Mirror Image Carb?

[lakehouse]

I finally found some time and warm temperatures to get back on my nemesis, in trying to solve my engine issues. To bring new readers up to speed, here is a quick review of what I am fighting, and what I have done on this 1989 Elite E.

PROBLEM: When the motor is cold, it starts easily initially, but when holding the throttle at mid RPM for maybe 15 or 20 seconds (and the motor sounds good and strong with revving up quickly), it simply dies. Then it won't start again unless it is finger choked. Removing the carb drain plug, there is still ample fuel in the bowl. Checking the spark shows a good, solid spark, so I feel confident that ignition is not a problem. Letting the motor (and bistarter) cool down to ambient temperatures, the motor starts right up again. Mousewheels was kind enough to supply some pointers to check out, but all were futile. Tweaking the mixture and idle speed didn't make any changes at all when running, and the color of the exhaust didn't reveal a rich or lean condition either.

BRIEF HISTORY OF THE SCOOTER: This scooter was given to me by the original owner who bought it brand new in 1989. It is an Elite E, with the sb50p set up (I believe). It was parked outdoors, uncovered, and had not run for 8 to 10 years. He was NOT mechanically inclined, and it was a challenge for him to replace the spark plug. Therefor, it has not been tinkered with at all, until I became the new owner, that is. It is 100% factory original, with NO modifications made whatsoever. It was neglected, unfortunately, but I am attempting to resurrect it and get it running again like it once did.

WHAT HAS BEEN DONE SO FAR. As previously stated, it has good spark, and always has. The gas tank was removed, cleaned out with lacquer thinner, and compressed air. A new fuel shut off valve was installed, along with a new fuel line, and fuel strainer. A compression test shows between 115 and 120 PSI with a cold engine, and a closed throttle. The muffler had dirt dobbers build a mud nest inside the outlet to the point that no air could pass through it. That was cleaned out and free flows now with no restrictions. I have vatted the carb twice in carb cleaner, all passages blown through with compressed air, and no obstructions are to be found. I have pulled it apart at least a half a dozen times or more, and never found any "hidden" passages that could be blocked. The float level is set according to the service manual, and the needle and seat work freely like they should. The bistarter bench tests at 5.2 ohms, and travels approximately 0.125" when fully extended.

WHAT I HAVE FOUND AS OF TODAY: When the engine dies, I have removed the fuel bowl and measured the remaining fuel. There appears to be more than ample fuel to keep the engine running. The bistarter seems to be fully extended and to be blocking the passage that allows the carb to enrichen itself when cold. In other words, I believe it to be working like it should. I have done an extensive vacuum leak test on all surfaces that might be a source of a leak, and found none (spraying carb cleaner at all mating surfaces and vacuum connections). The carb has the original #68 jet that came with it new, which should be good for my area of about 1,000 feet in elevation. The previous owner said that he never had any issues with the scooter when he was using it, and it ran just fine and sounded good. It always started easily, even when hot. He just lost interested in it, and when his grandkids moved out of state, he parked it. I cannot tell any difference in the motor running if the air box is on or off, but it normally is off, as it is easier to finger choke the carb to get it to start up again and/or to keep it running.

MY QUESTION: I have been looking almost exclusively at the fuel system and carburetor as being the problem. I have fought a too rich condition, followed by a too lean condition when trying to restart it after it has ran for a brief moment. Could there be something out in left field that would cause this sporadic running, and/or something I have missed or not thought of? I ordered and received a new carb with the same physical dimensions, but the location of the bistarter is in the wrong place, preventing me from using it. Plus it is manufactured by somebody other than Honda, and the internal parts are not interchangeable at all. Mousewheels thinks it is for a Spree and not an Elite like I have. I'll take his word on that one, as he knows more about these things than I do.

CONCLUSION: My "gearhead" friends (who don't know too much about 2 stroke motors) are tired of me using them as a sounding board and asking questions that they cannot answer. I know it is nearly impossible to be an armchair quarterback on dilemmas like this, but I would appreciate any thoughts you might have that could possibly help me figure this beast out. When I accepted this scooter, I wanted a project to keep me busy. But it is rapidly turning into a career and an obsession with me. I have swung wrenches on various mechanical things for over 50 years, and have a mechanical engineering background to boot. But this little motor has me pulling what hair I have left out of my head in trying to get it to run like it should.

If you have any questions or any thoughts, please let me know. I'd hate to part the scooter out just because of something stupid that I am overlooking, and can't get the motor to run like it should. Does anybody have a good working carb that they can lend me to try and see if I am in the correct direction in solving this problem? We can talk more of you do. I'd gladly put up a deposit!

