Surging and loss of power/engine dying above second gear

[gaines]

I just got back from a ride. I wanted to go a few exits down the interstate to Hickory Hollow, however once I got on the interstate and tried shifting up to fourth gear the bike started loosing power and ended up dying on me. I pulled over on the shoulder and got it started back up, but wasn't able to get any more power than second gear. It seemed the harder I tried to push it the weaker it got to the point where it would die again.

I ended up getting off at the first exit and taking a back road home so I could keep it in first/second gear.

I know that my #3 carb's idle jet isn't firing and we had to replace one of my main jets with a #15 instead of a #10, but other than that I know of no problems with the engine.

After we got finished rebuilding the carbs last Saturday it was surging on the way home, but I thought that was probably air in the gas line or some other condition that would pass.

Any clue what may be the cause of this?

[John]

The problem may be in the gas cap vent. Try riding with the cap cracked open, and see if it still acts the same.

[HobbyMan]

did you try running it with the "choke" on? When they were cleaned, there might be something that got dislodged and did not come out. It may have plugged something up.

[Hired_Goon]

I have a similar problem at the moment caused by fuel starvation. Happens at cruising speed, starts to splutter and cough for a while. For me , it is petcock problems. All I do is put the left petcock on prime and she picks back up again.


A classic a few weeks ago was me heading out on a ride and the bike really started playing up. Put both taps on prime and it rode better but not perfect. Thinking heard about it while riding I remembered I had lifted the tank 2 inches the day before to put 2 new rubber bushes on the frame cos the tank was rattling.

Sure enough when I stopped and looked I had pulled off both vacuum lines from lifting the tank and they were neatly hiding the nipples behind them.

[Ken Talbot]

Surging could be from a vacuum leak. Did you sync the carbs and adjust the pilots after the rebuild?

[gaines]

John,
I will try opening the gas cap and see if it makes a difference.

HobbyMan,
I did run it with the choke on. In fact, I tried leaving the choke pulled all the way out because it was dying on me, but that didn't fix the problem.

Hired_Goon,
I absolutely plan on checking all my lines. I ordered some new fuel line tubing and will probably re-do my lines when I check them.

Ken,
We did synch the carbs and adjust the pilots. Actually, Nashville_Bill did, but I watched.

Thanks so much to everyone who has replied with questions and suggestions. I will post back with updates as I check things.

[HobbyMan]

Try this: Open the float bown drains and put the petcocks on prime. MAke sure that you get good flow on all carbs. Sometimes after I rebuild a carb, the float pins will stick in the up position not letting the fuel in. If that is the case, you can stick a hose up to the drain, you can just suck on it and it will free up. Once gas flows through it, it won't stick any more.

[nashville_bill]

Gaines - We noticed that the fuel line was very old and brittle when we worked on the bike on Saturday. It was also kinking in the bends which could stop the fuel flow. Do the fuel flow test described by HobbyMan to see if you have sufficient fuel flow getting to the carbs. If you don't then you've found the problem -- if you do, then pull the spark plugs and see what the color is. The color of the plugs will tell you a lot about what is happening inside the cylinders. If you find any that are wet, then that cylinder is running too rich and probably has the float stuck open.

[gaines]

I took off the old fuel line, measured and cut the new fuel line last night. Now I'm just waiting until daytime to crank it up and see if that solves my problems.


That valve on the left petcock came out again. I used some adhesive that says it works on metals to stick it back on making sure that any gas remaining had evaporated and am letting it sit overnight before reconnecting it. Hopefully it will stick, however I'm still checking eBay for a new petcock (among other things) just in case.

[gaines]

Originally posted by HobbyMan
Try this: Open the float bown drains and put the petcocks on prime. MAke sure that you get good flow on all carbs. Sometimes after I rebuild a carb, the float pins will stick in the up position not letting the fuel in. If that is the case, you can stick a hose up to the drain, you can just suck on it and it will free up. Once gas flows through it, it won't stick any more.

Now that I'm in a position to do your test, I've realized I don't understand what you're saying I should do. You'll have to forgive me as I know next to nothing yet about engines/carbs. How do I open the float bown drains?

[oseaghdha]

The Drains

Are onthe bottom of each bowl.
I believe it's a 10MM plug.
Not sure the sucking thing will work unless the vent is pinched closed.

[HobbyMan]

On 80 carbs is was easy. On 78/79 carbs the vent had to be pluged.