am finally getting a better feeling on how this "package" works. Air movement into the port at 6:00 when looking at the intake opening (or front) of the carb, is transferred into the small holes of the emulsifier tube that sits on top of the jet. That air flow is imparted into the fuel that is on top of the jet in the tower, thereby lightening it and allowing for the air flowing in the venturi, to lift fuel into the flow path, and ultimately into the engine itself. Fill a glass near the top with water, place a drinking straw into it, and blow. Water will flow well over the rim of the glass. All kids know that! This is the principal of lightening a fluid column with air, creating an air lift effect.

If I am correct on how this works, why is my carburetor going against the laws of physics, and not doing what it should? Am I on Candid Camera or something? Has someone placed a curse on my poor, neglected scooter? Let's see what happens this time around after putting it back together and firing it up. By then, I will need a nap and give my brain a rest!

If you have been following my dilemma, thanks for your time. Keep an eye out for my next posting to see when and if a solution is arrived upon. Keep your fingers crossed for me and in finding the root of the problem.

Andy

[lakehouse]

OK! The carb was installed, vacuum port to the carb was plugged, and a hand vacuum pump was used to open the fuel valve. Everything associated with the carb was installed as it should be, and I was using the OEM bistarter. Both adjustment screws were turned out from bottom approximately 1 7/8 turns. Upon the initial cranking of the engine, it started virtually immediately. However, it would not idle without giving it a slight twist of the throttle. Attempting to get it to idle on its own, adjusting the idle speed and richness screws had no effect on the smoothness or RPM range. After running for 2 3/4 minutes, at what sounded like about 1500 - 1800 RPM, I had to give it a bit more gas to keep it running. Then it died. Restarting was a bit difficult, and it took numerous tries of 5 second intervals or so for it to fire up again. When it finally did start, I gave it WOT and could only achieve what I think would be about 2000 - 2500 RPM max. I have always had this same issue of no RPM whenever I had the air box installed. (The air box is spotlessly clean, and NO filter element is installed during testing.)

I had been thinking that perhaps having the air box installed would create enough of a back pressure, or choking effect due to its restrictions, to cause the fuel to rise in the jet tube and the emulsifier, to keep the engine running normally. Guess I was wrong again.

Needless to say, I don't want to spend any time on the cosmetics of the scooter until it runs like it should. What good is a new seat cover and fresh paint if it doesn't run and roll down the trails? Guess this just isn't my day......again! LOL

Andy

[mousewheels]

Man - can you write up a storm
Going to take more than this morning to catch up....

--- Float needle setting

This is the first time I have run across a non-adjustable float in a carb of any kind. And your thoughts would be......?? If there is no adjustment, why is the spec given in the service manual?

The float adjustment has been on spec for most Honda scooter's I've had. There are a few things though, making the check reasonable.

• The pin at the top of the jet is spring loaded. Sometimes they get sticky and could stick partially depressed. That would make fuel level higher than normal
• There are close, yet different float needles in the wild: Honda Spree and Honda Gyro had different Honda part numbers for the float needle. The look nearly the same and drop right in
• ) There are aftermarket float needles sold which fit. I bought some from a lawn equipement shop. Definitely not the quality of OEM at the body and tip.

I bought a Gyro from a backyard mechanic who fixed Sprees and Gyros, and ended up with a Gyro whose float level was too low to supply fuel to the bystarter. Would not start cold without a prime, then ran lean.
After puzzling over a while, I swapped a needle in from a working Gyro, and the carb was back in business.

Here's a pic comparing the offending needle and the one from a working Gyro.

Spree_vs_TG50_FloatNeedle_B.JPG (50.97 KiB) Viewed 6886 times

[mousewheels]

After running for 2 3/4 minutes, at what sounded like about 1500 - 1800 RPM, I had to give it a bit more gas to keep it

Hey - I'd say you found something there. Prior to feeding an external vacuum, didn't you observe the engine only run 10-15 sec?

A couple minutes is getting into where the bystarter would be closing.


--- Carb bottom (Fuel bowl)
Hmm - Interesting about the SB50 carb having a low bystarter orifice. I pawed through some pretty crusty bowls to get more info but have no SB50 carb on hand. Will post results today/tomorrow.

