[LAsfinest_SS750]

I wanted to go to a single carb on my '05 VT750 Spirit. Purchased a pair of heads from an '06 Aero and swapped out. Found out the Spirit cam rides on 4 journals and the Aero only has three. So had to use the Aero cams. Put a 34mm Mikuni on it, seems to run good. Just finished this job. I hadn't found all this info before I started. It's been interesting.

so you’re saying you actually mated are heads to run single carb?

 

[LAsfinest_SS750]

No the 750 Cams were put in sandwich bags in a box, never to be reused.
I pulled the gears from the chains before realizing they were the same damn part.
It was all done at one time, I had complete NT650 heads and I dissembled them using a C-clamp valve spring compressor, before diving in.

did a test removal on my VLX600 motor, if I can maintain the cam gear it will make the swap super quick. The whole swap under an hour. I pulled back the tensioner to allow slack and boom that’s a direct fit.

 

[LAsfinest_SS750]

@CSRoad, so disassembly easy, reassembling is a bitch. I totally get why you said whole lot of paper towels. I had so much anxiety trying not to drop the retainer keepers. I did take 10min to unassembled but about an hour to get the keepers in place. Camshaft was a breeze so one side done. I felt bad for my son because I was yelling at him to “hold stead” like a pirate to get those keepers in. Saved the front for tomorrow, do you the torque specs by chance?

Rear is complete, as you can peep and you can see the dual springs vs single springs from stock.
The VLX600 were a tad huskier compared to the VT750DC.

Used two equal sized height sockets as spacers then bolted down a 10mm wrench, add zip ties to prevent movement, then put some tape to keep it from sliding. Used 21mm wrench to leverage it down, badabing bada boom keepers are free.

 

[CSRoad]

Without a helper or three hands those keepers are miserable.
I do like your tool set up, ingenious. It's one of those "Why didn't I think of that" things.

 

[Alex05]

Due to hot weather baking my shed and family stuff my "two day" project dragged on for a month.
But now it is finally up and running with valve springs and cams from a NT650 Hawk GT.
It now finally feels like a 750 did when I was a kid, it feels like a different engine.

I have not swapped out the exhaust yet, but I'm sure it is a bottleneck in the performance at this point.
I put Uni pods on the carbs, and followed along with stretched and heat treated slide springs to stop the slide flutter and fuel spray that is usually the nightmare of such installations. Slow jets are 42, main jets are 140 front and 145 rear and the Dynojet jet needle is on the second notch. The plugs look OK, but I'm going to have to go richer still with an exhaust change. My rev limiter is set to 6800 rpm that it hits readily in second and third gear, didn't want to cover ground faster than that while sorting it out.

Things I have learned:
I changed the valve springs without pulling the heads, making your own valve spring compressor is a pain, making 3 for different locations is worse.
I would probably pull the heads if I was doing it again even though I had good compression, despite what the manual says it can be done without pulling the engine.
Just for entertainment, stock intake springs you can remove with your thumbs, just grab the keepers with a magnet!

I almost forgot the most important thing: If you use a 4mm wrench when setting your valves tie a couple of feet of string to it. Those things are tiny and if they have a long tail it is harder for them to disappear. "Ah ha I've got you", is way better than "WTF did you go".

NT650 valve covers fit the VT750 although you lose the place for the secondary air cleaner and the crankcase vent is just a hose connection of the rear one and is noisy.
As the bike is now it only takes unplugging the spark plugs and four bolts to remove the covers to check the valve clearances.

I have attached a picture of how it looks with no added trim.


View attachment 282334

Just a bit of an update, since I had it out for a couple of hours of backroad riding today after some in city holiday stop and go.

All has turned out as I hoped. The jetting isn't quite right, it almost looks like I should swap the front and rear mains, but nothing too drastic plug colorwise and I will leave it as it is 'til I change the exhaust and to less restrictive carb boots, hopefully this week.

