The Service Dept

THE SERVICE DEPT

WALT FULTON

DO WE WIN?

I am running a contest to see which of my favorite bike magazines can be of the greatest degree of assistance in my current dilemma. The winner will receive my undying gratitude, the runners-up the slightly diminished returns. Please, now, don’t despair of winning the grand prize and drop out, I need all the help I can get.

My bike is (was) a ‘69 CL450 Honda. Medical history: While the engine was totally stock, but with Jardine headers, Bates Glasspak megaphones, and Filtrons, it experienced high-speed miss under load-usually from 7000, sometimes higher-that I thought to be an ignition problem, but couldn’t trace. The engine was rebuilt, stock except for port and chamber matching and polishing (no reshaping), Mega-cycle Engineering’s “PM 2020” road race cams, and an ignition total advance increase to 48 degrees by bending weight stops so the idle setting remains the same. This aggravated the above problem, changing it from a miss to a complete cut-out at just over 7000. Ignition scope when tested appeared to be excellent.

I finally traced the problem to the carbs by running it on the Dyno and peering down its throats. The answer: The slide in one carb was not opening all the way. I experimented with new and used slides and tops on carbs, but with no significant change. All this time the bike idled smoothly and cleanly at the normal 1100 rpm, both with stock and PM cams. I replaced that carb with one from a new K6 and still had a problem. I replaced the other carb. Beautiful-runs strong, no miss. Except for one thing: It refuses to idle

properly.

With number 150 mains and 38 or 40 or 42 pilot/slow jets, the idle needle set at anything more than open enough to run (about 1/3-1/2 turn out), and the idle stop screws backed out, the bike will start easily and can be held at idle with the throttle. Speed screws can then be adjusted to hold idle, with the carb vacuum balanced (via my custom closed-end water manometer), and everything’s fine. Until I open the throttle. At all. Then the speed climbs to 3000 and will not come down until either speed screw is backed off enough-about 1/4 turn, at which point the speed will fall to idle. Quickly turning the screw back will hold idle, until the next turn of the throttle. Twiddling throttle shafts does nothing, so, with the above, I would conclude it’s not a cable-slack problem.

Going up on the pilot/slow jets seemed to help, but with 42s it doesn’t run clean until 4500, and after shutting off normally, the plugs-B9Es-are very sooty-black and dry.

As near as I can tell, there are no air leaks between carb and engine: rubber spigots are silicone-sealed to the head; clamps on the spigots have been tried in various positions, with various tightness; manometer plugs are screws with Orings and silicone grease under the heads (same as the old carbs, which idled).

The valves are set cold to PM specs — .003 running clearance-with a “tenths” dial indicator, and, due to modifications of pivot shafts, do not change their settings, as stock 450s are wont to do. So, no tight intakes, and even if so, wouldn’t the old carbs have been affected the same way?

I have also tried the needles/needle jets from the old carbs. No change.

As near as I can tell, the K6 carbs differ from my earlier ones only in details: different needle /needle jet; different mixture screw; larger main and idle air jets; two holes instead of three under the throttle plate for off-idle operation; different speed screw stops; different number on the throttle plate. The only ones that appear possibly relevant are needle and jet, air jets, mixture screw, and off idle holes. But which, if any, and why?

I’ve run into two other K6s that had this problem, one new, one used, but it could be tuned out of both, at least mostly, by judicious twiddling of mixture and speed screws. I should be so lucky. The only twiddling results I’ve had were that the bike would hold idle if the carbs were grossly unbalanced, but that ’s no solution.

A digression: I noticed strange noises for some time before teardown about 15,000 miles). I found them to be due to rubber in the cam chain idler sprockets that had been eaten by mysterious gremlins, allowing the sprockets to wobble laterally and get chewed upon. No, I never “helped” the chain tension. It’s been adjusted hot and cold. I use Valvoline 20-50 racing, which, according to local Valvoline people, is identical to “20-50 four-cycle motorcycle oil. ” I have heard of a Honda service bulletin in the past that stated certain oils and/or oil additives could cause this, but just exactly which ones they failed to mention, and my local shop contacts couldn’t find it.

I’ve been fighting first the miss and then the idle since last July, I’m almost bald, my fingernails are bloody stubs, my therapy bills are mounting, and I’d dearly love to get some riding in without having to worry about what happens when I come to a stop, which even the best of us must occasionally df^J

Gordon B. Church Seattle, Wash.

Totally stock except for....The items that you mentioned have a direct effect on the performance of the CV carburetors.

These mixers are governed by the air flow through the venturi, a change in the exhaust system or cam results in different engine pressures.

Without having a stock bike it is difficult to diagnose your problem; you have thrown in several unknowns. For starters, though, we would look for a stuck slide. By changing carbs you have eliminated this. Next, how about the ignition advance? It is possible that the springs on the unit are not strong enough to return the advance to its idle position, or they may be stuck in^Mie position. This can be corrected b;^ftting a new spring or doubling up on them.

If this doesn’t help matters, we suggest that you start all over again from stock and go from there.

CARBURETOR DIAPHRAGMS

I am the proud but somewhat disillusioned owner of a 1968 350cc Honda. Upon examination of the carburetor diaphragms, I found serious splits in the rubber, obviously the cause of recent bad performance.

I have called all the dealers on the peninsula, but I am unable to locate a single replacement. Worse than that, I have been told that Honda has ceased production of these items.

I have tried fixing the diaphragms with silicone glue, but this is Æ^y temporary at best.

I should like to solicit your help and advice in uncovering the full story. It is inconceivable to me that a manufacturer like Honda could pull a stunt like this. I can only assume that the computer has somehow swallowed the part number.

In the event that the real replacement parts are unavailable, I can think of two alternatives and perhaps you can add to the list. Will the later diaphragms work in the early ‘68 carb? If not, I could change to the new SL diaphragmtype carburetor. I am a little wary of this since lam unaware of the full effect this change may have on performance, etc. Also .what mods would have to be made in order to make the SL carbs fit?

This whole thing is especially aggravating to me in view of the fact that I am really a Norton fan, but resisted the temptation on the basis of the av^kLbility of Honda parts.

Keith Taylor San Jose, CA

Honda’s parts situation isn’t as bad as it seems. We checked with American Honda in regard to your problem and the^informed us that the parts you req^M have not been discontinued. Besides that, all diaphragms for CL350s from the earliest to the latest, are interchangeable.

Perhaps one reason for this misunderstanding has to do with the addition of a separate parts book for carburetor pieces. Unfortunately, not all dealers keep up on these things. We suggest that you check back with a good dealer in your area and try once again, armed with this information.

If this still leaves you without satisfaction and the parts, then take pen in hand and write to American Honda, Customer Relations, 100 W. Alondra, Gardena, CA 90247. This last resort will get you results! Irfl