Rpms stop at 5k when accelerating under load

[D0wn5h1ft]

I've tried searching through the forums to find a similar problem but I haven't seen anything that is exactly what I'm dealing with; probably because I don't know how to word it for the search.

Took the '79 standard out for a spin today after finally getting it put back together but when I'm accelerating in any gear the rpms go up until it hits exactly 5k and the it starts to stutter. Acceleration is very strong up until this point (I actually lost a bit of traction on the rear tire) but it comes to a halt at 5k rpms. It's almost like the engine is bogging down and it stutters even if I go WOT.

Side note: in neutral I can rev all the way up to redline without any stopping or stuttering.

Also:
-Brand new coils and spark plugs and spark plug wires
-Triple checked the ignition, everything looks good
-Stock jetting: 42.5 pilot, 110 mains

I'm not sure what to call this problem otherwise I'd do more searching for it.

[XS1100 Newbie]

I have had this problem for over three years. I got it to go to 7000, and that is where it is at now. A few months ago i was working on my carbs, and evidently set the floats at the right height or something, but it would run on up to 9000 with no problem. I had some troubles with synching, and flooding, and while working on the carbs over a period of 3 weeks, i lost that ability, and have not been able to get it back. After that, i was convinced it was in the carb settings. I will work on it more this spring, if i don't sell it first.

[CKlamer]

Sound like you hit that point where your bike is starving for fuel. Could be a setting and or could be some garbage in you carb or your lines. But for some reason at 5000 it's not pulling enough fuel.

You can do some major engine damage if you continue to ride it at that level with it running lean on fuel.

But working on my newer bike mine was doing the same thing and turns out on my Fuel Injectd bike the fuel pump was not supplying enough fuel at 5000 RPM's and it started to spit and sputter.

But we put it on a dyno and at 5000 it would literally go off of the chart lean. Of course the stupid stealership would not listen to me and test the fuel pump first no I had to and remove all of my PCV and Autotune to prove it was not that.

Good Luck hope you get it working.

[trbig]

Mine did this with those cheap Emgo pod filters on it that had the rubber lip partially covering the intake jets.

Another idea is to check your timing advance system. Remove the left side cover and see if it rotates freely. Several people have had to take theirs apart and clean/lube that bearing the advance rotates on.

[WMarshy]

Reach down and pull out the enricher while it is stumbling at 5K to see if it clears up and takes off. If it does then it will confirm a lean condition. You might need a bigger main jet if your air box and exhaust is modified... but this is an easy way to check for lean condition. You could also pull your plugs and see what they are telling you.

BTW, I surmise from some of your other carb posts these are the later style carbs (80+) in which the 110's would be stock? If not the 80+ carbs, you need to go up to 137.5 mains for the stock 79 carbs.

My other thought is, do you have the right emulsion tube for the style of carbs? Should be a 300FJX-2 for the 80+ carbs (specials), and 5GZ6 for the 79 and earlier (stamped into the side of the nozzle).

http://www.xs11.com/forum/showthread...ghlight=Nozzle

[MarkD]

D5hift-- I'm running a 79F (Standard), and put new jets in upon carb rebuild/ clean in the spring. I ordered Mikuni jets , as I read that the kit jets (main) are crappy. Stock jets= 42.5 pilot/ 137.5 mains. I have no problems with higher revs. I run the stock airbox, too, and sort of baffled pipes.

[D0wn5h1ft]

I am running the 80+ carbs, the MNS special ones to be exact so the stock jetting is correct. I have a set of 120 mains that I was going to try but I'm already afraid it was running rich because if I rev it in neutral, as the rpms go down I'll get a pop pop or two of (i assume) un-burned gas flashing in the exhaust.

Also, when I originally had the 120 mains in the bike had almost no power starting from stop but when I switched back to the 110s it was completely fine. Which doesn't make a lot of sense to me since the mains are really only supposed to affect the high rpm/large throttle opening range.

[mack]

Carbs

If it's a 79 F you should be running the old carbs with 137.5 mains vs the 115/120 mains in the 80+. The pilots are the same but the starter jets in the old carbs are 32.5 Vs 25's.
You should switch back to the proper carb bodies. You'll find that they are a much better style with way more tuning possibilities.
Your description of the problem is where two things happen, the carbs switch to the mains and the advances should be working. If one or the other are not functioning properly, you will hit an RPM wall. I trust you have checked the advances as well.

[motoman]

I am running the 80+ carbs, the MNS special ones to be exact so the stock jetting is correct. I have a set of 120 mains that I was going to try but I'm already afraid it was running rich because if I rev it in neutral, as the rpms go down I'll get a pop pop or two of (i assume) un-burned gas flashing in the exhaust.

Also, when I originally had the 120 mains in the bike had almost no power starting from stop but when I switched back to the 110s it was completely fine. Which doesn't make a lot of sense to me since the mains are really only supposed to affect the high rpm/large throttle opening range.

My Venturer is at the same dielemma right now(from Venturer running Dielemma thread), 5K, hits a wall. Have same carbs(81Special/5GL16metering rods which use 110mains for stock). Idle circuit is now working perfect once I changed out the tired old ignition coils. Likely gonna have to go back thru removing emulsion tubes and all, and re-cleaning all the tiny holes in them with a toothpic again, since this issue IS main circuit related. (This all came about when leaving it parked/covered in garage for a year with fuel in it, but no additive/stabilizer). This just added to the initial ignition dielemma, which was resolved.

