Service
SERVICE
Thy bowl runneth over
I own a 1978 Suzuki GS750 with an R.C. pipe, new jetting, K&Ns, and a new head and valves. The problem is: I gas-foul plugs like crazy. Part of the problem is a faulty petcock, which 1 replaced. Still, when the bike sits for more than 10 minutes, the gas in the fuel line, from the fuel filter to the carbs, vanishes into the carburetors, but nothing comes out the overflow lines. My dealer says it can’t be happening, but I’m the one who rides it. Any suggestions?
Michael Gipson Woodlake, California
One way or another, the fuel is entering the combustion chambers and wetting the plugs by seeping past the float needles in one or more of the carburetors. Since you did not tell us whether just one of your plugs tends to get wet or if all of them do so, or how badly the plugs are fouled, it's hard for us to be more precise about a suggested cure. But it sounds as if you definitely need to check the float in each affected cylinder's carburetor. Replace the float if it doesn't (float, that is), and replace the float needle and seat in any case.
On the other hand, the comparatively small volume of gasoline involved here (the amount in the fuel line between the fuel filter and the carbs) should not be enough to foul plugs on regular basis. This indicates that your Suzuki might have a weak coil or some other resistance in the ignition system that is preventing a sufficiently hot spark from reaching the plugs, thereby allowing them to foul too easily. Most dealers have diagnostic equipment that will test the strength of a coil's spark.
If the coil is suspect in any way, either replace it or consider replacing the entire ignition system with one of the aftermarket ignitions that generate much hotter sparks.
Calming the killer Beeza
You printed a letter in your August Service column from Jerry O’Shaughnessy relating difficulties with his BSA Hornet. Please let me contribute some helpful hints from one BSA owner to another.
1) Lay off the nasty names. Try something nicer, like “Beeza,” “Birmingham vibrator,” etc. These things listen, and their feelings are easily hurt. This leads to vengeance.
2) Forget anything other than a Champion N-3 or NGK B8E plug. An N-5 is too hot, so live with the fouling.
3) Since these bikes were meant for high-octane, leaded fuel, this is what you must use. Of course, since you must blend your fuel, you can be creative. I suggest 45% unleaded high-test, 45% aviation 100LL (blue) and 10% ethanol. The ethanol limits overheating tendencies, which can be quite pronounced.
4) Make carburetor spacers out of '/2-inch Micarta for insulation (same reason).
5) You have (presumably) had seizures, so I suspect your piston-towall clearance is too tight, pistons not properly cam-ground, etc. Immediate disassembly is called for to rectify the damage this has caused. You might be able to save your new pistons (not likely). Remember, run ’em real loose because of marginal cooling with this motor. Also, stick with stock pistons and don’t raise the compression ratio. If all you can get is 10:1, make a head gasket of thicker copper sheet to reduce the ratio to about 9:1.
6) Finally, stick with stock jet sizes as called for in the manual.
And please, love the old girl. She will surely respond and reward you by returning a piece of your youth.
Robert W. Luedeman
Signal Hill, California
Bucking bronco
I’m experiencing an unpleasant “hobby-horse” ride on (the “smooth” California cement) freeways with my ’85 Honda VF700F Interceptor. I do not understand suspension dynamics and why this is happening, and would appreciate a recommended procedure (and rationale) for manipulating suspension settings to minimize this effect. I weigh 185 pounds, and the settings I can adjust are: 1) TRAC anti-dive (4 positions); 2) front suspension air pressure (0-6 psi); 3) front rebound damping (3 positions); 4) rear suspension air pressure (0-43 psi); 5)
rear rebound damping (4 positions). Are there suspension upgrades you could recommend to improve the freeway ride?
Pete Ward
La Jolla, California
Most of your rough-ride problem is the result of excessive seal-to-shaft friction in the stock Showa rear shock.
The seal fits so snugly around the shaft that the shock cannot compress and extend easily and freely enough; thus, the rear suspension is effectively locked on small bumps and ripples, causing the back of the bike to jounce up and down. On larger bumps, the force of impact is great enough to make the shaft move, so the suspension more effectively absorbs the bumps.
The best solution is to replace the rear shock. We know from experience that Works Performance (8730 Shirley Ave., Northridge, CA 91324) makes a shock that greatly smoothes the ride and provides better overall rear-wheel control; but a few other companies also offer rear shocks for VF700/750F Interceptors, including Fox Factory (544 McGlincy Lane, Campbell, CA 95008) and Progressive Suspension ( 11129 Ave. G, Hesperia, CA 92345). Presumably, those shocks will also improve your bike's ride.
You'll probably find that once the new shock is in place, the ride is acceptably smooth. But if it isn 7, consider installing new fork springs, either from Progressive or Works Performance, with 0 psi of air pressure in both legs and the rebound damping set on the No. I or No. 2 position. Don't bother fiddling with the TRAC settings, since they have an effect only while the front brake is applied. 0
