Could this be an electrical problem...?

[rider]

Okay: 1979 SF.

This has been puzzling me for quite some time. The bike runs fine as long as its moving at a decent speed. If I go slower, or, for some frightening reason, stop at a stoplight my bike will die. As far as I can tell, the engine is flooding with gas. A terrible work around that I developed for this was to barely open the petcock (unless I'm going to be riding at 80mph on a road trip), and whenever I come to a stop light, I need to turn off the gas completely. As I'm sitting there at the stoplight, I need to wait for a slight increase in RPMs or some excessive sputtering and then turn the fuel back on for a few seconds. And I'm almost out of ideas as to what could cause this.

I've taken the carbs out and made sure that they weren't leaking. I've cleaned them out several times as well. I've also checked my petcocks, found a small leak, rebuilt them so that they don't leak, and the problem still occurs. I've also changed all my fluids and my spark plugs (which looked very dark). I've also taken off the airbox and put air-pods on the bike, this doesn't seem to have an effect.

So, could this be an electrical problem? Or an engine problem? I'm assuming either of these are the only two possibilities, but I'm puzzled, and I'll confess that I don't know how to check either one of these.

Also, the problem seemed to get progressively worse over time.

Confused...
--Rider

[Ken Talbot]

From the plug colour, it sounds like you may be running way too rich. Among other things, than can be caused by incorrect float levels. It can also come if after-market jets have been installed that are way too large. First place I would look is the floats and the float valves and seats.

[Dragonrider]

I second Ken...floats/seats or float levels. One other thing to check....SF? Special? Make sure you are not sucking gas down the vacuum line to the octopus (failed octopus)...that could account for it too...

[mitch]

air intakes

Air intakes might be leaking. open some propane up not ignited from a tourch down by the ait intakes if it speeds up shes sucking air..................MITCH

[John]

It sounds to me like the float level is way too high because the float needles are not regulating the fuel flow. Check to see if the needles are actually closing when the bowl is full of fuel, The needles have been known to cock in the seat assemblies, and not seal off. You said that you could regulate the fuel with the petcocks when you come to a stop so I would look there.

[TopCatGr58]

Also,

Are the pilot jet caps still in place?? IF not, they can be sucking up too much fuel directly thru the bowls, instead of thru the access port via the main jet!?
T.C.

[Winterhawk]

Maybe they have aftermarket K+L like pilot jets in it. Install OEM and give it a try. Lots of bike shops can't figure this out because they look on the jets and the number is right but the hole size is way to large.

[xs650mike]

Yeah, I heard on the 650 list that K&L jets are all wrong!

[rider]

Wow, thanks for the list of replies.

Ken and John: It's definitely running too rich in certain places, but never at the start. When I first turn it on everything is running fine. It's only after a couple of minutes that the problem sets in (which makes me really excited when I think I've fixed it!) The float levels are set at what the Clymer manual has told me to set them at. Also, I pulled out hte floats and plunged them in hot water to check for a float leak (all the searches that I had done here told me that that was the likely problem). Yet there wasn't a single air bubble. I left them in the water overnight, and they were still on top when I looked at them the next morning. I think that the floats are all stock, and they look like they're seated right (from the pictures in the Clymer manual). Are there other ways to test this?

Dragonrider: Yes, it's a Special. And the octopus had been faulty, but I pulled that off a year ago. So it has been running off gravity and doing fine for a while. Otherwise, I would have jumped at that. I do have another octopus that I don't think is faulty that I could put on if that would fix the problem.

Mitch: Sounds like a great idea, I'll try to make it to the store tonight to grab some propane to test this with. Actually, would spraying DW-40 near it accomplish the same test? Or does it need to be a gas?

John: When I take the carbs off and reconnect them to the fuel tank, there isn't a leak, they stop the gas after they fill up (I haven't done this test for the last month, so I should probably redo it). How should I test it any other way then this?

TopCatGr58, Winterhawk, xs650mike: The pilot jet caps are still on there, and they this problem existed with the pilots that the bike had when I bought it and with a set that I got from Mike's XS. They're also the stock size that the Clymer manual suggests.

Overall: So should I try to make this bike as lean as possible and see if that fixes the problem and then retune from there? Otherwise are there other tests I should do?

--Rider

[skids]

OK, a couple of things more to check:

Is the exhaust system cracked or the baffle crapped out (look for broken weld under the heat shield by the pegs)?

Is the breather hose and the airbox connecting nipples clear?

A plugged pilot air jet (located in the inlet bell) could cause more full to be drawn because the holes in the sides of the pilot jet will not be "air-bleeding."

[rider]

I cleaned out the pilot airjets in a carb clean that I did a few weeks ago. I just pulled those out and set them soaking in carb cleaner overnight. So I don't think it's them.

When I had the air box on there everything was clear (I did check that). I just replaced the air box with some air pods (with the number of times I was pulling out the carbs to check on this, I got tired of dealing with the air box).

The baffle did blow out on a set of mufflers that was on there before. The problem started with that crapped out set. I'm coming back to this problem after I've put a new set on them.

So the problem existed in each configuration (blown mufflers, new mufflers, air box, air pods).

Also the air jets didn't look clogged when I took them out to clean them originally. I just did it to be thorough.

The new mufflers seem to be sealed on there pretty well, and I don't smell any exhaust coming out of anywhere except the back...

[LoserShoes]

Sounds like the enricher circuit isn't working, or should I say it is and isn't shutting off. Starts good then runs crappy after it warms up is sign of a stuck choke.

Steve

[TopCatGr58]

Hey Rider,

Perhaps the problem continued due to similar changes that fixed one problem but created another? You had airbox, but bad pipes, fixed bad pipes, but then put on pods. Have you tried running it without the pods for a little while?

Some Pod filters are known to have too thick or prominent a lip around where they fit onto the carbs, restricting air flow into the airjets, causing a severe rich condition, and poor performance in the mid/higher rpms. Just another thing to look at??

Also the 79SF carbs have the carb body float vent ports just above the bowl fuel inlet ports where the "T's" connect. Although you've cleaned the carbs, folks have not realized that the vent tubes that connect to the vent "T's" had gotten clogged, and so wasn't venting the float bowls properly. You have Pods installed, so where/how have you run the bowl vent lines?? Hopefully you haven't "T'd" them to each other??
T.C.

[rider]

Yeah, TopCatGr58, I didn't connect them together. I figured that would be bad. But, I also didn't know what to do with them, or what to do with the big tube that attached near the bottom of the breather box. So I just left them unattached. Do you have any suggestions of what I should do with these hoses? I don't think that I want to cap them off, but I'm not sure if I want to leave them completely open.

--Rider

[TopCatGr58]

Hey Rider,

Check out crankcase breather thread for suggestion for large hose!

For the carb ones, you can put them onto a "T", and then put a fuel filter on the end of the single line coming off the "T", that way they are vented, and bugs and stuff don't get into the line!
T.C.