crazy high rpm prob

[Chad]

Hi their to all, I've got a 79 xs11 standard that is giving me a fit. I cleaned the carbs really well, and replaced all the jets and float needle and seats.
I have 137.5 mains 42.5 pilots float level is 25.5mm. I have sync. carbs to near perfect and the intake boots are in great shape

The bike is completly stock, exhaust, airbox, jetting ect.

The bike starts and Idles GREAT sounds beautiful and when in neutral will rev to 9000 rpms but when I take it for a ride it hits about 5500 rpm's and won't rev any higher. Pull in the clutch and will rev back to 9000. I can be at a dead stop and dump the clutch at 9000 and will take off spinning the back tire and go about 5 feet and then back to 5500 rpm

I have replaced all the fuel lines and vacuum line. They are routed correctly and flow good. I have tried with with the gas cap off and still does it. The vent lines are good and can blow thew them and not pinched. Plugs are a little dark but still look good

The vacuum advance holds 5.9 in all day long and I took apart the mech. advance and freed it up and lightly lubed it, the springs feel really tight compared to my old brit. bikes. when I put a timing light on it with no vacuum advance its right on the F mark and with the vacuum advance hooked up on the number 2 carb not the boot it only goes up to 40 degrees. Is this correct?or should it be closer to 55 or 60?

I ohmed the pick up coils and they are both at 759 ohms after I repaired the hole harness. It had several bad spots so I replaced all the wires correctly and I checked the ohms at the TPI box and traced the wires as well to make sure no insulation break down.

I have not took apart the TPI box yet to check for poor connections.

I would appreciate any input this thing is driving me crazy. Thanks

[Larrym]

Backwards....

According to my "clymer's" manual, at 1000 rpms the timing pointer should align with the "F" mark on the timing plate with the vacuum advance hose connected.

Normally on a car the timing is set with the vacuum advance hose disconnected and plugged. On these bikes this is not the way the manual says to do it. (Sounds sorta backwards but I did it the way the book says...)

Also when the vacuum hose is disconnected, the rpm's are increased to 5200, and the pointer is supposed to be at the 36 degree mark.

If you set the timing to align with the "F" mark with the vacuum line disconnected then the timing is off.

[mro]

WOW ... “Sounds” like you actually read thru the tech tips.

These beasts will run even with the vac advance disconnected and plugged.

No vacuum leaks?
Carbs...
Diaphragm, pliable and no holes?
Needles not worn? Springs OK?
Where did you get the carb kits? Some kits do not use OEM jets and can be a problem.
May need to check that the round cylinder thingey’s slide up/down smoothly and when you push them up by hand should return at about the same rate.

With the air box off, safety glasses on (in case it decides to back fire in your face)
you can stick your face down there and watch the slides go up and down (sorta tremble too) as you rev it. Will not go up much but all should rise/fall about the same rate.

Did you clean the plug wire caps/connections?

mro
Welcome to XS land

[mro]

Only mistake I noted

TPI box

TCI

I've not run accross one that works but fails only at higher RPMs.
Randy is the TCI guru, maybe he will see this and chime in.


mro

[randy]

Could be lots of different things...

Poor compression....

Vacuum slides that leak....

Valve clearances...

Restricted exhaust...

Just what comes to mind.

[Chad]

Thanks for replying

Hi their, well I have taken the carbs off a couple of time to double check that the slides are working correctly and no holes in the diaphrams. The carb kit is a K&L and had the correct jets 137.5 mains 42.5 pilots and 25.5 float hight and all the carb passages I can get carb cleaner though and feel compressed air through each passage.

I forgot to post my compression readings sorry it is 170,160,160,155psi

the carb boots have been repair by a tire and hose place and have been pressure tested and do not leak

The exhaust appears to be in good working order I can't really see any thing restrecting it I will investagate some more on that

I checked timing again and vacuum hose connected it is still on the F mark but stll only goes up to 40 degrees with the vacuum hose connected

thanks for the info about the bike running strong with vacuum advanced still hooked up I've got a feeling that the TCI box is my problem but I want to make sure everything is good first thank you all for your help and any more Ideas I would love to hear them!! I can use all the help I can get thanks

[TDodge7]

how do the plugs look ? when mine was running pig rich it would rev up to 9k no problem when it was on the side stand , but once you put some load on the engine it would get to 5.5k and fall flat on it's face .

[TopCatGr58]

Hey Chad,

Folks have found the incorrect style of pilot jets in their K&L kits, and so here's a guide to look at the ones you have.

There are two styles of pilot jet, the BS and the VM, and the VM's will cause overly rich circuits even if they are the correct size!



They should have 6 sideholes total, not 8 IIRC. Widowmaker recently posted and this solved his severe rich problem.

You have OEM airbox, this similar symptom is known with Emgo Pod filters due to restriction of air around the inlet bell ports, but with the airbox it shouldn't be a problem. Have you checked to make sure the snorkel is clear...folks have found rats nests and such, one guy found a socket wrench he had lost down there restricting the air flow!!
T.C.

[Larrym]

Take my carbs, please!

If you have gone through the carbs again (verified the proper make of jets) and you are still having this high rpm problem then it may/may not be the carbs. I agree that it sounds like you've read all the tech tips and done about as much as any reasonable person would do.

I have a good "test bank" of carbs that I cleaned/adjusted and used to diagnose a problem I had on my bike. They are jetted and set for the stock set up like you have.



They are boxed up and ready to ship.



If you substitute these carbs on your bike and the problem still persists then we rule out carbureation and start looking elsewhere.

I pay for shipping out to you and you pay for shipping back. If these carbs help you find/correct your bike's problem and you make a donation to the site here I wouldn't object.

PM me if interested and we can go from there.

[Radiation]

Center Stand

Did you try putting the bike on the center stand and then running it in gear? It may not work without any road resistance.

[Chad]

Thank you to all

Thank you to all I really am thankfull for your input sorry haven't worked on it lately I will check the pilots and I want to check the pick up coil gap and ohm the coils and double triple check the wiring

I'm a tech at an aftermarket bike shop and have had to put it aside and work on something else to make some money this is the best forum site I've ever seen you all know yours stuff and thanks for the help

As soon as I figure it out I will let you all know what the problem is

[Chad]

I fixed the crazy high rpm prob!!

I Finally fixed it!! thanks to all your help you guys are a great help!

Turns out I'm an idiot, when I got the bike in I took the carbs apart and soaked the jets and cleaned the floats and the rest of the carb. So I had the carbs apart and was waiting on the carb kit and the intake boots to come in before I put it back together.

I checked the Pilot jets again after seeing the post about the 2 different jets in the K&L carb kits and it was the same as the old jet and like the one it said to use.

I had put all the old carb parts in an old jet kit plastic box as I was diging around I noticed some flat head plugs!!!! about that time I thought I was sick!! OMG!!! how could I of left that out and been in the carbs so many times and didn't think that the bike was running that rich!

I put the plugs over the pilot jets and took the bike for a spin and HOLD ON! this thing will move! I was really pleased

So now I know that if you leave the plug off the pilot jet hole the bike will run too rich (it still gets gas through the hole where the emulsion tube is)

The reason I was thinking that it was electrical and not carb is that I could take the air box off compleatly and the bike would run a little worse I'd put the air box on and leave the filter and lid off run about the same, put it all back together and put a little tape over the intake snorkel and would run worse.

My reasoning behind the little bit rich was that I thought if it was not sparking correctly I'd have poor combustion and look rich from unburnt fuel

I have done my more air less air tests many time before on different bikes(air box off then tape over snorkel) and has never let me down, now I know different thanks for all your help!