Honda XRV Forum banner
1 - 19 of 19 Posts

·
Registered
Joined
·
9 Posts
Discussion Starter · #1 ·
Hi, my AT seems to have suffered from lockdown. Had been using it to commute to work but since lockdown it's been sitting in the garage. Have taken it for a run around the block once or twice but a few months ago while out, about half way round the run, while engine braking coming down a hill it started seriously backfiring. Limping home had to keep it below 3K revs to keep it from backfiring. When stationary the bike would stall unless you gave it a bit of throttle.
When I got round to looking at it a few weeks later I could see there was a coolant leak from the rear cylinder and from reading on here and other forums I diagnosed the problem as being a blown head gasket. Draining the oil and coolant there was none of each in the other, implying gaskets probably OK. Replaced base and head gaskets anyway and o-ring for the water pipe into the cylinder - which I reckon was the cause of the coolant leak.
Put it all back together again and absolutely no difference. Started fine but had to give it a bit of throttle to keep it ticking over even when warmed up. Increase revs slowly and everything fine until about 3K revs and the backfiring starts again. A backfire every second or so. Take it up to 5K and the backfiring gets more frequent. Didn't want to take it any higher than that.
Anybody have any ideas what this might be?
Oh, and another point. I've a magnetic oil sump plug and stuck to that was the end of a tooth of a sprocket. See pic attached. It's quite fine, not off the camshaft sprocket and checked the oil pump drive sprockets too. I'm thinking it's off one of the transmission sprockets in which case it won't be related to the backfiring problem. Maybe wishful thinking.
Bike has 97K miles on it but I keep it relatively well maintained.
Thanks.
Finger Vehicle door Thumb Bumper Gadget
 

·
Registered
Joined
·
1,084 Posts
Have you checked the choke is working correctly? It may move on the lever okay but can still stick. It was fine when you left it I would think its an easy solve if you can find the problem. Have you check all electrical connections to coils. I would also try it with fresh fuel from a bottle.
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #3 ·
Thanks een705.
I'll try blanking off the chokes - I recall reading on here that you can use the "caps" on the brake callipers.
I was so convinced it was the head gasket that I hadn't even considered an electrical issue. So much so that I haven't even changed the plugs - I use iridium ones but thinking about it they could be a few years old, though they looked fine when I had them out. Failing that I will check the coils. And you've got me thinking it might be a problem with the CDI unit. I'll see if I can test it too.
I flushed the petrol tank out a few times with fresh petrol so don't think the problem lies there but will try if any of the above don't solve it.
Thanks again for your suggestions. Might be a few days before I get round to doing any of the above but will reply once done.
 

·
Registered
Joined
·
1,084 Posts
That's right and dont forget to re-use the spring I think this might be the cause and fairly easy to do.
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #5 ·
Quick update. Changed the plugs, no difference. Checked the resistance on the coils and all good, plus there is a good spark at each plug. Will check the CDI unit next then if that's OK will blank of the chokes. een705, leaving this to last just because it is awkward to get at them to spanner them back in - though screwing the "brake calliper caps" in might be easier. And thanks for pointing out to re-use the springs.
 

·
Registered
Joined
·
49 Posts
Maybe you need to clean the jets in the carbs ? When bikes are left to stand the fuel evaporates leaving sludge which can block the jets. I’ve come across some really interesting cases where you wouldn’t believe how much crud builds up from a small amount of petrol
 

·
Registered
Joined
·
1,368 Posts
Your jets are gunked from continuously evaporating fuel. Take the carbs apart and clean them up. This is very common on bikes that are not used but started every once in a while...
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #8 ·
Thanks Martindebule and Massive Lee. When I took the bike out it was running well for the first 10, 15 minutes of the journey and then started the back firing. Is that likely going to happen with blocked jets? I suppose a bit of gunk could have moved about. Been away for a few days so haven't done anything since checking the coils. Hopefully get a bit of time this week to look at it again.
 

·
Registered
Joined
·
49 Posts
Difficult to say really. It’s always worth cleaning out carbs if bike has been standing. I took my mates float bowls off his Guzzi few years back to clean the jets. Couldn’t believe how much crud had built up, like it was growing an alien in there. Get can of carb cleaner and crack on with it mate. If it’s not the carbs it’s got to be ignition
 

·
Registered
Joined
·
38 Posts
Blocked jets is highly likely here after the layup.
Petrol will gum up as has been suggested, though I think you'll see that the small drilled holes will be blocked when you hold the Idle jet and Main jet to the light on one or both carbs.
If you're removing them, have a read up and balance them properly on refit with a pair of guages.
Set the idle mixture too for best slow running.

Sent from my SM-G955F using Tapatalk
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #12 ·
Haven't done anything yet! Well, apart from watching some videos on cleaning carbs. As I found it easier to detach/attach the chokes with the carbs off I will check and clean the jets while blanking off the chokes.
Thanks Bardley, I will have a read on balancing the carbs too and if it's not beyond me do that too.
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #13 ·
Started cleaning the carbs but ran into a slight problem in that the top of the pilot screw sheared off. See pics. I wasn't even putting much pressure on it, trying to loosen before screwing Automotive lighting Automotive tire Motor vehicle Headlamp Automotive design Automotive tire Locking hubs Bicycle part Motor vehicle Rim in to get the number of turns. I guess I'll have to drill a slot in it to get it out. Or leave it alone. All the rest of that carb was clean, no gunk anywhere. I'll take the other carb apart first before returning to the pilot screw on this one.
For reference I followed this video - mastorakos:Cleaning carburetor on honda xrv 750. - YouTube . He has a few others including synching the carbs.
 

