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  #1  
Old 13-11-2008, 09:16 PM
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Ukkid76 Ukkid76 is offline
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Accelerator pump, "doing without itl!!!"

Well here is one for the records,

I have a 03 1450 Road King it has to date:

(amongst a host of other upgrades)

Pistons ď1550Ē 22868-00
Hi-compression 10.5:1

Barrels to suite 16546-99

Cylinder Heads 16952-99c
Bathtub from the 1340 era converted for the 1450 twin cam

S/E Exhausts 65115-98B

Mikuni carburettor 42mm 28040-02
(Re-jetted subject to Dyno recommendations!!)

Air intake manifold 29635-99

SE-211 Cam Kit-Screaminí Eagle 25152-00

Perfect fit Pushrods 18403-03

Adjustable ignition kit 23704-01

I put all this up to let you know what engine I am talking about,

While at the Dyno shop in Southampton we noticed that the bike had a lul on the map as it was throttled up,

After trying all sorts of things to sort it out we decided it could be the ignition not advancing quickly enough or the exhausts not being exactly right,

Nevertheless the map and the gas analyzer did suggest that the engine was tuned correctly and the air/mixture was as good as one could get it,

So I drove it home and yes it was most certainly better than before,

But as I used the bike it would pink badly if I tried to accelerate from below 2200 rpm in any gear, this continued all the way down through Italy and home again,

I had to drop it down a cog to raise the rpm then accelerate normally, this was a pain and sometimes the pinking sounded damaging!!

I soon realized that it was the acceleration jet pumping in excess fuel and causing the pinking, so I adjusted it to a minimum, while this helped a little it still didnít stop the pinking,

So I removed the accelerator pump pin, (an easy job on the Mikuni42mm) and stopped the accelerate pump from working at all,

Now hears the thing after a couple of rides of about 10ish miles I can say the engine has never performed, sounded, or accelerate better even in this cold weather!!

I can accelerate as much as I like at any rev and in any gear (without being stupid) without any pinking at all,

The only thing I noticed is I have to have the choke on a little longer when first starting than normal but not that much, perhaps this will improve when the weather warms up!!

If you want to know more just ask, Iíll do my best to answer,

Sorry about the long winded thread but I thought someone would like to know what I had found!!

Or is this not a new thing!!!!

Dave Cox
North London
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  #2  
Old 13-11-2008, 09:47 PM
Scotty Scotty is offline
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Re: Accelerator pump, "doing without itl!!!"

Sounds good to me. If you tune a motor and get everything right, you not only give it more power but you make it run more efficiently, and by the sound of it thats exactly whats going on there.
Just out of interest, have you tried running on the high octain petrol that some stations do to get rid of the pinging?
UK high octane fuels range from 97 to 99.

I run the same comp as you with performance heads and high lift cams and find that i get no pinging at 97 octane and up.
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Old 13-11-2008, 11:16 PM
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the_monster the_monster is offline
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Re: Accelerator pump, "doing without itl!!!"

try higher octane fuels and additives, it increases the combustion temperature of the fuel and reduces its urge to detonate. Pinking is caused when the air/fuel mixture explodes outside the normal flame front, often when the temperature inside the combustion chamber is too hot to enable the engine to operate at maximum efficiency. Hence engines run best on cool damp days and the use of water injection systems and intercooler on turbo car engines (the fuel runs cooler and more oxygen rich enabling an more even burn or flame front - a bigger bang for your money).

I suspect that ditching the accelerator pump wouldn't have made a difference, but the time taken to do would have allowed the engine to cool sufficiently to be closer to the temperature at which the heads can operate at their optimum efficiency. This may also explain why the bike appears to be running better on the two ten mile runs, as it would require you to run a further distance for the engine to get up to heat.

It would be interesting to see how the engine performs on a much longer run.

For the record I run a hi-comp 103 stroked motor with 264 cams.
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Old 14-11-2008, 07:16 AM
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Ukkid76 Ukkid76 is offline
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Re: Accelerator pump, "doing without itl!!!"

Yes I do use high octane fuel at all times (when I can get it) and to be honest it doesn't seem to make a difference, well any that's noticeable,

The pinking appears to be a direct result of a squirt of unwanted fuel at 2200 to 2800 rpm anything above 2800 and there is no pinking at all,

If I were poodling along at 65ish in 4th at say 2200 rpm and wanted to accelerate I would have to throttle up slowly or drop it down a cog to stop any pinking,
this is the same if I were doing say 80mph in fifth and accelerated it would pink!!

Removing the accelerator jet has stopped it totally!!

I understand both the above quotes and will try this out on a longer run but to date I am very pleased,

One other thing,

One would assume that when accelerating away from lights or attempting to over take a car ect the motor would hesitate before jumping in to life!!
but that doesn't happen at all it responds to all throttle responses at all times weather you wind it up quickly or slowly!!


Dave Cox
North London
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  #5  
Old 14-11-2008, 08:23 AM
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SJC69 SJC69 is offline
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Re: Accelerator pump, "doing without itl!!!"

I'll start off by saying this is not the answer to your question, but what the accelerator pump does.

A carburetor is a means of metering the delivery of fuel to the engine under various conditions, it works with several distinct circuits which overlap to assist in a smooth transition from one circuit to another.

So basically all or most of the circuits are adjustable and two different circuits can equally perform the same function at certain times.

So most of the time a carburetor is working on compromise especially during transition from one circuit to another, not at ideal or perfection.

