MC 54 250B valve adjust and carb idle problems By bobf (Read 2,348 times)

[jennkarley]

I read all your post on this issue and I'm looking forward to hearing the final outcome if you get it running smooth BC I'm having the same issue.

[bobf]

I am expecting a solution soon. I am waiting for the delivery of an electrical part. A couple more may need to be bought before I find the one to fix the crazy running problems. If I don't get the part today it should be around then on Monday or Tuesday. Good thing they are not real expensive or I would just park the scoot on the sidewalk with a 'Please take me' sign on it.

I am now using the Honda trouble shooting guide for ideas. As you have read I did redo my air system to the carb and from the carb to the engine. It needed replaced as the flex was gone and impossible to get reassembled. Now I chase electrical ideas. Where I live there are no shops wanting to work on it. Sixty miles north in parts of Phoenix area there are shops that sell and service. Maybe one of them can help me if my current campaign does not find the problem.

I will post my successes and failures so keep looking on occasion.

EDIT: Part is now said to be delivered this coming Wednesday, 2 December. Will report how it goes probably on Thursday.

EDIT: Part arrive this afternoon, 1 Dec, in the mail. Tried but could not start with new or old. I think the battery was low so it is on charger. We have been having some low temps lately. Today it started at 32 degrees and that may have discouraged the battery a bit. Tomorrow it will be charged and when I have time I will try to run the scoot with old and new part. Will report my results afterword.

[bobf]

jennkarley and others. My new CDI did nothing for my scoot engine at all. It is the same as before. Runs at what ever rate it chooses. So another $10 wasted. Next, according to my older Honda Trouble Shooting list is the Ignition Pulse Generator, another $10 item. Not sure where it is located but will take some time tomorrow to find the part and see how it may be ordered and installed.

This piece meal way of testing and fixing is getting old. Sure wish we had some real scooter mechanics where I live. It is also backfiring as it is running roughly along but not running nicely. I never see backfiring in the Honda service manual. Maybe I have just missed the information.

[ellpee]

bobf, as much as we love you here, your piecemeal approach to your problems is not a good thing.Over the course of this thread I think you have asked about 3-4 ENTIRELY DIFFERENT problems. Focus, dude. I'm not JR, or any of the other Big Gurus on this thread/in this forum, but if I were, by now I would be totally exasperated with your way of asking for advice while almost totally ignoring what has come before. You might want to consider selling your scoot if that's the best you can do. Sorry to be the voice of doom here, but somebody has to say it.

[bobf]

What you call piecemeal approach is because I am following the Honda Helix repair manual now. I wish I knew what has caused all these problems. Over heating so fixed the radiator. Then engine fiddling around started. Tried forum help of new carb but that did not work. Replaced the air system as the older was not good any more. Still not running much at all so now using the Honda guides. Still not working and will continue to follow Honda guide as it makes more sense than the lack of help from the forum. Will also continue to post so others can see the futility of working on this scoot with no help from anyone. If I hit on the solutions I am sure others on here will appreciate it too.

Selling the scoot. That is my goal. Just need it to run first. Otherwise I will just have to give it away if not running. Next step is for the Ignition Pulse Generator according to Honda book. Wish I had ways to check and test rather than order and buy. A good dealer in Casa Grande would be a help. May need to go into Phoenix, closer than Tucson, in the end.

[wheezy]

Bob, I've read all your post to date and have a couple of thoughts. I saw you had adjusted the idle speed and replaced the carb. What setting is the idle/air mixture screw? From some things you've said (uncontrollable idle, extremely high head temp, backfire) it sounds as if you are running way too lean. That would lead to too much air or too little fuel, things like vacuum hoses, faulty fuel pump, blocked fuel filter or hose, air leak around intake manifold. I've even seen a loose enricher (choke) leak air by the gasket seal. I know you've replaced some of that, but it's worth a thorough end-to-end intake inspection for air leaks. I haven't seen anything electrical ever cause this.

Speaking of the enricher, you're reading the internal heating coil resistance, your 7 ohms is fine. You do want it warmed before you adjust idle mix and speed. Mine takes a minute or so of running to fully warmup.

For you and elpee, the designation 172MM designates the 250 motor. 172 is the bore, first M for motorcycle, 2nd M for 250cc. I pay more attention to type when I order parts, (Linhai 257 for mine, I go with VOG 260 parts).

[bobf]

Thanks Wheezy. I did replace the rubber air fitting between the engine block and the carburetor. I also put a new air tube in between the air filter and carburetor. Both of those items had turned hard and made it impossible to get them properly onto the carburetor.

