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Misbehaving Monza

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Sambike View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sambike Quote  Post ReplyReply Direct Link To This Post Posted: 30 Oct 2020 at 16:37
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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote c13pep Quote  Post ReplyReply Direct Link To This Post Posted: 30 Oct 2020 at 19:07
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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote iansoady Quote  Post ReplyReply Direct Link To This Post Posted: 31 Oct 2020 at 10:25
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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote c13pep Quote  Post ReplyReply Direct Link To This Post Posted: 31 Oct 2020 at 11:08
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 garageBig smile

CHRIS
you can`t have any fun in a straight line

Monza
Honda CB77 project

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Richard Hyatt View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Richard Hyatt Quote  Post ReplyReply Direct Link To This Post Posted: 31 Oct 2020 at 12:02
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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave P. Quote  Post ReplyReply Direct Link To This Post Posted: 31 Oct 2020 at 12:08
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.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 31 Oct 2020 at 12:23
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. 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 31 Oct 2020 at 12:26
Afterthought - a colortune might be good, so can see what the burn looks like in the cylinder. Might reveal something. 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave P. Quote  Post ReplyReply Direct Link To This Post Posted: 31 Oct 2020 at 15:54
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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave P. Quote  Post ReplyReply Direct Link To This Post Posted: 31 Oct 2020 at 16:11
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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Richard Hyatt Quote  Post ReplyReply Direct Link To This Post Posted: 31 Oct 2020 at 18:17
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?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote c13pep Quote  Post ReplyReply Direct Link To This Post Posted: 31 Oct 2020 at 20:35
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

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Richard Hyatt View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Richard Hyatt Quote  Post ReplyReply Direct Link To This Post Posted: 31 Oct 2020 at 20:52
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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Richard Hyatt Quote  Post ReplyReply Direct Link To This Post Posted: 01 Nov 2020 at 08:37
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


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 01 Nov 2020 at 14:44
Quote Deciding the problem must be fuel related I removed the carb for the second time to go over it with a magnifying glass (really), only for my sharp eyed girl (she is 20) to spot a faulty float ie. one float moving on its tang. Once replaced and the float height reset the bike fired up and ticked over smoothly, eureka, two cylinders working

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.

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