84 VF750F restoration - carb questions

Float level gauge made from a credit card....


VFR Discussion -> Gallery -> Viewing image -> float height gauge

 

yup, same idea. I'm gonna have a friend give it a second look for me and see if he thinks I have the levels right.

 

OK. Called in a motorcycle mechanic friend of mine last night. He double checked the float adjustment multiple times and it is right on at 7mm. Put it all back together but it was too late to test run. Something he said about coming across a similar problem made me also check the spark. I rigged up a jumper cable as a ground and checked each plug. I was not too sure but it seemed a bit weak to me. I did the checks on the coils and pulse generators per the manual. Swapped out the spark boxes with some spares I had, and picked up some universal plug wires from the local auto parts store. Spark seemed a bit better. Hooked up the gravity tank and she fired right up. But she is still spewing black smoke and running rich. At least now I can keep it running somewhat with the throttle. Tried turning in the mixture screws a turn, but that didn't make a lot of differance. Still burned up a quart of gas in about a minute or two of running. As much as I hate the though of pulling the carbs again I am thinking about swapping the slow and main jets for the ones I have out of an 83 even though the main jets for sure are differant. I can't think of anything else to do the try to isolate this.

I did get the bike in pieces, and it hadn't run since 2002, so it is probably a combination of things.

Any further advise would be appreciated.
Steve

 

Hi Steve

Saw this website and it is with full of a advices for your bikes.Hope this helps Site is :VF750 Honda Magna Sabre VF700

Best regards

Gunnar

 

You probably know but floats setting is measured without depressing the needle plunger. I had this ordeal with cars a couple times and strangly enough valve timing was off, bluburing black smoke, spitting back, ran like shit, sounded radical thou. Never had it with a bike so I don't know. The piston (diaphram) needles are assembled correctly...spring on top of needle. Good luck, you should be a carb master after all this. It can't suck fuel thru any emmission crap like a purge valve on this model?

 

SUCCESS!!!!!
And I am cooking up a crow to have a bite right now. Back to the first suggestions made when I posed the question - I should have listened and tried swapping the jets sooner. The ones in the carbs LOOKED OK. So - what I did as a last resort was soaked the jets out of a spare set of carbs I has for an 83, and it worked. The main jets are differant, but at least it worked. I will check some parts diagrams and see if the slow jets are the same in the 83 and 84. Maybe I will put back the original mains to see what affect there is. Now to beg borrow or steal a set of vacuum guages to sync the carbs.
Thanks to all that posted suggestions. This is a great resource.
Steve

 

Good Job!

Sounds like the previous owner ad libbed some carb parts or did some 'drill' bit jetting. I hate it when people do that.

 

Note to self - when I buy a basket case bike and rebuild the carbs I will buy new jets. Looks like this is the same problem I have been having with a CT70 that I have been messing with for my neighbors son. Repeat to thy self: new jets are cheap, new jets are cheap, new jets are cheap......

 

CT70 with quite some time on it that's running rich and fouling plugs maybe? Usually the culprit is the needle jet/ needle. Unlike the bigger bikes the needle jet is just brass and with use it wears the hole too big from the needle going up and down. So when the needle is in the idle position/throttle closed, more fuel leaks past than is supposed to. It usually helps to adjust the clip on the needle...but the real 'ticket' is to replace the (Honda speak) needle jet set...includes needle, needle jet and clip. Assuming the engine is good, (and they usually are) that makes 'em run like a 'million bucks'. For how simple a machine those old CT's are it's amazing how good they can run.