losing one cylinder at high RPMs on the highway

Are ya having a problem with your rig? We'll try to help. Share your tech tips and experiences here. Dr. Billy Glaser, author of the "Unofficial 750 Ural Service Manual" site myural.com, is moderating this section.
Forum rules
Here is the place for you to ask questions about or share your experiences about servicing or repairing your Ural or Dnepr. Please post topics concering modifications or accesories in the "Modifications and Acessories" section. Please post oil related questions in the "Oil Threads" section.
nosbearatu
Comrade
Comrade
Posts: 73
Joined: Tue Jul 02, 2013 10:34 pm

losing one cylinder at high RPMs on the highway

Post by nosbearatu » Thu Jun 07, 2018 1:25 pm

I have been having a niggling issue on my 02 Bavarian Classic. Last summer I started having issues with the bike while driving it on the highway. One day, I was out driving in the country at around 55mph and the bike suddenly started running rough and surging. I pulled off to the side of the road and looked everything over and let it sit a minute and it started and ran fine, until I reached highway speeds again. What seems to be happening is the bike will get on the highway and run at 3500+rpm for 5 or so minutes fine and then it will start stuttering, it seems like it is dropping a cylinder. If i back of the throttle for 30 seconds or so, the power comes back, but if I push it past that point it goes haywire again. Driving around town at 20-40mph doesn't bother it and it runs fine and that is most of my day to day driving. So I used the bike the rest of the summer last year and so far this year just moving around town and staying below 55mph. Last year, when it started I checked my in line filters and pulled the petcock to check the fuel filter there and everything looked good. This past weekend I redid a compliance fitting that was causing some popping on deceleration and I was hoping that was the problem, but this morning I had the same power issue when I tried to take the highway to work. Other than at speed, the bike runs beautifully and starts effortlessly with the kickstarter (I need to fix the starter relay, it hasn't worked for several years now).

My question is where should I look next? My next thought was to open up the carbs and check the float valves and the floats. It feels to me almost like one cylinder is running out of fuel and then letting off the throttle allows the float bowl to briefly catch up. Would a bad float do this? I though when floats went bad flooding was the common issue.
2002 Ural Bavarian Classic
Minneapolis, MN

Donbmw
Hero of the Soviet Union - 2018
Hero of the Soviet Union - 2018
Posts: 229
Joined: Fri Nov 18, 2016 7:47 pm
Location: Monroe, Louisiana, 71203

Re: losing one cylinder at high RPMs on the highway

Post by Donbmw » Thu Jun 07, 2018 1:46 pm

I have 2 of BMW’s and my Triumph TR3 do this to me. It could be fuel or electrical. In my case it was ignition. From spark plug wires to the after market ignition system.
2015 Patrol, 1980 R65, 1982 R65 bought new, 1975 R 90/6, 1959TR3 Triumph

Don

rivers
Hero of the Soviet Union - 2018
Hero of the Soviet Union - 2018
Posts: 8993
Joined: Sat Jul 24, 2010 10:04 pm
Location: west WA

Re: losing one cylinder at high RPMs on the highway

Post by rivers » Thu Jun 07, 2018 2:23 pm

My first thought was how old are the plug wires? As Don mentioned could be either elec or fuel but I'd think ignition system.
Joe
014 GU
"I'm lost but I'm making good time."

Obo Scribe
Hero of the Soviet Union - 2018
Hero of the Soviet Union - 2018
Posts: 391
Joined: Thu Dec 15, 2011 5:35 pm
Location: Lancashire

Re: losing one cylinder at high RPMs on the highway

Post by Obo Scribe » Thu Jun 07, 2018 3:07 pm

My feeling was fuel (vacuuming the tank), but you gotta start somewhere, so toss a coin and dive in. My basic rule of thumb with any of my bikes is to start with the cheapest fix and work my way up the list of possibilities
2003 750 Dalesman, 1975 CB400/4, '93 CBR900RR, 2012 DL650, 91 Ducati 750SS . Twenty eight bikes in the last six years, my missus thinks I have a bike problem. :boogie: ..
Chorley, Lancashire, England
'Oboto Sobatmas' - sponsored by Deuchars, fuelled by stupidity. http://obotosobatmas.blogspot.co.uk/

User avatar
Wildhorse Cafe
Hero of the Soviet Union - 2018
Hero of the Soviet Union - 2018
Posts: 1526
Joined: Mon Sep 08, 2014 5:28 pm
Location: King City, California

