Not another carb thread!

[Furious D]

After rejetting my 38's on my 81 I have ran into another problem. The bike starts runs and idles fine but seems to run out of fuel.Tank is fulll, I have checked to screen, float levels are right on but it willl run out of fuel after a few miles. It normally refires without too much trouble but dies again. tanks is clean and I was running a small filter which I removed to see if that was the problem.

I have tried the petcock in all 3 positions and it doesnt seem to make a difference.

Any ideas ?

 

[grizld1]

A few, actually. I'm going to assume you've tried running with the gas cap open to see if the cap vent is blocked, that you've been through the ignition and know that the coil, pickup coil, igniter box, kill switch, and all contacts are good, and that you've actually narrowed the problem down to fuel depletion caused by the demands of the big motor. If so, you might try lowering your float level (raising fuel level) to the max specified. If that doesn't do it, you might try larger float valves; I'm pretty sure you can use needles and seats for VM carbs with a little tweaking.

 

[gggGary]

Take off the float drains, put a catch pan under, does lots of fuel continue to flow out?

 

[Furious D]

I had not thought of the tank vent, I will check that out tommorow. It seems like I am getting plenty of flow from the petcock when it sets in the drive, It ran for at least 20 minutes without a hiccup. But maybe the problem show itself when the fuel is sloshing around in the tank?

 

[grizld1]

Don't overthink it, D. Vent blockage won't be total, and if that's the issue it will show up in high demand situations. Gary's suggestion is right on the money; with the plugs out, a blocked-up cap will slow the fuel flow as soon as low pressure develops in the tank.

Don't assume a fuel issue, though. I had something similar happen once after installing a brand-new Boyer ignition--bike would run like a champ then suddenly die, fire right up again, run great for awhile, die again; sometimes all it took to restore fire was to flip the kill switch off and on before coming to a stop. I was able to meter out everything but the igniter box; swapped in another that I had lying around, and that pegged it--no more grief.

I could add more cautionary tales, but here's the moral of story: 80% of carburetor problems are caused by the ignition.

BTW, ignore the suggestion of larger float valves; I reread your post and realized you weren't talking about an extreme big bore (over 800 cc.) motor. Somehow my addled brain added a digit to the year of your machine and took that as the displacement....

 

[Furious D]

It looks like it might have been the vent. I took it apart and the the vent was plugged. Went for a little ride today and it seemed to run fine. A little more tuning on the carbs and it should be good to go.


grizd1, How are things down in Carbondale? Spent a few years down there in the 80's. I miss the food and the fishing. One of these days I will take a ride down your way to see how things have changed.

 

[grizld1]

Yo D, C'dale is there, but things haven't changed for the better--creeps with too much money have bought up a lot of the countryside, and what they don't carve up the good ole boys do--more vineyards, McMansions, and doublewides, and the goddam county pours asphalt on everything that can't get up and run. I used to get in 6 miles of gravel road practice every time I rode to town, but now my gravel surface reflexes are shot for lack of use. You have to ride to Missouri to find any really open backroads these days.

Send me a PM when you head down this way, we'll do some riding.