·
Commuter Extraordinaire
Joined
·
536 Posts
Interesting one. Normally, if there's evaporated fuel crud in the carbs after a bike's been standing a long time (assuming the carbs haven't been drained down) it generally affects the slow running (pilot) jet which is a lot smaller in diameter than the main/needle jet. This results in poor running at lower revs, and once the main jet comes into play at around 1/4 throttle it runs far better. A blocked pilot jet can however be bypassed by activating the cold start circuit ("choke") albeit it won't run as smoothly as it does with a clean pilot jet.
If the bike runs fine up to 3000rpm one could assume the slow running circuit is working as it should.
Backfiring often is due to an air leak into the fuel system at the inlet or exhaust side, causing late detonation. Whereas misfiring is normally due to an ignition fault.
I'll be interested to hear how you're getting on.
 

·
Registered
Joined
·
37 Posts
Started cleaning the carbs but ran into a slight problem in that the top of the pilot screw sheared off. See pics. I wasn't even putting much pressure on it, trying to loosen before screwing View attachment 166618 View attachment 166619 in to get the number of turns. I guess I'll have to drill a slot in it to get it out. Or leave it alone. All the rest of that carb was clean, no gunk anywhere. I'll take the other carb apart first before returning to the pilot screw on this one.
For reference I followed this video - mastorakos:Cleaning carburetor on honda xrv 750. - YouTube . He has a few others including synching the carbs.
I had a similar problem with my previous XRV pilot screws. On one side the screw had only one quarter left. Then I cut a slit with a dremel cutting disc and slightly heated the carb with blow torch. After that I put the carb in the freezer for half an hour. After the second heat-freeze cycle the screw was undone very easily.
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #16 ·
Interesting one. Normally, if there's evaporated fuel crud in the carbs after a bike's been standing a long time (assuming the carbs haven't been drained down) it generally affects the slow running (pilot) jet which is a lot smaller in diameter than the main/needle jet. This results in poor running at lower revs, and once the main jet comes into play at around 1/4 throttle it runs far better. A blocked pilot jet can however be bypassed by activating the cold start circuit ("choke") albeit it won't run as smoothly as it does with a clean pilot jet.
If the bike runs fine up to 3000rpm one could assume the slow running circuit is working as it should.
Backfiring often is due to an air leak into the fuel system at the inlet or exhaust side, causing late detonation. Whereas misfiring is normally due to an ignition fault.
I'll be interested to hear how you're getting on.
Thanks Steinberg. I've found that the pilot jet on the rear cylinder carb was blocked. The bike isn't ticking over so the blocked pilot sounds like the cause of that but as you say it doesn't sound like it would be the cause of the problem at 3K+ rpm. I know nothing about carburetors though. The float chamber rubber seal on that rear carb was pretty solid so I'm going to order new ones. While waiting for it to arrive I'll try sticking the carbs back on and see if cleaning them out has made any difference. I'll try capping the chokes too.
I see Wemoto sells a carb repair kit (Honda XRV 750 S Africa Twin RD07 95 Carburettor Complete Repair Kit Parts at Wemoto - The UK's No.1 On-Line Motorcycle Parts Retailer) that has jets as well as o rings. Does anyone know if that kit is any good or where to buy a good one?
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #17 ·
I had a similar problem with my previous XRV pilot screws. On one side the screw had only one quarter left. Then I cut a slit with a dremel cutting disc and slightly heated the carb with blow torch. After that I put the carb in the freezer for half an hour. After the second heat-freeze cycle the screw was undone very easily.
Thanks nhadjinikolov. I tried removing the the screw from the other carb too and same problem the quarters started to shear off. As per my post above I found the idle jet was blocked so now clear I'm going to stick the carbs back on and see if that has solved the problem. ie. I'll leave the screws as they are. If not I'll try your trick to see if I can get them out.
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #18 ·
The bike is running smoothly again. To recap what I did. Gave the carbs a good clean, in particular, cleared the blocked pilot jet and blanked off the choke on each carb. Because I did the two things I don't know whether blanking the chokes was needed but the choke on the rear carb had a bit of junk in it so it being clogged up may have caused the 3K+ backfiring. I'm in two minds whether to connect the choke cables back up again, I never used the choke when I was using the bike regularly but for completeness I feel they should be connected.
I've left the pilot screws (with the sheared heads) in there as I imagine I will make a right mess of them getting them out. I bought the Keyster carburetor repair kit from Wemoto but they've to order it in so hasn't arrived yet (Keyster Complete Carburettor Repair Kit Honda XRV750 RD07 93-95 Parts at Wemoto - The UK's No.1 On-Line Motorcycle Parts Retailer). It comes with pilot screws, and jets and seals, but I think I will just hang onto it until the next time I run into problems with the carbs.
Thankyou everyone for your help, much appreciated.
 
1 - 19 of 19 Posts
Top