MV Agusta Forum banner

f4 sr 750 idling rough when hot

5K views 42 replies 11 participants last post by  Donsy 
#1 ·
my sr 750 has started idling rough when it gets hot. it only seems to do it in stop start traffic.it's going to the mechanic next week i just want to try and narrow down what could cause it

thanks rob:f4:
 
#36 ·
Hi Rob, thought this was all sorted.

Don't worry, the 750's are sound bikes and work well when everything is right, obviously something is wrong here, it's just a process of tracking it down.

First as it's a 750 it is a few years old now. Some stuff will be worn or perished or needing adjustment. I assume you have downloaded the manual and have some degree of mechanical knowledge.

Can you describe the symptoms in more detail for me, my 750 when stuck in city traffic does get up around 102 and the engine note changes as the cooling fans kick in (yours should have twin rads).

Mine does run a bit fluffy here and requires a bit more of a handful and revs to move off easily, all returns to normal when you get some air flowing through the rad this is all normal stuff, is yours like that?

When did the bike last have a TPS calibration check, a fuel filter replaced, and the throttle bodies balanced/synched?

You have made a thorough inspection of the fuel lines under and inside the tank? Did you clean the gauze filter on the pump body, all this is simple stuff and in the manual, rubber does degrade if in doubt get new lines.

A PC111 will help the bike but not solve the high temp issue, it is always going to get a little rougher when over 102 degrees plus.

Did you replace the fan relays and checked they work, these are small black relays four pin type about an inch long by half inch. And finally check the breather pipes from the tank filler cap down through the pump body are clear and not blocked, then see how she runs.

jimboF4
 
#38 · (Edited)
this is what i've done so far
changed the injection air sensor it seems to have improved idle
new fan sensor the fans now work and you can hear the map change when they come on
throttle bodies balanced
tps checks ok
new air filter and spark plugs
power commander and mapping it now runs a lot better than it did it still needs more mapping down low but we couldn't do it because of the rough running/idle

short trips it runs fine but if you ride for 20 to 30 minutes it starts running rough and idling rough even if the temp sits around 85c
i think the coils may be breaking down but i'm not sure
thanks rob:f4:
here's the dyno chart stock air filter and exhaust
 

Attachments

#40 ·
Rob

Does sound like one of the two coil packs is going down, a good diagnosis tool if you have a set is to connect up the throttle balance gauges and run the bike until she gets hot. the balance gauges will indicate on which cyl or cyl's the miss fire is occurring, works for me.

If it is a coil double check leads and caps for splits etc.

Good luck and keep us informed.

jimboF4
 
#41 ·
Rob

Does sound like one of the two coil packs is going down, a good diagnosis tool if you have a set is to connect up the throttle balance gauges and run the bike until she gets hot. the balance gauges will indicate on which cyl or cyl's the miss fire is occurring, works for me.

If it is a coil double check leads and caps for splits etc.

Good luck and keep us informed.

jimboF4
i'm getting some coils from cag i will post the results when i get them

rob:f4:
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top