1986 VF700c Honda Magna poor fuel milage

[Tuscon 11]

I purchase a 1986 VF700 Honda Magna with 22,000 miles on it that sat for quite a while. The friend that I bought it from is a meticulous mechanic, he cleaned (disassembled and soaked) and set the carbs but the fuel milage is only about 20 mpg on the highway and aroung 15 city. When the bike is throttled up there is some black smoke from both pipes which indicates a rich mixture to me at high rpm. Does anyone have any ideas as to what I can do to fix this problem?

[Sev]

Rejet !

[Tuscon 11]

When the carbs were gone through the guy readjusted the floats. What would be the result if he got them wrong?

[insaneV4Honda]

How is the performance on the bike? I guess what I am wondering is other than black smoke, how does it run? Does it idle OK? Does it rev up and pull strong through the gears? I have been experimenting around with the pilot jets and have found that if they are set too far away from the factory settings, fuel mileage goes down the drain. Many people who rebuild these carbs without ever doing them before, miss the fact that there are pilot jets located behind aluminum plugs or they remove them without checking the amount of turns they are from bottom. I'd be glad to offer advice with a little more information. Good luck! Sean.

[Sev]

Okay, the pilot jet is from 0 to aprox 1/8th throttle at that point it doesn't do anything the needle jet takes over. At 3/4 throttle the needlejet is irrelevant and it's all main jet. Changing the pilot won't adjust the anything above idle or just off idle. So it'll only affect your milage if you're idling all the time.

And you're not working on the pilot jets you're adjusting the air/fuel mixture AT idle. That's the adjustment screw. If it's before the carb it adjusts air, after the carb adjusts fuel (I think, I get those confused sometimes). Generally speaking with a stock bike you don't need to fiddle with those, even if you do it's easier and safer to just change out the pilot jets inside the carb itself then to drill out that aluminum plug.

If you have an automatic punch you can use it to pull out that plug. Just hammer it in using the self actuating whatever it's called (you mechanics know what I'm talking about). Then lever the plug out like a wine cork.

If the float heights were set too high then you would be running rich, and if you they were set to low you would be running lean.

You can double check the float heights (the procedure and heights will be in the manual) then double check your jet sizes.

Without looking at the carbs themselves, and the bike over-all... it's not really possible to know exactly what's wrong.

[insaneV4Honda]

I agree on some points and disagree with others. I used the wrong terminology in my previous post. I should have used "pilot screw" instead of "pilot jet". On these bikes, the pilot jet is in the carb bowl along with the main; and they are not adjustable. The pilot screw adjusts air on these carbs; not fuel. The jet meters fuel and you adjust the air with the screw. I do agree that the pilot screw only effects throttle operation less than 1/4 throttle but when you are at a cruising speed, generally you are less than 1/4 throttle. I played with this setting and found I could adjust my fuel mileage as low as 45 MPG to as high as 54 MPG all with staying within 3/4 of a turn of the factory setting of 2 1/2 to 2 3/4 turns out depending on the year of the bike. I can't quite quote the year and settings but generally speaking, they are all between that setting.

My main concern for the original problem was if they were neglected during the carb overhaul, they could either be dirty or mis-adjusted which are both problems that I have faced and fixed.

Definately, definately the floats could be too high. Generally when rebuilding these carbs, you can't screw up the float heigth. Some floats are adjustable and some aren't. Depends on weather or not you have a metal tab on the float versus all plastic. To be honest, unless you are abusive to these carbs, rebuilding them is almost idiot proof. Heck, if I can anyone ahould be able to. Cleanliness is the key. Hope to hear more of the problem so we may help. Good luck. Sean.

[Tuscon 11]

The pilot screws are now set to 2 1/8 and the idle is fine except for the first ten seconds or so when the bike is first started the idle goes to about 2100 then drops back to about 1200 like it should. (factory pilot screw settings on this bike is 1 7/8 ) I have played with them quite a bit and it has so far only affected the idle. The poor milage has been very consistent through out the entire range of settings.

The performance is ok especially above 3 grand but it could be better. The floats do have metal tabs and the guy that cleaned the carbs adjusted all four of them which is why I am thinking that he might have gotten it wrong. I am going to try and pull the carbs this weekend to check the jets and floats. Thanks for the help, i'll let you know how it checks out.

[Sev]

Air/fuel mixture screws affect idle. So unless you're sitting at idle all the time they will not affect your fuel mileage.

[insaneV4Honda]

I have owned many V45's but all of them have been either 82's or 83's. In my experience, they could be better performers between idle and 3K RPM. All that I have owned seem to come alive above 3K RPM. Aftermarket exhausts can help the bottom end some. The 83 I just restored now has straight pipes all the way back and it is a scream right off from idle. I think you are on the right path with the float heigth being too high. One helpful tip I can give is if you have the non-adjustable type of float, you can change the thickness of washer under the needle seat to adjust float height (if you already knew, I'm sorry). I had to do this with an 82 that I had and it is a real pain. The carbs may be slightly different on the 86's so my tips may be in vain. Keep us posted on your progress and good luck! Sean.

[mydlyfkryzis]

Are you riding with the choke/enrichment circuit on?

Is the choke really off when the lever is off?

Are your brakes dragging?

Just some other stuff to verify..