Bonneville America Forums Forums Technical Forums General Tech What the heck is going on???

Ah yes, riding time just around the corner, time to finish all winter mods and get ready for the road. Got done a-wrenching, and fired her up to balance the carbs. About half-choke, good deal. Running a bit rough, but not too bad. Pushed in the choke to idle while I balanced. Got 'em balanced pretty easily. Let her run just to hear the sound once again (been a long winter). Anyway, after about 5 minutes or so she starts to sputter and backfire a bit from one side, and then dies. Would not start again without re-choking. Checked the new plugs. They were a bit loose so I tightened them. Checked under the cap of the carbs to make sure I got the diaphram in place after de-shimmimg the needles. All looked good. Retightened all around the new intake manifolds. Fired her up and after 10 minutes she died again, only this time not much sputter and no backfire. Won't start with the choke, and when she does a nice loud backfire. Kind of at a loss. Does this sound like an old gas problem maybe? I had gas sitting in the tank but I did add StaBil last fall. Any other ideas for symptoms like this?

sounds like either bad gas or leaking air bigtime. Check the squirrel condoms for cracks.

dirt in the hidden filter maybe or rebalance the carbs. Adjust the mixture, dirty plugs (gas soaked maybe) Let it run long enough to overheat? When I do that kind of work I bring the bike to operating temp then put a fan to blow across the engine. Could even be an ignition going bad.

Better mechanics than me have already replied but it does seem like a vacuum leak might be the culprit, especially since it's backfiring. That's pretty much exactly the way my rotten squirrel condom behaved. Or, it could be the dreaded "vent tube lock" in conjunction with old gas...have you checked the vent hose for kinks or blockage? Might drain the float bowls just to see what comes out as well.

- new squirrel condoms on
- replaced hidden filter with an in-line (cleaned it)
- balanced carbs twice
- did install the air mix thumbscrews...was pretty careful not to lose springs and o-rings. have them turned out 2.5.
- tank is off for balancing - no vent hose hooked up

Sure hope it's not the ignition. For now I guess I'll get some new gas and see what happens. And recheck for leaks. Thanks for the suggestions Pat, Ian and Ed.

OK very simple and stupid idea but if the tank is off,are you sure it isn't tilted too far forward so the gas just isn't getting to the carbs? At this point from what you have said I would look for a leak like Pat and Ed have said and double check that your needles are seated correctly. I can't remember your whole set up but might want to open those mixture screws a little ,especially if you still have the 42s in there. It does sound like a fuel/air problem to me. Stuck/bad float. Have you left the gas on without running it and looked for leaking gas? Or used a clear tube on the bowl drain to see that the levels are up where they should be?

Make sure the tip over valve is in it's proper orientation. (with no vent tube that wouldn't matter just something to check when you reassemble.)

Ian- I use a clear hose form the petcock to the carbs when I do the balancing so I can see the gas. I'll go over all connections again to hopefully eliminate any leaks. Same with rechecking the needles. I'll drop the bowls and check the floats also. I did have a tube full of gas when the engine was shut down and noticed no leaks. Just for the record I'm running 150 mains with 42 pilots and no shims at about 500' elevation, with open pods and Specialty Spares short slashes. Probably be this weekend befrore I can get back to it but I'll post my results.

When checked all of above if still the same I have found that the bike has to be really warm before balancing ie a good half hour ride the difference is amazing dont ask me how I know

Blessings
Nigel

On the electrical side, have you checked the pickup sensor gap? Mine was way out of the new spec and I'm pretty certain it's why I was only running on one cylinder after changing the rear tire...that about tops it for your unrelated cause and effect symptoms...one day when I get real brave I'm going to put the old CDI back in and go for a long ride because I truly believe the sensor gap was the culprit.

What I meant was put a clear tube on the nipple that gas comes out of when you drain the bowls and hold it up along side the float bowl then open the drain to check the float level. The gas will fill the tube to the same level as the float chamber. This probably isn't the problem but doesn't hurt to check, also probably not the problem but a 42 pilot is probably too small and probably lean with only 2 1/2 turns. I am just brain storming and trying every possible cause. Pick up gap as Ed says is a real possibility too. Very hard to diagnose without laying hands and ears on the machine. All we can do is read your input and take an educated guess. Wouldn't hurt to check the coil plugs and any other connection under the tank you could have knocked loose while balancing.

P.S. No need to drop the bowls if the clear tube says the float levels are good unless you want to up the pilot jet.

OK guys, got me on this one. What and where is the pickup sensor gap. Is that something that's addressed in the shop manual?

Tech Vault

Thanks Chy.

It is in the manual but it's easy, right under the RH engine cover.Didn't go read the tech vault but don't forget if you are looking in the manual that the gap has been decreased to .8mm.

Great pictures Moe.

Check that the tank breather is clear. It can get blocked by crud, so no air gets into the tank and this stops the petrol flowing into the carbs.

Ok, so I get some fresh fuel and add some Seafoam just to be safe. Again fires right up with the choke. Push in the choke and keeps running 5-10 minutes and dies. Will not start again with or without the choke. Dropped the bowls soon after and there is almost no fuel in them. On the bright side no backfires after tightening everything again. Does it sound like it's starving for fuel? Float and/or needles gummed up? What?? It's finally starting to get nice here...go to get rolling!!!

It's probably worth noting that last year I had the same air intake and pipe setup but was running 160 mains with 1 shim. Plugs were pretty sooty so I went down to 150 mains and no shims. Could this reduction leave me with not enough fuel to keep up with the open air flow?