Thanks to those of you who took the time to read this, and are thinking about why the motor keeps stalling out. Oh, and I do NOT have the parking brake locked at all, as the rear wheel is free to spin when revving, in case you were wondering. Let's see if any of you can really make me have a very Merry Christmas or not! LOL

Andy

[noiseguy]

When cleaning the carb, did you remove and clean the emulsion tube? This is the brass tube underneath the main jet, it can be pressed out by pushing on it with a dowel of wood from top of carb through throttle slide hole.

I still don't understand what exactly the bike is doing, so answer me this: The bike starts easily when cold. How long will it idle for before shutting down, assuming you don't play with the throttle?

[lakehouse]

Yes, the emulsion tube was removed from the capillary tube that it, and the main jet sits in. I even pulled a strand of copper wire from a piece of electrical cord, and ran it through each hole, and blew compressed air through it too. No clogging there.

On a cold start, it will idle for about 10 or 15 seconds, and I have to feather the throttle to keep the RPM up, and the engine running. Of course, that's at in elevated RPM range since the bistarter is in effect thus adding additional fuel to the venturi. I really cannot get to idle very well when cold, and none at all after running briefly. My first thought was a lean condition, but when I use a single finger to finger choke the carb, a few drops of gas drip out of the carb opening. But that doesn't happen all the time.

There are times I feel that I have a too rich condition, and yet other times, I think it is too lean. Originally I DID have a rich condition, as I found a leak between the chambers of the fuel shut off valve. When I sucked on the vacuum line, I got a few drops of fuel out of it. That's when I change out the valve, and it has not happened again since.

I also have tried shutting off the fuel richness mixture all the way, by bottomed out the adjusting screw. It ran somewhat OK at mid range, but no idle. Then I gave it four complete turns out, trying to make it overly rich. It really didn't change the running characteristics at all. And I did that in increments of 1/2 a turn of the screw at a time.

As stated, when cold, the engine fires up instantly, seems to idle at about 2000 - 2500 RPM (Just a guess) and sounds really good. It revs up like it is supposed to, and I grin from ear to ear! The it dies just like it would if you hit the kill switch, and will not restart unless I finger choke it.

How is this for a mind blower? Have you ever run across this scenario before? My 4 stroke friends just shrug their shoulders and admit that they know nothing about 2 strokes. I'm beginning to feel the same way myself. LOL

Thanks for the questions. Any further thoughts?

Andy

[mousewheels]

Sure is a sticky issue. Running for only 10-15 sec is not long enough to point to an issue where the bystarter is keeping it running, then closing. It takes a couple minutes to warm up and fully close in weather up here. Comment below is a clarification upon the mixture screw:

I also have tried shutting off the fuel richness mixture all the way, by bottomed out the adjusting screw. It ran somewhat OK at mid range, but no idle. Then I gave it four complete turns out, trying to make it overly rich. It really didn't change the running characteristics at all. And I did that in increments of 1/2 a turn of the screw at a time.

The mixture adjustment should show a difference. A clogged pilot jet would be a first point to check, but I've seen enough comments in your thread it's likely been verified. I verify by squirting carb cleaner into the pilot, and watch for it to dribble out the carb venturi OR the clean air path at the airfilter end of carb (See pic below).

--- Mixture screw -- In is rich, out is lean --
The screw controls air flow. The pilot jet orifice meters fuel. Turning the screw all the way in reduces air, but does not limit fuel flow. Thus the idle mixture becomes richer rather than leaner when the screw is turned in.

Here is a pic being prepared for the 'wiki:

Carb_pilot_system_A_sm.jpg (106.08 KiB) Viewed 7783 times

[lakehouse]

A whopping THANK YOU for the information and especially, the pictures. As you can probably tell from my posting, I was under the impression that turning the mixture screw in causes the fuel mixture to lean out, and not enrichen. That helps me start to understand this carb a little bit better. Most automotive carbs that I have worked on in the past, turning the mixture screw inwards leans the mixture out. And of course, that's at an idle condition RPM only. At least I think so, as it has been years since I have fooled with performance carbs of any kind. But your photo makes sense now, because if it were regulating the fuel flow, the needle would have to have a seal of some sort around it to prevent an external leakage.

