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Breva 750 Dies at low RPM, Need some suggestions

J

jcburris

Just got it firing!
Joined
Oct 8, 2011
Messages
7
Hello,

Here is the short story, just bought this 04 Breva 750 , orig motor chucked a rod at 4500 miles, owner complained to Guzzi until they sent him a motor, motor was installed by previous owner, according to him, never ran right after engine replacement. I bought the bike knowing it had "stalling" problems. Bike will start and idle fine, if you can get it up past 3000 RPM or so runs fine, but under that it quits when you close the throttle, and some times as you apply throttle, it will re-start and idle again, but if you rev it, it just quits, applying throttle after you rev it ( like to keep it running) does no good, it dies anyway, also the tach seems to loose its signal as it returns to zero before the engine come to rest. I have checked all connectors, and replaced the crank trigger (pickup) with no change, all wiring looks good, connections clean, tapped on all the relays and jiggled wiring while the bike is running, etc Any suggestions??

Thanks for your help

CHRIS
 
Chris, the short answer is to have a dealer hook the bike up to their electronic scan tool to check sensors, ECU (engine control unit), and other parameters. It'll be a quick thing to do, and it checks so many items that it's worth it.

There's a scan tool for riders too, called the VDST (veh diagnostic scan tool) from Technoresearch. The shop on this forum (Guzzitech) is a vendor. It checks the things the dealer tools can, and costs approx. $220. Often at Guzzi rallies people will have one set up, so you can test the bike there. I've got one, and it's a great tool, but a little pricey.

Joe
 
If everything checks OK and the TPS is set correctly (electronically) look to see if the "sacred screw" has been tampered with. If so you will need to replace the throttle body with one that hasn't been tampered. Occasionally then come up on e-bay. It looks like there isn't a dealer near you. I suggest you join the Moto Guzzi National Owners Club http://www.mgnoc.com/ and contact the state rep. He may be able to turn you onto a local guy that can help you out. If you get the VDSTS go through this thread https://www.guzzitech.com/forum/160/1676.html
 
Thanks for your help so far, today I fiddled with it a little bit, the left bleed air screw was all the way in, and the throttle blade was held open with the throttle stop screw (Is that the sacred screw?) I changed the screw to to just keep the throttle blade from closing completely and sticking, then using a carb synch gauge set, synched the throttle bodies, and they took about the same amount of turns (1.5) on both air screws to get equal readings at idle, I adjusted the linkage to synch the reading at about 3500 RPM and it idles better but still dies when you snap the throttle shut, I am going to order the VTSD and see what is going on with the TPS and re-set it, The sticker is unreadable on the ECU, is this a problem? How do I know what ECU I have? Its a 10/03 manufacture Breva 750

Thanks Again

CHRIS
 
If you do not have a dealer near you in KY a trip down to Moto-Nexus in Hendersonville NC might be a option. They would be glad to help you out, good tech's.

Bill
 
jcburris said:
Thanks for your help so far, today I fiddled with it a little bit, the left bleed air screw was all the way in, and the throttle blade was held open with the throttle stop screw (Is that the sacred screw?) I changed the screw to to just keep the throttle blade from closing completely and sticking, then using a carb synch gauge set, synched the throttle bodies, and they took about the same amount of turns (1.5) on both air screws to get equal readings at idle, I adjusted the linkage to synch the reading at about 3500 RPM and it idles better but still dies when you snap the throttle shut, I am going to order the VTSD and see what is going on with the TPS and re-set it, The sticker is unreadable on the ECU, is this a problem? How do I know what ECU I have? Its a 10/03 manufacture Breva 750

Thanks Again

CHRIS
Click to expand...

You may have just screwed it up by moving that screw, but since the butterfly was sticking shut, it probably was already moved. Start looking for a set or unmolested throttle bodies. I was able to pick up a set on e-bay for about a hundred bucks. It is easier to change the set than just one in my opinion. If you give up on finding a set, then just buy the left TB new. You can download parts and service manuals from this site. The ECU on the 750 Breva is the 15RC. Read the VDSTS thread completely and change one of the channels in VDSTS to alphlin_0.
 
Thanks for the info John, The throttle stop screw on the left throttle body was turned way in, with the air bypass screw closed the vac was still lower on the left cylinder (with correct valve adjustment) I'm sure it had been moved, is there no procedure to set this adjustment? On most other throttle bodies its my understanding that the stop is to hold the butterfly just open enough to prevent sticking, it idles now with equal vacuum and 1.5 turns on the air bypass screws on both cylinders, so I would think the position of the throttle butterfly is the same on both sides...?? I did order a VDST today, so I guess Ill wait and see. Since there is no MAP sensor on this setup, is the injection a pure AlphaN setup? and if so, do these bikes run correctly or do they have quirks in the injection even when correct?

Thanks Again

CHRIS
 
jcburris said:
Thanks for the info John, The throttle stop screw on the left throttle body was turned way in, with the air bypass screw closed the vac was still lower on the left cylinder (with correct valve adjustment) I'm sure it had been moved, is there no procedure to set this adjustment? On most other throttle bodies its my understanding that the stop is to hold the butterfly just open enough to prevent sticking, it idles now with equal vacuum and 1.5 turns on the air bypass screws on both cylinders, so I would think the position of the throttle butterfly is the same on both sides...?? I did order a VDST today, so I guess Ill wait and see. Since there is no MAP sensor on this setup, is the injection a pure AlphaN setup? and if so, do these bikes run correctly or do they have quirks in the injection even when correct?

Thanks Again

CHRIS
Click to expand...

Take a look at the post by Mike C. on this page. https://www.guzzitech.com/forum/196/3768.html?start=10 Note that on the small block, both air bypass screws must be open to some degree to have a satisfactory idle speed. I tried it with a 750, but wasn't happy with the result and just replaced the TBs. The 750s will not idle with both air bypass screws closed. Perhaps if you closed the throttle stop screw slowly until the bike dies you might be close enough.
 
I've got my my V7C to run fine with one air bypass closed, so don't fret about that. Do a search on this board, and there are some good articles on tuning. Try search for "throttle body synchronization" and the like. You should pull up a good article on what screws to touch, and what to avoid. One guy even wrote about recalibrating the system if your "sacred screw" has been shifted.

Changing the whole throttle body pair is an extreme. Try other things first, and save that as a last resort, or even "no resort."

Good luck with the VDST. Let me know how it pans out.
 
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