VFR750 FG 86 Running on 3

Hi All
I'm new to the site and have just bought an 86 VFR750 that is only running on 3 cylinders.
This is what I've done so far...
1) Found cylinder 3 not running at all- cold down pipe.
2) Swapped plugs over
3) Swapped coils over
4) Measured valve clearances ,bit tight but OK for now.
5)Did a compression test ,same as the other rear cylinder ,they were low but tested cold
6) Checked jets in the carb ,all clean.Also checked that there was petrol on the float bowl.
7) Checked that there was vacumn at the mouth of the carbs
then
8) Used a Colourtune (kind of a glass topped spark plug so you can see the colour of the ignition flame within the cylinder ) to check spark in the cylinder and found now that when I open the throttle the cylinder fires,but not on tick over or a very low revs.
So I am now going to remove the carbs again and clean them all and do the float hights before balancing them as I might have disloged some muck in the carb by putting my hand over the mouth when it was running ?

If you think I have missed somthing please comment.
Thanks

 

What were your compression readings? You should try to perform this on a warm engine to get the most accurate results. Are your carb insulators in new/like new condition?

Spark plug wires OK? When you swapped coils and plugs did the problem, stay in #3?

 

#3 carb's pilot circuit is plugged.

 

Thanks
Hi Mr Dukie, I could not do the comp readings on a warm engine as No 3 clyinder was not running ,the carb rubbers have seen better days and I will get a new set as well as carb bowl gaskets,and yes the problem did stay with No3 cyl.
I think My Grey might have it ,I'll do the carbs tomorrow and let you know.
Have you heared of a trick of reviving tired rubber seals (float bowl gaskets) by wrapping them in a petrol dampend cloth overnight and they should swell to somewhere near the origional shape ? Never done it ,but I'll give that a go too.
Cheers chaps

 

That's worked for me !

I've had several VFRs just out of overwinter or long term storage have 2 or 3 leaky float bowls the first time they get fuel, so i walk away and tip a pint.

Next day i check again and usually see that only one is still slightly dripping, but i'm anxious for a ride, so i go on a 15 minute loop, and usually after the warmup everything's sealed up tighter than that blonde at your bus stop's knickers.

 

Just prooved the gasket theory,I removed 3 of the gaskets last night ,had to clean them off as they had a coat of instant gasket on them! Anyway left them over night in a petrol soaked rag in a container .Cleaned up the 4th gasket this morning let it soak for an hour or so whilst I cleaned that carb and did the float hights which were all out .Put the carbs back together and the only one that leaked was the last one I done .It's now soaking in a rag.
I'll let you know if it runs ok ,then I'll balance the them. Fingers crossed.

 

Right.
Installed the carbs (no float bowl leaks) adjusted the tappets,changed oil/filter then started the bike. Now all the cylinders running fine but with a bit of a tappety knock. Ballanced the carbs -well out . now running sweet as a nut.
Just need a new piece of fuel hose then I'll book the MOT ,phone the insurance co and I'll be back on a VFR750 for the first time in about 10 years
Thanks for the help.