86 vfr700-a running issue

Problem. Starting the engine is no problem. When it runs one or two cylinders cuts out, the cutout is random. sometimes cylinder 1, or 2, 3 or 4, sometimes 1 and 4, sometimes 2 and 3. Bike has new battery, new fuel pump. I've determined the cylinder not firing by measuring the exhaust pipe temps. I have rebuilt the carbs and have had them apart many times. Thinking this an electrical issue. tested the stator by ohming the three wires, the reading are within specs. anyone have any idea what is happening.

 

Hello.

I would have thought the stator affected charging only, but I guess you have confirmed the battery is charging OK.

Have you replaced the plugs? Old ones could be a problem.

How are the coils, in terms of basic resistance checks? How are the connections between coils and ignition box? In the UK, we have a great time clearing out damp-related corrosion from connectors, and it is well worth the check.

How long does the engine run for, from cold, before the problem manifests? Does it appear to be heat-related, or does the issue crop up sooner (pointing to vibration effects, maybe)?

 

The stator supplies power to the coils and everything else. Have yet to check whether or not each leg coming off of the stator is 120v AC. The plugs are good (new), the coils match specs, Don't have the the Honda tool to check the ignition module, but do have a spare(runs badly with either brain box). The problem is immediate upon starting, does not change with engine temperature. I have cleaned the connections on the coils but think I should replace the wires from the brain box.

 

Intermittent cut-out on random pots... Seems like vibration. It could be worth wiggling all related wiring while the bike is running, to check for a response (eg. pot cutting-in 0r -out).

I must check my manual: does the stator supply the firing pulse, rather than the battery powering the brain and then coils? I know that a CX500 can run without a battery, as one of the stator windings does just this... Still - it would be all or nothing, I think.

 

I ran my racebike without any part of the charging system, including the stator. Battery powers everything.

Pulse coils are on the starter clutch side.

 

As above, bike should start and run on battery power alone if you have at least 12.6 volts .

Suggest you go to the plug on the cdi box and inspect wiring.

 

yes, replaced plugs, coils resistance in limits, connections clean all wires OK no breaks or shorts. Bike runs badly from cold or hot start, does not improve upon warming. general thoughts; carb air leak, stator bad and shorting to engine and frame, float levels inconsistent or high or low. Manometer shows low vacuum all cylinders at 1500 rpm. fuel pump is new and working fine. Key "on" not running, no fuel leaks or odor.

 

yes, replaced plugs, coils resistance in limits, connections clean all wires OK no breaks or shorts. Bike runs badly from cold or hot start, does not improve upon warming. general thoughts; carb air leak, stator bad and shorting to engine and frame, float levels inconsistent or high or low. Manometer shows low vacuum all cylinders at 1500 rpm. fuel pump is new and working fine. Key "on" not running, no fuel leaks or odor.

 

fresh fuel present in sufficient quantity ?

 

Just a thought jesii, have you checked your earth wires & connections

 

yes, fresh fuel and plenty of it. Engine uses alot of fuel when running, no leaks from lines or carbs.

 

cleaned and repaired ground connections. Check for voltage "leakage" with key off. shows milivolts, do not remember reading.

 

Another thing, it could be that your spark unit (30400-ML7-601) is fubared. Can you obtain another unit to test this hypothesis.
And have you checked your choke circuit is operating correctly.

 

I have a second spark unit, same results.

 

replaced all parts in choke (fuel enricher) circuit.

 

Thank you all for your thoughts, I'll keep "picking away" at the problem and hope I stumble upon something.

 

Have you checked valve clearances, also test for compression on each cylinder. Ht leads are these ok.
Inlet manifold rubbers do not sit properly unless you fit the carbs as per Honda manual.
Clutching at straws here I know but you might have start right back at beginning with simple things first like checking colour of each spark plug this can tell you a lot as i am sure you know.

 

check compression first. If ok, then look at leads.

 

Pulse generator and its connections (above the clutch cover)? The FSM check is pretty simple.

(BTW, you should be able to take the stator, etc. out of the equation. The charging system only supplies juice to the battery — the battery powers everything)

Joe in IL
V4 Dreams (.com)