This is a fairly long post but I think the details are important.
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I need a little help. I have a 2001 FLHT with Vance &amp\\;\\\\\\;\\\\\\\\\\\\\\; Hines pipes, big sucker, a gear driven cam (not sure which one), and a Mikuni HSR 42. The engine is the stock 88 CI version. I ride mostly at 2400 feet in Boise, Idaho.
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I rejetted the 42 using Joe Minton's formula (and increased the gas mileage from a max of 36 to a max of 43. Not bad.
•17.5 idle jet, leaner than the stock 25 or 20.
•98 needle, leaner than the stock 97.
•50 accelerator pump nozzle way down from the stock 80.
•The main jet is now a 152 not a 160.
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When the weather is hot (over 90)&nbsp\\;\\\\\\;\\\\\\\\\\\\\\;and I have less than 1/2 tank of fuel my bagger is having some pretty serious issues. Namely the bike just acts like it ran out of fuel. I sit at the side of the road and wait... maybe two minutes... maybe five minutes. Then the bike starts up and all is well. Sometimes it stalls again in a few minutes... sometimes it doesn't.
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Yesterday it stalled in the morning before the temperature was too hot but it started up after three minutes. Later in the day when the temp was over 100 degrees it took me fifteen minutes to get her going.
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I talked to a Harley mechanic who said it could be the gas cap or it could be the petcock. So I took her out for a short ride and sure enough... she stalled after ten minutes of riding in yesterday's heat. I opened the gas cap then put it back in. The bike started immediately. Same thing after ten more minutes. This morning I go for a ride to try to duplicate the problem and the bike refuses to stall at all.
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Does anyone have similar experience? Does anyone think the carb mods are the problem? Does anyone have another idea? I'm not thrilled about going on a long tour with this little issue hanging around.
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Thanks for your help!!

 

Sounds like the cap is not breathing properly and it's creating a vacuum in the tank that is not allowing fuel to flow to the carb.

Steve

 

Could be the case ez... it just seems too simple. I think I'm suspicious that rebuilding the carb like I did might have caused the problem. But a vacuum in the fuel tank could sure cause problems. I'll buy a new gas cap tomorrow and see what happens.
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By the way, your bike is a beauty Steve.

 

Sounds like a fuel cap to me too, but a crank position sensor can do that too!
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as for the Joe Mitnon jetting, that sounds wayyy to lean to me, and a different technique than I use.
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I use the Head-Quarters Mikuni kit, which is a needle Jet that is 2 mm narrower than stock and i tune with the stock jet needles. I give the engine the pilot jet that starts the engine the best, and just give the motor the main jet that it wants for best power and use the needle clip settings to bring the main on&nbsp\\;sooner or later to tune out the pinging and bring up the torque. at your alttude a 50 squirter sounds too lean, but its all up to the bike. Im still using the #70 that came in mine. the 60 gave me a sever loss of power so I put the 70 back in.
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my bike has the #27 pilot jet and a 165 main now and is averaging 44 to 46 mpg.
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the hi milage area on a bike is that place just over 1/4 to 1/2 thottle which is where the HQ Mikuni kit leans out the circuit, so leaning out all the other areas seems pointless to me unless the bike just dosnt need the fuel.

 

I've tried the Minton mileage kit, and I found the 17.5 is out to lunch. 20 works in my build, but is still a little lean with 1 turn out on the screw. I find the 98 needle works fine. The 50 pumper is OK but a 60 is perfect. I run the 165 main and it too is perfect. Make sure the vacuum fitting on the back of the carb is properly plugged off if you don't have a vacuum source hooked up to it. That is a good source of leanness.

 

When tuning my carb the only way I have been able to adjust the screw is to drop all the way to a 15 pilot. Even with the 17.5 I can back out the screw until it falls out and the engine does not respond. If I use the 15 the sweet spot is at about 1 1/4 turns. I went back to the 17.5 because of the stalling problem. (When I have mechanical issues I start backing out changes to see if I caused the problem.)&nbsp\\;\\\\\\;For some reason, my bike doesn't appear to like much fuel. Maybe it's altitude, maybe it's the TC88, maybe it's just???
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With the stock setup (25 pilot, 80 pump, 160 main) I got 27 mpg between Boise and Twin Falls. My brother (snowmobile mechanic) and I dropped the needle, went to a 152 main and a 22.5 pilot and I got 41 mpg going home. With Minton I've gotten as much as 43 with no power loss and an exhaust that is now a little grey instead of greasy charcoal black.

I generally don't believe in coincidence. But in this case the rejetting and the stalling seemed to happen at about the same time. By pure dumb luck it could be the gas cap. And it does seem that the stalling is happening on ever increasing frequency. I'm off to High Desert Harley to buy a new cap.
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Question on the petcock. The vacuum hose is plugged into the petcock. But I read someone on this forum suggesting moving the spring to the other side of the diaphram in order to turn the petcock into a free flow rather than vacuum actuted. What's your opinion? Is the vacuum just a problem looking for a place to happen or is it the right way to go?
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I'm thinking of going back to the 160 main with the 98 needle. Not sure it matters much though. Maybe I just like to play.
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Hi Mentor... what model do your ride? Is it a bagger? The mileage you report is just outstanding and much better than most guys get unless they have a newer FI model with stage 1. My brother has an '08 Road King and gets about 48 to 52 riding 2 up.
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By the way... I went to the Harley store and the parts guy said he had the same thing happen to his ride. A new gas cap fixed it. I put on the new cap and so far... so good!! (I must say that $18 for a two dollar gas cap is a little outrageous. Sigh... the price we pay for riding motor company steel.)

 

I ride a Dyna, but 3-4 other guys here with HQ builts ranging from 95 to 120 ci in&nbsp\\;baggers&nbsp\\;ALL get over 40 mpg!
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I would have to say the the Mikuni 42 out of the box is suited more towards a 95 in engine. so I think that fattening up your main may not be nessesary unless it wants in. maybe the 155, and for the pilot, I would not try and use the manual for the pilot tuning. in that they say: if you turn the screw past 2.5 turns and the engine dosnt start to idle down, put the leaner jet in stuff.
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I think that U should use the part the says if the best idle is with the screw less than one turn out part, and tune to that, and&nbsp\\; and get it to run the best at 1.5 to 2 tuns out and dont look back! Im using the HQ Needle jet and the # 96 needle now and i get great milage. and arm stretching torque.

 

Thanks for the input.
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A miracle happened. I put on the new gas cap and the carb now responds to air flow adjustment (just a little... nothing dramatic). At 1 1/4 turns the idle smoothes out and the bike sounds great. That's with the Minton jets with the exception of a little leaner main. I didn't swap back to the bigger main jet.
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I took the bike from Boise (2400 ft.) to the top of Bogus Basin (7000 ft.) and the thing was burblin rich. Okay, I can live with that because I might also head for the Oregon coast where the bike will be a little lean. Overall, it runs great. I can live with 32 mpg into a 30 mile headwind or 43 in calm conditions. Not sure the batwing will allow much better than that.
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I'll have to investigate the HQ build though. The jets seem huge... but maybe you're closer to sea level.
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Thanks again for the chat.
Much appreciated.

 

could be sludge in tank lossening in heat and clogging fuel filter above petcock
flush tank and blow out petcock and lines
chang filter its 12 bucks
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