Misbehaving Monza |
Post Reply | Page <1234 5> |
Author | |
Sambike
Guzzino Joined: 13 Oct 2020 Location: Durham, NE Engl Status: Offline Points: 11 |
Post Options
Thanks(0)
|
Sounds too obvious, but try a set of known to be good used plugs. New plugs should be perfect, but sometimes aren't, even from a reputable dealer. I got fed up with faulty NGK's, changed to Bosch, end of problem.
|
|
c13pep
Senior Member Joined: 31 Aug 2017 Location: Doncaster Status: Offline Points: 2110 |
Post Options
Thanks(0)
|
I have replaced plugs for others but even swapping sides has no effect
CHRIS
|
|
you can`t have any fun in a straight line
Monza Honda CB77 project |
|
iansoady
Senior Member Joined: 23 Jul 2017 Location: Redditch Status: Offline Points: 2402 |
Post Options
Thanks(0)
|
Does it have the electronic ignition rather than points?If so I could imagine a problem with the electronic advance circuit (which probably retards the spark at low revs rather than advancing it at high).
|
|
Ian
1952 Norton ES2 1986 Honda XBR500 1958-ish Greeves/Triumph in progress |
|
c13pep
Senior Member Joined: 31 Aug 2017 Location: Doncaster Status: Offline Points: 2110 |
Post Options
Thanks(0)
|
It has the points so no luck there
On this very depressing day both with weather and the forecast of another lockdown I am trying to sych myself up to go and have another session in the garage
CHRIS |
|
you can`t have any fun in a straight line
Monza Honda CB77 project |
|
Richard Hyatt
Senior Member Joined: 14 Oct 2019 Location: Dorset Status: Offline Points: 1097 |
Post Options
Thanks(0)
|
From many years as an AA man at the side of the road, I learnt think simple and work from there !
We all know you need compression , a spark and some fuel to burn. I used a red ht neon ht tester in many of my diagnoses to explore why the customer's car wouldn't run correctly. This £2.50 plastic thing went in-between the plug and the ht cap and served to let me know where to look. At least you could see what you were up against ! No spark at all Weak spark Good healthy spark , in which case look for fuel side I think you've already stated 160 psi both sides , so forget that. Just checked ebay ,Sparkrite ht neon £1.95 , buy a couple , one on each cylinder. Go from there.
|
|
Dave P.
Senior Member Joined: 12 Jan 2015 Location: Northants Status: Offline Points: 5573 |
Post Options
Thanks(0)
|
I know you have checked the mechanical timing device but would it be worth checking it again. It sounds as if it's not advancing properly until it's spinning fast enough (4000 rpm)to overcome some sort of stiction.
|
|
TO LIVE OUTSIDE THE LAW YOU MUST BE HONEST.
1971 V7 Special. 1972 850GT. 1970 T120 Bonnie. 2009 500 Bullet. |
|
Mike H
Senior Member Joined: 21 May 2014 Location: East Anglia Status: Offline Points: 8733 |
Post Options
Thanks(0)
|
Yeah but no but, that would affect both cylinders. Same mechanism does both. Need to get it hot so it's showing the fault then start looking at things.
I did a google on engine won't run when hot, other ideas came up like cracks open up due to expansion, eg a cracked head, gasket fails to seal because of expansion, that kind of thing. I did have valves failing to close on the 850 once, when hot, but didn't stop it firing at slow running just a loss of power. |
|
"Chicken nuggets don't dance on a Tuesday."
|
|
Mike H
Senior Member Joined: 21 May 2014 Location: East Anglia Status: Offline Points: 8733 |
Post Options
Thanks(0)
|
Afterthought - a colortune might be good, so can see what the burn looks like in the cylinder. Might reveal something.
|
|
"Chicken nuggets don't dance on a Tuesday."
|
|
Dave P.
Senior Member Joined: 12 Jan 2015 Location: Northants Status: Offline Points: 5573 |
Post Options
Thanks(0)
|
Of course, you're right Mike. I'd forgotten that the fault was only on one cylinder. Worra dummy!
|
|
TO LIVE OUTSIDE THE LAW YOU MUST BE HONEST.
1971 V7 Special. 1972 850GT. 1970 T120 Bonnie. 2009 500 Bullet. |
|
Dave P.
Senior Member Joined: 12 Jan 2015 Location: Northants Status: Offline Points: 5573 |
Post Options
Thanks(0)
|
No one has mentioned the "Chokes" yet, have they?
If one of them is not seating correctly or the piston rubber is damaged that can cause erratic running. Particularly at smaller throttle openings.I had this on the 850GT a couple of years back and searched for ignition problems. (On the side of the road in Belgium)Then found that the L/H choke cable had mysteriously lost the 4mm of slack that it should have thus the enrichment passage was open. I never did find out where those 4mm had gone! |
|
TO LIVE OUTSIDE THE LAW YOU MUST BE HONEST.