Mine otherwise runs smooth as silk in the lower rpm ranges with no black plugs from a previous weak spark. This will be fine for the upcoming ToyRun this Saturday, after which I can again pull carb bank and see what's restricting the main circuit. Likely will find nothing in particular, and just meticulously re-clean everything, double check float settings to be all identical levels and things will very likely be just fine without ever really pin-pointing to an actual cause.

Will actually have been first time ever bike is having main circuit running issues, but will post findings in my previously started Venturer running dilemma thread in near future.

Double check all your ignition circuits, using an actual meter. May be surprised to find some actual all important missing 'smoke'.

[D0wn5h1ft]

Took it out for a spin just now and tried pulling out the choke like suggested before. The "rpm wall" at 5k was significantly worse with the choke pulled out like this which tells me it isn't a lean issue, right? Still running 110s.

Based on that I feel like it's a fuel starvation issue OR a main circuit issue but I'm not sure how to solve that.

I did notice something peculiar, I'm getting a little white smoke out of my right pipes and almost none my left ones (it is cold so sometimes it's hard to tell the difference between that and condensation). I have the dual mac exhaust with the 2 sets of manifolds, where #1 and #2 go to one and #3 and #4 go to one. It's the pipe with #3 and #4 that's throwing a little smoke. This is AFTER I have taken it out for awhile but it also does it on start up.

Also, I noticed when starting it that the #4 cylinder seems to be a bit challenged as the bike warms up but once it's going it doesn't seem to be a problem anymore.

[D0wn5h1ft]

If it's a 79 F you should be running the old carbs with 137.5 mains vs the 115/120 mains in the 80+. The pilots are the same but the starter jets in the old carbs are 32.5 Vs 25's.
You should switch back to the proper carb bodies. You'll find that they are a much better style with way more tuning possibilities.
Your description of the problem is where two things happen, the carbs switch to the mains and the advances should be working. If one or the other are not functioning properly, you will hit an RPM wall. I trust you have checked the advances as well.

How do I go about checking the advances? I assume you're talking about the vacuum advance and I made sure that can rotate freely back and forth like someone suggested in a previous thread.

[mack]

Advances

Steve did a nice thread on the mechanical advances complete with comparisons between the years. Very interesting. It should be in the links section or under the engine maintenance section.
The manual talks you through the vacum advance check, but in a nutshell, you use a midi vac and if I remember it should be fully rotated at 5.9. You can also check it's effect when checking your timing. If I remember your post. It will go over 5K while on the center stand. You can take it up to 5.5 K and disconnect the vacum and see that it reads 36 degrees then hook it back up and it should read 52 degrees if I remember correctly.
Read Steves thread though, it's step by step with lots of pictures.
The mechanical advance is usually the culprit with sticky mag action or spring issues. The one I took out of the E was completely rusted into one piece, so it had not possibility of ever rotating as required.
If you want a set of original carbs for an F, send me a PM.

[TopCatGr58]

Hey Downshift,

Okay, Mac 4-2 exhausts...but do they have any baffles or are they wide open/unstricted=LOUD?! Secondly, running OEM airbox or Pod filters??
As Tod stated, the cheap EMGO style can cause problems if not mounted with velocity stack type mounts! Popping on decelleration is actually a sign of lean, the butterfly closes when you release the throttle, and the resultant temporary lean condition induces the popping.

The timing parts are the MECHANICAL centrifugal parts BEHIND the PU coil plate...that's the part the Vac. Adv. is connected to. The cent. adv. parts can get rusted behind there, and so they won't fly out or rotate the timing plate for the proper POWER level of advance needed for the 10-36 degrees BTDC amount of advance. The Vac Adv. will only provide 16 degrees of maximum additional adv. during cruising/lean throttle input, but it's only applied to the already max. 36 degrees of adv. once the engine reaches ~5k.

T.C.

[D0wn5h1ft]

Hey Downshift,

Okay, Mac 4-2 exhausts...but do they have any baffles or are they wide open/unstricted=LOUD?! Secondly, running OEM airbox or Pod filters??
As Tod stated, the cheap EMGO style can cause problems if not mounted with velocity stack type mounts! Popping on decelleration is actually a sign of lean, the butterfly closes when you release the throttle, and the resultant temporary lean condition induces the popping.

The timing parts are the MECHANICAL centrifugal parts BEHIND the PU coil plate...that's the part the Vac. Adv. is connected to. The cent. adv. parts can get rusted behind there, and so they won't fly out or rotate the timing plate for the proper POWER level of advance needed for the 10-36 degrees BTDC amount of advance. The Vac Adv. will only provide 16 degrees of maximum additional adv. during cruising/lean throttle input, but it's only applied to the already max. 36 degrees of adv. once the engine reaches ~5k.

T.C.

I tried running without my pods on and all I got was back firing out of the carbs! You could see the little explosion where it was happening so I put the pod filters back on. I don't think they are the same emgo pods that most people have because the way they mount is different from the ones that I had on my '78E.

If it's lean should I try bumping up the mains to the 120s I have and give it a shot? Also, I'll check the mechanical advance tomorrow afternoon but this was a good running bike before the PO had disassembled it (I received it in a few "parts buckets"). I'll also wipe the plugs down with some acetone before I go out to see what color they turn and then I'll post pictures.

[natemoen]

Well, you need to first COMPLETELY disassemble your carbs. Pull the caps on the idle mix screws and clean everything.

Then we will go from there.