Disconnect Accelerator Pumps

ah yes but, Keith my old son you are forgetting that the float bowl might already be nigh on half empty because of the flat out 2 mile stright before the slow corner, and as we all know on a low fuel tank, say one third full, that alone can creat a misfire, then you mash it down through the box and squirt raw gas all over the now running lean plugs......

it will run for years this one
CLEM
 
CLEMTOG said:
it will run for years this one
CLEM
Click to expand...


  Well if you continue to issue forth bizare theorys based on cockamamie misconcieved ideas about how things work and expect them to remain unchalenged then indeed it will CLEM, me old son.


    Keith
 
nick7 said:
anyway, since my highly intelligent thoughts on the matter( :D) were comprehensively disregarded by the skilled chap entrusted to thoroughly sort things out a little while back (er, Keith refitted them all without reference to me), and the bike is bloody fab, I am leaving be. But remain unconvinced
Click to expand...

Keith, you're pissing into the wind on this one, but at least you haven't had to endure the personal insults levelled at me the last time I tried to counter the subjective bullshit with a bit of science, physics, practical experience and knowledge.

The real mystery is why , when you know the answer to everything, would you need to get someone else fix your bike! :D :D :D :D
 
I would think after a two mile run at full throttle near 130mph+ for any length of time..the floats still should be full. If not, your carbs are starting to running lean and burning valves and pistons.

Even if the floats could theoretically be near empty, assuming some fault with the float valves, petcocks, fuel filters or fuel tank ventilation..they have plenty of time to refill and the combustion chamber/valves to cool hauling the bike down, braking to enter a slow corner.

images


Just don't go full honk for miles down the road with little fuel in the tank too.
 
G'day Clem

I think your theory is pretty dodgy too. You said you were happy to listen and learn, so here goes ...

No argument that 14:1 A/F ratio is about right. But when you open the throttle, the first thing that happens is a gulp of air is sucked in. But the fuel in the float bowl is much denser than air and it has to pass through a little orifice which acts like a damper valve. In addition, there's a sudden increase in air pressure in the throat of the carb (or loss of vacuum). So with fuel inertia, viscous damping and low vacuum all acting against an instant response, it takes a little while for the fuel flow to catch up to the air flow. In the meantime, the engine runs lean momentarily. It's the job of the accelerator pump to correct that and maintain the 14:1 ratio during that brief lean period.

Re the throttle blipping on down-changes: When I do that i don't go anywhere near throttle openings where the pump ramps would be called into action. The engine is unloaded when the blip happens so it doesn't take much of a throttle opening to pick the engine revs up to match the road speed in the lower gear. Watching other riders, I've never seen a big enough wrist action to think that others do it much different to me.

Also, the pumps don't flood the cylinder with liquid fuel. As Keith said, opening the throttle from idle to WOT will squirt about 0.2 CC of fuel down each intake, which is just a small drop. It will flash to vapour as soon as it hits the back of the hot inlet valve. The rich mixture certainly won't accumulate in the cylinders and make the motor bog down when accelerating out of a corner. The cylinders are flushed with a fresh charge every 2 revs of the motor, so nothing accumulates.

If your bike is having fuel starvation problems, then I reckon you need to look for a cause other than the throttle pumps. The petcocks, fuel lines and float valves should flow more than enough to keep the floats bobbing at or very close to their set height under all conditions.

I'm not convinced by the fuel consumption argument either. Without pumps, the engine performance won't be as sharp as it would be with the pumps, so you may end up using a wider throttle opening to make up for it.

We could argue for ages on the throttle pump issue, but the most important point I can't argue with. It's your choice to set up your own bike and enjoy it however you like. If you're happy with it then I guess that's all that matters.

Cheers,
Cam

 
Don't buy that half-emptied bowl theory either... probably only evolved 'cos nobody could really be bothered to find out why SFCs faltered with the pumps.  The lighter crank don't need an extra wallop of fuel to spin it up, perhaps the pumps only caused flooding in that case.

