Intermittent Problem

[hillsy]

My friend thinks there is a proportioning valve in the rear carb so we are going to check that too

There isn't - the float is the only thing that governs the fuel level in each carb.

[Lechy]

But there is a screen behind the float valve body that can get blocked.

[emoji41]

[OhmsLaw43]

Replaced all that

[WintrSol]

I’m actually going to put a pressure gauge between the carbs to see what’s going on. Going to machine a straight tap instead of a petcock to see what that does too. My friend thinks there is a proportioning valve in the rear carb so we are going to check that too

You will find that the fuel pressure it really low - when pressure builds a bit, the pump shuts off, until a float valve opens.
No proportioning valve, just a pass-through above the float valve inlet. When the rear carb is full, the fuel goes on to the front carb; some may go forward while the rear is filling, just because of the restriction in the float valve of the rear carb.

I really think you should see if the fuel pump flow rate holds up through a whole tank full, just to see if the blockage is in the screen above the petcock, or a blocked fuel vent. The results of the test will differ, depending on which it is.

[OhmsLaw43]

Now it’s interesting. Rode the bike home (36 miles) with the petcock on reserve and it ran fine. We have had the petcock apart so maybe we didn’t get it back together right??? It’s over $100 for a new one.

[navigator]

There are brand new Aftermarket Fuel Petcocks on ebay for around $20.
Also many used OEM.

[hillsy]

Kits are the way to go with fuel taps - you rarely need to replace the body.

[Herb]

Have you thought about a sticking carb float? I had a bike that the float would stick in the up position, but not every time I rode.

[OhmsLaw43]

Found a new one on eBay for $50. Won’t be in until Monday but it’s raining all next week anyway

[hillsy]

Found a new one on eBay for $50. Won’t be in until Monday but it’s raining all next week anyway

Did you take the old tap off and look at it or are you happy just to keep throwing money at it?

[OhmsLaw43]

At this point I’m ready to part the damn thing out. 50 bucks is a small amount when you suspect the only part left in the fuel path for both carbs. I’ve tried everything electrical except for the ignition and the kill switch and even ran the bike with the fuel cap off to prove it’s not a venting issue.

[hillsy]

The front carb is angled down whilst the rear is near horizontal. This can create issues peculiar to the front.

The LC had both carbs angled down and was notorious for the needle jets to wear out prematurely.

I'd be 99% certain you have a fuelling issue here - you just have to be a bit methodical with checking everything out.

[OhmsLaw43]

Took the petcock back apart and pretty sure I found the problem. The cone that selects between on and reserve had a worn slot in it. When on it only went half way. On reserve it would catch and go full reserve. I’ll know more tomorrow when I take it for a test

[OhmsLaw43]

I’m done. Finished over it. Did the same thing again this morning

[Lechy]

Looks like you need to go back to square 1 and start your investigations over. I can't remember if you chaged your fuel lines (too lazy to re-read from post 1), Old fuel lines can disintegrate from the inner bore causing a blockage. New fuel lines can easily kink if not OEM, Take a flashlight and closely examine the lines with the pump in place, easily kinked just before entering and leaving the pump. Remove the tank and make extra sure that the tank is not going to trap or move the line from the rear to front carb. With all lines in place, remove the fuel line from the front carb and from the petcock, replace the tank blow through to see if there is a clear passage (not a good idea to use compressed air as it can damage the valves and springs in the pump). Remove the petcock and blow back therough it in run and reserve positions. The pump runs at around 3 psi. Next time it happens, immediately feel the pump to see if it is pulsing rapidly or not, if it is rapid, you have a blockage from tank to pump, at idle the pump should pulse every 10 seconds or thereabout. A while back My pump went out so I got a Chinese one from E-Bay, didn't last 1000 km, got a Japanese made pump for a Mitsubishi locally US$ 30, cut the mounting lugs off and it fitted perfectly, never had a problem since.

[emoji41]

[rocksandhammers]

I'm pretty sure he said he replaced the fuel lines and that they weren't kinking. So far the only part of the fuel system it sounds like you haven't inspected yourself is the actual carbs. You said you had a guy do them that was good at carbs. I think it may be time to crack into them, at least the front one. Maybe the float levels got fucked or a jet got clogged that he missed. You won't know for sure until you inspect it yourself,

So far it seems like everyone is focused on the fuel system, and probably rightfully so, but is it possible he has a bad ignition coil or something going to the front cylinder?

[OhmsLaw43]

Yep new fuel lines, new fuel pump with another one on the way and all the electrical has been replaced. It’s funny that in the afternoon it runs better and actually made it all the way home (with traffic slowing me down) with no problems. When it fails it’s just like it’s running out of gas. First the front cylinder starts sputtering and popping then the the front goes dead. After about a minute the rear cylinder goes dead and I have to pull over. If I wait for a couple songs on my Bluetooth I can fire back up and run again. Seems to happen more in the cold morning than the warmer afternoon

[Lechy]

You could have a blocked fuel cap vent, next time it happens pull the cap off and listen for air being sucked into the tank.

[emoji41]

[rocksandhammers]

[quote="OhmsLaw43"It’s funny that in the afternoon it runs better and actually made it all the way home (with traffic slowing me down) with no problems. When it fails it’s just like it’s running out of gas. First the front cylinder starts sputtering and popping then the the front goes dead. After about a minute the rear cylinder goes dead and I have to pull over. If I wait for a couple songs on my Bluetooth I can fire back up and run again. Seems to happen more in the cold morning than the warmer afternoon[/quote]

Lechey and the others would know better than I do, but this sounds like an issue in the carbs. Like maybe the jet needle is getting stuck because there's an issue with the throttle slide diaphragm seal?

[OhmsLaw43]

I’ve ran with the cap off and it still does it. It’s just odd because it affects both carbs. Also when it starts doing it I can still get on the gas just fine