No the reduction should be very close to what you want,if you still have that 42 pilot like I said it is probably too small and should be a 45. That being said , it isn't the reason your bike won't start. How many turns out are your mixture screws? Starting on choke and running for a few minutes and dieing sound like a pilot issue but no gas in the bowls would do it too. Check the floats move freely, make sure the tip over valve is working, make sure tank is venting including the tip over valve working properly, double check for a clogged filter.

Your mains/needles have nothing to do with starting/idling that would be in the pilot circuit if it's a fuel problem.

You said your plugs were sooty, have you changed/cleaned them?

EDIT: Ya know I went round and round like this with Tom (brokenfixed) until he finally brought it to me and I had it running perfect in short order. It is very hard to diagnose something when you can't see or hear it. We all can only speculate and take educated guesses to try and point you in the right direction.

It may be that the carb vent line is clogged and the bowls are starving for air causing the float level to remain too low. Can you pop that tube off the tee and see what happens?

Ian,

- mix screws are out 3 turns
- floats seem to be hanging freely
- right now the tank is off as is the vent hose...I'll check the vent gizmo on the tank to make sure it's not blocked
- got new plugs
- recently cleaned filter

I appreciate your and everyone elses input. I realize it's a shot in the dark at best from 1000 miles away. I'll address all suggestions and recheck some of the more obvious things. Seems like for some reason once the bike gets warmed up the gas flow stops.

I meant the carb bowl vent tube, it's in that T at the top of the carb stack and runs under the frame where critters and debris can block it. If it doesn't allow the air to flow freely the gas won't be pushed up the jets once the bowl level starts lowering. A different kind of vacuum problem but it is a possibility.

Ill be the first to admit that this sort of issue is not my forte BUT...on a recent ride I expereinced a vapor lock issue. Unscrewing the gas cap resolved the issue for a few miles till it happened again. I wound up keeping it a bit loose that day. Granted it was ****** rain.

For those more experienced than I ....
Whats the possiblity the issue is as simple is a vaporlock situation?

Z- had the same problem exactly last year myself. Turned out it was the ball valve in the tank vent hose that had gone bad. You can test this by removing it from the hose and seeing what happens. Found out they were about $30 OEM only and just left it out. Makes no difference as long as the bike stays upright. May replace later, assuming I get running again.

You stated that your floats appear to be free but are the needle valves that ride on the floats also free or stuck closed? If they are stuck closed, your floats will move down but the needles will remain on their seats not allowing fuel into the bowl. Over time, some fuel will seep in. Once you start the bike up, the fuel is used but can't be replenished. Pull the bowl and turn on the fuel petcock to see if fuel drains from the needle valves. Better yet, once your bike stalls, open the drains on the carb bowls and see if fuel comes out.

This is assuming your fuel feed to the carbs is clear. I've seen fuel cause needle valves to stick in their holders over time.

actually, I didn't think about this before but if the screen on the petcock gets clogged this will happen too , that is assuming there is a screen on our petcocks. So if all else fails and you have no more ideas check that out.

EDIT: Forgot not running off the tank.

Hey Ian -

I've got a Pingel installed, and I can see the clear tube full of fuel down to the carbs, so I'm getting feed from the tank. Seems like it just kinda stops flowing after running for awhile. I'm going to check all of the vents and hoses around the carbs in the AM to make sure something is not bound up.

Gregger -

What you describe sounds pretty close to what I think I'm seeing. I get enough fuel to the carbs when I'm trying to start cold, with choke, and then it's like the flow just stops when the bike warms up. I've looked at the needeles but I'll check them again to make sure I didn't miss something.

I know you have the clear gas line but if the float is stuck closed the gas line would still be full of fuel but not getting into the carb but if it was a petcock problem you would probably see the tube empty. Just trying to help and if I think of it I post it.

Much appreciated. Thinking along the same lines. Fuel is in the tube. My way-so-amateur guess is a problem between the floats, needles and maybe the carb vent. Will hit those tomorrow and see what happens.

The breather seemed ok Jan but I will run try with the cap off next. Thanks.

Same old song and dance. Made sure tank vent, fuel filter and 'T' vent are clear. Watched fuel run from the tank to the carbs. Fires right up and runs even after I dechoke for 10-15 minutes then just starves it seems. More, but not a ton more fuel in the bowls. Gonna check the floats tomorrow. If that fails time to take everyting off and give it another shot. Must have missed something when the carbs were off for the mods. I guess the good news is it was snowing today....

There is an easy way to check you float levels.

Put the bike on a stand or otherwise level it. Place a clear tube on the drain nipple of the bowl. Hold the other end up above the fuel tank. Open the bowl drain valve (screw). The fuel level should be +/- 1/4" from the gasket of the bowl and carb body. I can post a pic if this is not clear.

Bryan

This is waaaaaay out in left field, but since I'm grasping at straws I'll toss it in anyway. Could it be possible I'm letting the bike idle too long without moving and it's overheating? Pretty sure in the past I've idled longer without this problem but who knows. It's been anywhere from around 35-60 degrees in my garage so it's not exactly sweltering. Probably not but worth asking. Anyway today I try to determine if the floats/needles are working properly and go from there. Thanks to all that have taken the time to contribute so far.

What was the last thing you changed in the fuel chain when you were modding?

Also, when Stevieh had a similar problem it was a tear in the manifold sleeve hidden under the clamps so that's yet another spot to check.

Well, as far as the fuel chain goes this winter I switched out the stock intake manifolds and rubbers for the billet aluminums from newspeedy.com, deshimmed the needles, replaced 160 mains with 150's, and replaced the stock air mixture screws with the newspeedy.com thumbscrews. Although I know it would be best to perform mods of this nature separately I took advantage of seasonal down time to get as much done as possible.

Ten minutes seems a long time before running out of fuel if its a float problem.....Could it be maybe an electrical problem? Maybe a coil overheating an shuting down? Or the dreaded ecu.