Really getting to miss the one SB50 carb I had. It was in nice shape - see 'wiki photo - Link

[lakehouse]

Thank you for the compliment (I think) on my writing abilities. I tend to get diarrhea of the fingers when I'm on a keyboard. Occupational hazard of being a Realtor for 15 years, and working with overseas buyers on many occasions. (We have a large USAF base here.) But I wanted you to get the total picture of what I have been battling, and what I have done since day one in getting this to run right. I was hoping that would minimize any doubts or questions on your part since you don't know my mechanical aptitude and/or my analytic abilities. (I have a mechanical engineering background, and owned/operated a machine shop for 18 years, FYI.)

I did notice a rather unusual needle with the float setup. It looks like the tip is a synthetic (neoprene?) of some sort, and I almost felt it to be spring loaded just a bit. But at that point, I was starting to imagine things though. I did try the float and needle out of the new carb in the OEM carb, and it seemed to work OK. It did open and close, but so did the old one. I never noticed any difference in the way it made the motor run. And the OEM needle I have looks exactly like the ones that you sent a picture of. TY for the photo too!

I am still puzzled by the air box dilemma. Obviously, the scoot ran at the factory, and for the 500 miles of its limited life (actual total mileage) perfectly with the air box and filter element in place. Now when I put the air box on, it chokes the engine severely to where it will barely run, and only at WOT. And no RPM's can be achieved above an idle speed either. I think this should point to something that is the root of the problem. If the overall setup I have at the moment is too lean, wouldn't the restriction of the air box cause it to come closer to the "normal" air/fuel ratio? (That's what I was hoping for.) And if it was overall too rich, I would think that the motor would die instantly due to the decrease/restriction of air flow. (Which it normally does.) Hmmmmm!

This morning my game plan is to swap out bistarters, even though the new one fits loosely. Oh and BTW, when I had the vacuum pump in place yesterday and was using it to open the fuel valve, I held about 25" of vacuum and it stayed at that setting until I bled it off. So that's a dead end also. I'll try the new bistarter initially with the air box in place and the side the cover off. If it seems to run like it should, I'll put the side cover back on and see if there is any difference it how it runs.

If this dilemma doesn't make you scratch you head with one hand, and your butt with the other, I don't know what would then. This is at the top of my list of brain teasers that I have encountered. It sure makes me feel ignorant! LOL Catch you later then.....and have a good one.

Andy

As far as the idling running time, initially I never tried to hold the RPM's to an idle. It was not only difficult to do, but I didn't see any need for it and I wanted to hear what the engine sounded like in the upper RPM ranges. Then when I did let it idle down to tweak the adjusting screws, it would just die. I was shooting from the hip when I estimated the 10 - 15 second range. But yesterday, I took my kitchen timer to the garage with me to get a more accurate idle time. That's where the 2:45 +/- came from. But with the air box in place, an idle RPM was all I could get with a WOT condition.

[bonesv]

As far as the idling running time, initially I never tried to hold the RPM's to an idle. It was not only difficult to do, but I didn't see any need for it and I wanted to hear what the engine sounded like in the upper RPM ranges. Then when I did let it idle down to tweak the adjusting screws, it would just die. I was shooting from the hip when I estimated the 10 - 15 second range. But yesterday, I took my kitchen timer to the garage with me to get a more accurate idle time. That's where the 2:45 +/- came from. But with the air box in place, an idle RPM was all I could get with a WOT condition.

I'm feel so sorry for your scooter. I wish I could help.

[lakehouse]

Thanks for the sympathy, Bones. I wish you could help too. It's rare that I let a mechanical device get the best of me, and this is no exception. Sooner or later I'll either figure this one out, or circumvent the problem without finding exactly where the problem lies.

I appreciate you reading my "novelette" regarding my fuel problems. I'll keep posting until it is rectified. Have a Merry Christmas to you and your loved ones.

