MC 54 250B valve adjust and carb idle problems By bobf (Read 2,677 times)

[bobf]

I found no way to do TDC and valve setup so I am now using the top side idea of loosening the screw, move the lever to minimize the clicking, then tighten the screw. Looks good in the films but my engine does not work that well.

1. If engine is not working those adjusters are difficult, to impossible, to move.
2. If engine is running, the front adjuster still needs encouraged to move and he back adjuster is free for about 1/2 the range.
3. Loosening the screw allows me to move the adjuster till the clicking gets reduced but then holding the adjuster with one hand and using the wrench to tighten the screw just is not happening. The screws go into a spinning action, back and forth, making it difficult to get a socket or wrench on them.

What I have been doing is watching a black mark I put on the adjuster and trying to get the adjuster tightened with the mark in the remembered location. Problem is that the adjuster wants to move as I tighten the screw, even though I am trying to hold it in place with pliers.

Carb idle seems go wander as I adjust things. For a while I thought I had the car set as it was running at about 1100 rpm on the gauge. I went to lunch, came back and now it would just rush up to 2,000 then on up to 3,000 and even higher. I was turning CW and CCW and finally the idle settled down to a little over 1,000 again. Slower than 1,000 and it stalls, higher seem not good as the wheel wants to spin.

I will continue to tweak the valve settings hoping for better balance and that if they are closer to proper, maybe the carb will begin to idle slower and the engine run a lot smoother. It still does not have a smooth idle nor does it have a smooth running at higher rpm's. It seems to surge and back off in most throttle settings. Sure not smooth like it was before. Maybe I should go back to the original carb if I can't get things settled soon.

Helps and hints appreciated. I hope it is not a valve train problem requiring surgery.

[bobf]

Not having much luck with the adjustments. Idle just does not settle down. It seems to surge or dies. Sometimes it runs at start and sometimes it need a bit of throttle to get it going.

Questions:

1. Front adjuster is for Intake or Exhaust? Knowing that I will know what the rear adjuster is for.

2. What causes at times a back fire and stall? Valves or carb idle or both?

3. What causes the surging while idling? Valves or carb idle setting or both?

4. Good strategy for setting the engine? Valve first then the carb idle, or doesn't matter?

Not too satisfied with my progress so far. I get it sounding pretty good. But then things go wild and the engine does strange things like start surging and idle goes up or down without me touching anything. Then I try once again to reset the valves.

[bobf]

OK, I have been reading off the web and have found one wrong idea I had. I have been trying to keep the idle down to about 1,000 rpm. Just had my brain readjusted as I read about 1,800 or so. I had forgotten that and know I had it written somewhere, just can't find it. Alternative is to raise idle till the wheel starts turning, then slow down the idle till the wheel stops turning.

Tomorrows project will be to reset idle and then see how things are going.

[bobf]

Problems still with the idle. When I try to keep it at 1,800 is when it just does whatever it thinks it wants to do. I have stood there and watched as it raced up to 4,000 and then dropped way down and died.

I tried again to set the valves, not much different from where I had them. Maybe they are OK.

Could I have left off a vacuum hose? Is the carb acting up? I am lost again.

Sure wish we had a Chinese scooter shop here in Casa Grande AZ.

Any help or suggestions. I am lost and tired of the way it is running.

[ellpee]

Since the engine is a Honda clone, and it's just a valve (?and carb?) adjustment, maybe you can find a Honda cycle place that'll take it on?

[bobf]

Thanks ellpee. I have been looking for scooter shops here in Casa Grande but none show up on the web. Maybe if I look for a Honda shop they might take a look.

First I am going to go back to the original carb. This new one seems much worse. I was just out in the garage, the throttle cable seem correct, but the idle would range from stalling to trying to run at 1,500 then zooming on up to over 4,000 and dropping down to stalled again. Some back firing going on at various times and speeds.

Have had this machine for about 6 years now and only have 250 miles on it. It started off with a leaking gas tank through the sender unit. Then the problems with health, moving, heat here, and plenty of these just poor operating times for my scooter career. Sure hope maybe your idea may work. So far it is the best idea I have had on this thread. Nobody else willing to say experience taught them whatever.

First, I will try going back to my original carb to see it that may be a help.

[bobf]

OK, have finally put the old carb back on and put the air cleaner and tube from air cleaner to carb on again.

