Help with '84 VF700F

Hi All,

Well, about a year ago I prepped my 1984 VF700F for some fun rides and some distance rides. A little while later, she quit running right, in the neighborhood so I managed to get her back home without having to push ... yay. After weeks of general t-shooting (pulse generator replacement, coil/wires/plugs replaced, even picked up one used spark unit off Ebay) I got nowhere. At wits end and totally frustrated, I bought an '07 and promised myself I would get back to my '84. Betwixt then & now I rebuilt the carbs.

So, this weekend I put enough of her (my '84) back together to try t-shooting again (also installed a new Yuasa AGM battery). Same f'in problem as when I last worked on her. Without the choke (fuel enrichment circuit) on, I can crank all day (seems like) without so much as a chuff, with the choke on she'll actually kind of start/run (< 10 secs) in a ragged fashion, as if not all cylinders are firing. If I disconnect the fuel line and direct it into a jar when I crank the engine, I get pulses of fuel with each cycle.

So what now? I don't want to put a bullet in her, I kind of love the old girl. Can't sell her for much, especially in her present condition. I'm considering picking up a hobby priced oscilloscope and taking a closer look at the spark units. This would actually be cheaper than buying 2 spark units to try out. Has anyone analyzed these spark units before?

Obviously I will appreciate any help I can get although I may have received all there is a year ago :^).

TIA,
Anders

 

I was given this web site by Gunnar it has helped me hope it will help you out.

http://users.rcn.com/kochc/moto/spark/ig_repair.html

 

Check the fuel pump. I had a similar issue with my 84 700 and sure enough the fuel pump had gone bad. The fuel pumps are garbage. I ended up going with a gravity feed setup and the bike runs soooo much better now. The fuel pump only puts out a couple of psi of pressure and it is not really needed. If you search on here you should be able to find several threads covering this issue.

 

I’ve rebuilt by bike, gosh, I don’t know how many time. Once, cause I had to, the rest, well, just for fun, and cleaning. Perhaps I can help.

Engine needs three things to run, (yes I know we all know this); Spark, fuel, and air.
So, lets just do process of elimination here, and fix your problem.

Air – take the filter out of your air box, and ensure the feeding ports are clean. (light alcohol works fine. – There “Air” section is covered. If the bike runs now, then you need to replace your air filter, and ensure your air path is clear.

Fuel – Using carburetors, get a jar of unleaded gasoline, (I use the premium stuff, for a good hot fire, just for this test). Disconnect your fuel line, and hold the line in the jar, above the carburetors, for a more of a gravity feed system. (Remember your engine needs the fuel to be a mist, and not just dumped in.) If the bike runs, then your problem is getting your fuel to the engine.. check the fuel pump, fuel filter, and the filter at the bottom of your gas tank.
Pull your jets and clean them. They can get dirty easy. Running bad fuel, sugar in your tank, letting your tank get too empty, or running out, etc etc. If your bike runs after cleaning, congratulations, you just fixed your problem.
Buy a can of octane boost, and put some in your gas tank. Turn your start switch to the off position, and crank it a few times. Let the bike sit for ~ 20 mins. Set the start switch to on, and crank the engine. If it starts, or starts and stops after a few mins, your engine is in severe need of a total tear down. Piston heads, ring seals, cylinder walls, oil, etc etc. BUT before you do this, proceed to check the spark.

Spark – this one’s really easy.
First, put a meter on your battery. Ensure your battery is good.
Check the fuse in your starter solenoid. If its good, then put a meter on the ground of the battery, and the positive of the starter solenoid. Crank the engine, you should get 14V. If not, replace your starter solenoid.
Double check your manual, but your firing sequence should be something like, 1, 3, 2, 4. Not all bikes are the same so double check this. Ensure your wiring from the sending units are wired correctly… I.e. wire 1 is plugged into cylinder 1, wire 2 is plugged into cylinder 2 etc etc. If the bike starts, then your problem was your wires were mixed up. Hey, it happens.
Buy one spark plug. Disconnect Wire 1 and put on the new spark plug. Lay the spark plug (now plugged into the wire), on something metal. The engine casing is fine, as long as you have metal and not paint. (some areas of the frame will work too) crank the engine slowly. Watch for a spark. Do you get one? If yes, reconnect your spark wire, and move to the next one, reusing the same known, good spark plug. If one doesn’t fire, then buy check that sending unit for a broken wire, or damage. If none can be seen, or repaired, then buy a new one. (I have seen sending units with the wires attached, but the post is broken off inside. What a pain to find)
If all 4 wires fire, then pull all your spark plugs, and replace the spark plugs. (buy the pre-gapped ones).
So far, we have ensured you get a spark, and that your spark sequence is correct.

Now from Engine function there are a few items which could be indicators as well. I will list a few.
Backpressure: open the exhaust headers to ensure no restriction is present.
Starter motor: this motor could be wearing down. Pull it and check it for movement.
Rectifier: loosing power converted from the generator is not going to keep the bike running past a few seconds.
Generator: get your meter out again, and check. If you had to rewire it recently, check the wiring, and the connection to ensure you aren’t over charging or under charging the battery and rectifier
Fuse panel: I know its stupid, but check it. You’d be surprised to learn that some systems are inter connected with a common ground.

Good luck! Keep us informed of your progress.

 

Check the wire harness

Hey

If you can nearly be sure that every thing works and you have spark on every plug.I would check then wires if they are ok then I would the pressure on the cylinders if that is okay put just 1-2 ml of gasoline into the cylinders put the spark plugs back on and crank if nothing happens then you know it is the spark.The site witch Volks6000 has given up use it to find out.But remember that spark unit for cylinder 1&3 controls also 2&4 so if that is damaged nothing happens

Best regards

Gunnar

 

Forgot one thing

Hey

I forgot that you need to install puls genator right in that is right distence from the rotor wheel if that is wrong you will not have any spark.You said that you changed the spark wires did you check out the resistors inside the spark caps.

Best regards

Gunnar

 

Thanx for all the responses/advice. I'll start this weekend with fresh fuel and fully charged battery and go from there :^).

Anders

 

IF YOU could drag it into my garage, i feel certain i could fix it.......

 

got it !

thanks for the support !

 

What was the problem?

 

Vfr 87 Resurrection

No spark !

 

What part was bad? Just curious so that if I have a problem with mine I know where to look.

 

Vfr Resurrection

I was thinking that it could be the cdi unit !

 

Thanks for the info

 

Hi,

Well, today I found time to do a little t-shooting. Using an external spark plug, I checked each coil wire for spark. Moving the plug from 1 - 4, each gave a spark that I could see in a fairly well lit (not total daylight) garage. The plug I grabbed was gapped at .40 - .42.

So now it's on to fuel methinks?

Anders

 

have you ever do anything with the carbs.... ie rebuild . I'd pull them and give them a once over cleaning with lots of carb cleaner and air. if you have a fuel pump then jumper the relay to see if the pump is working like its supposed to. also check to make sure that the tank is venting. fuel filter new???

 

Hi Volks6000,

I have an aux. fuel tank that I'll hang above the bike and feed directly to the carbs fuel line, this will bypass the fuel tank and pump altogether. I plan to check the float level as well, with one of those level gauges made specifically for this purpose. And I'll go over the carbs as suggested.

Thanx,
ACE

 

A piece of clear tubing that costs 10 cents?

 

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