Thumper Club Forum
Technical => Bike Problems/Questions => Topic started by: Clubman44 on October 03, 2018, 11:50:36 AM
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Need a bit of help my Xbr runs fine up to about 5000 rpm in the gears however above that ther is a reluctance to rev out, in top gear it gets to about 4000 and then it starts to miss now and again,I wondered if perhaps the coil might be on its way out?
Regards Rod.
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With the (non-thumper) CX, that us often a sign of the stator failing.
Hope something simple with the XBR!
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I going to start with the basics and change the plug,cap, and lead. And see where I go from there,I don’t think it’s fuel related.
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Always a god plan - it's too easy to imagine the worst snd start ordering parts!
Even if you don't think it's fuel (ie bike is regularky used, you didn't leave it out in the rain, and it was fine until it wasn't), it may be wofth draining the float bowl into a container to see if there's water/paint flakes/ rust in there.
Hopefully someone more knowledgeble than me will have replied by then! ;) cheers!
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The way I'd look at the problem.
It may or may not be fuel related. But if is fuel, based on the described symptoms, it sounds as if it is unable to give max power. You need the most power the faster you go, generally speaking. So in top gear at a reasonable lick the engine is loaded. Max power needs max fuel flow. Assuming you've not been tinkering with jets or anything I'd consider the possibility of a partial block. Thing is, one can check this kind of thing without replacing parts in the hope that's the cure. Next thing I'd do is get the the symptom to repeat itself consistently time and again so you've a solid theoretical base. Maybe find a steep hill and then you can see if the symptom occurs in the lower gears, lending more evidence that it is power related or not.
Just throwing ideas in the pot.
Cheers.
Edit: max power also needs max air flow. The air filter would have to be in terrible state tho.
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If the electrics are OK, it might be a damaged diaphragm in the CV carb not letting the slide lift up?
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Well I changed the plug and cap, the ht lead seems to be sealed into the coil. I also put a meter across the coil the resistance on the primary was 00.5 according to the manual it should be 0.18, could this be my problem, the secondary circuit was correct.
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0.5 what? If ohms that's a low value in my experience. Digital meters do tend to have zero errors that need to be taken into account.
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Stuck choke plunger?
Or as per SteveC CV carb diaphragm.
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Have not had a chance to test the bike yet, Iwill try over the weekend, I have checked the choke plunger. The diaphragm I will check, however the carb is a right pain,with the one piece manifold.
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Interesting thread. My (complete) XBR has had a similar issue recently but I've not had chance to sort it yet. Loping along in top @4000 rpm (reads 60 mph on my clock) feels like it is running out of fuel. Drop down and it will rev through 4000 but will then hesitate higher up the band, however in fist and second it can red line without noticing an effect. The carb was cleaned this summer with a full service kit installed - it is a knuckle scraping pain. The valves are spot on. The plug & cap are new. So the one item I need to pull apart is the fuel tap (and check the fuel line is clear) as I'm suspecting that it might be that that is harbouring some crud. This weekend I'm hoping to get the time and the weather to check it.
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Interesting thread. My (complete) XBR has had a similar issue recently but I've not had chance to sort it yet. Loping along in top @4000 rpm (reads 60 mph on my clock) feels like it is running out of fuel. Drop down and it will rev through 4000 but will then hesitate higher up the band, however in fist and second it can red line without noticing an effect. The carb was cleaned this summer with a full service kit installed - it is a knuckle scraping pain. The valves are spot on. The plug & cap are new. So the one item I need to pull apart is the fuel tap (and check the fuel line is clear) as I'm suspecting that it might be that that is harbouring some crud. This weekend I'm hoping to get the time and the weather to check it.
It's something affecting the engines ability to develop full torque and power by the sounds of it. Same as above. Not a massive help but a clue nonetheless
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What's the mileage?I only ask because a few years ago i ran a ratty £500 XBR with high miles and it never did pull right.I was told it could well have been due to wear in the engine. Just a thought but i hope i'm wrong!
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Been following this link too. As Xbally asked, it would be interesting to know the mileage. If it does prove to be carb related and not electrical I would suggest getting the carb ultrasonically cleaned rather than treating with carb cleaner. I have done this with a couple of xbr carbs and whilst they weren't suffering as badly as yours, it definitely improved things. Not cheap, and I know the carb on an xbr is a sod to remove but probably worthwhile together with adding a fuel filter.
