Bike drops one cylinder when cruising

[craigcjc]

Hi all, maybe someone out there has had this problem, bike is an 86 Honda Vtwin 750 shadow, riding round town etc no problem but when I get on motorway and cruise the bike drops a cylinder, I slow down and it comes back to two. Thought it may be the coils so I tested them and the resistance is fine, still believe that it's electrical or could it be a tappet problem?

[caseye]

Hi all, maybe someone out there has had this problem, bike is an 86 Honda Vtwin 750 shadow, riding round town etc no problem but when I get on motorway and cruise the bike drops a cylinder, I slow down and it comes back to two. Thought it may be the coils so I tested them and the resistance is fine, still believe that it's electrical or could it be a tappet problem?

Look out for Leathel here in KB he has had same bike and similar problems.

[leathel]

my issues stemmed from a fuel pump putting to much pressure on the float valves causing them to leek and flood the carbs a little, fouled the plugs as a result which is what gave the miss (fouled plugs)

It does sound electrical and I would also check the leads and plugs for issues (look for tall tail carbon traces)

Also check pulse generator plugs etc to ensure they all have good connections

[craigcjc]

just took bike for a spin down motorway left mt wellington got as far as tamaki off ramp drpped cylinder again then no electrical at all no lights on dash etc. waited a minute then bike started fine. cruised back great south road no issues. So it seems that when bike is under load ie overdrive and constant cruising is when it happens.

Anyone know a good electrical bike guy that may be able to sort this out.

cheers

[spanner spinner]

you could have a faulty Reg/Rec unit or charge coils, I have seen these units drop one leg of the three in the charge circuit so that they still charge but at a reduced current rate. This leads to low power output a low revs and weird electrical issues like misfiring and cylinders cutting out. The coil with the longest wiring run will always drop out first. May not be this but worth getting check so it can be eliminated. I use to do this as a job so the check is not just a battery voltage check as a full load test needs to be carried out on the charge circuit. The best way of checking is to remove the battery from circuit after the engine is started and use a large capacitor to carry the charge load (capacitor is wired up as if it is the battery). You then monitor the voltage across the battery main leads the charge circuit should maintain better than 13 volts at idle with the lights and indicators on. If the voltage drops start looking at the charge circuit. You may also have a burnt connector in the stator wiring remove the l/h side cover and look for a plug with three yellow wires going into it, inspect this plug for burning. if whoever you take your bike to looks oddly at you when you ask for a load test on the charge circuit (they may have a charge load tester as well which will do the same job just as well as the capacitor test) go to the next place.

[craigcjc]

thanks for the info will get it back to shop for testing. Ill check the stator wiring as well. The fact the electrics died all together i think points to electrics and load as when the coils cool the bike cruises fine but under constant load in OD it fails. Want to be sure before i splash out on new coils cause they are not cheap on ebay. Anyone sell coils for this sort of bike in NZ.

[rok-the-boat]

Undo everything that has an earth connection and clean it. Sometimes paint gets in the way. It could be a simple as that ... if lucky ...