ok, this is very unexpected

just got my 83 VF750F today, love it

question though

what would make the right side exhaust blow cold/room temp air, and the left side blows hot air, as expected with any exhaust of course...????

it makes no sense, one would initially say...you need a heat source to have heat.....so you would think....no fire on that side of the motor, but that just can't be it, that side has two cylinders, front right and rear right on that one side of the manifold, so no fire on two cylinders..???

i dont think so...been riding this thing all afternoon, runs fine, unless the motor could have two non-firing cylinders and still run strong and smooth...???

something makes no sense whatsoever......the right side exhaust has a small leak at the end where the intermediate piece meets the collector exit on that side, but it's not big, you have to feel for it, you can't just tell by listening for it......, but there's plenty of air coming out of the end of the exhaust pipe on the right side.....it's just not hot.....

is it possible that one side of the motor heats up before the next? like maybe the heat doesn't really spread out until the thermostat kicks in and circulates the water through the block?

this is not after riding it for a while, i have had it up on the center stand working on a few things for a few hours, so the motor was virtually cold (had to choke it a bit to start it), and 5 minutes after starting it and letting it idle, you can't even put your hand on the left side comfortably, but the right side isn't even what i would consider "warm"???

 

update:

ok, yeah, something is very weird.....or maybe i dont understand the way this engine works

with a carb per cylinder, could it be that not all four get gas evenly...that is, could it only supply fuel to two cylinders at cold idle until it warms up or only under more throttle?

i mean literally, the left side of the manifold is hot as hell as it should be, the right side is barely warm, huge difference

 

Make sure the right side cylinders are firing becuase it will still push air and the crank will move the pistons up and down (but you knew that). Had a friend once who had a HD that on plug was not firing and you could smell the unburnt fuel. Other than that, I am not sure what to check. Sorry I wasn't more helpful.

Vinny

 

well

after some more tinkering, it appears that under idle throttle, the engine does not feed fuel or not enough to matter to two of the cylinders

i cranked it up again, after checking spark on these two cylinders on this side of the bike, and tried opening up the throttle, and at some point, the right side suddenly blows hot ass air out, like the left side.....

so it appears that the four carbs are synchronized in a way that it fuels all four at half or so throttle, and cuts it back at low idle........makes sense, less fuel useage at idle, and would run cooler when idling in traffic as well

at least i hope that's what is going on, even though this is my first bike, it's not my first four cylinder honda motor, and on all the cars i have had, if one cylinder was not firing correctly, it ran like absolute crap, sputtering and so forth, and unless i just dont know what a good running VFour feels and sounds like, this one is running great

 

you know, I think your carbs just aren't synced right.
I have an 86 vf500 that I drove around. It lacked some power but It really still sounded great and drove fine.
I took the carbs apart today and found one of the main jets had fallen out and the other was clogged up.
So essentially I was running it on 2 and a half cylinders and didn't know it.

In your case, all four cylinders are eventually running but on one side they are running a little slower (less throttle open) I would think that this would slow the bike down.

I don't think they would make the bike run that way. I know some newer cars shut off one or two cylinders at highway speed. But they also open the valves so the pistons don't have to compress anything and slow down the engine.

Thats just my two cents.

 

yeah, i dunno, the guy i got the bike from works on them and said he completely redid the carbs

but i also noticed in the Honda service manual, it indicates the need to use some sort of vacuum assembly to synchronise them properly, and i dont think he did all that

 

i verified with him today, he did not have the synchronizer device to do a proper synch on the carbs...

perhaps that's all it is

 

Do the downpipes all heat to the same temperature?, if they do it's just a characteristic of the exhaust balance box, early vfr models did the same thing