Bike cutting out

[Da-Bubble]

Hello,

I have a 1979 XS11 Special. It has the Kerker 4-into-1 and a drilled airbox. It sat for about a year before I bought it. I drained the gas and ran some sea foam thru it. It would pull hard on top end but at part-throttle it had a backfire. I took the carbs off and dipped them then rejetted with Mikuni 145 mains and 45 pilots per a chart I found on this site.

NOW....with everything back together it starts right up, and will rev freely when it's sitting still but when I ride it, as soon as I get on the throttle it starts sputtering and cutting out. I bypassed the octopus and ran inline filters. Thought it might have been an air bubble in them so I plumbed it directly from the petcocks to the carbs, still the same thing. I set the floats according to the Clymers manual. Can a float(s) out of adjustment cause this problem.

P.s. I've got good compression and spark on all four cylinders.

Please help!

Thanks,
Scott

[John]

Well I'll be dipped

You didn't dip the cabs in the caustic carb cleaning solution did you? If you did, please tell me that you removed the throttle shaft seals, 'cause if you didn't, you will now. That stuff eats the rubber in the seals and you will have a vacuum leak. The spray type of carb cleaner or the same product in pourable form, is safe for the seals, and is recommended. I wouldn't recommend soaking the rubber bits in the cleaner for an extended length though. A couple of cans of carb spray, some very thin copper wire, and compressed air will do the job just fine.

[Da-Bubble]

I dipped them in the one gallon Berryman's carb cleaner. I removed everything rubber I could see. Is it a sure thing that they're screwed up now? Where are the seals? Also, why would the bike rev up just fine like it's ready to scream, then only cut out under a load (while actually riding it)?

[John]

After re-reading you original post, it may be that the jetting is too rich. I have done an 1179 big bore, aftermaket exhaust, and Uni foam air filter, and I only needed to go up one size on the mains, and left the pilots stock. 145 mains may be way too big. My carbs are 78's, and as you know the stock main jet is 137.5. You will find the throttle shafts seals, well, on the throttle shafts. The butterfls are controed by the shaft. The carb syncing screws are on the throttle shafts. Run the engine at around 2k rpm, and spray some carb spray onto the seals, one at a time. If the rpms change at all, you have found your leak.
Did you completely disassemble the carbs, and poke through the the small holes in the emulsion tube and pilot jets, and remove the pikot screws, or just soak the barbs while they were still fully assembled?

[Da-Bubble]

I rejetted according to this chart ReJetting Chart

I took the carbs apart, dipped everything, then blew everything out with compressed air. The long tubes with holes in them that slide out of the carbs (emulsion tubes?) were taken out, soaked, then blasted with a can of B12. I saw it spray out all the tiny holes. I;m pretty sure I cleaned everything I could. Can the floats be set too low or high and cause it to starve for fuel? I'm trying to figure out why the act of accelerating makes the motor cut out while it revs fine sitting still.

I will spray the throttle shaft seals tomorrow to see if the idle changes.

[John]

It is possible that the problem is electrical. You'll need to ohm out the spark plug caps, wires and coils. Could be a problem there especially under a load. It's really hard to diagnose a problem with a keyboard and monitor. so I'm just throwing out some ideas.

[prometheus578]

I, too, think the main jet size is a little large. What do the plugs look like? And I agree about the vacuum, too.

why would the bike rev up just fine like it's ready to scream, then only cut out under a load

Because it's under load, which will 'amplify" any other small problem that the bike has.

[Da-Bubble]

The plugs are all solid black with carbon (not oil). Does that mean it's way rich? Will that cause it to cut-out? I've got a sinking feeling that I have to take all this SH*T apart again! Is this the fun of owning an XS11?!

[Da-Bubble]

Also I just remembered that the guy at O'reilly's sold me NGK BP8ES plugs rather than the BP6ES. He said they would just be a hotter plug. Is this a problem? I don't see them on the list of acceptable plugs.

[Da-Bubble]

ok I keep finding more info. The guy at O'reily's was a dumbass (big surprise) With NGK the higher the number the COLDER the plug. So my 8 is colder than the factory 6. Plus on NGK's website it says "Rich air/fuel mixtures cause tip temperature to drop, causing fouling and poor driveability". So I'm rich anyway with the larger jets and I'm running a colder plug! Jeez.

[prometheus578]

'Bursting Da-Bubble"

Wow... almost like the scene in "2001...", were the proto-human reaches out and touches the monolith!
Now you're getting some where.
Change plugs... change jets... and see what happens.
Da-Bubble... you will "evolve" into a Guru in no time!

Is this the fun of owning an XS11?!

Yes it is. But once you get it all dialed in... it stays there, and the real fun begins.

[Dennyz]

Jetting,

145/45 is what my 'F' is jetted to and it pulls strong through all gears. To run this jetting, carbs, valves, timing chain, coils, wires and ignition must be in top shape.

Assuming the carbs are in good work order, I would suspect possible pick-up coil problems.

[Dennyz]

Spark Plug temp range

I am surprised at how many people selling spark plug don't know what they are talking about. It is one of my favorite arguments to start at the parts store.

Spark plugs don't make hotter spark, the coils do that. Plugs are rated by the heat range they operate best in.

I have not had much luck with changing plug ranges to fix a tired or poorly tuned engine. Stick with new correct plugs.

[prometheus578]

...From the mouth of the man who brought you the "jetting chart".
I agree with Denny... I don't change plug heat ranges to correct other symptoms.

[Da-Bubble]

No one has mentioned the floats. Clymers says to set them at 1.012" from the "gasketing surface". Well the gasketing surface is inside a lip so I measured the difference with digital calipers and set them to .900" from the lip. This is equal to 22.89mm from the lip. I've seen guys talking on here about having them set at 25mm. Is that a huge problem?