750GT Rolling Basket Challange

Post pictures of your twin cylinder Bevel Drive Ducati (pre-1985) along with a description here.
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geodoc
750 GT
Posts: 169
Joined: Thu Jul 18, 2013 2:57 pm

Re: 750GT Rolling Basket Challange

Post by geodoc » Tue Jun 03, 2014 1:54 pm

That's why they call it a shake-down, right? Well there are a couple little defugalties that came to light after a few test rides.

Right away I felt pulsing from the front brake lever. Measured the disc run-out at .011", way too much. I found a machinist here that has a proper set-up to grind both disc surfaces at the same time. We'll see. If that doesn't work, then new disc.

Clutch slipping when you give it much throttle above 4500 RPM. The springs are the ones that were in it & measured within spec. It had a Surflex plate kit in it with little apparent wear when I got it and they were retained. The most likely culprate looks to be weak springs. Steve has a new set on the way to me and then we'll see.

Oil leaking from what appeared to be the upper rear cyl. intake valve cover gasket. Lots of playing around, different gasket w/ Permatex non-hardening sealant after gatting perfectly flat. Still leaking. Switch covers with one from the front cyl. Still leaking. A close inspection after a short run and it appears that the may be the dreaded Ducati porous casting demon. If you look at the picture, you can see to the right (outboard) of the round casting boss (picture right, lower), there's a little trench with bits of black stuff. That black stuff is the remnants of sealant that I picked out of there while cleaning up the head (if I recall correctly from 10 months ago). Oil was pooling up in there and draining down to the rear fins and manifold and pooling on the engine case below - ugly.

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So cleaned and cleaned and cleaned with brake cleaner while hot. Applied green wicking lock tight, let set-up overnight and then apply JB Weld over that. Set up over night and then fingers crossed.
Last edited by geodoc on Mon Aug 06, 2018 10:42 am, edited 1 time in total.

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geodoc
750 GT
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Re: 750GT Rolling Basket Challange

Post by geodoc » Wed Jun 04, 2014 7:45 pm

A day of fiddling and 2 defugalties fixed.

The oil leak did turn out to be a porous casting and the green locktite / JB Weld treatment has it nice & dry.

Took the front brake disc off and figured out how to mount it up to the brake machine after it was exhumed. Lots of trying different combinations of cones and collars for the machine and got it mounted up. Trimmed it down to straight inside and outside at the same time (forgot to take pictures - oops), remounted and ta-da .......... no more pulsing. It remains to be seen if this will stay this way or whether it will warp again.

Now just get the new / stronger clutch springs in and work a bit on finer tuning the idle and it should be ready for some miles (since I'll be taking it down to WA state in the Mt Baker foothills to see what's like when you spank it a bit.

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geodoc
750 GT
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Re: 750GT Rolling Basket Challange

Post by geodoc » Thu Jun 05, 2014 4:31 pm

The shake-down cruise reveals an opportunity for "finger trouble".

Riding along in the sunshine diggin' it and it starts to shows signs of getting leaner - time to switch to reserve. Flip the petcock levers .................... sputter, sputter ........ die. Whuh? Shake bike with ear to open fuel cap - nothing, bone dry. S***T! .............. Call garage-mate Tom & get rescued with a gallon of gas.

Back to the shop and learn that THESE Orlandi petcocks are 'off' (90 deg from vertical), 'reserve' (straight down) & 'on' (90 deg. opposite 'off').

The same LOOKING petcocks on every Guzzi I've ever worked on are: 'off' (90 deg from vertical), 'on' (straight down) & 'reserve' (90 deg. opposite 'off').

I tested before I installed to make sure that both on & reserve were flowing, but have to admit to not noticing the positions - I assumed it was the same as the other ones. Bad, bad bad.

Also, measured the reserve amount and even with shaking the bike back & forth on the lift, I only got a little more than a liter! YIKES! Maybe with riding motion it would be a little more, but only 1 liter seems awfully little. Anyway, we're talking only 15 km. / 9.25 miles for reserve at about 35 US MPG / 6.7 L/100km (seems like a conservative estimate), so better carry spare fuel to Eastern Washington or take extra fuel stops.

