CX500 GL500 650 Global

GL,
I don't think that it is only because of the pump. That is only squirting a small amount of fuel at the very start of the acceleration. It has to do wit the fact that the carbs can deliver the needed amount of air to the motor, with out giving the fuel jets an abnormally high vacuum signal, and drawing more fuel than the motor really needs.

Blindstitch2002 wrote:

sheppola wrote:
Buy a new Petcock and filter

Simply said. Having trouble convincing myself to spend the money since I still get over 100 miles on the first two gallons.

Actually why not when you are near a DIY/Hardware store see if you can find a bit of plastic tubing and make a pipe to go on the petcock you have to re-make the main tank height inside?Couple of pennies.You don't need the filter part if you have cheap inline one

LRCXed wrote:GL,
I don't think that it is only because of the pump. That is only squirting a small amount of fuel at the very start of the acceleration. It has to do wit the fact that the carbs can deliver the needed amount of air to the motor, with out giving the fuel jets an abnormally high vacuum signal, and drawing more fuel than the motor really needs.

I understand what your saying about the signal strength/fuel metering but I think there's more to it than that. Here's why;

In my HUMBLE opinion, either carb WILL provide adequate air flow and signal strength for low and mid-range operation, which is the area we're really discussing here for MPG. We really are not talking about comparing the carbs as air 'restrictions' - remember, we are restricting the carb already with the throttle plate - so total venturi / bore size is irrelevant. This doesn't really come into play until we crack it WIDE and start to see the limits of air flow through the different bodies.

Two more cents (or non-sense)
Larger carb w/out an accel pump MUST be fatter on the front end, no way around that in my mind. The needed fuel must come from somewhere......to think otherwise is to think the accel pump was added for no reason at all. IMHO the reason it was added was to compensate for the leaner (emissions) fuel circuits in the later carbs. Why else would you add to the cost and complexity of an already functioning system? This would fly in the face of basic production cost economics - a few dollars more per carb/bike/car adds up fast in a volume production scenario - likewise so do all those tiny squirts of fuel every time you twist the throttle off-idle.

So if this theory holds water, why then can the larger carb be more efficient, well because it is providing MORE finely atomized fuel over a BROADER operating range than a carb with an accel pump would (in theory) and therefore should 'stay out of the mains' LONGER. And by longer, I mean over the majority of the range we are using in a mileage comparison scenario - i.e., idling, low speed and steady state cruising NOT W.O.T. hammering.

Am I splitting hairs here? Probably, but that's what were all doing when discussing MPG for bikes that are already FINELY tuned.

As you point out these bikes in the US were restricted around the 1980s+ because of emission rules and also the politcal stance to try and curb Janapnese imports I think.Things like the resistor plugs,tab on the idle mixture screws etc none of which are really needed now at the bikes ages.I agree that a larger bore carb may well be giving better atomization.I can't really say for the acellerator type as they weren't fitted to Standard UK/Euro models AFAIK and I've rarley seen them on this side of the pond.

I'm glad you bring that up, I think it helps bolster my position (damn I'm full of myself today aren't I - glad Larry's still in bed ).

Carbs with leaner front end needs accel pump, leaner carbs also need to be 'in the mains' SOONER and therefore longer or over a BROADER range of operation. I know this flies in the face of emissions, but so does the accel pump itself. Either way this is confusing no matter how you look at it IMO.

Do you mean to replace the straw inside?

Yep.I think about 2" to 2.5" would do it.Even a bit of fuel pipe?

GL, your right about the finer atomized fuel, and the way you explained it. Much better than I did.
Basically we are saying the same thing. I think that the larger CFM has a lot to do with it atomizing the fuel better. I'm having a hard time explaining it here, Not awake yet.

LRCXed, same here, caffeine doesn't seem to be working today....hard to explain this stuff any way

Blindstitch, I imagine height of the reserve pickup tube can be fiddled with to change reserve volume. What do you guys think about making it a bit shorter, to reduce the potential number of times that you switch to reserve? Reason being, I've read posts that state reserve is not filtered and on my tank, I can't fit even the shortest inline filter between petcock and carb without a 90 degree bend/pinch in the hose.

Any thought or suggestions?

My plan is to watch the trip odo with hopes to never use reserve, but you know how that goes .....

Both on and reserve are filtered by the strainer but I wouldn't trust it since it has caused me a lot of problems and is better off gone. You could shorten the straw but then you would be truely screwed if you didn't have some back up gas. I picked up a 33 ounce fuel bottle and a sportman shop and it's in my saddlebags so I am not worried and I think WisconsinCx has done the same after both of us running out of gas the same day.

There has got to be a way to run an inline filter on your bike without kinking it. What if you use a longer hose and twist it around differently than the one you have.

My brother also has this filter on his bike that I cant seem to find anywhere.
The filter is a two piece and can be taken apart and cleaned by the removal of a screw.There is a gasket or oring in it so it can be tightened and used at any angle 0-360

On my bike I can pretty much watch the crap float into the inline filter when I turn the reserve. I don't do it very often maybe twice a season but there is a decent amount of small particles built up and I change the filter every two months just because they are cheap and why not. It's only going to help.

GL,
I have seen the small clear plastic filters at the Honda shop that had one end at 90 degree angle, and one end straight out at the other. I have been wanting to get one, but forget every time I get parts from them. It might help you out.