Curious Fueling Issue

Back from the full ride. Generally everything seems improved. With only the main tap open, I could occasionally see a draw down of fuel level in the filter at stop lights etc. This seemed to not happen as often with just the reserve tap open, and not at all with both taps open (tank basically full). So perhaps some flow resistance at the main tap pre-screen, the clear in-line filter or both. The filters BTW are the sintered brass type, not just the fine mesh screen type. Perhaps the main side one has particulate loaded after around 3k miles.
 
Tornado said:
Back from the full ride. Generally everything seems improved. With only the main tap open, I could occasionally see a draw down of fuel level in the filter at stop lights etc. This seemed to not happen as often with just the reserve tap open, and not at all with both taps open (tank basically full). So perhaps some flow resistance at the main tap pre-screen, the clear in-line filter or both. The filters BTW are the sintered brass type, not just the fine mesh screen type. Perhaps the main side one has particulate loaded after around 3k miles.
Click to expand...
I put sintered inline filters in mine and removed the petcock filters, so I knew when they were cleaned that the line was clean (and is much easier to inspect/clean the inline filters than either the banjo or petcock filters). I stopped seeing particulate in bottom bend the clear lines after.
 
gortnipper said:
I put sintered inline filters in mine and removed the petcock filters, so I knew when they were cleaned that the line was clean (and is much easier to inspect/clean the inline filters than either the banjo or petcock filters). I stopped seeing particulate in bottom bend the clear lines after.
Click to expand...
I've ordered some fresh sintered in lines and translucent tygon line. Will consider removing patcock screens.
 
flow test the fuel lines to check you have sufficient flow remove the carb drain plugs open the fuel tap and check what passes in 1 minute
if you have 200 mains in the carbs you need a minimum flow of 400 cc through both carbs ( 200 per side ) time for 1 min and see how much volume the lines / tap will flow
if you have a sufficient flow rate to fill the chambers there should be no air in the lines if not check taps filters and internal tap bores which can become restrictive if they have viton rubber seals they may have rotated , it may also be wise to purge the fuel lines open both taps allow the chambers to fill then loosen the banjos to bleed any remaining air from pipes it may be a high spot in the fuel line / filter body trapping air
 
Tornado,
Can you post a picture of the clamps you are going to use with the tygon line. I have never used any clamps for a lot of miles and never had a problem but don’t have any in-line filters.Just the ones in the petcock and the screen on the bottom of the carbs.Also,what is your source for the sintered filters?
Thanks,Mike
 
Today is not as warm as last few outings where these issues were happening. But may not be a factor.

And it well might have been. Inline filters close to the engine, can do weird things on hot days. In any case, the symptoms pointed directly to a fuel delivery problem that could be caused by several things, and it seems you have now covered them all.
 
Tornado said:
Always possible but issue remains when turning on either tap (reserve side rarely gets opened so it would've had to clog without much fuel passing through).
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At first start up I open both taps and watch fuel flow through both hoses. After I'm convinced the bowls are full, I close the reserve tap.
This helps keep the tap working and I know it's not clogged.
 
The taps in this tank are BAP and have had about 4k miles of use since fitting a few seasons ago. Tank is also that same age (reproduction tank that I got new). It is cleaned and oiled for over winter storage. No obvious rusting within and still looks like clean steel inside. So debris loading should be minimal.
Will try to reverse flush through the pre-screens on taps with tank in place and fueled using a syringe to see if it improves flow.
 
YING said:
Tornado,
Can you post a picture of the clamps you are going to use with the tygon line. I have never used any clamps for a lot of miles and never had a problem but don’t have any in-line filters.Just the ones in the petcock and the screen on the bottom of the carbs.Also,what is your source for the sintered filters?
Thanks,Mike
Click to expand...
Clamps I installed yesterday on existing black hose (a MotionPro packaged hose, relatively thin walled 1/4"ID, quite flexible).
IMG_20221018_1020382~2.jpg


I find these seal much better than standard Jubilee type esp at these smaller diameter fittings.

Filter and tap:

IMG_20221018_1019309.jpg



Filters from a local motosports shop but new ones ordered from Amazon here:

Race-Guy 1/4" Fuel Filter 90 Degree for 8423-01-9909 Honda Yamaha Suzuki Kawasaki Snowmobile Motorcycle Dirt Bike ATV UTV Quad Replace 8423-01-9909 (10) https://a.co/d/2zbiZkt
 
Is it just a trick of the photo, or does the feed pipe angle in, close to the barrel? Could the fuel be overheating?
 
concours said:
The MotionPro fuel line seals with no clamps on the many, many applications I've used it.
Click to expand...
Hey Tornado, sounds like like a case of fuel starting to percolate in the carbs. If you last fueled up in late sept early oct, you got winter blend gas. Its boiling in the carbs, float is dropping in the froth, then bubbling up the lines. Its better when you are going fast because airflow through the carbs is cooling the body, hence your problem at idle, likely on warmer days. Im also a norton owner, but get this very often in our carb equipped classic cars this time of year. We mix a few gallons of high performance racing type gas to ease the issue. Search fuel blend/vapour lock/percolation issues with winter gas, lots of good info onthe net. Tony, Maple, Ontario.
 
