1987 VFR700F2 Won't Start - Posible Spark Generator Issue

I've been asked to start a new thread on this topic

I'm new to the VFR family. My history is with Hondas of the 70s, of which I still own a number of them. The VFR700 is so much more complicated than my CB750ks. I've read through other threads and it sounds like I'm SOL if in fact my 1987 VFR700F2's Spark Generator is toast.

I've gone through the procedure in the "Ignition System", section 18, of the 86-87 VFR700F/FII Honda Service Manual. All 4 coils had between 2.9 & 3.0 ohns each. I didn't test the ohms referenced in the "secondary coil inspection", but I removed the rear 2 plugs (easier to reach) from the engine to visually see that they all had spark and they did. I also placed a timing light on each of the 4 spark plug wires while cranking over the engine to see if the strobe worked. It lit up with each cylinder.

Next I tested the Pulse Generator as described on page 18-4 in the shop manual. My ohm meter showed 295 ohms across the yellow and white/yellow wires and 300 ohms across the blue and white/blue wires. I could be testing something wrong but the instructions are pretty straight forward. The manual says to replace the pulse generator if it's not 450-550 ohms.

On the fuel side... I drained the tank, and replaced the fuel lines just because. I drained the fuel from he carb bowls. Used the engines started to fill the carbs with fuel and checked the bowls to see that the fuel made it there...It did. There still could be an issue with the jets, but I haven't gone there yet until I figure out what's going on with the Pulse Generator.

Question: Is it possible to have spark at the plugs without a properly working pulse generator?

It seems spark generators are hard to find. I thought it wouldn't hurt to ask if anything has changed with someone making an aftermarket Spark Generator. I'll keep looking as I hate to part out this clean VFR. :blue:

Any help/advice would be appreciated. Thanks in advance!

 

Is this a bike you've had for a long time that used to run, but has been in storage or a bike you recently purchased that hasn't been run in a long time?

295 and 300 ohm sounds fine. I wouldn't worry about that.

So you do have spark when turning the engine over, but it's not actually firing or showing signs it wants to crank?

Assuming it has decent commpression, I would make sure you have a good battery, maybe a car battery attached with jumpers, so that your coil voltage stays high while cranking.

Measure the coil voltage with the key on and again while cranking. If it dips too low, like 9 or 10 volts, then the bike won't want to crank. A weak battery that sags voltage could be your problem.

Also keep in mind that these bike are old and usually will have electrical connectors that are dirty. So you may have 12 volt at the battery, but after going through the main fuse, ignition switch, etc... the voltage at the coils can be a lot weaker.

If coil voltage is weak while cranking and your battery is healthy and strong, then you can temporarily add a jumper wire from the battery positive to the 12v coil wire to keep it high.

Also don't rely on the gas in the carb to start it. Spray a little starting fluid or carb cleaner down the carb throats with the throttle open and then hit the starter button and see if it wants to fire.

Double check you have spark as well, just to make sure you didn't accidently flip the ignition kill switch to off.

Let us know what happens.

 

I remember helping a guy here who had a similar problem to yourself where it just wouldn't crank. He assumed his battery was fine because it was cranking over nice and fast but it just wouldn't start so he thought he had all these issues with the ignition system and was checking all this stuff. It turned out that his battery was actually sagging voltage wise while cranking while at the same time cranking the bike over fine. All he had to do was swap in a new battery and boom, that sucker fired right up. He wasted months fiddling with it.

So for sure, these newer ignition systems are more voltage sensitive compared to the older style points type ignition systems. Everything else about the 70'S and 80's bikes are about the same.

 

Where in Sacramento are you?

 

Get ahold of TC (above) as he's the ace #1 helper for Cali riders.:love-struck:

 

Gentlemen, First off that's for all the information. I really appreciate it. Let me see If I can answer all the questions...

Unfortunately, the guy that owned the bike passed. I bought the bike from a friend of his. So I don't have any history on the bike. I do know that the guy that owned it was a top ranked Formula V SCCA racer/builder/Fabricator. So he was a very good mechanic. Also all of the California Emissions have been removed. It seems to be like one of the forums recommends. It looks like the bike went down once on the right side. Just fairing damage I believe. Right now all the fairings are off. The fuel pump works but is not the OEM pump as the inlet and outlet are not curved. Aside from all that, the bike is in pretty good shape. Much better shape than some of the CB750s I've purchased. If you care to see my bikes, visit JVCYCLES on Facebook.

The battery is brand new. Just bought it a week ago. I've got it hooked up to a Battery Tender also. I found a pulse generator on ebay that was poorly titled. Since they seem so hard to find I bought it. It should be here next week. It came of a 1987 VFR700F2 like mine.

JasonWW, Thanks for the advice. I will try everything you recommended tomorrow or this weekend.

I live in Sacramento (Fair Oaks), where it looks like Toe Cutter also lives. For all I know we've met before. I'm a member of the local VJMC and was a HOG member but didn't go to the local meetings.

Question: For CB750s there is a "bible" that explains everything about restoring the bike. It's by a guy tagged "Hondaman". Is there anything like that for the early VFR hondas?

Thanks again...I'll keep you posted on my next steps.

 

The bike cranks fast but wont fire. Not even a pop! I've pulled the rear 2 plugs and they spark. The front spark plugs are a bitch to get at. They remain unchecked. But when I connected the timing light to the front spark plug wires, they both lit up the timing light. No idea if it's a strong spark or not. I'll have to measure the voltage. I also checked to make sure the kill switch wasn't stuck open. It was working fine as checked with an ohm meter.

 

Did you spray something into the carbs to help them fire up?

