Fuel flow through 32mm amal bowl

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I noticed this problem after buying a set of carbs from Jim, the PWK's and called him on it saying it starts to crap out at highway speeds. He suggested a fuel flow problem.
"Check your cap vent, measure your flow out of the tank. I haven't had anyone call saying they were having problems." I am paraphrasing of course.
So Jim, I love these carbs but are you now saying there may be a fuel flow problem with your carbs and you are looking into it?
I would really like to know as it really sucks riding to 70mph and having to slow to 55mph or slower for the fuel to catch up.
I checked everything. It never did this with my Amals
 
How much water does a PWK flow in comparison?

How comparable is water to gasoline for this test? The specific gravity of gasoline is 0.6 - much lighter than water.
 
The Mk I Concentric 900 series float bowls have the float needle seat machined into the casting, not a removable seat. They were available in a variety of seat sizes. As I mentioned above, the standard size for motorcycle carbs was a .100" seat opening, with .125" available for high flow, and a .156" opening for alcohol use. For alcohol use there was also a different float needle that was machined for more flow around it. In addition to the motorcycle applications, Amal supplied float bowls with smaller openings, .052" and .062", for lower flow applications like stationary engines. If you ended up with one of the lower flow carbs on a motorcycle, you could certainly have problems getting sufficient flow for high rpm.

The different float bowls are still available at

http://amalcarb.co.uk/generic-900-series-mk1.html

If they have a larger option available for alcohol, I haven't run into it.

As far as I can tell, all the Mk II Concentric float bowls have the standard .100" float needle orifice. I would think they would have a larger option available for alcohol, but if so, I don't have any info on it.

Ken
 
I'm researching fuel flow because I learned that a few customers had problems with the JS flatlside carbs starving for fuel. Something changed with the manufacturing process and now the float level has to be set up differently. This was hard to figure out because only a few customers had this problem and I did not have this problem on my "test" carbs.

They should flow about 8 oz a min with a full tank of gas (7 oz should be OK). To get this right use a 4mm (.160) tall metal strip and place it under the float tab, then force the float all the way to its limits to bend the tab (see photo).

Fuel flow through 32mm amal bowl


This should give you about 4mm of float height (.160") before the tiny spring loaded tip of the float needle starts to move (see photo). You can get as much float height as you want as long as the float still shuts off the fuel (idle is not effected).

Fuel flow through 32mm amal bowl


So all this fuel flow testing is to make sure that the flatlside carbs are working well and adjusted properly - those who experience starvation - take the steps explained here. I now test the fuel flow (and check or modify a dozen other things) for every JS flatlside carb (PWK) before it goes out. I appologise for any inconvenience this fuel starving may have caused.

I can get up to 10 oz a min with some drilling and this is what I now do for single carb customers (single carbs need more fuel than dual carbs). I recently made a full throttle run through the gears to 100+ mph with a modified 34mm JS flatslide single carb and had no missing.
 
Hi Jim, mine only faulter very occasionally after big throttle openings up hill on twisty roads, usually after being cranked hard over on big sweepers, just baulks a little when I get up right again. Does this for both left and right corners and big throttle openings.
Do you think this flow issue would be the culprit?
I have tried same piece of highway with just one tank fuel valve open and again with both fuel valves open , so not an issue of flow from the tank.
Regards Mike
 
Brooking 850 said:
Hi Jim, mine only faulter very occasionally after big throttle openings up hill on twisty roads, usually after being cranked hard over on big sweepers, just baulks a little when I get up right again. Does this for both left and right corners and big throttle openings.
Do you think this flow issue would be the culprit?
I have tried same piece of highway with just one tank fuel valve open and again with both fuel valves open , so not an issue of flow from the tank.
Regards Mike
Click to expand...

Sounds like you're a bit rich. Raise the needle clip one notch (or order a leaner .099" needle jet and start with the needle clip in mid position).
 