The downside to this mod other than needing an aftermarket ignition box to take advantage of it, is the loss of some low end flexibility, more like a motorcycle and less like a tractor. It cares more which more about the gear it is in when you roll on the throttle and it requires more throttle when you are starting out, I don't have a tach on it yet, but I would guess the engine likes it above 3000rpm and comes on strong where the stock setup is switching to running out of breath mode above 5500 rpm.

I'm still running with the previous 6800 rev limit, I'm not too worried about pushing it to a 7500 red line and will probably set the limiter to 8000 rpm. The valve train can keep up, the NT650 redlines at 8500 and is rev limited to 9300 rpm. The other more sporting versions of this engine design all seem to be able to routinely make it past 100,000 miles with routine maintenance despite considerable higher rev. limits than the 52 degree VT750. The other versions all have offset cranks though and also have shorter strokes and therefore less piston speed. The pistons are what I fear are the weak link in VT750 abuse.
If/when I finally blow it up I'll let you all know. (-;

Did the camshaft change make the bike sound any different? Did it give it a “choppy” idle?

 

[CSRoad]

Not really, I changed to the NT650 idle spec which is 1200 +/- 100 rpm up 200 rpm from the 750 ACE setting, so it is pretty smooth.
Not lumpy like a vintage Pan Head with a 3/4 Race cam. (-;

 

[Troy Jollimore]

If mine ever feels like it did when I was a kid, I’ll know it is probably seconds away from blowing itself sky-high! 😂

 

[Alex05]

Not really, I changed to the NT650 idle spec which is 1200 +/- 100 rpm up 200 rpm from the 750 ACE setting, so it is pretty smooth.
Not lumpy like a vintage Pan Head with a 3/4 Race cam. (-;

Not really, I changed to the NT650 idle spec which is 1200 +/- 100 rpm up 200 rpm from the 750 ACE setting, so it is pretty smooth.
Not lumpy like a vintage Pan Head with a 3/4 Race cam. (-;

thanks! Another question, how did you change the idle spec? Did you get an adjustable cdi?

 

[CSRoad]

I do have a programmable ignition box, but I just adjusted the throttle stop to match the NT650 manual figures.

 

[LAsfinest_SS750]

I do have a programmable ignition box, but I just adjusted the throttle stop to match the NT650 manual figures.

Just scored NT650 Carbs, I currently rebuilt my factory pair which are 34mm, do you think I stand to gain anything from the NT650 carbs vs the factory, What’s your take?

 

[CSRoad]

I've played around with my stock carbs (36mm on my '99 ACE, IIRC
they went to 34mm at some time in '01) and the 36.5mm Hawk carbs.

I think my Hawk GT carbs came from a flood bike and were priced commensurately with that condition. (-:

The Hawk carbs are more open in the area before the slide, obviously a larger bore and definitely do make more power, but mine are still a work in progress and I switched back to the stock carbs as they are better behaved at slow speeds in stop and go traffic, it is all a matter of tuning. I'm hopeful I will get them dialed in and smoother next year.

For the boots I use OEM NT650 boots with both carb sets as they have less restriction and I use Norma 9mm "Euro style" hose clamps to hold it together and leak free.
The "Choke" plunger is different with the Hawk GT carbs, uses the plunger with the needle like the VT1100's, it swapped over to the stock cable fine, but I haven't really used it for more than a few seconds at a time.

 

[LAsfinest_SS750]

I've played around with my stock carbs (36mm on my '99 ACE, IIRC
they went to 34mm at some time in '01) and the 36.5mm Hawk carbs.

I think my Hawk GT carbs came from a flood bike and were priced commensurately with that condition. (-:

The Hawk carbs are more open in the area before the slide, obviously a larger bore and definitely do make more power, but mine are still a work in progress and I switched back to the stock carbs as they are better behaved at slow speeds in stop and go traffic, it is all a matter of tuning. I'm hopeful I will get them dialed in and smoother next year.

