Vintage Dirt Bike Q & A

Well, I got fuel flowing from the tank, I have a spark and I have thoroughly cleaned the carb, but she won't start . I have had newer bikes but this one has me a little stumped. It has holes for two plugs in the head. I have the wire on the plug that is straight up and down. i have never seen a choke like this one either. The lever goes up and down which is choked an which is normal?

Spark plug gap is .028 spark plug is NGK B8ES. point gap .012. I have 2 mr175. Here are some problems you may have. Both of my bikes needed float needle and seats. 1. The needles appeared good on carb cleaning but were flooding. This may be part of your problem. Also, at .032 your gap is too wide. This bikes don't put out great spark. Close your gap, this maybe another part of your problem. Make sure you are using a new plug. 2. Both of my exhausts were plugged up. This causes bogging on throttle and no power. I took my mufflers to a radiator repair shop and had them put in their caustic tank over night and they were good as new.
The bikes run strong and trouble free. So new plug gapped at .028. Set point gap at .012. New float needle and seat. You can get on Ebay use MT125 kit. You would find a kit for MR175. Same kit. Set timing to F with timing light. If you don't have power clean mufflers and good luck.

Thank you very much. IF I can get this bike to run I can ride with my son this summer.

What kind of bike is it? I don't know of a honda that had two spark plug holes. I have a Honda MR250, but I also have a 1972 Suzuki TS125 enduro. This bike has two spark plug holes. I had fuel and spark and mine would not start as well. If this sounds like the condition you are experiencing, do this:

1. Pull off flywheel plate (4 screws)
2. disconnect clutch cable and remove case over flywheel (more screws)
3. don't forget to remove flywheel case or you will break it taking off the flywheel.
4. remove flywheel with puller after nut is removed
5. My guess is you have a broken keyway between the flywheel and crankshaft. This will throw your timing off.
6. If you kick start the bike now and it backfires or kicks back at you then you definately have a timing problem.

Let me know if this helps

Bob

It is a MR 175. I think it is a 1975 but am not sure. I thought it was a 76 until I found a link here, Now I am thinking 75 because the first number in the serial number is a 1. I have had people tell me to burn out the muffler to clean it out. Will this work? It had set for about 2 years until i got it. The piston was stuck, so I put some marvel oil in the plug holes and it came free. It kicks good It just wont kick over.

I went out and kicked on it a little. It is wanting to kick over it just won't follow through. I have re-gapped the plug. I don't know how to check or set the timing. Which is the "choked" position? With the lever up or down?

Lever down = Choke On
Lever up = Choke Off

You shouldn't have to remove any cables to pull a fly wheel. Maybe the engine was seized before you got it from running without oil. Is there any compression? My MT-250 has 2 plug holes. You are correct using the vertical one.

Scott,
Is the spark blue or yellow. If it is blue, you have good spark. Is it is yellow the points are incorrectly gapped, or worn. If they are worn pull flywheel off with puller. If you don't use a puller you could break the flywheel. Hard to find part, but it your bike. Use a points file or 600 grit wet/dry or emery, fold over a small piece and pull through points; while putting pressure on points to keep them closed do this a few times. Put flywheel back on and gap the points. To gap points look though opening when the f mark on the flywheel is in about the 12 to 1 o'clock position. Then set points to approx .012. If you can't fit in the feeler gauge. Eye it up with the gauge. It is a small gap setting. The timing is set with the point gap so you can't be far off. It will start. If you are getting a good spark and the correct amount of fuel. You are useing new fuel I hope. When you had the flywheel off you would have noticed if the woodruff key was sheared. As in a privous post, this would cause a starting problem. But I think it is fuel. As I posted before, both of my bike had similar problem and it was the float needle and seat. A plugged muffler will not cause a starting problem, just power loss and bogging. Good luck

IF you can see spark jump the plug gap and are getting fuel there can only be two reasons the bike won't start.

Timing or compression.