Re: losing one cylinder at high RPMs on the highway

Post by Wildhorse Cafe » Thu Jun 07, 2018 3:16 pm

Compression Check!
2011 Patrol Higgs Bison Super Collider formally known as the Orange and Silver Pumpkin Coach
2006 Shinny Black, Tourist, Tatyanna

When you set out on your journey to Ithaca
pray the road is long , full of adventure, full of knowledge
not expecting that Ithaca will offer you riches
Ithaca has given you the beautiful voyage

C.P. Cavafy

nosbearatu
Comrade
Comrade
Posts: 73
Joined: Tue Jul 02, 2013 10:34 pm

Re: losing one cylinder at high RPMs on the highway

Post by nosbearatu » Thu Jun 07, 2018 6:32 pm

Checked compression (engine cold), both sides were right around 100 psi.

Pulled the wires and measured resistance, 5k ohms on each.
2002 Ural Bavarian Classic
Minneapolis, MN

User avatar
URAL CT
Order of Suvarov
Order of Suvarov
Posts: 3371
Joined: Tue Oct 02, 2007 4:20 pm
Location: Plano, Texas

Re: losing one cylinder at high RPMs on the highway

Post by URAL CT » Thu Jun 07, 2018 7:07 pm

Long shot...but one of the jets, main or idle (unlikely the idle, but check it anyway) may be plugged or partially plugged. Could be the plug wires too but ya checked those already.
I worked on a friend's 2012, but on his, the left cyl was not firing at idle. Found the idle jet plugged, got that fixed. While the carbs were opened up, we changed the float needles too. We went riding then it started misfiring, after much scratching of head & posterior, I suspected ignition. Took the tank off & sure enough, the black wire from the hall sensor had one strand left connected & broke off once we touched it. Replaced the hall sensor & all is good. We took it for a 50+ miles ride & it hummed like it should. Now the tranny spring broke...but that is another drama. :mrgreen:
CT
2007 Patrol
Plano, TX

User avatar
Lmo
Hero of the Soviet Union - 2018
Hero of the Soviet Union - 2018
Posts: 4466
Joined: Wed Jun 10, 2015 3:19 pm
Location: Central California via So. Indiana

Re: losing one cylinder at high RPMs on the highway

Post by Lmo » Thu Jun 07, 2018 7:10 pm

2002 = first year for 750cc fitted with Type IV ignition system... with two-part rotor.

Pull the front cover, check to see if the two-pieces of the rotor are secure.

Easy to spot; two-piece on the left, one-piece on the right. If it's loose ignition can be full-one variable with inconsistent performance.

If it is loose, you might be able to have it tack-welded back into position,

Image
source: http://myural.com/interrupterreplacement.htm

It may not be this at all, but it's an easy thing to check, and a couple of guys have had this happen recently. I replaced mine.

If you need to replace get one from Lutz > http://ural.ca/

edit...


I just thought of this test, I learned it when my own rig's ignition was failing .... take the bike out for a run, when it starts to cut out, switch off the ignition and immediately turn it back on. If the engine catches and runs normally again it is more than like the ignition module.
Lew Morris
Dnepr w/ '06 Ural Drive Train
C5 Power Arc
125/42 jets
Drilled slides/
.030" shims

1973 BMW R75/5 (original owner)
1947 HD FL (long gone, forever regretful)

nosbearatu
Comrade
Comrade
Posts: 73
Joined: Tue Jul 02, 2013 10:34 pm

Re: losing one cylinder at high RPMs on the highway

Post by nosbearatu » Fri Jun 08, 2018 9:33 am

Yeah, I replaced the rotor with a one piece a few years ago. I think today I am going to open up the carbs and see if there is something plugging it.
2002 Ural Bavarian Classic
Minneapolis, MN

User avatar
Albuquralque
Order of Victory
Order of Victory
Posts: 19255
Joined: Thu Jul 19, 2007 2:46 pm
Location: Albuquerque, NM

Re: losing one cylinder at high RPMs on the highway

Post by Albuquralque » Fri Jun 08, 2018 11:47 am

nosbearatu wrote:Yeah, I replaced the rotor with a one piece a few years ago. I think today I am going to open up the carbs and see if there is something plugging it.