I think there are some previous tips on xbr carb removal on this site if you check using the search facility.
Good luck
Tony
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I took the Xbr out for a test ride today, it seemed to run quite well, the missing I was experiencing at 4000rpm is still there but not so bad as it was before changing the plug and cap, which seems strange to have a partial cure. I am still thinking the I might replace the coil in the near future, the bike has 36000 miles on it. I will report on any further progress, but I would like to thank everyone for their advice.
Rod.
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Mine is 42k. Managed to get out yesterday having swapped the tank from my build bike just to have a comparison. After a few warming up miles no issues with 1st, 2nd, 3rd going to the red line and 4th almost; 5th revs through the 4k without issue but got the issue at 5k but it rode through. Back to home and found that the starter motor had decided to just make 'clicking' noises - the joys of classics - so just as well it has the kicker! Fuel tap and filter in tank has been duly cleaned (no sign of crud in tank) and I'll be taking it for longer runs next week, hopefully, to see how things are. If all else fails I'll get the carb out and borrow friends ultrasonic bath* again.
*I'm told that those foot spa's are similar but we chucked ours some time ago!
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Check the fuel tap is flowing the correct amount of fuel, I had a similar problem on the RS500 , bigger carb but standard fuel tap so not flowing enough fuel to fill the float bowl at high RPM so would misfire. If you've got a blockage or restriction it might do the same thing.
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My update, having taken a tad longer than planned, is that the 'clicking noise' was resolved with a new battery (old one had died) and the ultrasonic bath worked its magic on the carb and the bike now revs through easily with no issues at any RPM. Hopefully Clubman44 has managed to get sorted too.
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Pleased to read that the simple diagnostics have proved correct and all now appears well. Happy miles. ;D
Go canny, Bill
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Just a little update I fitted a new Honda coil, and a iridium plug but there’s no improvement it’s still hesitating at 4 to 4500 rpm in 4 and 5 gear not sur where to go, maybe a run on a rolling road might turn up something.
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Just a little update I fitted a new Honda coil, and a iridium plug but there’s no improvement it’s still hesitating at 4 to 4500 rpm in 4 and 5 gear not sur where to go, maybe a run on a rolling road might turn up something. Sounds like a good idea. Keep us posted.
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I had exactly the same problem. Dirt from the fuel tank was blocking up the carb.
It was a bit fiddly to get the carb completely free of dirt and little shards of metal, which probably came from the inside lining of the fuel tank. If you take your fuel tank off and shake it a little bit can you here sludge moving around?
I ended up getting a fuel tank from eBay which was thankfully in better condition than the original.
If you get stuck I should have a spare carb lying around that I could post (and loan) you.
Good luck.
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Thanks for the offer Tony, I have got the bike booked in this Saturday on the rolling road, should know a bit more after that.
Regards Rod.
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Sorry for not coming back earlier however I wanted to be sure the problem had gone away. On the Dyno the bike performed faultlessly He. Couldn’t find anything wrong with it, I was very sceptical, however I rode it home and it seemed fine I have been using it since with no repeat of the problem. I can only assume it was some kind of carb blockage, that cleared when the bike was put under a heavy load on the dyno
Regards Rod.
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Thanks for posting your conclusion. Nothing worse than getting to the end of a thread like this and finding it unresolved.
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What were the readings? Power/torque.
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Will try and find the read out and let you know although from memory it was about 32 at the back wheel.
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Cheers. Just curious, as others will be I imagine.
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Definitely! Good question. :)
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Trust me, he's full of em. (Good questions that is 😁😁)
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I checked the printout from the dyno run it was 32.8 at 6500rpm max torque 29.25 at 3800rpm not too bad feels like more, this was with a fish tail velocette silencer fitted.
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I checked the printout from the dyno run it was 32.8 at 6500rpm max torque 29.25 at 3800rpm not too bad feels like more, this was with a fish tail velocette silencer fitted.
Thanks for that. Always useful to hear what these things actually put out. About what I expected. From (distant) memory did honda claim 45hp crankshaft? Anyhow it's amazing how far 32 hp goes, out in the real world ain't it. Enjoy the bike! 😁
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SteveC is the man with all the info on the alleged heavy breathing on the test bikes made available to the press. Shocking! :o