Have never had fuel starvation problems with stock taps or carbs, either on a dyno, held flat out for minutes or on the motorway, flat out for miles!  If the strainers are clean, flow of the stock petcocks is enough to power the friggin' space shuttle!  It's when the fuel is low and you need to change to reserve while belting along on WOT that problems may occur.

With a responsive engine in a lighter bike, the pumps can become quite superfluous.  In a quest for better consumption, I have reduced the pump stroke of the PHFs on my RGS.  The engine is stock, the bike is bloody heavy, it makes a noticable difference in performance, but one I can live with. Consumption has dropped dramatically, though.  I ran the 3C without pumps in the 36mm PHFs for years, didn't miss them for a second! :D

piet
 
nick7 said:
On the pump jet issue, I recall my old XT 250 had one..presume large singles would benefit, if there is any at least in theory. Have no idea how my KTM 690 Duke R manages, though fuel injected. Does the thing, by whatever means, do something akin to  what a pump jet does?
Click to expand...

Nick,

All fuel injection systems will have an acceleration enrichment routine to deliver extra fuel when required.  Of course there is no physical pump on the throttle body, the ECU just tells the injector to squirt more fuel.  My EFI system on the RGA has a multitude of tables to control acceleration enrichment at various throttle openings and rates.  Reminds me I need to crank them down a bit.  :)

The fact the feature is present on modern injection systems might suggest that the requirement for them is real.

cheers
Steve
 
My take is this, Dellortos Carbs wouldn't have designed them as part of the carb if it wasn't necessary. My SFC carbs don't have pumps so why go to the trouble of designing new carbs with them if they weren't needed. I've always ran them in my triple. I'm pretty sure Dellorto know what they're doing.
But at the end of the day it's your bike and you can do what you thinks best
 
I took 'em off on my 180 because I wanted to do something to lighten the throttle action- something that I have a problem with on the RGS too.  Can't say I noticed much difference apart from a much lighter throttle, although the carbs may well have been shagged.  Still have the hesitation on the RGS that I had on the 180 whacking open the throttle through a corner.  Mikunis cured that problem...

Anyway, it's a totally reversible thing, so why not try it?
 
Reggie3cl said:
  Still have the hesitation on the RGS that I had on the 180 whacking open the throttle through a corner. 
Click to expand...

  Have you checked whether the accelerator pumps are working correctly?



    Keith.
 
Don't be silly, now that I have someone nearby who knows these old bangers properly I am going to confine myself to balancing the carbs and changing the oil only. :D   I do know that they were OK on the 180 cos I measured them.  I think it must be my riding style.  My dyno guy said that this would always be a bit of a issue and changing to CV carbs solves the problem of course.  I really only piped up to say that as it was easily reversible it's worth doing and seeing how it feels.
 
Keith I wish you would speak English, and Bob you almost spoiled this one,
plenty of reasoned argument for retaining the pumps, but not much for removing them, at least a newcomer can form an opinion, and why not try both with and without and take it from there on a personal level, we would all be interested.
CLEM
 
The 750 SFC WITHOUT pumps came after the 73 triples WITH pumps, the first SFC had 36mm Spanish made Amal concentric carbs (no pumps) the later ones had Dell PHF's's and still no pumps, they carried that on right through to the end of SFC750 production, but all the while the road triples and twins ('73 on) were fitted with pumps.