Does the fuel that is being "used" by the bistarter, come from the fuel bowl itself, or is there a separate reservoir that it draws from? I ask that b/c upon initial start up, it only runs briefly, while the bistarter is enriching the mixture. When the "secondary" reservoir becomes void of fuel, the engine dies, which would account for the inability to restart the cold engine. Especially since when that happens, there is ample fuel in the main fuel bowl. (NOTE: Once after initial start up and running, until the engine died, I carefully removed the carb, and the fuel bowl, while keeping it on a level plane so as to not loose any fuel. It had approximately 1/2" to 5/8" of fuel in the bowl, which should be enough for the main jet tube and air flow to draw fuel into the venturi, and keep the engine running.) But if there isn't a secondary, or a start up reservoir of fuel, I am puzzled why it doesn't stay running and/or cannot be restarted when there is fuel in the fuel bowl.

I let it sit overnight and attempted to start it this morning. It would not start. Probably because every time I took the carb off and put it back on, I sucked on the vacuum line to open up the fuel valve to fill the carb bowl with fuel. It always starts cold then. I have NOT tried to cold start it with the bistarter installed, but not wired into the electrical circuit, just to see if it would start or not. I am betting that it would not make any difference at all, and I would have the same results. Next time I go into the garage (it's 30 degrees right now and a bit chilly out there), I'll fill the fuel bowl as described, unplug the bistarter, and see what happens when I try to start it up.

To me, the passage(s) that carry the fuel from the bistarter circuit into the venturi. are what is allowing me to start and run the engine. But when the bistarter starts to close the passage(s) off (or runs out of fuel) is when the engine stalls out on me. It's as if the feed tube for the fuel that the jet and pilot jet are in, for some reason, is not drawing fuel up high enough for the venturi to take it into the intake manifold. And again, there are NO BLOCKAGES. Of that, I am sure of. I can feel air flow through every opening and passage, along with being able to pass a wire through them (where accessible).

In rereading this posting, I think that I/we are on the right track. It's just a matter of finding what's causing the problem. If you have the time and are interesting in further trying to help me solve this problem, I am open for a phone conversation to toss ideas back and forth. From your postings, it sounds like you are a guru to these scooters. It's always nice to meet an expert in any area when it comes to issues like this. What are your thoughts on the previous paragraph?

Andy

[noiseguy]

It would be worth your time to read up on the bystarter in the Wiki. The bystarter does have it's own reservoir. I expect yours is working b/c cold start is working. The reservoir is part of the fuel bowl.

Running for 10-15 seconds cold, and stopping, tells me that you've something wrong in the idle circuit. The bystarter takes about 2 minutes to cycle in colder temps. You should be able to start and idle the bike from cold for as long as you care to let it run. If it was running for 2 minutes, then shutting down, I'd tell you that your idle jet is still plugged. As it is, I think You need to run through the idle circuit again.

If it was the float valve it would be obvious... spilling fuel while running from the overflow.

The reason that plugging off the carb off gets it started is that when you do that, the engine vacuum pulls gas straight out of the bowl since it can't pull air, and not in a way that it would under normal operation. This primes (and sometimes floods) the engine.

And by the way, this is not a 2 stroke vs 4 stroke issue. The same carb could be used on smaller 4 stroke engine as well. The main issue is that most folks that say they know how to work on things frankly aren't that knowledgable about *how* they work, they just swap parts until the issue goes away. I expect your friends fall into this camp.

If you still can't get it going, you're going to need to start posting pictures of the carb, inside and out. Typically the issues are obvious on inspection if you know what you're looking for.

[mousewheels]

Yes - as noiseguy says check the 'wiki link for bystarter fuel bowl and orifice detail.Wiki link to bystarter topic - click me

When the "secondary" reservoir becomes void of fuel, the engine dies, which would account for the inability to restart the cold engine. Especially since when that happens, there is ample fuel in the main fuel bowl. (NOTE: Once after initial start up and running, until the engine died.

I carefully removed the carb, and the fuel bowl, while keeping it on a level plane so as to not loose any fuel. It had approximately 1/2" to 5/8" of fuel in the bowl, which should be enough for the main jet tube and air flow to draw fuel into the venturi, and keep the engine running.)

1/2" is too low. it's 0.7" from bottom of bowl to the fuel orifice feeding the bystarter fuel reservoir. Verify fuel is above the orifice feeding the bystarter fuel bowl
If the level goes below the metering orifice the bystarter circuit will provide extra air, but no extra fuel -- giving a lean condition. It will also not re-fill until the engine is cranked, *plus* a delay because fuel metered by the orifice slowly dribbles into the well.