To achieve a good quick acceleration most carburetors without accelerator pumps tend to have the circuits affecting this part running slightly over rich to prevent stalling, thus at all other times less than ideal.

This is where the accelerator pump comes in, it provides for just that quick pull of the throttle by injecting additional fuel and thus removes the need for the over richness of other circuits, it is normally adjustable by jet size, timing etc and can be set to operate at different settings and times with varying amounts of fuel injected.

So yes a carburetor does not need to have an accelerator pump and will work quite happily without, but normally if one is fitted and adjusted correctly the whole operation will be far more efficient. It will also be smoother with a much better quick acceleration response along with better fuel economy than one without.

That at least is the theory and the normal outcome.
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Old 14-11-2008, 10:45 AM
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the_monster the_monster is offline
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Re: Accelerator pump, "doing without itl!!!"

If the problem is only occurring at a certain rev range, which from what you have said would appear to be 2200 - 2800 rpm.

The problem may be your choice of head and piston combination. From what I recall, there are fuelling issues when you combine the hi comp pistons with the htcc heads, which by the sounds of things sums up your situation. The cure can be as simple as running different plugs. However, I know with the 16592-08 heads Harley do not recommend using hi comp cast pistons. As to what the difference is to your heads apart the last 2 numbers, I'm not sure.

Have you tried using an octane booster ? as this would give a better burn, I use one all the time on all my bikes, especialy the older ones.
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Old 14-11-2008, 11:30 AM
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BigKev BigKev is offline
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Re: Accelerator pump, "doing without itl!!!"

I remember someone else on here posting a similar thread.

I guess, when you start 'tweaking' your engine, the normal rules no longer apply and you have to see what works best for you.

Keep updating us as you try running through different conditions - I find this really interesting.

Cheers, Kev
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Old 14-11-2008, 12:01 PM
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banquo banquo is offline
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Re: Accelerator pump, "doing without itl!!!"

Interesting post....

Quote:
Originally Posted by Ukkid76 View Post
If I were poodling along at 65ish in 4th at say 2200 rpm and wanted to accelerate I would have to throttle up slowly or drop it down a cog to stop any pinking,
this is the same if I were doing say 80mph in fifth and accelerated it would pink!!

Removing the accelerator jet has stopped it totally!!
That's great, but what it means is that you are comparing better performance on a set-up with no accelerator pump, with one where you had problems, and had to pussy-foot to stop excessive pinking. So, it's an improvement over what you had (and that's good) but it's not optimised, because Mikuni put that pump in there for a very good reason.

Quote:
Originally Posted by Ukkid76 View Post
The pinking appears to be a direct result of a squirt of unwanted fuel at 2200 to 2800 rpm anything above 2800 and there is no pinking at all,

One would assume that when accelerating away from lights or attempting to over take a car ect the motor would hesitate before jumping in to life!!
but that doesn't happen at all it responds to all throttle responses at all times weather you wind it up quickly or slowly!!
Both the above suggest it's running far too rich. The whole point of the pump is that rapid throttle opening causes immediate weakness, because air responds more quickly than fuel. A big dose of air, and not enough fuel causes weakness, and hesitation, until the engine speed catches up. If you can pull a fistfull of throttle and not experience any hesitation, then you must surely be running far too rich already?

If that's the case, you could end up with pinking problems caused by carbon fouling, both of the plugs, and inside the head, both of which can and do cause pre-ignition.

I know you've been on the Dyno, but have you done a plug chop, to see what they look like? Any sooting?

Disconnecting the pump has made things better for you, but all that demonstrates is that something else is wrong, because disconnecting it should have given you a very noticeable flat spot....?

Just an idea....
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Old 14-11-2008, 02:24 PM
Scotty Scotty is offline
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Re: Accelerator pump, "doing without itl!!!"

Quote:
Originally Posted by banquo View Post

Disconnecting the pump has made things better for you, but all that demonstrates is that something else is wrong, because disconnecting it should have given you a very noticeable flat spot....?

Just an idea....
Not so sure you are right there.
I have a very similar set up but use an S&S super E and the fuel pump is pretty much turned off, i only have it slightly turned on 1/4 turn to help with starting, as UK Kid the bike doesn't need it to run well, if i turn it off, everything is fine. And plugs show its running bang on, thats two plug checks, one at around 40 and one around 80
The only time i get any pinging is if i run on normal unleaded. I find it runs best on BP Ultima BP Ultimate UK - 102 octane but runs well on 97 with very slight pinging under load in to high a gear as does UK Kids's. But thats what the next gear down is for
If it doesn't ping whilst accelerating through the gears that tells me all is well. And if it pings under load whilst in a higher gear while under load then thats just telling me its in to high a gear.
I've run this set up for years with no adverse affects.
In a nutshell, high octane and use the gearbox and i dont hear no pinging

I would be interested to hear what the plug chops show on your bike though, i think the jetting might be to blame. If the plug chops are fine i would be tempted to go up one jet size that covers the 2800 rev range. If you dont need the pump that doesn't mean that the next jet up is big enough to cope when it comes off the slow running jet.
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Old 14-11-2008, 02:44 PM
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Re: Accelerator pump, "doing without itl!!!"

Quote:
Originally Posted by Scotty View Post
Not so sure you are right there.
Neither am I; certainly no expert
Like I said, just an idea. Interesting to see the outcome.
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