You can tell is you have a decent amount of compression just by kicking it. My MR250 is a bear to kick and you can definately teel it has compression without a gage. If the bike is trying to start and has what I metioned before up top it sounds like a broken keyway. My MR250 busted one also when I started restoing her.

Bob

I have not paid attention to the color of the spark. I will check that in the morning. The fly wheel is behind the cover on the right, correct?

It is a beast to kick so I am thinking the compression is good. It will actually try to run for about 2 seconds then die. If you touch the throttle in those 2 seconds it will die. My son's '83 rm was doing the same thing and it turned out that the passage from the fuel line to the float valve was clogged.

And yes I am using new fuel, AND I even drained the old fuel out

Y'all are a great help. I really want to get this bike running, she is too cool to be parted out

As Robert posted, I may be the keyway. The flywheel is under the cover on the shifter side. The small cover on that side is the timing cover. I still believe it to be a fuel problem. After it runs for those 2 seconds, pull the plug and see if it is wet. If it is wet at all, and the spark is good. It is feeding too much fuel. Also, If your mufflers are plugged it will bog. So, pull of the muffler and start it. If it starts and you have throttle response than the mufflers are clogged. Let me know how it goes. Hope you get her running. You can purchase a carb kit which included the needle, seat and all the jets at http://www.siriusconinc.com/ The mt 125 kit is the same as mr175. Good luck it a fun bike

How much marvel oil did you pour in there? It may be fouling your plug. When I first got my 74-MT running after a 13 year break is smoked like mad for the first 15 minutes. I fouled a lot of plugs getting it going. I used several old plugs and dried them with a torch in between. By the way, you don't want to have anything important behind it. I covered my wifeÌs new van with oil that settled from the smoke cloud. I have broken flywheel keys before but it may be a little early to check that. You should be able to touch the points up with a narrow file with the flywheel on. I picked up my file kit years ago at a gun show. DonÌt be beaten on that flywheel or shaft with a hammer. The correct tool makes it easy and wonÌt damage anything. They are often on Ebay. Probably the same as the 73-74 CR or 73-76 MT. It screws into the center hole in the flywheel. It does not grab it from the outside edges.

I poured in about 1/3 of the bottle of mystery oil. Some spilled out though. When I kick it smoke puffs out of the exhaust. When I have pulled the plugs they still smell like the mystery oil. Is there something I can do to get it out now that I am done with it. I am leaning toward a fuel problem myself. I noticed yesterday that When you first turn on the fuel you can see it running through the filter for a minute then it comes out the puke tube. I can shut the fuel off and turn it back on and it quits. I am thinking the float valve is bad.

Sounds like you have at least 2 problems. You need a new float valve and your plug is oil fouled from the mystery oil. You should change the valve but may still be able to get it running with what's in there. If it's sputtering I'd put the choke in the off position (up), turn the petcock to the off position since you know the float is full and overflowing, hold the throttle wide open and kick it until the plug fouls, dry or replace the plug and repeat. Eventually the oil will burn out. It should run longer and longer each time.

Of course the correct way is to pull the head and cylinder clean the rings and change the float valve adjust and reassemble. But that takes gaskets and a carb kit and I never do things right the first time anyway. Some of these bikes eventually loose the crankcase seals and suck oil from the transmission or air behind the flywheel, especially if they haven't run for a long time and dry out.

You may want to get it started to ensure it's not sucking air or oil before putting more work, parts or money into it.

Here's a link to the correct puller on ebay.
http://cgi.ebay.com/ebaymotors/ws/eBayI ... gory=35625

I agree. I think a new float valve will do wonders for this bike. I am still needing to check the color of the spark. I have never had anything that had points that I had to work on so I am not exactly sure howto adjust them . It does not sputter and try to run on every kick. MOre like every ten kicks or so. I am going to try fouling and cleaning the plug over and over again tomorow.

I am very grateful to all of y'all. this is a great board.