So the SFC with Dells sans pump  was fitted by the factory after the triple with pumps

oh all right I admit it, I am losing this one
CLEM
 
Passing swiftly over Bob's  hypersensitivity to whatever past comments he may be alluding to but which have been long forgotten by everybody else :D :D :D, helpful comments on the fuel injection aspect duly noted, thanks.any idea, given the symptoms I mention, how to disable the auto enrichment to improve that bike too and stop me ending up on my (pert) arse?! :D
Actually it does have 3 mapping settings, before you tell me..but am being too macho to go to "rain" and lose shed loads of power
Nick7
 
CLEMTOG said:
The 750 SFC WITHOUT pumps came after the 73 triples WITH pumps, the first SFC had 36mm Spanish made Amal concentric carbs (no pumps) the later ones had Dell PHF's's and still no pumps, they carried that on right through to the end of SFC750 production, but all the while the road triples and twins ('73 on) were fitted with pumps.

So the SFC with Dells sans pump  was fitted by the factory after the triple with pumps

oh all right I admit it, I am losing this one
CLEM
Click to expand...

Clem,
SFC = PHB!
Paul
 
CLEMTOG said:
So the SFC with Dells sans pump  was fitted by the factory after the triple with pumps
Click to expand...

Because the SFC was a racing motorcycle and therefore didn't need pumps since it didn't (shouldn't) have the throttles whacked open at low revs...

--
Dick
 
CLEMTOG said:
oh all right I admit it, I am losing this one
CLEM
Click to expand...

I don't see it that way. I think you have put forward a case for a no pump carb and that must be possible.

Guzzi small blocks up to 750cc used to run PHBH carbs quite successfully. I have 2 V65's at home and neither suffers any noticable hesitation. Thats about 320cc per 30mm carb choke.

I was prompted to think about this a while ago when they banned pumper carbs from one of the historic class racing series. A guy racing an old LM II was trying to get PHM 40's without pumps to use. Getting non pump carbs to work on thye track, as has been mentioned, isn't as difficult as due to the higher revs the hesitation is minimised due to intake velocity through the venturi.

I think if you do remove the pumps and a hesitation comes in then as long as you are willing to swap some bits then any lag should be able to be reduced to a very manageable level.

To reduce hesitation the venturi velocity needs to be increased. There are a number of ways of doing this but reducing the carbs instead of the usual trend of "big is best"  will do this. Sure you may lose a few legs at WFO but if you value your license these days is that such a bad thing? It will have minimal effect at anything close to legal speeds and will improve response.

A few things can also be done to adjust the carbs. In a case like this the needle valve needs to be more than just adequate. You would want the float level to be at full height. A heavier float may also be necessary to help keep the fuel up near the ports but more importantly, as we are talking fistful of throttle the main jet and needle are the main feed. A change of atomiser with side feeds that go up to just under the float fuel level would help a faster delivery of fuel when the needle is raised.

To try and compensate for this extra fueling at wider openings then a smaller idle jet and bigger slide cut away would assist down low and I'm thinking a shorter needle with a thicker top and more severe taper. Less gap between needle and atomiser would help restrict flow at lower openings whilst the shorter needle with more severe taper would deliver extra fuel when cracked open. I'm still thinking this may still be over fueling for normal use (in sight of a radar gun) but due to the submerged side feeds in the atomiser the main jet can be reduced too.

I haven't had the need as all my PHF's still have working pumps but when I get time I'm going to play with the alpino and see if I can get it to run without causing a global fuel crisis. My first thought is to go from the PHF 32's to PHF 30's. After that I will play it by ear. I do have a set of PHBH 30's that I may experiment with too.

Not anti pump just like to think an issue through for understanding.

Rod


 
There used to be different sized nuts that held the bowl on Delorodes,do the bigger nuts have an effect on keeping fuel supplied.There are also different size needle and seats,from memory the std Pantah one was 150 and they were hard to get in OZ so I went o the next biggest a 200 I think.The bowls on my CV Kehans are maybe 1/4 the Deloro size and I haven't had any starvation problems and that with 38mm carbs.Yes the CV have a different supply and demand need.
 
the different sized float bowl nuts also had different sized main jet holders, this "dropped" the main jet in relation to the float level, i wonder why Dellortto did that/
CLEM
 
You must log in or register to reply here.
Back
Top