Topic: idling issues after about an hour of running. help?

[clayman74]

it doesnt often do this but a few times after a typical day of riding around town my 76 550 will start to choke up a bit. it will die with the throttle closed and loses all low end power.

gonna pull her in the garage and check everything out but any help or ideas would be great!

[scunny]

hows your charging system ?

[TwoTired]

Low voltage may be a possibility.

So could spark plugs sooting up.

Do we assume you have a totally stock bike, like what rolled off the showroom floor?


Information systems work like this:
Garbage in, yields garbage out.

[BobbyR]

Certainly check your plugs. You use the term "around town" so I assume stop and go or low speed. These bikes like to run, and they run better if they have been really run. Check all of the usual suspects including a bad plug wire, these things use waste spark so the motor is part of the circuit, if one wire is dodgy or a plug fails the mating cylinder will not fire.   

[dave500]

check those plug caps!!the restistance should be around5khm,ill almost lay money on it.

[TwoTired]

I'll almost take your money!



 

[scottly]

Clay, this is how I would approach this problem. Since it sounds like the bike runs ok when cold, and the problem shows up when it's warm, I would suspect a rich mixture. That's why a choke is used for cold start-up. Since it does rev up ok, I wouldn't tend to think it would be ignition related. As others have said, read your plugs. Trouble-shooting properly done is a one step at a time thing. Check your plugs and report back.   

[dave500]

might just be time to go over the points/timing etc.

[scottly]

I repeat: check (read) the plugs and report your findings, before you go off on any wild goose chases...

[TwoTired]

Could also be something as simple as a dirty air filter.

...or, that it hasn't had a complete 3000 mile 3/mo tuneup in 20 years.   

[scottly]

Plugged air filter rears it's ugly head the most at high rpm, full throttle operation. I learned this lesson the hard way, when I finally gave up trying to fix my '66 C200 and took it to the honda shop. They told me the rings were wore out, and charged me a fantastic amount of money to "Fix" my bike (at the time, it was a fantastic amount of money; I was about 14 years old). Anyway, it turned out, (no thanks to the Honda shop,BTW) that the whole problem was the plugged up paper air filter. (Yes, I had blown it out with air, numerous times)

[TwoTired]

My experience with the paper air filters is that they get too restrictive with about a year of use.  Then the plugs start to soot up.  Honda wants you to replace the filter every six months/6000 miles.  Sooner if you operate in dusty conditions.  You can back blow the filter a few times.  But, it will never flow "as new" ever again after use.

Reports are that if your bike has a flow restrictor ahead of the filter (some euro models), you can get longer life out of the paper filters, as the filter does not provide the most significant flow restriction in that case.

[BobbyR]

My experience with the paper air filters is that they get too restrictive with about a year of use.  Then the plugs start to soot up.  Honda wants you to replace the filter every six months/6000 miles.  Sooner if you operate in dusty conditions.  You can back blow the filter a few times.  But, it will never flow "as new" ever again after use.

Reports are that if your bike has a flow restrictor ahead of the filter (some euro models), you can get longer life out of the paper filters, as the filter does not provide the most significant flow restriction in that case.

What would be a good alternative to paper filters? Or is just changing out every six months the best practice?

[mick750F]

   One of these would do the trick...I think TT likes them. 

http://www.denniskirk.com/jsp/product_catalog/Product.jsp?skuId=30803&store=&catId=&productId=p301214&leafCatId=&mmyId=#fitment

Mike

[TwoTired]

I switched all my 550s except the 78K (still has stock, restrictive, exhaust system) over to the Uni NU4055 Foam type.  Clean, re-oil, and reuse every 3-6 months.  It was the best economic alternative I could find, as the stock paper filters got to be $50 per replacement.  (Which is why I tried to double the time interval/use out of them.)

Technically, I don't think the foam filters the air quite as well as the paper one.  But, since I'm not riding on/in dusty roads/environments, it is an acceptable trade off.

Keeping the air filter clean also helps the fuel mileage quite a lot.

[clayman74]

now i feel like a jerk. this many replies already and i left out that its running open velocity stacks and a dyna3 haha. otherwise pretty much stock. the motor got a rebuild about a year ago but i have only had it back on the road recently.

thank you guys so much for all the suggestions.

[clayman74]

reporting back. had a feeling it was a fuel flow issue. seeing as i have the CDI ignition and the plugs are in good nic i stared her down for a bit and realized the fuel lines i had run were damn near laying on the intake manifold.

diagnosis: vapor lock

prescription: fiberglass insulation boot from dads old chevy.

but you guys have got me thinkin on things to go over during this "shake down" period.
thanks guys.

[scottly]

Hmm, vapor-lock? I don't know. The manifold shouldn't get that hot. As the fuel vaporizes, it has a cooling effect....

[clayman74]

well my other thought was not enough air coming into the tank to replace the gas going out. so just to be sure i did a quick "shim" under the filler cap edge with a piece of bailing wire. either way i rode the 15 miles home and no problems. we shall see. as i said its shakedown time and every night im in the garage doing post ride checks.

[scottly]

There was another thread somewhere on here, and someone suggested a plugged gas cap vent. The person with the problem reported hearing air hissing after the motor was shut down. Hope you got it fixed!!!

[xenoscr]

Was the gas tank lined with Kreem or another sealing product? I had issues with the 750 when I stupidly sealed my vent hole with Kreem. Lesson learned.

XenosCR

[dave500]

scottly,that air hissing may have been pressure escaping from the cap,mine does that.,if the bike has been left for a day all is silent,then lift it off the stand and shake it and itll hiss a little.,if its hissing either way in or out it should somewhat,if theres no noise that may be worse ,no pressure in or out.

[scottly]

Some good points there, Dave. However, if the hissing is due to low air pressure in the tank, it would impede fuel flow, whereas higher pressure would aid it. I have experienced the hiss after shaking my bike, which I always attributed to higher pressure.

[dave500]

um,i think if its hissing,and say it is low pressure,(vacuum)surely gravity fed petrol couldnt cause that much noise(vacuum),then if it did that would equate to flow somewhat?but then again if you had high pressure from a blocked vent say on a ride ,the pressure build up would cause flooding?where i live its hot all year round and fuel expands easily, i dont have experience with severe cold weather,if my vent was blocked ide end up with a 45 litre tank or carb flooding.,if the vent is truly blocked the bike will stop or stumble badly all over the rev range in a short while,i wouldnt expect to get an hour of riding with a blocked vent?

[scottly]

You may be right, in that the hissing is more likely caused be positive pressure. One thing for sure is that if the vent is plugged, the gravity feed of the fuel will indeed cause the pressure in the tank to decrease, eventually to the point of restricting the fuel flow. I once flattened an unvented tin fuel can on a big block mopar during a test drive, with a stock type mechanical fuel pump.