Measuring accelerator pump output-Boxer

I've never tried to do anything like this, but one idea is just to pump each carb 10 or 20 times to get a larger volume to measure. But I'm not sure how consistent these pumps are, ie, they may have a normal variation (for a single carb) of +/- 10% or so from one operation to the next. I'm not a statistical expert, but with a variation like that, the more samples you take, the more the real difference would be lost or "averaged out".

Another thought would be to get very small glass tubing (like used to capture blood samples in a med lab), and just touch the tubing to the drop of fuel from a single sample. Hopefully the surface tension of the fuel would cause it to be "sucked up" into the tubing. You could then get a relative comparison of % difference from one carb to the next (length of fuel in the glass tube). If the ID of the tubing is accurate and known, you could also calculate fuel volume.

Just a couple thoughts... may be other better ideas given some time and thought. Let us know what you come up with!


Rick

 

David: If you have any interest in seeing such a thing, I can scan and email a copy of a two-page article in the Lancia Club newsletter dealing with accelerator pump output in 60's vintage Lancias, written by the Tech Advisor. It seems that most carburetted Lancias put out far too much fuel from the pump jets, and he discusses what can be done about it. Send me a PM with your email address if you're interested.

 

Years ago when I rebuilt the 40 IDS carbs on my 911 I remembered measuring the accelerator pump output. I looked out in the garage and sure enought there was the device I used to measure this output. I had to make it and I used a small plastic tube (don't remember what the tube was) and then I scribed a line on the side of the tube at the volume needed. You can get medical syringes or irrigating syringes from a medical supply house or dental lab or office. These can measure just about any volume...10th of a cc. Just draw up .8cc of gas in the syringe and transfer it into the tube. Then mark the height of the fluid on the side of the tube. I had a string tied to the tube to lower it into the carb and under the pump jets. This should give some way to measure within +-.1cc./ml. I really wonder how accurate the output needs to be as it just supplies a sudden burst of fuel to compensate for the lag in fuel between the current throttle position and quick acceleration and until the carb's regular function catches up. (The tube's outside dia. was about the size of a pencil so I think the tubes mentioned above might be too small). Well good luck.

 

If what you are trying to do is properly tune the pump shot. There is a more direct method. I did it for my Daytona. And, I will do it for my 365bb boxer, probably next week.

The tool you need is an LM-1 or LC-1 wideband AFR meter from Innovate Motorsports. These are the ONLY 2 widebands that will work for this. All others ( AEM , DynoJet, et al ), are WAY TOO SLOW to do this. The LC-1 is so fast that it can pick out differing individual cylinder mixtures at the tailpipe, up to about 2000RPM on some cars. New toy for setting idle mixture screws comming soon for this one.

The LM-1/LC-1 record actual AFR/Lambda fast enough that you can actually see the change in AFR vs. time graph when you hit the accellerator. It becomes obvious if the volume is too high/low or the orifice is too large/small. Becuase the shape of the trace in the graph will either be shallow and long, or deep and short, etc.

Also great for jetting, etc.

 

http://tools.baumtools.com/popup_detail.jsp?id=15972

Designed exactly for what you are asking.

You may also use something like a miniature syringe used for diabetic or veterinary applications,


KO

 

Yep. I've done it "old school" as well. Gunson's Color-Tunes, etc.

I have used injection/mixing syringes as gaduated tubes for such things.

A standard #22 mixing needle/syringe holds 3cc with 0.1cc gaduations. And, the needles screw off. ( that just doesn't sound right )
A box of 100 is about $25.00 You can probably get a few at the local pharmacy on the cheap.

The #26 syringes are 1.0cc and have tighter graduations, usually. I think that's the smallest one with a removeable needle.

On a DCN ( Daytona ) , it's easy to remove the pump nozzle and press the syringe ( less needle ) in with an o-ring. I'll have to look at the Boxer carbs to see if the same works.

Did you catch my thread on adjusting the float height with shims under the needle-valve seat and a straw?
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Dr. mike, I read that with interest as well, and actually had a few questions.
I also added a link to your carb adjustments in the 'Boxer Repair Thread' sticky over in the Boxer section. Any follow-up information you might have as to how well it worked out would be great!

David, this is also an interesting topic you have here, and I look forward to see how it works out. When I get around to my carbs, hopefully I can do the float adjustments and accelerator pump adjustments at the same time.

If it works out well, please link it to the boxer repair thread.
John

If anyone else knows of any interesting boxer repairs, please link it to the boxer repair thread over in that section.

 

I don't know if this is too late or if it's already been covered but I saw this a couple of weeks ago.
Maybe this would help?

http://cgi.ebay.com/Carburettor-Pump-test-tool-Dellorto-DHLA-Weber-DCOE_W0QQitemZ300101019634QQihZ020QQcategoryZ72205QQrdZ1QQssPageNameZWD1VQQcmdZViewItem

Bob S.

 

Here is another:
http://www.biekerengineering.com/products.htm