Bonneville America Forums Forums Technical Forums General Tech Fouling Left Plug

I'm working on the 01 Bonneville America that was in the movie "Daredevil". It has been sitting for 3 or 4 years, has 300 miles on it and the owner needs help getting it running. I cleaned the carbs, put in new plugs, changed oil and filter, changed the battery, but I can't keep the left cylinder from fouling the plug. It doesn't foul at idle, just when the throttle is opened and after its been run 10 to 20 miles. Any ideas? Thanks, Jim

Checked float height also.

Switched coils and checked resistance in spark plug leads.

Check the left float. after troubleshooting a similar problem thats the one thing that seems most likely, assuming it's not OIL fouled, in which case there may be uch more serious problems such as rings.

Ok, well we posted at the same time. Is it oil fouled or dry and sooty?

Does anyone know the spec for the float height. The left and right were the same, so I moved on.

Before you start ripping it apart - Get a can of Sea-Foam and a fresh set of plugs. Put the recommended mix in some fresh fuel and see if it works itself out. Sounds like it gummed up somewhere. A likely place is the float is hanging - However, It would seem to me that if it where the float alone, the problem would be worse at idle that at speed.

Would you believe I did use Sea-Foam in it. Needle valves are working free and easy. I cleaned the seats with carb cleaner and a Q-tip. This bike is 100% stock. What about the diaphams in the carbs, would that cause this problem? If it doesn't foul at idle, doesn't that eliminate a broken oil control ring? The fouled plug is black and wet. I'm getting pretty quick at yanking the carbs off. Closest dealer is 2-3 hours away, wish I had a book with some specs.

Also check that the choke plungers are both going in all the way when you push it in. And if it's a california model try looking at the evaporitive loss (emissions) system. Thats what was causing mine to foul, tho on BOTH cyliners. Not sure if it could affect only one, but there is a hose coming from the carb balance tube that goes to a valve on the Ca models. The valve apparently wasn't opening all the way causing the floats bowls to fill higher than normal, and when i removed the hose and replaced it with one that just hangs down below the engine the problem seems to have ceased and the bike is running noticably stronger. seems that would always affect both sides, but you never know.....and it could be some other problem with the EVAP. Of course if it doesn't have the evap system the point is moot. But having been in a movie i would think chances are good it's a california bike. and even some other states have been known to sell bikes equipped with the EVAP, which i'm beginning to believe may be more problematic than anyone has realized and may be the cause of a lot of fuel problems. Try the hose trick i mentioned and cap off the carb and manifold nipples and see how it does if it has the EVAP crap.

The diaphrams WILL cause a problem if they were cracked. One way they often get cracked/ripped is the carb is gummed and someone twists the throttle. If the carb is bound, that can rip the diaphram. If you twisted the throttle and felt a snap. That could be a possibility. Please don't ask how I know - Its an ugly, embarrassing story.

What happens when they crack?

The first indication is that it won't run for crap. I don't know the technical reason, but suspect it upsets the air/fuel mixture - probably a vacuum thing. And somewhat like you indicated, the problem isn't particularly noticable at idle, but when you open it up (in my case, anyway) it would break up and miss fire. There was a lot of black smoke and the plug did foul on that side. It should be easy enough to check. But that seems like far more a remote thing than just gumming up. I'd hate to see someone tear stuff apart when they may not have to. But, if you're exhausting the posibilities - exploritory surgery is an option. Good luck.

Everything was moving just fine when I first tore into it. The float bowls and all the jets below the fuel level in the bowl were covered in a green goo. The slides moved just fine. I might pull the diaphrams out and give them a good look. The bike didn't run all that bad today when I went to get some more fuel, but this isn't my bike and I don't know how it is supposed to run to begin with. Maybe the more I run it, the better it will be. I need to make a run into town tomorrow for a couple more spark plugs and a 18mm spark plug socket, so I'll report back in tomorrow. Thanks for all the input from you guys. These forums are great.

Wierd that the plug would foul because i would think it would actually run much leaner. With a diaphram thats got a crack there wouldn't be enough vaccum to pull it up, so the needle wouldn't go up as high making it leaner. At least thats what it seems like to me, tho i could be missing something. But the thing that make the slide rise and thereby making a richer mix is the vaccum pressure. If i'm wrong i'd like to hear an explanation because i'm curious.

