engine miss

gotta 78kz650b2....dyna ignition, wires, coil mod....started missing and popping the other night and the next day it progressively got worse....at 3/4 to WOT pulled and ran great....just cruising or at idle it popped, backfired, spit, sputtered.....I adjusted the cam chain, changed plugs, but still does it...I don't think it is a fuel issue, if so, it wouldn't run at WOT...I was thinking maybe timing advancer?????...any suggestions

Some thoughts --

Pulling and running great at 3/4 to WOT suggests compression and valve clearance okay, and same for timing advancer likely being okay.

Were any old plugs sooty and fouled?

Would suspect excessively rich mixture due to either (1) pilot screws set too rich, (2) service fuel level in float bowl being too high, (3) clogged passage in pilot circuit, (4) air leak at carb holder or vacuum nipple cap, or (5) loose clamp or bad connection between carb and carb holder.

Is an in-line fuel filter being used?

Good Luck?

nope....plugs looked good........no soot of fouling....yep inline filter.....I'm still stumped.....

Because old plugs looked good, thinking maybe pilot mixture is too lean.

Which carbs -- side located pilot air screw OR bottom located pilot mixture screw?

If pilot circuit mixture is too lean, turn side located pilot screw IN to richen OR turn bottom located pilot screw OUT to richen.

If it's a carb issue, am still suspicious of the pilot circuit. Possible clogged (1) fuel passage in pilot circuit, (2)pilot jet, or (3) pilot jet outlet and/or by-pass.

Too low service fuel level in float bowl could also cause excessively lean mixture.

Perhaps a low battery, which can cause more problems at idle and lower speeds. Has voltage across battery terminals been checked at idle and at 4000 rpm? Has fluid level and specific gravity been checked? Possibly load tested?

Possible fuel contamination, such as water in the gas?

Or maybe None of the Above!

But somebody here will have the correct solution.

Good Luck!

checked the battery at idle....11.5 volts......at 4000rpm.....12.5 volts.......switched batteries with my other kz650 that had 12.5 at idle and 14.5 at 4000.....same thing...........charging issues............thanks Patton............off to the electrical section I go..............

Thanks for the report.

Would assure good negative battery terminal to ground connection and wiring into and out of regulator.

Perhaps a faulty regulator? [Am unfamilar with testing procedure in this application -- hope FSM is available for directions]

If needed: Z1E Reg

Good Luck!

Post edited by: Patton, at: 2007/10/18 18:03