84 VF750F - Starting Issues

Hey guys, sorry to rag on you with the same ol' thing here, but I'm trying to fire up the old beast, but can't seem to get her to start.

I cleaned the carbs before putting her away last season, and it ran (sort of, you could rev it) but now the only way I can get it to catch a couple puffs of ignition is with some starter fluid sprayed right into the air box (no filter)

I'm going to check out the carbs again when I get the chance, but I don't have a garage and I work on it outdoors (I live in Winnipeg, it's still snowing here)

Fresh battery, pretty sure I have spark (will check) and fuel pump is working.

Any help greatly appreciated!

Thanks guys!

 

Well, I'm in the same boat with my '84 VF700F. So far, my spark appears to be good but all she'll do when turned over is chuff a couple of times and die. If I figure out what's wrong with mine, before you figure out your issue, I'll let you know what I find. If you get there first, I'd appreciate knowing how yours got fixed :^).

Thx,
ACE

 

Just to keep in mind

Hey guys

Just so you will know.If your tachometer acts funny when you crank (then I mean goes up and down crazy) then it is probarly your spark unit 1&3 beacause that controls that and spark unit 2&4 controls fuel relay.But if were you I would set a wire over the fuel relay.And then switch on the bike and crank.It worked with my bike to get it started.Then later I found out my compression was bad.Also take the spark plug out,hold your finger over the hole and crank if you get gasoline on your finger then is not carbs or fuel pump.But if the spark plugs are wet with gasoline then is something wrong either with spark or carbs.To much gasoline or no spark.Dip your sparks plug (all four) in gasoline then light them let the burn for til the fire dies out.Then put them in.Your spark plugs should have light grey color on the electrode,if they are black then maybe oil is getting in the cylinder or mixture is too high.Then the last timing is your valves right set.The camshaft are problem with these bike or the old camshaft not heard about the aftermarket.But good luck.

Best regards

Gunnar

 

Thanks! Where would I put the wire over the fuel relay? Like short it out? I'll check that out, cause as you said my tach jumps around when cranking.

Thanks again!

 

Check this out

Hey

Here is a website witch helps you figure out those spark units:http://users.rcn.com/kochc/moto/spark/ig_repair.html if you need more help just ask.But when your tachometer jumps up and down it is most likely spark unit1&3 and that unit controls also spark unit 2&4 because your bike starts on cylinders 1 or 3.If I remember this right.And you put the wire over the plus pole that comes into the relay and the pole that goes out to the pump.I THINK not sure that it was between white and black.

Best regards

Gunnar

 

Ok so I swapped the two cdi boxes, but to seemingly no effect. I'm wondering if it's because the bike is really cold, as it's -4C here (like 25F) As I was cranking her, she would puff a bit more and more, but still wouldn't catch.

Also, the tach still jumped all over the place with either cdi plugged in.

I haven't tried the fuel relay wire trick you said, but will soon. Gotta charge the battery. I've brought the cdi units inside to thaw per se, and check for moisture.

I'll keep you updated, send anymore tips my way if you think of any.

Thanks guys!

 

Doesn´t do anything

Hey

You cannot switch the cdi boxes beacause they are diffrent.One is bigger and controls more then the other.But you can try to switch the spark coils witch connect to the spark wires are located in middle of the bike under the gastank.Mesure the pulse genator also and spark wires and send to me the results.

Best regards

Gunnar

 

I'm in agreement. If you have a spark, and you have fuel, and your battery is good, then its just cause its so cold. keep tryin.

 

Ok update. Now I'm pretty sure it's the carbs (@&#$!) as when I was checking for spark, which all cylinders had (although some weaker than others, will be changing the plugs) I put my finger over each spark plug hole to check for gas and compression. The rear left hand cylinder (2? 4?) was the only one that shot fuel out (literally sprayed it right out!)

Also something odd, when I took off the CDI units to let the warm up inside over night, I noticed very suspicious green electrical tape wrapped around the tops. so I took it off and shook out some water which had been sealed in by the tape. After blow drying them on low with a hair dryer and reconnected them to the bike and the jumping tach needle disappeared! ...for a while at least. After they had been hooked up for half an hour or so (trying to start the whole way through, had it fire up kinda on ether) it started to show the jumping tach needle problem again. It would stop however, when the engine would catch a puff on the cylinder that was receiving fuel.