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geodoc
750 GT
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Re: 750GT Rolling Basket Challange

Post by geodoc » Sat Jun 07, 2014 5:30 pm

Tank badges came back from being clear coated. Very pleased.

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geodoc
750 GT
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Re: 750GT Rolling Basket Challange

Post by geodoc » Tue Jun 10, 2014 10:53 am

Test rides have not been what they might on account of a slipping clutch. Past 5000 or so RPM and anything more than gently easing the throttle open and it slips like crazy. Installed new springs in a vain hope, but no. So the low-down from Wolfgang and Guy both is that old friction plates in a bike that has not run for a long time will often harden to the point where they no longer function, even cleaned and sanded, just too hardened over time & disuse.

So in with a new set of friction plates (thanks Steve). Also discovered that the outer steel plate only had about half the 'ears' bent in as they are supposed to be. It looks like in the past that somebody tried to modify a regular plate & bend the ears in a bit. Careful examination showed that some of the tabs had been cracked in the radius while bending - trash. Steve to the rescue with a new bent-ear outer plate.

Installation later this week & (me-hopes), clutch slip will be a thing of the past.

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Last edited by geodoc on Mon Aug 06, 2018 10:43 am, edited 1 time in total.

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geodoc
750 GT
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Re: 750GT Rolling Basket Challange

Post by geodoc » Fri Jun 13, 2014 7:39 am

Installed the new friction plates and while screwing down the spring screws, they felt not quite right - like they were tightening, but not bottoming against the clutch hub posts. Previously, I had thought little of it, but this time decided to investigate.

Turns out that the threaded holes in the posts on the new HDESA hub were not threaded deeply enough to allow the spring screws to bottom the spring washers against the posts & hence preload the springs to the correct amount. They were about 1/4" short. So I ran a tap down the holes and now they bottom as intended. Lever effort is a little more, but not all that much.
Wonder if this was what the cause of the slipping before? Well, I'm not putting the old plates back in to find out that this point. (their thickness was the same as the new ones).

A test ride and no more slipping. A bit grabby, but I hope that after some km. the plates will bed in and have a bit smoother take-up. Now that I can rev it a bit - wow ........ it spools right up to 7K (as far as I, take it for a little while yet w/ about 500 km. on it so far). Bags of torque, smooth and an abundance of (as Kevin Cameron called it), 'super-good-ride-feel'.

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geodoc
750 GT
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Re: 750GT Rolling Basket Challange

Post by geodoc » Sat Jun 21, 2014 1:43 pm

Have about 1500 km on it now that I did a trip to Seattle and back (about 300 miles R/T from Vancouver). Went down the back way mostly, the fuel consumption was about 35 MPG (US) / 6.7 lt./ 100km. On the way back I just took the slab and it was about 41.5 MPG / 5.7 lt./ 100km maintaining about 70 MPH, 115 km/hr @ 4500 RPM. Not too bad. This is with 16/38 gearing. I've got a 36T rear sprocket on the way so it should improve it a little there too. Not a bad thing with only a 17 lt. fuel capacity.

Next week I'll be taking it to the dyno and doing some carb tweaking. It feels a little weak just off idle with occasional carb spit-back.

Otherwise, aside from clutch drag when cold, ran great. It's going to take a little while to get used to the cornering technique down. with it's lazy steering geometry and long wheelbase, it's not exactly as what you might call "flick-able". I'm taking a bit easier cornering in places where it's not unlikely that I'll need to change lines (gravel, etc.). Changing lines late in the game is not so easy compared to the 2001 Sprint RS or something more modern.
Last edited by geodoc on Sun Dec 27, 2015 8:46 pm, edited 1 time in total.

Ray O'Donohue
Parallel Twin
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Re: 750GT Rolling Basket Challange

Post by Ray O'Donohue » Mon Jun 23, 2014 4:46 am

Great machine! Beautiful work! PLEASE put 60-1 slides into your carbs and set your pumps for 5cc per 20 squirts .This is the proven set up and it will make a huge improvement in the throttle response problems of every Dellorto equipped GT750.We have discussed this here many times ,and I'm not going to get into a big discussion again.Please just do it,and enjoy your great new bike!

