48 UL Not running after rebuild

[26modelB]

We just got through doing a top end rebuild of a '48 UL. New valves, pistons, rings, etc. It has 45 PSI compression. Also new coil, plugs and plug wires. We also rebuilt the carburetor. Plenty of fresh gas. New points and condensor in the timer. The timing is on the mark both on the flywheel and timer. New fully charged battery.

Engine will run on ether only as if it's not getting fuel. It will run for just a few seconds. The float is not rubbing the float bowl and the needle is not sticking. We shot compressed air across the carb jet and could plainly see fuel spraying throughout the Venturi.

If anyone has any pointers on something we're overlooking it would be greatly appreciated.

[T. Cotten]

26modelB!

http://virtualindian.org/11techleaktest.html

Good luck,

....Cotten

[26modelB]

Thanks Cotten, I know we addressed a leaky manifold before we decided to do a rebuild but I don't think we looked at that since. As a matter of fact, we just screwed it right back into place and I think we used the old seats as well. I'll definitely rig up a little plate and pressure test it as you described in your article. I'll post the results here in a day or two.

[26modelB]

Hey Cotten and anyone else with suggestions,

We did the leak test on the manifold and found the rear cylinder was leaking around the inner threads of the nipple. We installed new nipples and new brass seals. Once we had those new parts in, we tested it again and we did manage to eliminate the leaks. Thanks Cotten that was something we had overlooked and your test did reveal a pretty bad leak.

However the engine will still only start and run on ether shots. We are currently taking the carb apart again hoping to find something obvious. This is a barn find bike and all that is known about it is that it that hasn't been ran since the late 70's. The carb is an M51 which is supposed to be correct for a 48 UL but we're not sure if this motor ever ran before with this carb. We're wondering if the Venturi is correct. Anyone with tips or pointers would be greatly appreciated.

[Steve Little]

Hi. The engine firing on ether shots prooves that the engine will run as it is.
Your pressure test of the manifold has eliminated that aspect.
Spend some quiet time with the carburetor. If the mixture screws are set to factory recommended "start" settings and the bowl has fuel in it the emulsion tube should deliver fuel to the venturi to idle.
If the carb has been unused for a decade or so, the brass parts of the carb may have reacted to moisture. If you have access to an ultrasonic cleaner or a tin of "Carb Cleaner", completely disassemble the carb, inspect and clean everything, then drop it in the cleaner overnight.
Im sure our resident carb expert will contribute his advise when he gets home from galavanting around Davenport.

[frichie68]

45 psi compression seems awful low . . .

[T. Cotten]

Model26B!

Please use fuel and not ether, if you MUST squirt anything down its throat.

The venturi should not prevent it from running (albeit poorly), even if it is poorly fit, 'wrong' size, or even backwards.
Please make certain the LS lift lever spring collar is in place, and also not upside-down with its 'top-hat' portion in the needle 'well' instead of up into the spring.
Please make certain also that the idle bleed plug on the idle side of the carb is not loose, and the gallery plugs are in place.

Frankly, I would bubble-test again, inspecting everywhere, including between the fins over the ports, as casting porosities can be anywhere, and cracks can be invisible. I have found fissures in the middle of manifolds, particularly around "invisible" repairs. The sparkplugs can leak, and I would also turn it through to open the intakes to snoop around each head gasket (especially if they are copper), and the headbolts.

Places that cannot be bubble-tested are the throttle bushings, and the manifold/carb interface. I arbitrarily grind the manifold flat, and lathe-cut the carb.

As always, you are at the mercy of your own observation, intuition, and patience...
Good luck!

.....Cotten
PS: I enjoyed the Meet enormously, especially the fall-like weather!
Couldn't 'galavant' much, though, as I found myself preaching bubble-testing to so many that had not heard the word.

[26modelB]

Hello everyone and thanks for your input. As mentioned in a previous post, we went through the carb a second time. We found that the high speed needle was binding. When we were rebuilding this carb the first go around we thought it was seating and we didn't want to force it. But turns out it wasn't. After fixing that and reinstalling, the bike is running fine now. Thanks again for all the advice.