Result was that the engine started right off but then went into a rpm race and surged up and down for a short time then dropped off and died. Really no different that the old carb. It was also back firing all along while it was running.

Now how about a valve job. Is that a big job to get done. How much is it to take off the head and carry it to a shop for repairs. I can order all the parts for about $60 and take them to the repair shop. I could also order a gasket kit.

Any good old engine types around to offer a hint or two? I could probably do the valve change myself but if the valve seats are needing refaced, I definitely could not do that and not sure about spring compression things either. But taking the head off seems to be something I could do, if that is the right thing for me to do for a valve job. Really don't know as I still have no idea where TDC is on this engine. So a tear down would really mess me up pretty badly.

I have some reading to do and also hope some might appear with comments.

[cyborg]

I would be checking the intake tract for air leaks,,,this can cause erratic idle

[cyborg]

i am wondering bob,,,how many miles on the beast

[bobf]

Cyborg, what do you mean by intake tract? I just described putting on the air ducts and air cleaner. What more is there?

I put the mileage just 3 or 4 posts up. Approx 250 miles. Unfortunately this machine has been a long term problem since I bought it. It has spent many weeks with the covers off and not running the streets. Right now I am in the process of putting in the floor boards and closing the front area. I am keeping he rear covers off till I get the engine running or the junk man takes it away.

[ellpee]

Everything from the air filter box, thru the "horn" that channels air into the carb, thru the carb, then thru the intake manifold to the cylinder. Filter clean? Everything tight? Any holes or cracks?

[bobf]

Hi ellpee, your list is pretty much covered in my installed air box, horn, to carb. Real hard to tell if perfect as you can only barely see the installed parts. They do enter the openings and I tighten the clamps. That is one of the toughest jobs to do on my scoot. A hold down screw on the horn is near impossible to do as it is down below the cable holding bracket. Pretty impossible thing to do but it is necessary as without that screw there is nothing holding things together.

Now both carbs had the same problem so I don't think they are both leaking the same. In the engine, I could only tell if I tore it apart and put new gaskets in. Can not see the rubber unit that joins the carb to the engine. I do have that clamp tightened. One more check over the mounting but that is about it. Heading for valve job as I see it.

I have seen posts on other forums that just point to valve jobs. So now learning more as I read more. I did find one that has a film of doing a valve job. But my PC now does not show those youtube films. Not sure why that quite and have not yet found the way to correct it. The films run but only sound and no video. Stop the film and the sound ends but a view of the video appears then. Pretty sad and frustrating. So I am also working on my PC while wanting my scoot to run.

[bobf]

OK, checked the air system today and found what I thought was tight to be loose. So I redid the entire air system again today and now have a real tight air system. So I ran it. It started right off at a bit high idle. Sort of as expected and then it slowed down as expected. Then it decided to race up to much higher idle speeds and then slower then higher then slower and finally it quite. Restarted and again it seemed to race and slow. Reset the rear adjust from just ahead of the mark more to the rear of the mark. Then it would not start. Then I put it just in the middle of the marker. It started and I thought maybe this is it. It ran briefly at a good idle but then started the surging again. Now just don't know what but a valve job. I rechecked the air system and it is still solid and the joints are tight.

Back to replacing the plastics. Finished with the floor panel and tomorrow will start on the front panels. They have about a half inch difference lower from the front panel bolt holes to the higher welded frame threaded position. So I have to find what is keeping the front panels down so much.

[bobf]

Happy Halloween!

Seems to be pretty light on attendance recently.

Did the front panels yesterday and now just have the rear panels to do. Still unsure of what is wrong with the engine so will not put the rear covers on yet. I may see if I can mount the seat and see if I can actually ride it with the balky engine. If so I might just find a dealer and ride it to him to have him listen to it and help with a decision.

[bobf]

Any one hear of this to be my solution?

Could be as I changed carbs due to uneven running. Now back to my original carb but still not good running.

I don't know the measurements on my scoot, have not had time to check out this part. It does not look the same as on my scoot. More wondering if this could be part of my problems. I have seen this part on other parts forums but more like what I saw on my scoot. Just not sure what to do so far. It may be interchangeable but won't know if I don't tear my scoot back down again, or at least take out the carb. Taking out is easy but putting it back in can be a big problem.

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