VF500F New engine problems

VF500F Runs on 3 cylinders after carb rev

So I have a 1984 VF interceptor which broke down 3.5 years ago. A valve broke and spit aluminium particles through the entire bike. Found them back from the air filter till the end of my exhaust, and everywhere in between. After I have stalled the bike in the garage all the time. I needed another bike so got myself a '94 VFR750 3 years ago and still have a lot of fun with it. Got myself a girlfriend which also got infected with the motorbike virus and I wanted to fix my broken bike a year ago. Bought another engine (VF500 Magna) at the motor scrapyard, but should not be an issue (the guy told me).

What I did so far with the help of a friend and a Clymer manual:
-Measure clutch assembly (thickness, wearing)
-Change oil and oil filter
-Change fuel filter
-Clean air filter and exhaust
-Change sparkplugs
-Disassemble, clean and assemble the carbs with new seals and floating needles
-Set the butterfly valves of the carbs (bench sync)
-Build in the new engine to the bike
-Complete the total bike
-Fixes some electrical issues (lighting and sensors, bad contact etc.)

Two weeks ago I wanted to start my engine and discovered it runs only on 3 cylinders. Number 4/front right is not working (read: exhaust is not heating, in contrast to other 3). After checking the #4 carb the slow jet was a bit stuck. Assembled and fired up again. Still 3 cyls were running... #&^%$@ But found out that I forgot the spark plug. So Tried again and it fired!! YEAH! Worked out.

Last week I tried again to fire it up, but ran on 3 cyls again. Did the same with #4 carb by cleaning the jets etc, but was not firing at all. My question is how can I make my bike running again? I did not change any screw settings when cleaning. The bike has no fuel pump anymore, because it broke down before the previous engine broke. But it should work out with gravity. All of the plugs spark and ain't wet. Also the engine gives compression within the sparkplug hole and creates vacuum through the carb/air filter mount. Thanks guys for helping me out! :biggrin:

 

I think if you are confident that you have a clean carb, then the most likely reason would be a lack of spark on #4. Could be as simple as a poor joint in the spark plug lead somewhere, but you could check the resistance from one plug connector to the other on the same coil (so from plug cap 2 to plug cap 4). My ST1100 uses a similar ignition system and has a spec of 22.5-27.5 kohm for this test. You could also compare to the 1-3 leads. If the resistance is out of spec you can unscrew the plug cap from the lead and check the bare leads, should be 13.5-16.5 kohm. If the bare lead checks out but the cap-to-cap doesn't, the cap might be faulty.

 

If you have fuel, a spark and compression, it should run. I would try new plugs if you are absolutely sure you had it running on all four before.

 

Thanks Terry and Jeremy. I will try both of your ideas later today. @jeremyr62 I have new spark plugs since I was rebuilding the engine and aren't wore. Secondly: can't it be the fuel flow is only enough to fill the carb but not enough to keep suction going when the engine is running due to a missing fuel pump? Just a random thought....


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If a float valve is sticking closed then sure, you wont get fuel but in my experience these tend to stick open and the carb floods. You can always check the bowl is full by loosening off the screw in the bottom the float bowl. Fuel should come out of the overflow. If the flow is good enough to run three then is will be enough to run four. Do you get absolutely nothing from #4? Not even a stumble?

 

A friend of mine took a look with me and we found out that the fuel filter was not providing enough fuel for the last carb, which I placed after the first try, when the engine was working. Is it possible (causes no direct damage) when riding without fuel filter? Or can I obtain a cheap replacing fuel pump from a Japanese manufacturer? Thanks!


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Sounds like you have fixed it then. My 86 engine doesn't have a fuel pump and no in line filter. There is a filter on the petcock and there are little filters built into each carb. I would have thought you would be fine running without a filter. There is a thread on VFRDiscussion about adding an extra line into the 32mm carbs found on the 84/85. http://www.vfrdiscussion.com/index....n-you-tell-me-about-my-vf500/#comment-1049656

 

Thank you very much and have a happy new year Jer!


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