Needless to say I'm going to be cleaning the carbs again.

Any other ideas? ;D

Thanks!

 

Only way to figure out CDI

Hey

Here you go.:http://users.rcn.com/kochc/moto/spark/ig_repair.html .This site helps figure out if your CDI box are toasted or not.But problem with VF700 ignition boxes is that they are in the worst place on the bike.If get new one or if you fix these ones seal with silicone or something other then tape.Because if water comes in those there will be problem like the tachometer problem.The carbs can just be full of shit.HAVE YOU TRIED THE FUEL TRICK.Might clean the carbs little bit.But I would keep my eyes on the CDI boxes.

Best regards

Gunnar

 

What does the fuel relay short trick do? Does it just un-restrict the amount of fuel pumped to the carbs upon starting? I'm pretty sure there's fuel in all the float bowls.

 

Hey

When you crank your engine your fuel relay send pulse signal to your pump.When you set wire over your pump (full signal). Then you can see if you relay is fucking with you.Just keep in mind when you switch on your pump starts then you try to crank if nothing happens for 5-6 sek then take the wire away.You can also see if every thing works by taking the fuel line between pump og carb apart and the crank then see if any fuel comes out of it.Just remember maybe this is not the carbs maybe are the valves damaged or don´t work right.

Best regards

Gunnar

 

Ok, so! Good news! The problem was indeed the carbs being gummed up from a rusty tank, so a decent cleaning did wonders it seems. It took a while to warm up (and a lil ether) but now she fires up fairly quickly, but doesn't exactly idle.

What appears to be steam (white gas that dissipates quickly) is coming out of the rear pipe, but not the front pipe. Both the heads are warm, but it could be heat through conversion.

I took a video (located here) but the sound is not great. I'm going to disconnect the rear cylinders and see what happens.

Any ideas?

EDIT: Ok so I'm pretty sure the white gas is steam, as it's spraying up against a cardboard box and leaving water (as far aas I can tell). It is still cold out, so it's probably just condensation. Either way, I figured out why it was only coming out one pipe. I was revving along when suddenly...POOMP! The muffler with no steam flies off!

The other one was blocked! So now I'm cleaning it. Do Supertrapp baffles have space in between them? Doesn't seem like mine do...

EDIT the 2nd: Alright, cleaned out the other muffler, threw it back on, problem solved! Hurray~! Fuel seems to be pumping well, she idles (despite the temp) and warms up decently.

Now onto tackling the brakes and cooling system!


Thanks again guys!

 

Don´t forget this

Hey

I would change the kopper rings between the engine and muffler.But it good that you found out what is wrong.

Best regards

Gunnar

 

Just for clarity here you can actually switch the two spark boxes on the int/sabre/magnas. Each one controls 2 cyclinders - plus one controls the tach and one controls the fuel pump.
When you switch them the wiring all lines up so the one that was controlling the fuel now controls the tach. Thus if you see the tach jumping it was probably affecting your fuel pump. The reason one is larger than the other is that it has the rev limiter. Sabre v4s in '82 didn't have the rev limiter so the two boxes where the same size.
To jumper the fuel relay you remove the connector and jumper two of the three wires (it's in the shop/haynes manual) which turns the fuel pump to always on when the key is on (though it only runs when there is low pressure on it's outlet side i.e. carbs need fuel)

 

It didn´t work on my

Hey

In my bike there are diffrent plugs for the CDI boxes so I assumed that it was also with him.NOTE: In some of these bikes, one ignitor is physically larger than the other and may have a different colored connector, but the two units should still be interchangeable. The larger of the two units has a rev limiter built in but is otherwise functionally equivalent..That is why I didn´t think it would work with him.

Best regards

Gunnar

 

On my 84 vf750f the cdi boxes are two different sizes and the two connector are different colours (1 red, 1 White) but the pinouts on the connector match up which makes them functionally the same.

Are you saying that your connectors have a different number of pins and won't swap?

 

No they swap fine, it's just that the red one (the larger cdi) has a rev limited on the pc board, since it controls the tachometer. The actual functionality of the cdi as far as controlling ignition remains the same.

 

So it some old mix in my bike

Hey

I cannot switch my cdi boxes beacause they have diffrent plug.Maybe this is something that someone who had the bike before me did I don´t know but there is no color on them.

Best regards

Gunnar