Problem with 750 GT

Hi Brett,
Balancing the carbs may help reduce the noise from the clutch.

"I tried swapping the coils but nothing changed and I let it idle on each cylinder separately but both ceased running intermittently again so it can?t be the coils."

It does sound like something that feeds/supplies both cylinders - Petrol from tank, Ignition signal from rotor,Battery.

Andy
 
 
Brett,

While in the clutch, check the fit of the hub on the mainshaft and renew the o-ring fitted in the rear of the hub.  Also check if the steel core is tight in the alloy bit.  When loose, you will see oil being squashed out between the steel and alloy when you try to rock the hub on the shaft.  Many are a bit loose with no great consequence, but you should keep it in mind that wheelies aren't going to do the clutch any good.  If the clutch drum still carries its' rivetted cover, chances are the 50-year old rubbers will be well past their best.  Movement between the chainwheel and clutch drum contributes further to clutch noise at idle speeds.  Obviously, the Jesus nut should be nice and tight, and secured with a lockwasher.

Check the voltage arriving at the battery, the DMC shuts off above 16V.  Headlight will be great should that be the case. :D

Check and re-check all power and earth connections regarding supply to the box.  Depending on how well they are supported, the wires sometimes detach themselves from the connecting pins in the big connector block.  Found a half-way-through fractured crimped eyelet connected to the battery (-)  recently, caused mis-firing as soon as revs rose over idle speed.  The fracture was not visible, hidden under heat shrink tubing.  Was a bit lucky finding that one as quickly as I did, could as well have taken hours as everything measured out ok.

piet
 
Have you tried supplying the DMC off a separate external battery pos and neg .

If you think it may be external RF I have been known to wrap the lot in alfoil to test.

 
once had to rectify a dislodged terminal inside the DMC multi-pin plug.  it had been causing an intermittent fault.
initially, the connector looked ok, but after careful observation one terminal was noticed only slightly dislodged & that was enough.

, have also found some dodgy kill switches and connections feeding the coils. so i agree with Will's suggestion to feed the ignition from another battery.

, have also found wires to the pick-ups can be at fault. i.e. dodgy wires that go open-circuit intermittently.

oh what fun!  :D
 
markQLD said:
once had to rectify a dislodged terminal inside the DMC multi-pin plug.  it had been causing an intermittent fault.
initially, the connector looked ok, but after careful observation one terminal was noticed only slightly dislodged & that was enough.

, have also found some dodgy kill switches and connections feeding the coils. so i agree with Will's suggestion to feed the ignition from another battery.

, have also found wires to the pick-ups can be at fault. i.e. dodgy wires that go open-circuit intermittently.

oh what fun!  :D

Just had a similar issue had to do a 1500K round trip to sort an intermittant fault, dealer had said that they had checked all the connectors and they were fine it must be the ECU !!! Always the ECU that gets the blame.........
this is what I found then the dealer told me oh thats a water proof dueche connector so we didnt bother to check it as they are fine.... yeh go figure and then some wonder why I dont use them.... they dont breathe
When the bike stalls do you still supply to the Witt ? and when running and misfiring what is the voltage at the supply terminal on the Witt.
Do you have a connector issue and causing you a voltage drop or an earth issue, check resistance to earth on the earth leads at the Witt.

One of the Ducati boys on a recent run broke down, the Sacsche box got the blame but when we fault traced the loom well the problem was actually when the box was wired in the boot lace connectors supplied with the kit were not used and well there ya go not the box's fault afterall..
Click to expand...
 

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Hi Guys,

Well this morning I started her up, no problem, then she started to miss again so I wiggled the wires at the plug to the DMC box and she really started missing and backfiring, so I turned her off and on again and tried the process again and then held them in a solid position after unclipping and replugging it back in, it settled into a regular idle for solid long time without stopping.

I then slowly put her back together and tried starting and idling overtime I put items back on.

Then I took her for a test ride for about 5km and only once did she misfire and let out a soft backfire via the exhaust.

So I am thinking it must be the wires in the plug and I may have to try to ensure they are all seated correctly and more solidly.

I am hoping that this has it rectified?.

I took her for another run the next day and again she ran well except for one misfire, so I am going to look into the DMC plug and wire connections as that appears to be where the fault maybe.

There is still a slight knock at the primary/clutch location so I will check that out next week when the cush rubbers arrive. I guess after 45 years they may well be a tad ordinary, maybe I should put a new primary chain on as well, although it does appear to be solid and no real wear.

I am also going to replace the dynamo belt.
 
I think the multi pin Witt connector is actually an AMP Superseal plug and socket like this:

mqgbYKnvKl6qLsjoovIN-nQ.jpg


I bought the pukka AMP/TE Connectivity crimping tool which has fine adjustments for crimping. There is a booklet with the calcs for setting it up.

As stated if you go too mad and overcrimp then the copper strands fracture (copper work hardens real fast), then you get people slagging off crimps for being fragile and they end up soldering them!
 
SimonR501 said:
I think the multi pin Witt connector is actually an AMP Superseal plug and socket like this:

mqgbYKnvKl6qLsjoovIN-nQ.jpg


I bought the pukka AMP/TE Connectivity crimping tool which has fine adjustments for crimping. There is a booklet with the calcs for setting it up.

As stated if you go too mad and overcrimp then the copper strands fracture (copper work hardens real fast), then you get people slagging off crimps for being fragile and they end up soldering them!
Click to expand...

Yes, crimping is hi-tech. Read a bit when installing a towbar kit on the Skoda - they are not allowed to solder elec cnxns on (European?) cars. The pressure is supposed to operate at a virtually molecular level with correct crimping!!! I have a great crimping tool but it doesn't have the fine adjustment you mention, Simon.
 
Yeah, Tyco (TE Connectivity) are a bit anal about it - it is a science!
It's not just squeeze her up tight and she'll be right.

Here it is  - I believe the little spoked wheel changes the spring tension on the crimp:

F3141362-03.jpg
 
The 750 GT is a simple and  very reliable machine.
Please stop trying to make it unreliable. Keep it reliable, with points.
Put all that electronic rubbish in the bin.
Paul
 
Well after testing the loom was ok by connecting directly to the battery she still missed continuously so I stripped the electronic ignition out and replaced and rewired the points back in and she runs like a dream.....
 
Brett64 said:
Well after testing the loom was ok by connecting directly to the battery she still missed continuously so I stripped the electronic ignition out and replaced and rewired the points back in and she runs like an erratically timed dream.....
Click to expand...


  fixed
 
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