tonycer said:
Hey Tornado, sounds like like a case of fuel starting to percolate in the carbs. If you last fueled up in late sept early oct, you got winter blend gas. Its boiling in the carbs, float is dropping in the froth, then bubbling up the lines. Its better when you are going fast because airflow through the carbs is cooling the body, hence your problem at idle, likely on warmer days. Im also a norton owner, but get this very often in our carb equipped classic cars this time of year. We mix a few gallons of high performance racing type gas to ease the issue. Search fuel blend/vapour lock/percolation issues with winter gas, lots of good info onthe net. Tony, Maple, Ontario.
Click to expand...
Well fuel is a fresh as can be, I have been doing lots of long trips with season on the bike. But I do agree temps might be a clue here. High speed or even continuous moving around town roads at slower speed seems just fine. Its when stopped at long light or in traffic jams etc that the idle dips can happen.
I do have single insulators at head/manifold joint. Maybe carb temps creep up enough to start fuel boiling in bowls and in banjo's, leading to vapour bubbles and build up through filters and reducing flow out the tap.
Gasoline components can start to boil at only 35 Cel according to Wiki. I know my carb bowls get much warmer than that while stopped.
 
Over the summer I had various tuning problems even with ethanol-free premium gas. Presumably it was summer blend but sometimes it's hard to keep track as I buy it in 5 gal. containers and dump it in whichever bike needs a dose. I have read that even with summer blend the Reed vapor pressure in not what it ought to be and I don't understand why it can't be higher.

Most of my starting and low-speed problems have gone away as the day-time temperatures are down to the high 70s, low 80s. In July and August it was over a hundred F and I had much trouble starting after sitting half an hour. Plus, low-speed running acted as though it was over rich. I haven't bought gas since August and still have 3-4 gallons to go. On my pickup I had similar starting issues. It acts flooded and blows black smoke till it clears. If it sits and idles when hot it will vapor-lock and just quit. I can see gas boiling in the glass filter bowl as it picks up heat from the exhaust manifolds. I've added shields that help but it's not enough. If I shut it down, the electric fan starts up and then it's OK. Still floods on startup. The pickup is now on winter blend but the bikes are still on summer blend.
 
Today's long ride observations:
Ran whole day with both taps open. Ambient high teens Celsius. Had 4 one kick starts. First of day/cold engine. Second was after an hour running, stopped for food about an hour. Next was about twenty min later at a fuel up stop, about 4 or 5 min of standing soak. Next was after another 45 min run, 35 min stop. Fifth stop, another fuel top up, 5min standing and she would not fire up until 6 or 7 tries. Bowls were warm, not hot to touch.
Never saw any fuel level drops visible in filters, but occasional tiny streams of bubbles either or both side filters. No idle dips of significance. Then on last 45 min to home, in rush hour traffic, I did see more streaming bubbles both sides, increasing the longer I was not moving. In some of the longer hold ups I did see fuel drops below top of filter one side or other when blipping, first time seen today.
So from this I take it that yes, heat soak into carb can lead to fuel vapourizing/boiling within bowl and or banjo, giving bubbles up lines. In severe cases, enough to reduce fuel flow down from tap. The heat soak might have also affect a poor starting situation. Unsure if over or under fueled when not firing up. I did ha ve throttle open a crack as my standard procedure.

Fuel is non ethanol 94 RON.
 
Last edited:
Tornado said:
Today's long ride observations:
Ran whole day with both taps open. Ambient high teens Celsius. Had 4 one kick starts. First of day/cold engine. Second was after an hour running, stopped for food about an hour. Next was about twenty min later at a fuel up stop, about 4 or 5 min of standing soak. Next was after another 45 min run, 35 min stop. Fifth stop, another fuel top up, 5min standing and she would not fire up until 6 or 7 tries. Bowls were warm, not hot to touch.
Never saw any fuel level drops visible in filters, but occasional tiny streams of bubbles either or both side filters. No idle dips of significance. Then on last 45 min to home, in rush hour traffic, I did see more streaming bubbles both sides, increasing the longer I was not moving. In some of the longer hold ups I did see fuel drops below top of filter one side or other when blipping, first time seen today.
So from this I take it that yes, heat soak into carb can lead to fuel vapourizing/boiling within bowl and or banjo, giving bubbles up lines. In severe cases, enough to reduce fuel flow down from tap. The heat soak might have also affect a poor starting situation. Unsure if over or under fueled when not firing up. I did ha ve throttle open a crack as my standard procedure.

Fuel is non ethanol 94 RON.
Click to expand...
Like Thomasa said, it all has do do with rvp. Its has nothing to do with octane, methanol content or how fresh the gas is. Even with the summer blend, the rvp is not what it used to be years ago. There are federal regulations in place in CANADA and the US that tell the refineries what the rvp is supposed to be, and when they have to switch from winter to summer. I believe its sept 15 in CANADA.
 
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