Andy

[lakehouse]

Let's see.....Will this be Chapter 23 or 24 of the never ending saga of me trying to get my '89 Elite E up and running again like it did when it was new? Seems like I spend as much time posting threads on this site as I do swinging wrenches trying to figure out carburetor issues. The drama continues today, as we had pretty decent weather here in north Texas. Especially for late December. That afforded me some time in the garage "praying" over it. LOL

Here's what I have done today (especially for MOUSEWHEEL'S benefit, as he is trying to do his best in helping me): I installed the new bistarter, and started out with the air box (and cover) attached, minus any filter element. The motor fired right up, and I did get it to somewhat idle (with a slight twist of the throttle), although it was very rough running. I ran it for about 4 or 5 minutes, and it never died on me at all. Upon giving it WOT, the motor gained RPM's ever so slowly, but nowhere near what the redline should be. (Like maybe 2500 RPM max., if even that.) Then I removed the air box cover, and it helped in gaining RPM's, but a far cry from what it should be. (It took 5 to 6 seconds to reach any kind of RPM's.) And in both conditions, tweaking the adjustment screws had no effect in smoothing the motor out, or in gaining RPM's.

Next, in desperation, I completely removed the air box and started it up again. It took four or five tries to get it going. Idling was non existent without playing the throttle until I found a spot where it would stay running. At this point, it was still rough running, and I was once again not sure if this was a rich, or lean, condition. I held what would be a mid range RPM (as of right now under these conditions), and put a slight portion of my finger over the inlet of the carb, to richen the fuel/air mixture just to see what would happen. I figured that if I was running lean, the RPM should increase significantly. And if it was running rich, it should start to stall out. And that is exactly what it did. It began to stall out. I think that would pretty much tell me that in its static setting, something is causing an over rich fuel to air condition. And by now, the bistarter should have completely shut itself off, as I was pushing the 10 minute running window. Agree????

And once again, my brain is frazzled, and I have run out of ideas. At least, in using this carb. But there aren't enough moving parts to create an overly complicated abnormality with it. And even if I somehow acquired a rebuildable carburetor from somewhere, what would be different with it? Would I run into the same issues? I have heard of some carbs being "unrebuildable" and never seem to work no matter who worked on them. Is this by chance, one of them? I've even considered finding another carb with a manual choke, and rigging up a choke cable. That is if the mounting holes, and inlet/outlet are the same. That's getting pretty desperate, isn't it?

I feel that I am overlooking something, but just can't figure out what it is. It will probably end up being something simple that I can kick myself in the butt over once it is discovered. That is IF it is discovered. I am at the mercy of any and all of you who have ever run into a problem like this. Please give me your thoughts and ideas, no matter how far fetched they may be. I am NOT beyond trying just about anything at the moment.

Thanks to those of you who have taken the time to read my whines and groans, and are scratching their heads along with me, in coming up with a new idea to try.

"And to all, a merry goodnight!" LMAO

Andy

[mousewheels]

Odd to run too rich on an SB50 or Spree with no air filter.

A break from looking at the carb would be to pull the intake and check the reeds for being slightly open or reed block wear. A big leak, and the engine will not start. A small leak could let a portion of the crankcase charge leak back into the carb, then pick up another helping of fuel on the next intake stroke.

-- mouse's worn reed block
Though likely has nothing to do with your issue, here's a odd failure - beach rental with a leakin airfilter.. Fine sand was on the wrong side of the airbox causing reed block wear as well as to the rest of the engine. Rental place ran it to the ground, marked it 'no power' then used it as a parts bike. One sorry thing to get back on the road Link

-- Bystarter orifice position --
Rather than fill your thread with off topic models and issues, A new thread has been created. The bystarter orifice on 3 different models are in the 0.65" to over 0.70", but the Spree bowl brought up an interpretation of 'what is the bottom of bowl' There is a step up in the Spree bowl, if measured there the orfice is about 0.55 from the step.

Anyhow, your carb is lower than all even with the step. Wish we knew why Honda/Keihin made that change.
Link to carb thread

[lakehouse]

With Christmas knocking at our door, it will be a few days before I can devote any time to dissecting any portion of the scooter/carb. Besides, I think I need a break right about now anyway. The only thing I have not inspected is the reed block and reeds as you described in your posting.

Regarding the fuel bowl itself and the provision for a possible alternate port location for the bistarter, I never noticed anything that resembled the photos that you referred to. That is with the exception of the photo that shows the casting that only has the solo port provision. For some reason, I never snapped any pictures of the bowl's interior, as I didn't think it would be relevant to my issues. But I am sure that the carb will be coming off again, and it's no big deal to pop the bowl off and photograph it.

