Hi, someone suggested that this forum might be a good place to ask for help, I hope so. I recently got a VF750SC )Sabre) that had been stood for 17 years gathering dust. After a fair bit of time and money spent on it, I’m now having trouble starting her up. I can get her started if I spray carb cleaner, or some such, down the air intakes, but after that it will only fire on cylinders 1 & 4. To be honest, it’s starting to drive me mad, and some of my friends as well. So far I’ve done:
new plugs
tested HT leads (re-wired one)
swapped both coils for known working ones
swapped both spark units for known working ones
checked compression
cleaned out carbs
checked there's a spark
checked the plugs are getting fuel
done the valve clearances
checked the timing
cleaned the carbs, again
I just wondered if any of you guys had ever come across this before?
that is a puzzle, im assuming you did drain any of the 17 year old fuel left in the tank out?..
if youve got spark, petrol and compression it should start or at least show some signes of starting…
only thing i can think of is its sparking at the wrong time… check see if the dot on the starter clutch and shaft are lined up, also check make sure your leads are on correct… if its same as a vf1000, left coil does rear cylinders and right coil does front.
may also be worth checking your petrol pump and fuel filter… it may be getting petrol but not enough to keep it going
Thanks for the reply Pete. Yes, I did put new fuel in, in fact I had to get a new tank as the old one was too far rusted to save [:(]
Yep, also checked the timing, and surprisingly it’s spot on. the leads will only fit one way. I mean I suppose it’s possible that 2 & 4 could be mixed up, but then it wouldn’t fire on 2 either. There’s no way to mix up 1 & 4.
My gut feel is that it is something to do with the carbs, as anything ignition wise just wouldn’t be logical (the problem would be with odds, or evens, not one of each).
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The one thing I’ve had trouble finding information on is a thing called the starter jet. the carbs have main, idle, and starter jets according the Haynes book of lies. Obviously, I can guess what they do [:)] but not how they actually work.
From what I can gather there’s only the fuel filter in the tap, and if it was a pump issue, then surely it would affect all cylinders. 2 & 3 seem to be running quite happily.
Why oh why do I seem to like old 80s bikes [:)] My other two are an 84 VT500 and an 86 GPX750
You say its firing and ( sort of ) running when you spray fluid into the carbs which suggests to me that the timing of ignition and cams is OK.I would be looking very definitely at the fuel inlet side. You say youve cleaned out the carbs but they can be notoriously difficult to clean thoroughly. Have you had them ultrasonically done ? The mixture passage ways are extremely small and only the tiniest of petrol gum in them can cause big issues. As Pete said - I,m assuming youre using fresh fuel as well ?
Good luck
I would also guess there is a problem with the fuel supply. I hab some issues to with my VF 1000 F. I also got the catbs out and cleaned. Did you remove alle the jets and cleaned them in an ultrasonic bath? My idle jets where so stuck, it to almost a whole day the get the dirt out of em. If you take the jet and look through them to a lamp, you should see a tiny tiny little bore.
im not really familiar with the vf750 sabre, but im assuming its fairly similar to the vf1000… there are 4 small filter baskets behind the float valve seats, you’ve probably seen them but thought i would just mention it as not everyone removes the seat when cleaning carbs… other than that i cant think of much else
Many thanks for all your suggestions, but after a week of tearing my hair out, I’ve finally got my answer… I was just going to end the post there and leave you in suspenders, but I’m not that nasty. I swapped the leads between 2 & 4 and low and behold the problem moved to cylinder 2. So a quick assembly of two new leads and it’s now firing on all 4 Yay! Next jobs are top balance the carbs, and figure out why the clutch isn’t working. But then I think it’ll be ready for its first MOT in 17 years.
Well done. Goes to show how unhelpful we turned out to be !!![:I]
Cheers
WELL IT WAS MY SUGGESTION HE CAME HERE AND ALL ADVICE HELPS TO DISCOVER WHAT ITS NOT, THEN WHATS LEFT IS THE ONLY THING IT CAN BE … Someone did suggest swapping the leads on this and another forum and eventually thats what he discovered the problem was so some of you were spot on …
take the fuel pump off and check it works by pumping fuel from a glass jar to another its 12 volt dc
these pumps get rusty inside and so does the tanks
I had a similar problem
hope you changed the filter and oil ?
hope this helps
quote:
Originally posted by windysolar1
take the fuel pump off and check it works by pumping fuel from a glass jar to another its 12 volt dc
these pumps get rusty inside and so does the tanks
I had a similar problem
hope you changed the filter and oil ?
hope this helps
Fuel pump seems to be doing its job, in the main. But will try your suggestion at some point. Yes, I have given it a full oil change, including the filter [:)]
Now having trouble getting it to idle properly. If you’re interested here’s a link to it running, and stalling : http://www.dogfriendlysuffolk.com/bikepics/VF750_Cutout5.wmv
BabySabre and fuel pump sounds strange to me. I renovated one, and did never find any fuel pump in it, just vacuum-operated fuel tap. Plug wire with loose fit in the plug end became familiar problem 
Probably only VF without fuel pump.
quote:
Originally posted by dnapekko
BabySabre and fuel pump sounds strange to me. I renovated one, and did never find any fuel pump in it, just vacuum-operated fuel tap. Plug wire with loose fit in the plug end became familiar problem 
Probably only VF without fuel pump.
After closer examination, you’re right, just vacuum operated. Discovered one of the carbs was leaking, so stripped down, and set all screws to standard, and now it’s idling OKish
http://www.dogfriendlysuffolk.com/bikepics/VF750_Running.wmv
sound like a v twin not a v4
Probably only VF without fuel pump.