Starting Help!!

Hi guys, I’m looking for some diagnostic help. 1985 VF500f2
I’m mechanically minded but I’ve never worked on a V4 before.
So I go to fix up my old VF500 that’s been sitting for a few years.
Stripped/ checked/cleaned the carbs, all looks ok, fuel pump works. Changed spark plugs, have a spark on each lead. (Currently using my car battery with made up leads)
It just won’t start tho.
it did run one time, when I had forgotten to tighten up the rubber manifold connectors tight, it fired up and ran away a bit so I shut it down. Mechanically it sounded sweet, so I know it’s a runner.
Last night I gave it a wee squirt of easy start but still NOTHING!!
So I’m back to thinking it’s the spark? Surely I should get something with that spray? The sparks are white, I thought they may be weak but a biker friend said they were fine. I’ve cleaned all the connections on the coils, swapped cables over (and back again). tested 2.8A resistance through the coils, It sounds like it’s close to starting but won’t catch and backfires.
Does the spark need to be blue? Or does anyone have any suggestions?

 

I think I’ve answered my own question, the spark needs to be better!! I didn’t want to buy a battery if it wasn’t a runner but that one time I did run up so I will buy a battery and eliminate my leads.
I clamped the + at 12amps and 12.5V when pushing the start button tho

 

12A & 12.5V is fine. When cranking volts get down to 10.5V, it won't fire the coils. It's not the battery. White spark is good. That leaves fuel. First thing, though - NEVER spray quickstart or any starting fluid into the carbs. It will destroy the rubber bits - especially the expensive diaphragms. In fact, I would take the diaphragms out right now and wash them in some mild soapy water.

Back to the problem - fuel. Did you open the carb drains and measure how much fuel came out of each one? Do that, then fill them for maybe 30 seconds and drain again to see if they are equal. Basically, the whole fuel system is suspect - tank, petcock, petcock sock, fuel filter, fuel pump (some years of the VF500 have them), hoses and carbs.

Good luck,
Glenn

 

Unless you can smell fuel after trying to start it I'd suggest the fuel pump either needs priming or has failed

 

Hi Pete, thanks but the fuel pump is good, I’ve hard wired it for now and it’s got good pressure.

 

Thanks Glen, I have a plastic bottle rigged up to the pump for now. I have not tried draining them and refilling yet, but I’ll give it a go and see what’s what.

 

thats good news but do you smell fuel after cranking?

 

your choke circuit maY BE clogged and not sufficiently enrichening starting mixture or wrong float settings. did you drain and flush the fuel tank and clean the petcock ?

 

Hi, yeah. I thought that too so I stripped out all the chokes on the carbs and cleaned them all out. the all seem to be moving as they should. I have eliminated the petcock and tank by rigging up a plastic bottle direct to the pump.
Last time I was in, it seemed to be worse than before, not even trying to catch where, the time before it sounded like it was very close to starting.
I will be back in the garage tomorrow night for another crack at it

 

you need to be sure the long brass tubes that duct fuel into the choke enrichment circuit are cleAR. try poking a .010" steel wire into the hole. the wire should go in about 33mm if the tube is open and clear. follow up with compressed air.

as a TEST, try using starting fluid sprayed into the airbox. if the bike starts, it's got dirty carb circuits. dija remoxe and clean the holes in the mixture screw passages ?

slovcan's warnings are not quite valid as very little to no starting spray gets near the diaphragms since it's being sucked into the cylinders.

 

Hi, yeah that was all cleaned out, looks good.
I was back in the garage tonight tho with a couple mechanical friends, again it was trying but still nothing.
We came to the conclusion that the CDI units may be at fault as that’s about the only thing we can’t test,
It was also giving a loud backfire at times.
Now I’m at the point, I’ve spent lots of hours on it, I’d be gutted to throw in the towel, but not sure if I can afford to take the gamble and buy new units.
Second hand ones are about £60 odd each so it’s a bit costly if it’s not them! Or if they even work right!
The fact it ran that one time kinda is throwing me off.
Maybe I need a simpler bike!

 

fur gob's sake, mate, use some starting fluid spray and make sure the battery is fully charged !

if you have sparks at the plug wires, CDI is OK. Maybe you just can't believe your clean carbs might not be workin right ?

since you're dealing with a VF500--one of Honda's most prone-to-fail bikes--you MUST do a compression test if it refuses to start !!!!!!!

 

It took me over a dozen tries to get my carburetors functioning. I was just not doing it correctly, not thorough enough, and made a few mistakes along the way. Eventually, following advice from squirrelman, Jeremy, Jrod rims, et al, I got my 500 running very well. I suspected many things else were a miss, so first I verified compression and spark. These things do not like to start on ether, and I endured some horrendous backfires. In the end the only problem was the carburetors. YMMV
Best wishes, and never surrender!

Sent from my XT1031 using Tapatalk

 

1. So the engine turns over....
fast or slow ?

2. CAN YOU SMELL FUEL?

3. What is the condition of the plugs NOW? - I dont care if they were new before, either replace with BRAND NEW SET or clean them - What is the condition of them?
These bikes make a CRAPPY spark so with the best will in the world if you have had repeated tries to start it then they are likely to be covered in fuel.....

HOWEVER,

If they are NOT COVERED in fuel, then you NEED to pull the carbs.

4. Are your plug leads in the correct cylinders?

 

I removed the carbs again, took them inside and sat at the table going over them, they are good for sure!
I took the plugs back out, cleaned them up, they ARE wet, still sparking.
Still nothing!! Just the occasional loud backfire (as if the timing is way off)
Are we SURE the CDI boxes are ok if there is a spark because in the manual it says there is NO test for these to know if they are ok and they can affect the timing?
I’m at the end of my rope now, I think the question now is: do I strip it down and sell it for parts or sell it as an unfinished project?.

 

Just one other thing, I have no pulsing on the Rev gauge when trying to start. I have nutural light, oil and high beam ok but I would have thought the revs would pulse when turning over?
Hmmm no I’m clutching at straws coz it’s sparking
I have fuel, and spark so is it timing? I’ve wired the coils as per book. The lower one feeding the front two and the upper feeding the back.
I swear it’s something silly I’ve missed but I’m out of ideas!

 

Spark boxes control the advance curve, but not so much as to prevent starting. The fact that you get an occasional backfire kind of points to the starter clutch being reassembled/reinstalled incorrectly. That is what determines the timing. BUT, you say it did run. You can confirm you have both wet plugs and spark. Are all 4 plugs wet?

Two things remain to be done. Swap the spark boxes and try again. Watch the tach. Also, if you only have 2 wet plugs, see if the other 2 are the wet ones after swapping the spark boxes. The other thing, which, I think was mentioned before - check the compression.

Don't scrap it yet.

 

Spark plugs - check
Carbs - check
IF THE ENGINE IS TURNING OVER FAST ENOUGH then the battery is fine - check

Now RECHECK the spark plug leads - I think you have them in the wrong positions...

This is due to the backfires... this is the easiest check to make... if they are correct (I personally doubt it) then ck compression....

 

How do I check the leads tho, I have bottom coil feeding front pistons left and right, and the top coil feeding the rear cylinders, I have swapped them over all ways but nothing in any order so they remain as per the manual

 

How do I check compression??