Before opening the carbs up.....why not swap them and take it for a ride? See if same cylinder still misses or if it moves with the carb.
"Put a little gravel in your travel"

Darrell - Albuquralque
2014 Patrol - Babe the Blue Ox
EFI Map OR 1.02
Throttle Body Vacuum Ports
K&N Air Filter
Raceway 2-into-1 Header (Right Side)
Previous Urals Owned: 2004 Wolf, 2006 Tourist, 2006 Patrol (TOW), 2006 Patrol (TOM)

User avatar
Msblu79
Hero of the Soviet Union - 2018
Hero of the Soviet Union - 2018
Posts: 1772
Joined: Mon Sep 13, 2010 8:00 pm
Location: Invading Upstate NewYorkastan

Re: losing one cylinder at high RPMs on the highway

Post by Msblu79 » Fri Jun 08, 2018 12:41 pm

Possible Fuel tank/carb vent plugged? Vaccum created in tank slows fuel flow causing bowls to run dry. Check vents on tank & carbs.
2010 Black Patrol

Who's Ur Grandaddy ?
Hero of the Soviet Union - 2018
Hero of the Soviet Union - 2018
Posts: 335
Joined: Sat May 18, 2013 7:02 pm
Location: oregon

Re: losing one cylinder at high RPMs on the highway

Post by Who's Ur Grandaddy ? » Fri Jun 08, 2018 1:01 pm

I'm betting that one of your main jets is plugged. They don't come into play till around 3/4 throttle , I believe. As it runs fine on low rpm . Or perhaps a float needle problem .
I work on my carbs attached to the bike . I lay on the floor on my back and remove the bowls , giving me access to the jets and float needles.
john
2013 FF gear-up
Mr Cob bulletproof skid plate
Powerarc ignition
Raceway titanium carb needles 4th notch from top
132 1/2 main ... 42 pilot ... air/fuel 1 1/2 turns out
7/64 drilled slides
Leftka III type airbox
Modtop mufflers

nosbearatu
Comrade
Comrade
Posts: 73
Joined: Tue Jul 02, 2013 10:34 pm

Re: losing one cylinder at high RPMs on the highway

Post by nosbearatu » Sun Jul 15, 2018 11:33 pm

Ok, update. I have dug in quite a bit to try and solve this. I went through the ignition system, swapped coils (no effect), used my multimeter through the whole system and everything appears to be working. I did shorten one of the spark plug wires since I was questioning the coil connection on one. This had the side effect of pulling on one wire while connected to the spark plug which could be causing some issues (I will be replacing both wires soon). I think the original source of the problem may have been a split in the left side air box hose that I discovered while going over things. I also pulled off the carbs and cleaned them. They were very clean inside, so I don't think that was it. While I had them off, I decided to finally replace my homemade old style carb mount (hard mount that bolts to carb) with the rubber Mikuni fittings that I ordered from Crawford. I RTV sealed the gasket to the head like Gene suggested and then put some on the other side of the gasket that mates with the rubber mount for good measure. I mounted everything up and set the valve clearances and checked the timing (it was fine).

After all of this I went to start it and it idles fine, but when I try to drive down the road it bogs down and runs rough with no power. It is also sputtering and popping when releasing the throttle. This is in first gear and it will barely pull away in 2nd. It also does surge. I did eyeball sync the carb cables and the idle jets are both set to 2 turns out. Is this something that out of sync carbs will cause? I am planning on replacing the plug wires when I return from vacation, but after that I am out of ideas and based on some testing I did this evening, I think the wires are working now, even if one side of the wire is pulled tight. Thoughts? Is there something that I could have done wrong in mounting the new carb flanges? It almost seems like I have a leak, but I don't see how I could.
2002 Ural Bavarian Classic
Minneapolis, MN

User avatar
xpatriot
Comrade Colonel
Comrade Colonel
Posts: 282
Joined: Wed Oct 15, 2008 7:50 pm

Re: losing one cylinder at high RPMs on the highway

Post by xpatriot » Mon Jul 16, 2018 11:19 am

Check your air filter is clean and installed correctly....I had exactly the same symptoms when I had flipped the rubber gasket in my air box over and was effectively starving the engine of air under acceleration.
1999 650 Tourist "The Moscow Mule"

nosbearatu
Comrade
Comrade
Posts: 73
Joined: Tue Jul 02, 2013 10:34 pm

Re: losing one cylinder at high RPMs on the highway

Post by nosbearatu » Mon Jul 16, 2018 11:27 am

I thought about that, I tried running it with the lid off of the air box to see if it was the filter. Still had the same trouble.
2002 Ural Bavarian Classic
Minneapolis, MN

Post Reply