Since your new to this bike, it might be good to verify compression. If you pull out the rear 2 plugs you can just stick your finger in the hole if it reaches and feel the suction and then the strong blast of air coming out. Do this with the throttle open. That should be good enough to tell you if you have compression. It's possible a couple valves are stuck open and that's why it's not firing.

 

JasonWW, GREAT advice! The Starting Fluid worked great! Man did it sound good to hear it run... After I sat there and stared at the bike for about 15 minutes thinking life is great, I decided to connect the fuel tank and try it again. This time...Nothing... Does that mean the fuel pump is not pumping enough? There is new fuel in the tank (5 gallons), new fuel lines to and from the fuel pump, and a new fuel filter. For kicks I took the line off the "out" side of the pump and ran a line into a cup. I ran the starter for about 30 sec and fuel went into the cup... 4oz to be exact. I don't have anything to test the pressure with.

Should I just purchase a new fuel pump for a cbr600? I even see a couple used VFR700 pumps on eBay. Any advice? Thanks again!!!

 

The pump seems okay, by your test.

Did you pull the carbs, keep them connected to the top plate, and open the float bowls, clean them up, etc...?

I assume you did, since you work with older bikes and know that carbs that sit get gummed up.

Also, did you prime the carbs, assuming they were dry after being cleaned and put back together?

The fuel pump has a safety relay that controls voltage to the pump. At cranking speed the pump gets tiny voltage. At idle it goes up, and higher rpms it goes up higher still. You can prime the carbs by putting 12 volts to the pump. It will run fast for a few seconds then stop. Or you can pour some fuel down the carb fuel line that the pump outlet attaches to.

Once the carbs have fuel, you'll need to choke them all the way and let it spin over. If your choke circuit (actually fuel enrichment) is clogged it's not gonna start on its own.

Can you describe what you've done to the carbs?

 

Thanks. I did prime the carbs but have not cleaned them yet. Even though I've become very good at rebuilding old Honda carbs it hasn't got to that fun level yet. Before I clean them, I'm going to test the fuel pump like the manual says to do. 12 volts via jumper for 5 sec. It says I should shoot for 27 oz per minute. If it passes that test then I'll rebuild the carbs. I think I might also try to prime the carbs the way you recommended, and see if the results are any different. Much better than the way I did it.

Any advice on new vs used (VFR700 OEM) fuel pump?

Thanks again,,,Today was a great day. Cool sounds these V4s. Like a Ducati with a wet clutch ;0)

 

I wouldn't worry about replacing the pump right now. Maybe just inspect the contacts under the cap. A little filing should help them.

If you haven't cleaned the carbs, then that's why it's not running. There are good threads in the 2nd Gen section on how to do it. Just don't seperate the carbs, keep them all attached to the upper manifold. You'll probably need new float bowl gaskets. They can probably be bought local at a hydraulic repair shop for almost nothing.

If your not comfortable with full carb teardowns, then maybe you could pay toe cutter to do it?

New carb boots to the engine are another thing you'll probably want to replace. They're not too pricey at $40 total or so. The dealer should have them or on ebay. These will eliminate any air leaks between the carb and engine, plus make it easier to install and remove the carbs.

 

Okay, I'll print out Toe Cutters tutorial on cleaning these carburetors and get started. Can't be any worse than the GL1000. I've order the new intakes and gaskets for he bowls. I'll keep you posted...Thanks again.

 

Just remember to not seperate the carbs. That's asking for trouble. There are delicate hard plastic lines that connect the carbs and they can be easily broken. Plus it throws off any synchronization the carbs linkage may have.

Once the carbs are clean and bench synced, it should run pretty good. Later on you can do a proper warmed up sync on the bike and really get it running smooth.

You might need some fine wire to clean the tiny holes. I use 0.25mm guitar string I got at a music store. It's cheap.

 

Got it... It seems pretty straight forward. Toe Cutter talked about swapping the bowls around so you can adjust the air fuel mix screw. I usually keep everything the way Japan created it, at least as far as the engine goes. Will I regret not doing this mod?

 

I've never heard of this modification. You can get to the air fuel mix screws just as it came from the factory. I use a flashlight and a "snake driver" tool.

I think if you swapped the float bowls around it would make it harder to access the drain screws. That's all.

 

I thought the pictures made it pretty self explanatory but it just moves the lock to the other side of the carb and oot of your way for adjusting. Does not move drain location or any other change to carbs other than move locking tab. May just be a California emissions thing as I don't see many oot of state carbs.

 

Okay, I found Toe Cutters link and pictures. The locking tabs look strange. Either my bike didn't have them or I modified them for easy adjustment many years ago and forgot I did it.

So if swapping the bowls around have no ill effects, then why not? Or you could just grind down the tab on that one bowl.

 

OK, The carbs were not that bad to get off the bike. The rubber intakes were very hard and stuck to the carbs. I'm glad I ordered new intakes. I got the bodies cleaned. Tomorrow I'll clean the jets.

 

Now's the time to try and clean the fuel enrichment/choke circuit. You can't really take it apart without removing the linkage so you just have to spray cleaner and compressed air around that area as best you can. Maybe Toe Cutter knows a trick to do it?

Before I put my carbs back on the bike I put some white paint on the idle mixture screws. Then when they are closed/seated, I use a black marker and put a dot at the 12 o'clock position. Then I back them out 1.5 turns so the dots are facing 6 o'clock. This helps later on when you want to tweak them on the bike. With a flashlight I can clearly see if it's turning and how much.

That's a clean looking bike/engine. Was it low miles?

Were the front pipes shiny like that or did you polish them?

I see 2 drain lines by the right foot peg. There shold be 3. One for the battery, one for the gas tank water drain and one for the coolant overflow tank.

When I got my bike I had to add a new radiator cap (cheap at local auto parts store) and new hose from radiator to coolant tank. That fixed all my cooling issues.