Bystarter_orifice_overview.JPG (42.75 KiB) Viewed 7771 times

But if there isn't a secondary, or a start up reservoir of fuel, I am puzzled why it doesn't stay running and/or cannot be restarted when there is fuel in the fuel bowl.
If the metering orifice is partially clogged, or the level has dropped below the orifice the refill time will take longer than expected.

-- Partial clogs?
Orifice size for the bystarter fuel bowl and pilot are small -- a little over 0.010". A 0.0005" build up on the walls changes dia by 0.001", changing cross sectional area by ~20%.

Though putting wires through a working carb is not recommended, I'd run run one through both pilot and bystarter orifice.

[lakehouse]

OK! I see where and how to post photos. And briefly skimmed over the section in Wiki on bistarters. As soon as I put some food into my belly, I'll read it intensely, and head out to the garage.

Briefly, I am assuming that my bistarter circuit is working properly, since there is no issues in starting the engine when the fuel bowl is full, and it hasn't been run. The problem then lies within the jet and surrounding devices. Correct? If I can get the fuel to be picked up, then I should be able to tweak the running conditions with the mixture screw. That all sounds plausible to me. I'll read further into Wiki and see what I find. (The pictures there are fantastic, and I wish I had that source 6 weeks ago. Thanks again for the lead and the link.) You guys are the greatest with all the help you have bestowed upon me so far. But the "fat lady" hasn't sung yet! LOL

Andy

[lakehouse]

I have disassembled the carburetor again, and still cannot find any blockages anywhere. I did take some pictures, but have to go back and resize them in order to upload them. I have a photo of light passing through the idle jet pickup tube, and the emulsion tube and jet with 0.020 copper wires passing through them to show that they are not clogged up at all. Spraying carb cleaner in the areas previously mentioned only results in dripping coming out of the end of the passages. I'll work on resizing the pictures and try to get them posted shortly, if possible.

Let's see if my photography skills exceed my carb diagnosis "expertise"! LOL (Don't hold your breath on either one! LOL!)

Andy

[lakehouse]

Here are the resized pictures. I had a couple more, but am limited to three photos. The remaining were just overall pictures of the carb anyway, and really didn't point to any details in particular.

I hope that this will demonstrate that my passages are open, but I cannot help but feel that we are close to finding the gremlin that is causing the problem. If plugging or contamination is not the problem, then how do I get the main jet/emulsion tube/ jet tower to pick up fuel? Although my float level is correct, do you think raising it another 1/8" would help at all? It looks as if the float level is nonadjustable, as it relies on how the plastic float and needle holder is molded at the factory. Or am I wrong on that?

What's next guys?

[evilone]

What about the tiny hole in the bowl? You need to see light there too.

[lakehouse]

If you are talking about the bistarter reservoir, yes that passage is free and clear also. Unfortunately, I cannot make light bend through that small of an opening. But air flows freely through it, and the bistarter circuit seems to be operating normally. If I understand what the Wiki states, that tiny hole is how the bistarter reservoir gets its fuel from the main fuel bowl when it fills with gas.

Thanks for the suggestion though.

Andy

[evilone]

Unfortunately, I cannot make light bend through that small of an opening.

It can be done with a small flashlight in a pitch black room.

[mousewheels]

[quote"evilone"]It can be done with a small flashlight in a pitch black room[/quote]
Room light is ok too, depending upon the flashlight. Small hole in plywood is used as a mask

Bystarter_orifice_light_setup_sm.jpg (50.13 KiB) Viewed 7737 times

[mousewheels]

If plugging or contamination is not the problem, then how do I get the main jet/emulsion tube/ jet tower to pick up fuel?

No need to focus there - The main jet and emulsion tube are out of the picture for starting and idling.
Components for the main jet circuit are designed and placed such there is no influence from idle to about 1/8 throttle. Pilot circuit and while cold the bystarter circuit provide all air and fuel.

-- OEM Bystarter is installed?
I am not sure what the state of your set up is, as several things have been tried. If the bystarter needle to air valve opening are not synchronized, you may have low fuel flow, but full air. I think you are running OEM bystarter right now, but if the Clone carb bystarter is installed, it could cause an issue.

-- Is fuel flow limited?
Having the engine start unaided code, run 10-15 sec, then not restart w/out your hand over the carb intake is one of your observations. Your observation the level in the bowl was 1/2-5/8" after it died and would not re-start lead me to post earlier it is possible fuel level got too low to supply the bystarter circuit.

-- Test idea --
If convenient, you could use an external fuel source OR after it dies, apply external vacuum to the fuel valve, then wait a minute or to make sure the bystarter well has time to be filled. If it will re-start at that point, then there was a fuel flow issue.