Vintage Hondas are really cool. I am biased of course since I spent much of the first half of my career coddling these simple yet elegant machines in Honda dealerships, and today folks with these bikes gravitate to me looking for help with them, which they get in my shop in Arizona. These ignition systems are denigrated by many, but they are actually very high quality and even high performance, once serviced correctly. Yeah, basic yet so pretty; so appealing and so responsive to proper attention. And these are admirable machines, and even more so today in a market of such high specialization and dizzying technology. One thing I learned early on while making my living working on SOHC fours was how important it is to correctly set up those ignition points. I have written an article on my website and in addition offer three booklets that focus heavily on ignition troubleshooting and in one case specifically on the Honda SOHC four cylinder point ignition. It's an important system to understand and maintain.
I rebuild a lot of SOHC four carburetors, and as I say, do special services on the bikes even today. As with all my carburetor customers, I emphasize with SOHC four clients the importance of cylinder compression, valve adjustment, and of course, ignition timing and ignition system condition. Many of my carburetor customers I think assume a little too much when it comes to their ignition systems. I once dealt with a customer who sent me back his carbs to look at a second time, and after almost 12 months of trying to help him, it came to light that he had in fact overlooked his ignition timing, all the while assuring me repeatedly that he had checked it.
Let me emphasize this in detail. The Honda SOHC four ignition is a really good system, if you know how to set it up, which is not at all an intuitive thing. Here are some examples of what I mean. Get my Optimizing the Honda SOHC Four Ignition book to get even more.
- The stock TEC or ND points are the only way to go. Honda long ago stopped selling them, which is too bad. You have two solutions. David Silver Spares has a limited stock of the original, TEC and ND brand points. Or you can buy used. Either way, it's well worth it. The Diachi points everyone uses are crap, pure and simple. The following pictures are from my book, Optimizing the Honda SOHC Four Ignition. Note the difference in construction. The pivots are really badly made. The points' bases are not flat (so when you tighten their screws the timing changes drastically).
- The adjustment ethic is out of the box for most people. The correct procedure is: gap, then time 1/4 using the base plate, then time 2/3 using the sub-plate, and lastly recheck gap. A number of things make this process a chore for most folks. The first is that nothing is mounted on center. Not the base plate, not the sub-plates, and not the points themselves. This means every adjustment of one affects the other because they all float on their own centers, irrespective of the crankshaft and irrespective of each other. A pro learns to deal with it, and I show some tricks in my booklet. First timers however usually go round and round and many end up very frustrated.
- Don't major in the minors, that is, don't focus on the relatively unimportant things. Some folks fixate on point gap. That's not it. The factory specified a range for a reason. It is acceptable to have the gap anywhere within the range, or even slightly outside it. Spend your energies on timing, the most important thing. Get timing on the money at idle and at 2,500 rpm, or the specific rpm mentioned in the bike's service manual. That's right, two places, and this of course requires a strobe timing light. And, don't use gap to change timing. That works for dirt bikes but not for multipoint multicylinder road bikes. Timing is adjusted by moving the base plate and the sub-plate.
- Ignition system condition. Almost as important as ignition timing, look for cracked coils, loose plug wires, loose wire to cap connections, arcing from plug wires to the vehicle, and bad spark plug caps. And if you have aftermarket plug wires, make sure they are not non-metallic supressive wire type.
- You're not off the hook if you have a Dyna S ignition system. Although they negate the need to replace points at regular intervals, Dynas and other aftermarket systems present their own problems. Most folks fail to set Dynas up correctly during installation. They need to be timed, for one thing, but they also need to be modifed to properly fit Hondas. Plus, don't forget that Dynas can fail too (and in fact many are now, 20-30 years after installation). These are facts. So you shouldn't assume just because your ignition is electronic that it is working correctly. Or timed correctly.
Again, there is a lot more in my book, so check that out. If you are having me rebuild your SOHC Four carburetors you will hear me remind you about the due diligence items of cylinder compression, valve adjustment and ignition timing and condition.