Well, this has been very educational. Thanks for all the comments. I have read the Amal tuning guides and everything else I have been able to get my hands on. They may be a good starting point, but each cylinder may breathe a little different and each engine may be a little different, especially with the age and wear on some of our engines. Each carb may come from the manufacturer set up a little different, too. Apparently Keihan's quality control is fallable as well.
Sid Biberman once wrote a very good article once about tuning Vincents. He basically said that if you listen to your engine, it will tell you what it wants. No mention of measurements, numbers, calculations or high tech test equipment. Listening to your engine is part art, part experience. Some oldtimers can tell by the sound of a motor if it is running lean or fat or if the carbs are not balanced. For me, it has been a lot of trial and error (mostly errors). It is probably time for me to re-read Phil Irving's book "Tuning for Speed".
 
Old timers can't heat that well any more and the gasoline is piked with lean burn oxidizers so might suggest a CHT and EGT gage and maybe O2 sensor to diddle into optimal w/o so much guessing or risk. Then a stop watch and a measured strip.
 
I confess to using my old Color-tune and I have an exhaust gas analyzer for initial setup, but I still like to smell the exhaust too (may be partly to blame for my idiosyncrasies). There is no substitute for road testing. Carburetion has always been my area of weakness so I have worked on that for a long time, like a weak backhand stroke. I have access to a dyno but right now the local club members are getting their bikes set up for Bonneville. Plus I don't feel like spending a day or two fiddling with tuning, since I don't ride at the edge much anymore. Where I live has extremes of temperature (95 degrees today) and altitude (6000 feet to 14,000 feet), so I there is no ideal setup that will work all the time. Most of the time when I ride with others I will hang out at the back of the pack and let the modern bikes take the lead and just casually cruise along. Let the 'busas and ducatis and whatever else take the speeding tickets and hit the deer and elk. Plus, I still have a few other parts of the bike to fiddle with. It still has the original alternator, zener diode, etc. and the isolastics have probably never been adjusted. It has come a long way since I bought it two years ago but is a now a good rider if not yet perfect. I plan to go to Wyoming, which may give me the time to do more fiddling and road testing.
 
I saw this thread and it looks and feels like what's going on with my carbs. (Thanks hobot for pasting it into my funky thread...)

I took my PWK 32's out today and bent the tab to raise the floats a little. They look like they will be a little higher so hopefully the fuel feed is better on highway speeds. I took the bike around the neighborhood but I can't get recreate the issue unless I'm going 70+ with heavy throttle for a few miles. Gotta either get on the freeway or one of my favorite country roads to tell.

I'll report back my findings in case anyone is interested.

Just for note I followed the directions I a 4mm spacer to measure the tab bending.

The carbs looked good for being on the bike for 6months. Slides are still shiney and everything looks in order in there. Just a little carbon but with a quick spray it dissapeared without wiping them.
 
OK so I took the bike out and officially tested it on the same road which I could not get to 100mph on. I also took it up a 5 miles grade against the wind where i experienced the fuel loos earlier with my wife aboard. I am happy to say that bending the tab and adjusting the floats higher made a big difference. I was not able to starve the fuel at all during this ride.

On the grade I was running the bike at a constant 75-80mph in 4th and it was around 5k rpm and heavy throttle. Head wind was around 25-35mph so combined with the speed and uphil;l the bike was put in a demanding position and heavy throttle was needed. Didnt starve at all, just kept going and tons of power.

On the way back I took a country road where there was not much wind, if any it was at my back. The road has some ups and downs and I decided to do a top end shoot at a couple of the dips. I couldnt do much though as I ran across three cops on the road so far.

On the first roll on I got the bike up past 100 and almost to 110mph! I saw the rpm climbing around 6k so I let off. The whole time I had tons of power. Totally different than the other day. As a sanity check I ran the bike up again on the next dip to see if I was tripping out or not. It spun up no problem. This thing is awesome above 75mph now. I never really mess with the bike in the top end but now that this bug is squashed its a different animal. I feel like I had a governor on the damn thing hahah

So to recap I just followed the directions on the 4mm bend the tab dealio and I guess that was enough to keep the float bowls filled during high throttle times. I cant complain about getting close to 110. thats more than I ever wanted.

Fuel flow through 32mm amal bowl


So if anyone else is having the problem please do yourself a favor and take the 20 min to pull the carbs and do the fix. You will be glad you did.
 
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