One thing I did notice this evening though. When reading through the service manual again in the carb section, an exploded view of the disassembled carb shows that there is an O ring seal on the air screw in the carburetor disassembly section. I think I remember seeing it when I first disassembled my carb a few months ago, and am quite sure that I reinstalled it when putting it back together. But now I cannot see it anywhere in the cavity, nor did it ever come out with the needle when I removed it time and time again. Is it possible that it is in an O ring groove that was machined into that passage? Or could it have popped out and I didn't notice it? And what effect would it have if it wasn't there now? I know the threads on the screw don't form an air tight seal of any kind, but would it be enough to cause most of, or all of my problems? Right about now is when I wish I had a bench flow tester to see what is going on. But wish in one hand, and........! You know the rest of that ditty!

Thanks again for the response, and a very Merry Christmas to you and yours. Keep safe, and I will get back to you in a few days. Ho, ho, ho!

Andy

[noiseguy]

Have you checked to see if the exhaust pipe is flowing freely? Rpm issue is very odd.

[lakehouse]

Most definitely. Way back at the start of posting this subject, I mentioned that dirt dobbers had built a mud nest into the outlet of the muffler. I was able to get the vast majority of the mud out with a long 1" drill (twisting by hand) though. Then I mixed up some hot water with dishwashing soap after blowing it out with compressed air. I filled it twice, shook it really good, and filled it again letting it set overnight. Another application of compressed air, and I believe that I am free of any dirt remnants. I can easily blow through it by mouth and feel no restrictions. And to top it off, I have tried running the motor with the muffler both on, and off as well. Again, no difference.

I knew that way back when Saab was selling their 3 cylinder, 2 stroke cars, they would have a tendency of loading the muffler up with unburned oil, causing such a restriction that the cars would barely run. Anew muffler would take care of that. But since my scoot has less than 500 total miles on it since new, I doubt that this would apply to me.

I hope you have a super Christmas day today, and perhaps tomorrow I'll check out the reed block and reeds. I doubt that I will find any abnormalities, but it would be one less thing to check and create doubts about.

This entire issue has infiltrated my household to the point that this is what (see photo) my significant other gave me as a Christmas present. She had it made up here locally. She knows how this has driven me to the point of going bonkers! LOL

Andy

[lakehouse]

I guess my posting of a few hours ago didn't go through. Probably my fault. This carburetor situation still has be bum-fuzzled! LOL

Today, as per the suggestion of Mousewheels, who has been a wealth of information to me, I pulled the reed block and closely inspected the reeds and block itself. I could not see any deformities, damages, unusual wear, or contamination anywhere. I am totally satisfied that it is like it should be in order for it to run like it did on day one. And as I expected, when I pulled the spark plug, it was extremely wet with fuel. (I am assuming it was fuel with a slight amount of unburned oil, as that would be logical in a rich running condition.)

What now friends and neighbors?

Andy

[lakehouse]

After further delving into my carb situation while wearing a jeweler's headset (with the magnifying glasses and loop), I did finally find the miniscule "O" ring that seals the mixture screw on the carb. It was in place, and not missing like I previous thought. I also remeasured the gas level in the fuel bowl (with the float set at the correct height), and found it to be 7/8" from the bottom of the bowl (internally) and not the previous 1/2" to 5/8" as previously reported. Again, that's measured after removing the bowl from the carb body. There is more than ample fuel sitting above the bistarter refill port that supplies fuel to the bistarter well. And there are no indications that Honda ever had planned on using a higher or lower port, and then plugged it as in the previous pictures. (Attached is a photo of what I have.

Perhaps a new set of seals might do some good, as these seem to be getting flattened out a bit. Although I don't have any gas leaks externally,everything is good and dry. My previous experience in ordering a carb kit was disappointing, as the wrong kit was sent. And the supplier said that was all he has for a 50cc Honda carb. (It was a totally different shaped body/bowl seal and needle/float components.)

In reading any and all the posting done in the last few months regarding carburation issues, it appears that there are numerous people with similar problems besides me. And a few sound like the exact same problem too. Fellas have gone through their carbs only to find that they run rich (occasionally lean) after rebuilding. I would call that strange coincidences, wouldn't you? What are we doing wrong or overlooking? All I can do is keep digging and try to come up with a solution that I would be happy to share with anybody who reads this forum. That's if and when it should happen.

What now Batman? I'd hate to "jury rig" some plugging in the carb to slow down the fuel flow somehow. Any ideas? I'm still begging. LOL

Andy