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Breva 750 idle missfire?

F

Facade

Tuned and Synch'ed
Joined
Jun 14, 2009
Messages
40
This week my Breva has started acting up.

Tuesday it stalled when I was about 1/4 mile from home when changing down to come to a stop. It started back up with a tickle of throttle.

Saturday i had done about 12miles, stopped for 10 minutes, restarted no problem, then when I pulled up at traffic lights, the idle became rough. I caught it with the throttle, and rode home o.k.

Ticking over on the side stand, there is an occasional hesitation- the bike rocks and carries on.

I bought it 2 months ago, with only 300miles at 12months old, so it had the 1st service when I bought it. Now it has 1500 miles. It did use a pint of oil early on, then settled down.

I could change the 'plugs- maybe the oil burning fouled them, but it was perfect right up to last week.

Does it need the TPS setting now it has settled down? Maybe it is just a case that the service and setup were done too early.

I don't have any means to set the TPS except to take it back to the Dealer. If it gets worse, I will have to, but it is quite a way to go.

the idle is about 850-900 on the revcounter, same as when I got it. It never needs any choke to start, or to ride, and the weather is warm and dry.
 
I'm sure the technical folk will chime in. For whatever is worth my Breva idles at 1.000-1.100 rpms, which I believe should be correct idle. A TPS reset probably wouldn't hurt it as well as a throtle balance. Check the plugs, though my original ones are okay at 8.000+ miles.
 
Your idle is to low should be about 900 when warm. Don't touch the TPS or the throttle linkage! Remove the side covers by the throttle bodies just 1 allen head bolt and they pry off the stops. First check that all the clamps are tight on the intake hoses. If there seems to be no leaks you'll look at the bottom of the throttle bodies. There is a brass screw this is the idle air bleed screw.Take a pen and mark where the slot for the screw lines up to the body, it just a referance mark. Try turning them out 1/8 turn at a time to raise the idle make sure you turn them the same amount going back between them till you get the idle where you want it. Take it for a ride if it still dies try raising it a bit more, I wouldn't go more then 1050. Hope this works
Nutman
 
Thanks for the replies.I suppose I ought to check for leaks, disconnected/split pipes before I touch anything. ;)

If it were a Honda, first thing to check would be carb synchronisation.

I looked at the manual about synchronisation.

As I read it, I use the vacuum gauges to check it at 2000rpm, which will enable me to check that the butterfly linkages are balanced. (If not the same- back to the dealer!)

I then raise the idle with the bypass screws. Although the manual doesn't say this, shouldn't I just use the gauges to set both cylinders to the same vacuum whilst bringing the idle nearer to 1000 with the screws?

I'm not touching the TPS as I don't have any means to reset the ecu.


Normally, on a Honda V twin, I would balance the linkage to give the same vacuum at idle:-to eliminate poor idle and hesitation at pick up, and check for the same vacuum at half speed.
 
Facade,

To raise the idle, open each air bypass screw about 1/4 at a time until you get about an 1100 RPM idle. There is no other way to adjust idle speed on the small blocks, all done with the air bypass screws. Do not touch the throttle stop screw, or the high speed linkage adjustment screw. Your syncronization will be off, but it may be anyway.

To do the job properly you will need to buy VDSTS software, and an instrument to syncronize the TBs, or, just take it back to the dealer. Without the instrumentation there just is no way to work on your idle problem. If you search the forum for syncronization topics and download the workshop manual you will have the needed information, but without the tools, you may only make matters worse.

This one thread may give you an idea of what is going on. https://www.guzzitech.com/index.php?op ... 9684#20030
 
Right.


I took it out this morning, and had trouble starting- it took 3 goes, and a while before it settled to idle.
Went for a ride, and got the synchroniser gauges out, but my adaptors are M5, and the Breva is M6.

I spent an hour making a pair of adaptors to fit the vacuum gauge taps on the manifolds, connected it up, fired it up and

1) it settled to idle dead on the 1000 line on the Rev counter
2) the synchronisation is perfect, both at idle and 3000 RPM.

Go figure :huh:
 
It looks like the next step is to get the TPS set with software. Also when you hook up with VDSTS/Axone/Navigator it may reveal error codes to investigate. Also when you hook up to software you should check to see if the sensors are reading correctly.
 
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