20 Most Recent 1973 Honda CB 100 Questions & Answers

most of those little hondas are 2thou inlet 3 thou exhaust

With points cover off,slowly bring engine to the highest point on the points cam.Its easiest to do this with the spark plug out,and slowly spin the engine with the kick start. Once you get it to the highest point on the points cam,the points should be "open". Insert feeler gauges untill you find the correct one...(it should have slight resistance). The check what the recommended gap is for that model. After finding the recomended gap,use the feeler gauge that matches the recomended gap,and isert between the points. There should be two screws,one on each end of the points. Loosen those two screws,and the body of the point will move,one way to "open": the gap,the other to "close" the gap. With feeler gauge between the points contact,close untill you feel slight resistance when moving the gauge back and forth,and tighten the set screws on the points body.

They are not a rocket ship, but I would expect closer to 50mph .
need good air filter element.
ignition advance springs can cause a problem, or the advance may be sticking.
need good battery, recheck point gap, timing and valve clearance.
check for exhaust blockage(see if it revs better without the muffler)

You have probably tried most of these, but there is not much else, they should rev sweetly right though the rev range

The Honda CB100 has a 4-stroke, single cylinder engine. It runs on straight gasoline, so you don't need to add any 2-stroke premix when you fuel up. On the other hand, you'll probably want to check your valve clearances about every 1500 miles or so--these little engines get run pretty hard, and valves out of adjustment will rob you of desperately needed power. With only 1 cylinder and 2 valves, this doesn't take long at all, once you've done the job a few times.

If you are in gear when your rear tire locks up, that will also stall out your engine. Conversely, if your engine seized up while you were in gear, that would lock up your rear wheel from the other direction. However, as it sounds like you can restart your engine, that's probably not the case. One way to check is that if your wheel starts to lock up, immediately pull in the clutch. Your engine should keep running, even as your rear wheel is skidding along.

If the problem is in your rear wheel, there aren't a whole lot of things to check. This bike uses a rear drum brake, so check to see that's not binding in any way. I suspect that it won't be. A stronger possibility is that your rear bearings are worn out or insufficiently lubed. If they get hot enough and expand enough, they'll seize up your rear wheel. Pulling the rear wheel and cleaning / lubing the bearings would eliminate this possibility. If the bearings are dark colored and/or have flat spots, that's a sure sign that they've been abused and need to be replaced. A third possibility that comes to mind is that your chain and rear sprocket might be excessively worn. An old chain, with one or more rusty links, could kink up and jam. I once bought a bike with a nasty old chain and it did this on occasion. It would work fine for a while, but then kink up. Replacing the chain (and the sprockets, because they, too, were very worn) solved the problem for that bike.

Sounds like the jets are clogged in the carburetor. Try running some carburetor cleaner through it first. If that doesn't help then you will need to have the carburetor rebuilt. Hope this helps. Good luck.

Have you tryed Ebay.com?

It will be close to the battery and have wires running to the battery. The closest image I could find is from a 1976 CB125. It looks like Babbitt's has one in stock. $80.00 US. Go to the site below where you can see a parts diagram for your specific bike. You will select the actual brand, year, model, etc., once you go to the site. Part numbers and prices are also shown. You can order parts from this site. In the event no price is shown on a particular part and/or the notation "Not Available" is in the description, the part is not in stock. www.babbittsonline.com/pages/parts/viewbybrandand/parts.aspx

You should be able to adapt the '76 rectifier if it is not exactly the same.
Can I get a “very helpful” rating on this answer?

www.ronayers.com
and /or your local dealer.
Ron Ayers is what i have used in the past for my tire purchases

Sounds like time for a new battery. A battery is only good for about two years. Then it starts to loose it's charge quickly and then it will not take a charge. Check the water level in each cell. The water should cover the top of the plates in each cell. No water = no charge. Install a new battery and start the engine. Put a volt Ohmmeter on the terminals as the bike revs to around 2500 rpm. The meter should show 14+ volts. If only 12 or less, the charging system should be checked.

Remove the water trap bowl at the bottom of the petcock, (gas valve). Is there any water or trash in the bowl? Drain a cup of gas from the tank. Is there any water or trash in the cup? Dump it, clean it and re-mount it, ( not all bikes have a water trap bowl ).

Drain the carburetor. There should be a screw on the lower side or bottom of the carb float bowl. Remove the screw then replace it after the fuel drains. Turn the gas back on and wait a minute for the carb to fill with gas. Install a new stock NGK spark plug and try to start the engine. If the bike doesn't start and run properly then shut off the gas and remove the carburetor from the engine.

Remove the float bowl and clean the entire carb with a spray carb cleaner from the auto parts store. Wear protective goggles to avoid getting spray in your eyes. Spray into all the little airways and fittings in the carb. Remove the idle screw and the air screw on the outside throat of the carb and spray into the screw holes as well.
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Be sure to put these two screws back in the same hole they came out of. IMPORTANT > do not tighten these two adjusters down. Only screw these in until they LIGHTLY seat. Now turn each adjuster one and one half turns outward. Put the rest of the carb back together, clean the air filter and install the carb. Let the float bowl fill then start the engine.

A “very helpful” rating for this answer? Thanks!

Hi there sandy am wondering if you fixed the problem and what was the cause of the power loss as I have exactly same problem but the bike squeels bad if it sees a hill

It sounds like the normal gas supply tube is stopped up. You could remove the gas valve from the tank and clean it, or you could just leave the setting on reserve all the time. If you are hesitant about removing the valve you could try applying air pressure to the gas supply line to blow the obstruction into the tank, but removing the valve is best. If you still have problems let me know and I will look at my old CT70 for more ideas. The way the valve works is that it has two lnlets, one at the very bottom of the tank for the reserve setting and the other a little higher up, so that it will quit taking in gas while there is still some left while on that setting. A problem like yours may indicate that you have rust or sediment in your tank.