I will take a look into that adjustment on the carburetor. I know that it is on this Honda set up page I am using. In fact it is the next item after I look into the Ignition Pulse Generator. So we are moving along. Sure appreciate your inputs.

One more time consuming thing to do is to try to make sure I have all the vacuum and other hoses where they should be.

[bobf]

Was trying to find how to change the idle mixture screw. I can't do it until I buy one of those right angle screw driver things. Sounds a bit complicated as I must use the special screw driver and when happy with the idle. Take the carb out and hope I don't bump or change the screw before I get the special cap on it. Maybe it doesn't matter anyway.

Today, while working on the scoot I was able to get it to idle at about 2,000 rpm or a bit higher. Much less and it would just stall out. While doing these longer runs I was thinking about what at least two have spoken of. Possibly dirty gas.

Six years back, when new in my garage in Colorado I remembered wondering how much gas I actually had in the tank before a ride. I remember taking a piece of home wire and dipping it into the tank, but lost it and it sank to the bottom. So today, I tried to find and retrieve that wire with a grabber/holder I recently bought at Lowes. I started to push it around the bottom of the tank with the grabbers opened. then let the grabbers close and pulled the thing out. On about the third time the grabber came up with this old forgotten piece of wire. Much of the white plastic was gone and just a bit near the end of the wire. I guess most of it has gone through the carb and burned up.

Since I pulled this wire out the motor has idled better and longer. I have been able to adjust the rpm's to about the 2,000 rpm level and it will sit there and idle for long periods. Below the 2,000 rpm level it wants to stutter and choke to death. I think I am on to something so later next week I will empty the tank, get rid of the gas, and refill with known clean gas from the pumps. Then we will see how things will go.

Recently I have had SeaFoam added to the gas for helping to clean the pipes and carb. Will do that again with the new gas.

Right now I am preparing for eye surgery on Monday and bandage removal on Tuesday. So I will wait until I feel my eyes are ready for working with gas and engine fumes. Then go back to what I hope is successful removal of trash from the tank.

Thanks for all your patience with me so far. Hoping this to be a bit of success and soon the engine run as it is supposed to do.

[ellpee]

You MIGHT be able to just loosen the clamps on the air tube and manifold -- not remove, just loosen a bit -- and be able to rotate the carb enough to get decent access to the mixture screw ....

[bobf]

Thanks ellpee. That might work. Off to the doctors soon so will look into that after I go back to work on this problem child of mine. Even if rotated there is not much room in that area for the tubing and hoses needed for running. Worth a look for sure.

[cyborg]

you used a plastic coated electrical wire which you dropped into the tank and the insulation chemically melted?,,,i would be checking the fuel tap,,,most if not all have a screen,as a filter and it may be plugged up with melted plastic goo,,,,(that's a technical term ),that may be the lean condition symptoms the engine is displaying,,,,,,,,,,just a thought Bob

[bobf]

Thanks Cyborg. Since adding the SeaFoam to the tank I have been able to get some rather long periods of running. I just tossed all the gas and refilled yesterday. Added more SeaFoam and intend to keep running it to try to move out anymore of the melted plastic. Your idea sounds good and worth a try. Where would I find this screen you are talking about. Is it in the tank? The fuel pump? Or someplace else? I will give the books a look see and try to determine where to look.

This will not happen right away as today I had my right eye surgically corrected and may not want to get too close to the gas for a few days. I go to the doctors tomorrow to take the big patch off and will ask how he feels about gas fumes and my eye.

[rooman]

I wonder if you have the head off or just separated enough to look, you can turn the crankshaft until the piston is at top. Then find the position where the cam is not opening any valves, you'll have between 60° and 80° of free mouvement according to some web posts. Having found TDC you can reset the valves to factory clearances to start then turn it over by hand to check no valve tapping against the cylinder. Just my penny's worth...

[bobf]

Thanks rooman. That is exactly the way I did set the valves. I could not get them set to my satisfaction while it was running, so I set them cold and not running, and then back one mark of the adjuster item. The one mark is supposed to be the .004 inch we are looking for.

[cyborg]

the screen/filter will be over the pickup tube in the bottom of the tank,,,it'll be made of polyethalene clear whitish like milk jug plastic,,,i'll bet you a ten spot the screen is partially clogged with the plastigoo,,,,you probably can see it thru the filler with a flashlite,,,,or if youre a thrill seeker use a match,,,,you'll lite up like a christmas tree,,,,HEY tis the season and all,,,just sayin