Question The bike runs however the engine does not want to come to a slow idle. Carbs have new parts. Could the the ignition springs that control advance be weak or broken and thus timing stays advanced?
AnswerM. Miller, this condition can come from a number of sources.
1) Weak/broken camsprocket advancer return springs.
2) Ignition timing not set properly. Ideally, the spark timing should be at the F mark at idle (set statically) and the advancer should swing the spark lead out to 45 degrees above 3300 rpm and then return to retarded status at idle. With weak/broken return springs, the spark timing jumps out early and has a tendency not to return fully to the F mark. When spark timing is set at F and LF marks at idle, you will find that the spark timing advances differently at full advance from side to side. The cause of this is that the point cam, which runs in the right side camshaft has a sloppy fit, so the point cam wobbles around at various engine speeds, causing variations in spark timing. All you can really do, without repairing the springs and loose point cam is to set the ignition timing at full advance on both sides. Those are the II marks on the rotor, approximately 45 degrees out from the T and LT marks. You have to do this with the engine running, using a dynamic auto timing light. Once both sides are dialed in, you will probably find that the idle timing is split with one side about 5 degrees retarded from the opposite side. This will cause a erratic idle and difficulty setting idle mixture screws, as the spark timing variances are changing the vacuum signal to the carburetors.
3) Idle speed set too high. Must be adjusted AFTER the spark timing is set and with a hot engine. These bikes should require choke and run a little rough until they are warmed up. Be sure that the throttle cable is not pinched, kinked, restricted or rusted internally, causing the cables to hang up inside the housings.
4) Air leaks in the intake tract, stemming from flattened out O-rings, warped carb mounting flanges and cracked insulators.
5) Carburetor slides sticking in the bores, due to warped flanges and overtightening of the flange nuts. Flatten out the flanges with a broad single cut file so the are smooth and even. Install new o-rings, and gently tighten the nuts down. If the slides continue to stick, you will have to determine the location of the high spots and then gently sand them down.
6) If you put KEYSTER carb kits in the carburetors, the metering may not be correct for that application. In the past I have found the kits to be way out of calibration, but they are supposed to have fixed that by now.
The only way to really have the bike run correctly is to ensure that there is minimum slop in the point cam/camshaft interface, plus make sure that the return springs are snapping the weights back all the way at idle. There is inherent looseness in the design, so they are often a few degrees of slop, even with new parts.
Once the spring tension issues are dealt with, you can overcome the point cam looseness by installing one of our E-ignition systems, which are magnetically triggered and don't care how much slop there is in the point cam fit. Not a cheap date at around $300, it is the best modification/improvement you can make to these engines, allowing for accurate timing at idle and full advance, plus no maintenance issues after installation.
Bill Silver
www.vintagehonda.com