1971 V7 Special. 1972 850GT. 1970 T120 Bonnie. 2009 500 Bullet. |
|
Richard Hyatt
Senior Member Joined: 14 Oct 2019 Location: Dorset Status: Offline Points: 1097 |
Post Options
Thanks(0)
|
Just re-reading things,
Both cylinders run fine from cold up to 4000 rpm. Then, when warm , one side fails below 4000, other side fine. Hope I've summarised correctly. From cold you might need a richer mixture , so if the choke on 1 side wasn't closing 100% then the engine could deal with the extra richness. But when it didn't need the extra fuel , ie hot, the 1 side would flood out. OK Is the failing side plug black and wet? Hmm , choke? As suggested earlier not closing fully I know you've changed condensers recently but have you changed them side to side to see if a duff condenser exports the problem to the other side?
|
|
c13pep
Senior Member Joined: 31 Aug 2017 Location: Doncaster Status: Offline Points: 2110 |
Post Options
Thanks(0)
|
Exactly right Richard however above 4000 rpm the bike goes like a train when warm and it`s just like a switch when the second cylinder kicks in.
If it was a choke then I would expect some coughing and farting occasionally when flooding but there is nothing not even the smell of excess fuel, just the sound of a 250 single until 4000 rpm when it just takes off. Checking the plugs is very difficult as I am generally just trying to limp home. The major problem is that I`m `running in` so don`t really want to go beyond 4000 rpm yet, so running in lower gears is problematic also. Because of the switch effect I`m at a loss as to whether its fuel or ignition CHRIS
|
|
you can`t have any fun in a straight line
Monza Honda CB77 project |
|
Richard Hyatt
Senior Member Joined: 14 Oct 2019 Location: Dorset Status: Offline Points: 1097 |
Post Options
Thanks(0)
|
OK with you
Are you able to run it on the stand to this magical 4000 threshold? Use a fan blower on cold to cool the engine, may need a pal to assist. Try those neon ht testers though as they can be used whilst riding(or as above)and may show this magical cut off visually. With a crisp cutoff such as you have , I'd suspect something electrical , but wouldn't discount anything. If you establish an ignition failure at 4000 via these neons , then you can work on exporting the problem to the other cylinder via swops. You've already swopped the coils, don't forget to swop condensers. I can't remember if you've swopped ht leads and ht caps. Just reread, if it goes well over 4000 then there's plenty of fuel. Could the float needle valve be sticky and at 4000 be vibrated off its seat ? Allowing plenty of fuel. Needle not got a little ridge on it where it cuts into its seat? 2nd edit, If it runs on 1 up to 4000 then you could use these neons on the plugs from 0 to 4000. If you have sparks all the way from 0 to 4000 then you have a fuel issue at this lower range! Remember these neons show the spark, the colourtune will show the overall fuel burn (spark and fuel burning )
Edited by Richard Hyatt - 31 Oct 2020 at 21:05 |
|
Richard Hyatt
Senior Member Joined: 14 Oct 2019 Location: Dorset Status: Offline Points: 1097 |
Post Options
Thanks(0)
|
Me again,
Re re reading what I've put above. Do try to buy beg borrow a colourtune. Why? The colourtune shows the burn colour , blue for good , reddy for rich. Go for a ride or let it run on the stand from cold on both pots until it gets hot enough to fail.(if you have the neons as well , have them installed during this). You can visually see what is happening in the garage then on each cylinder , lost spark when hot or 0 to 4000 , colder exhaust pipe on 1 side? Whichever cylinder has gone? Determine this. Now , if you still got both sparks at hot and both sparks at 0 to 4000 and both neons are good , reliable and bright red all the way?. Now think of fuel problems. OK, still hot and failing, put colourtune in 1 side , 0 to 4000 , is it bluey all the way up ? Yes , no? Swop sides , is that side bluey all the way ? Forget reddy flashes with bits of richness here and there , is the explosion/burn happening all the way 0 to 4000. Phew |
|
Mike H
Senior Member Joined: 21 May 2014 Location: East Anglia Status: Offline Points: 8733 |
Post Options
Thanks(0)
|
This has got to be it. Fixed, working again, stopped being fixed, not working again. 5 miles is may be just when it stops working, then no fuel, aka too low in the float bowl. Lots of tnrottle means you can force it to go, but then under a certain throttle height it don't won't to know. Seems kind of llke what happens when you're running onto reserve. Or running out that is, need to switch reserve. |
|
"Chicken nuggets don't dance on a Tuesday."
|
|
Post Reply | Page <1234 5> |
Tweet
|
Forum Jump | Forum Permissions You cannot post new topics in this forum You cannot reply to topics in this forum You cannot delete your posts in this forum You cannot edit your posts in this forum You cannot create polls in this forum You cannot vote in polls in this forum |