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geodoc
750 GT
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Re: 750GT Rolling Basket Challange

Post by geodoc » Mon Jun 23, 2014 8:35 am

Ray O'Donohue wrote:Great machine! Beautiful work! PLEASE put 60-1 slides into your carbs and set your pumps for 5cc per 20 squirts .This is the proven set up and it will make a huge improvement in the throttle response problems of every Dellorto equipped GT750.We have discussed this here many times ,and I'm not going to get into a big discussion again.Please just do it,and enjoy your great new bike!
Heh Ray,

Yeah, I reckoned that the fatter slides might be in order both after reading about other people's set-ups on the forum here & the bit of stuttering just off idle. I've got a pair of used but serviceable earlier style slides in my dellorto parts box that will fit the 32's, though I can't remember where I got them, probably some 36's off a Guzzi. They are however 60/3's so the pump action starts earlier than the /1's that are in there now. I'll try them and see.

GD

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geodoc
750 GT
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Re: 750GT Rolling Basket Challange

Post by geodoc » Mon Jun 23, 2014 12:11 pm

Ray O'Donohue wrote:Great machine! Beautiful work! PLEASE put 60-1 slides into your carbs and set your pumps for 5cc per 20 squirts .This is the proven set up and it will make a huge improvement in the throttle response problems of every Dellorto equipped GT750.We have discussed this here many times ,and I'm not going to get into a big discussion again.Please just do it,and enjoy your great new bike!
Heh Ray,

Yeah, I reckoned that the fatter slides might be in order both after reading about other people's set-ups on the forum here & the bit of stuttering just off idle. I've got a pair of used but serviceable earlier style slides in my dellorto parts box that will fit the 32's, though I can't remember where I got them, probably some 36's off a Guzzi. They are however 60/3's so the pump action starts earlier than the /1's that are in there now. I'll try them and see. Even with the earlier pump schedule, I can see if the 60's clean up the suspected leanness.

Early type on the right:

Image

machten
MHR / S2
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Location: Perth, Western Australia

Re: 750GT Rolling Basket Challange

Post by machten » Tue Jun 24, 2014 7:40 am

Gotta say, I've got a different view on the right slides for a 750 GT.

Kev

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geodoc
750 GT
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Re: 750GT Rolling Basket Challange

Post by geodoc » Tue Jun 24, 2014 8:18 am

machten wrote:Gotta say, I've got a different view on the right slides for a 750 GT.

Kev
What view have you got?

Ray O'Donohue
Parallel Twin
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Re: 750GT Rolling Basket Challange

Post by Ray O'Donohue » Thu Jun 26, 2014 5:20 am

60-3 is a later ramp/pump timing than the 60 -1,which gives immediate pump action off idle. You can probably do without the pumps altogether,particularly on those tiny carbs. The main thing you need is a richer slide,and the # 60 is it.An accelerator pump is no substitute for good carbueration,and given that you're not faced with the problem of getting good overall running with those monstrous 40mm carbs that other folks have to deal with,you are in good shape .

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geodoc
750 GT
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Re: 750GT Rolling Basket Challange

Post by geodoc » Thu Jun 26, 2014 6:42 am

Interesting little piece on Dellorto slides / ramps:

http://martysgarage.info/wp-content/upl ... umbers.pdf

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geodoc
750 GT
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Re: 750GT Rolling Basket Challange

Post by geodoc » Fri Jun 27, 2014 4:46 pm

Yet another porous casting leak, this time in the case just behind the kick starter shaft. It was pooling up and dripping out from between the case and selector cover. A copious application of PR1422 B1/2 aircraft fuel tank sealant after cleaning should do the trick.

Managed to pick up a few of these cartridges of the stuff for an air-operated SEMCO gun.The sealant was past it's shelf life so they were throwing it out anyway. Lucky too, it's usually $85 a tube! Lucky too that garage mate Tom had the application gun & a selection of 'snouts' so getting the stuff up where the porosity hole looked to be was pretty easy.

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