shudder at 4000 rpm

[raqumup]

i have done all i can do to my 79 XS1100 special accept rebuild the engine. my problem is at around 4000 rpm (any gear) the bike shudders like it is misfireing and then about 4500-5000 rpm it smoothes out it is more noticeable in the higher gears because i dont have all the power to just get past it like 1st and 2nd, has anyone had this problem and now how to fix it? please help
Thanks
Troy
i have put ACCEL coils and wires on it, and my old igniter box 1/2 of it went dead so i got another one from a junk yard, befor the old igniter box went dead it did the same shudder thing so i dont think its the box. it also does it with the original coils too.

[John]

Check the wires to the pick up coils. There is a post on that subject in the maintaince section here. It covers it very extensively.

[raqumup]

they are new and gaped to speck

[dfrooney]

I think you may have misunderstood John's reply...He's not talking about the spark plugs or spark plug wires.

A common issue for these bikes deals with the wires going to the pickup coil. They tend to break since they are forced to move around when the centrifugal advance moves. It is possible that the issue you are having is due to a disconnection in these wires when the advance moves to a certain position associated with the 4-5k rpm range. Check these wires thoroughly as the break may not be readily apparent.

dan

[Snow]

Check this repair guide out for a better understanding of what he is talking about - a lot of us have already done this to our bikes:
Pickup Coil repair

[pgg]

Sounds like a rough transition from pilots to mains?

[Geezer]

One thing I'd like to add is make sure the fuel lines are free flowing. A plugged screen in the tank or fuel filter can cause these kind of problems.

Always check the easy stuff first. ;o)

Geezer

[dwales]

I had a similar problem. Turned out to be a sooted up/blocked exhaust.

[raqumup]

i have replaced the pickup coils in the disrbuter as well as the ignition coils, i know about the porblem with the wires moving really fast from the vacuum advance and the wires breaking that has been rectified. my exahust is all new as well. fuel lines are new and i made sure that they are not kinked. do you have an sugestions on how to fix a problem with the trasition from pilots to mains? that could be the problem i dont know. i have rebuilt the carbs and synced them, i took it to a guy i met at colman power sport who had the same bike and rebuilt the bike to better than new he had pics. it looked really good but anyway he took the carbs apart and rebuilt them as well but when i got it back from him he said he had to lean the bike way out to stop the carbon buid up on the plugs. but it backfired way too loud after i got it back so i moved the jet needle to richen it up a little, it still backfires loud but after i got if back from him it sounded like a 12 guage shot gun went off right behind my head. it backfires when you let off the throtle (not a downshift) let the engine slow you down for atleast 5 sec. and ease back into the throtle it will backfire every time. the longer the engine brake the louder the backfire so i am dumping raw fuel for some reason as far as i can tell.
thanks
Troy

[ratbyk]

400 RPM Shudder

raqumup, also sounds like a rough transition from pilots to mains to me as well. Had exactly the same problem on Ratbyk as I went through it's rejuvenation. Solved it by going up one step on the pilot size.
Before pulling the carbs again make sure that the pickup coil wires are sound. As suggested in a prior post the vacuum advance causes short life on these wires and the first indication that they are failing is this stumble at a certain RPM in any gear.
Ken?Sooke
78E Ratbyk
82 FT500 "lilRat"

[raqumup]

rebuilt it

OK I have rebuilt my engine and found that the center crank bearing had spun. So replaced all crank and rod bearings, and replaced 2nd gear. I was to the point that I thought it was maybe a sticking valve causing the shudder, the shudder is really 5000-5500 RPM. So anyway I got it all together and rode it WITHOUT the bottom half of the air box on it and WOW the bike is so much faster and extremely smooth I figured it was the rebuild that fixed it. Now I believe that my bike could do a wheelie if I wanted to, don’t worry I have no desire to. So brought it back to my shop and put the air filter and air box on and the side covers and was going to ride it home and when I got on the road I hit the throttle and it rides like it used to, same shudder and it did not have the power it had without the air filter. I have a K and N replacement air filter (drop in) it is clean but it has done this since I bought the bike. I bought the new K & N filter shortly after getting the bike. I was wondering if anyone else has had this problem and what hey had done to fix it. I was going to go with the 4 pod filters but I have read that some people have had problems with certain brand filters and too much restriction, so what brand pod filters have the best flow, because all I can gather is I have too much air restriction with the stock air box. I can power through the shudder in the lower gears but on the highway I have to keep it below 5000 RPM.

[underdog57]

I had the shudder around 4500 rpm .
Adjusted the floats to 27MM and adjusted the idle mix screws .
No shudder ....
I have the stock air box on .
still am running a tad rich , but its close ..
let us know how it works out ...
Wondering in the jet needles might be worn ??

Bob

[mro]

Carb settings all stock???
137.5 mains
jet needle posistion 3
float height 25.7 mm

Filter XSasberating a "rich" condition,
all above contribute when rpm goes above 3,000.

Would check float height first and needle posistion before changing from stock settings.

Raising float a little will lean it out some.

My 80G seemed to be running lean, but was smooth and no hesistation at any RPM. Had cleaned and checked carbs several times. Other day re-set floats down a mm from stock setting. Have yet to test it out properly yet, but ride home was encouriging.



mro

[raqumup]

it still needs to be tuned properly but i had it tuned at a shop by a guy who knos this bike verywell and he was not able to get rid of the shudder either ( this was several years ago) he could not get the plugs to stop showing signs of rich condition, after he gave it back to me when i would engine brake and then accelerate it would back fire like someone shooting a shotgun right behind my head, so i richend it up a bit and that stoped the backfireing but it has always run rich. i just dont get why with the airbox off it runs perfect, thats why i want to go to the pods, for less restriction.

[trbig]

I bought the cheap pods trying to save a bit, and ended up wasting my money at $40. Go here....

www.aperaceparts.com

These are true K&N knock-offs, and they are a one piece design... which means you don't have to worry about the filter element falling off. At $60, they are about one third the price of K&N. They won't be listed though... you'll have to call them.

Tod