For the boots I use OEM NT650 boots with both carb sets as they have less restriction and I use Norma 9mm "Euro style" hose clamps to hold it together and leak free.
The "Choke" plunger is different with the Hawk GT carbs, uses the plunger with the needle like the VT1100's, it swapped over to the stock cable fine, but I haven't really used it for more than a few seconds at a time.

Hopefully, I can do a one for one swap with internals. Seller did advertise that it sat in outside and it is also coming from Florida, so hopefully it isn’t seize at all from Hurricane Ian but I’ll give a rebuild when it gets here.

 

[CSRoad]

Hopefully, I can do a one for one swap with internals. Seller did advertise that it sat in outside and it is also coming from Florida, so hopefully it isn’t seize at all from Hurricane Ian but I’ll give a rebuild when it gets here.

The floats are the same, but the float height is different IIRC 9.5 mm instead of 7 mm and you will need to bump up the main jet sizes.
I use 42 pilots, but I don't know what your combination is going to want for mains, going to be a bit of trial and error.

 

[LAsfinest_SS750]

The floats are the same, but the float height is different IIRC 9.5 mm instead of 7 mm and you will need to bump up the main jet sizes.
I use 42 pilots, but I don't know what your combination is going to want for mains, going to be a bit of trial and error.

I think imma set it as if it was an NT650 with velocity stacks and jetting with and open exhaust as per the carbjet calculator.
The diaphragm caps are larger than the 750 as I was hopping to keep the finned covers from TJB but now I can’t.

I looked at frame I may need to run the Velocity stacks for sure unless I wanna pack the in the foam from a uni-filer.

So scored NT650 carbs for $70 shipped, and they are gonna be in a Pinesol dip tonight, sadly choke was not present which is okay. I’ll be doing a full rebuild.

From the looks of it, it was pretty clean on the inside but outside was pretty dirty.

 

[CSRoad]

I'm waiting for your report back with the Revere cam and the tales of the smile on your face. (-:
The Revere cam is probably what I should have used actually.

 

[LAsfinest_SS750]

It will be a minute, but for sure after this winter season. I still have to pop off the covers, complete the timing mod, and then put in the Factory Pro shift Arm.

 

[LAsfinest_SS750]

I'm waiting for your report back with the Revere cam and the tales of the smile on your face. (-:
The Revere cam is probably what I should have used actually.

Another question for you, Have you done the 4 Degree timing mod, and also does the Ignitech CDI all for timing advance?

 

[CSRoad]

I did the "4 degree" mod when I replaced the clutch soon after I got the bike (2014), but backed it off when I switched to the Ignitech box (2015}.
The "4 degree" mod simply bumps the initial timing which then effectively shifts the whole advance curve contained in the stock ICM.

If you look at the Dyna3000 advance curves on the chart and imagine the stock curve moved up by 4 degrees + or - then you see the appeal of the cheap fix and its limitations.

Colorized chart thanks to Drive_Bye. Drive_Bye's Lead Sled

 

[LAsfinest_SS750]

I did the "4 degree" mod when I replaced the clutch soon after I got the bike (2014), but backed it off when I switched to the Ignitech box (2015}.
The "4 degree" mod simply bumps the initial timing which then effectively shifts the whole advance curve contained in the stock ICM.

If you look at the Dyna3000 advance curves on the chart and imagine the stock curve moved up by 4 degrees + or - then you see the appeal of the cheap fix and its limitations.

View attachment 305099
Colorized chart thanks to Drive_Bye. Drive_Bye's Lead Sled

Love it!

just put it back together, still need bowl gaskets, and I grabbed some Velocity stacks from eBay $11 a piece, I measured the inlet outer diameter at 54.75mm. Hopefully they fit, far cheaper than TJB at $100 plus tax and shipping.

 

[LAsfinest_SS750]

@CSRoad,

what do you need to do to get the bottom boots on?

I can not get them lined up.