Even though you cleaned the needles and seats, they could still leak. It doesn't take much to lose the seal and when it's gone, it's gone. Black and wet is fuel, so it's a spark, compression or fuel problem. You didn't say, but you might want to run a compression test. If you run out of options get a couple carb kits. Or just the needles and seats if possible.
Check carb synchronization too.

I just read a post on another site that called for 17mm float height, is this correct? This bike was set at 14mm. Thanks bigbill, I don't have an adapter for this size spark plug. The seats just press in, right?

Carbs off and upside down the float height is 17mm.
Carbs on you can check the fuel level with a clear hose on the bowl drain. The level should be within 1mm above the seam.

According to the book - the float needle seat is bonded in position.

I checked my flaots as per Grump's advice. But theres a second way if you want to double check. With the bowls off, set a caliper to 17mm or use any neasuring device that works for you. Put a small container under the bowl, then hold the float up being carefull not to put pressure against it at it's stop point. Turn on the tap, then slowly let the float down till it just begins to flow and measure the bottom of the float to the mating surface at that point. The trick is to have the measureing device lined up at one end to the mating surface already when you begin to lower the float. If you bring up the measuring device to line it up AFTER you have the float in place your hand will likely move some making the measurment innacurate. Having the measuring device already lined up to the mating surface allows you to get a visual on the amount of mm the instant the float is at the release point. Both tests showed mine as perfect. The clear tube test is easier since no bowl removal is necassary. But it can be innaccurate if you don't do it just right. I had it measure way low a couple times in a row, then realized it was something i wasn't doing exactly right and finallyt was able to get the right reading a couple times in a row. So it's a easy way to check, but if you want to be absolutly sure use the method i described because it's very accurate every time.

Change the coils your secondary winding is shot. Between the primary and secondary winding in oil to help keep them cool. What happens the oil is like brake fluid and if left for a long perid of time it will pit and degrade the winding. Primary side is for quick starting but as the RPM's go up the primary switches over to the tighter wound secondary which supplies the voltage which you have none and it will continute to run on the Primary but will not have enough voltage to burn the additional fuel thus the black and wet plug.

About that green goo. There is an air passage that emulsifies the fuel going to the idle and transition jets. If the goo (resedue from evaporated fuel) managed to clog this air passage, you will be pulling pure fuel through these jets. At idle, the idle screw has enough travel to correct the mix but, when running above idle but less than maybe 1/4 - 1/3 throttle, you are running on the transition jets. Should the air bleed passage be blocked, you could be pulling pure fuel instead of the air/fuel emulsion and that would make the mixture very rich.
If the mixture is nearly normal when you open the throttle wider and run the engine at speeds above 3500 RPM (with a load of course!) the main jet, slide, etc are probably working fine.

I switched coils left to right and right to left and the left kept on fouling. Grump said float height was supposed to be 17mm so I was 3mm too high. I did find the passage you are talking about Greybeard, I think. Is it the one down by the main and pilot jets that is just a tiny hole? I missed it on the first clean-up but stuck a single strand of wire down it on the second go-round and found it blocked. When I went back in this afternoon to adjust the float hieght, I cleaned and blew air through all the passages I could find. I've got new plugs in it and floats adjusted to 17mm,now waiting for a chance to ride and test it out Sunday. I sure wish this thing had a tach on it, but like I keep saying...Its not my bike.

I think you're on the right track. If you have the green goo, the root of the problem is going to be carb fouling. That crap gets into spots you'd never think to look. Any other issues will be secondary and will remain unreolable until the carb is cleaned and properly re-assembled. My guess is that by the time you read this you'll have already ridden around the block a few times!!

BEWARE THE GREEN GOO - Always do one of the following once you're rid of it
1. Use a fuel preservative and keep the fuel tank and float bowls full.

or,

2. Drain everything dry (Thats not just run it until it dies, but literally drain the bowls and blow the carb out when possible. Some I know who do this also mist the interior of the carb with light oil, wd-40, or Sea-Foam.

Just got back from a 10 mile ride. Still fouled the left plug. The plug was black and dry by the time I pulled it out, but I waited 10 minutes before pulling it to thaw out my hands, so it was probably wet when I stopped. It had a pretty good stumble at 1/8 to 1/4 throttle, but I don't know if it was the plug not firing or something else. I think I've done all I can do and may turn it over to a dealer to sort out if the guy who owns the bike says its OK.

Just to let you know, the left carb was missing the part of the needle jet that protrudes a tiny bit into the throat of the carb. I was ready to give up on fixing this thing!

How the heck did THAT come up missing? Did someone muck with your carbs?