36mm carbs on a stock T3?

[earemike]

Over the years I’ve formed the impression that 36mm carbs liven up the T3 BUT is that horseshite?

My square slides need a rebuild and my T3 feels gutless (but starts beautifully first time every time). I’m planning on spending some time on her this weekend  to get her running as nice as possible.

Thought I’d come to those in the know - so what do you say good folk?

36mm will be an improvement at highway speeds?
36mm won’t give any benefit without intake port matching?
36mm won’t add anything with those puny valves?

Forget 36mm and just find a nice 30/32mm carb?

Just rebuild the square slides?

Very interested in the opinions of those who have been there - I’ve never ridden another T3 so can’t really tell if mine is performing as it should. My lm2 is weak as piss compared to the B10 bike but is way stronger than the T3.

Happy Queen’s Birthday to the states down under celebrating it this weekend 

[Frenchfrog]

Raceco UK did a PHF carb rebore from 30 to 34 mm when they were in operation years ago. Looking at the inlet tract bore on a T3 head , that would seem to be the best size  but with a bit of opening up it could take 36 mm without any bother and this would be far easier and cheaper than boring a carb body.
I ran PHF 30's on my T3 and didn't notice any improvement ovet the VHB's but then why would any be apparent?

[Roy gardner]

If your T3 feels gutless compared to your LM, that is not a total surprise. The LM will make more horses at the top because of the 36's.


When old Guzzis feel tired I like to do all the normal things, compression test, points gaps & ignition timing. Often bad timing makes them tired. Then check out the mufflers, what have you got on there? There is some counter productive junk hanging off the headers of some bikes. I have a couple of mates with V7 Sports & 750S using the repro Silentiums, for example. Hopeless, they all complain their bikes wouldnt pull a sailor off your sister! My Sport has Lafranconis, makes a huge difference. My son recently made  new helical SS baffles for my rotten old original Sport Silentiums then I fitted them behind my LM 1000 Lemonvert motor, it made 59Hp on a dyno with the auto box & "lawmower" cam. No difference with Cali 1100 mufflers.

So dont rush into messing with your old square slides other than a clean out, or a pair of 36's unless you have good mufflers.

[pete roper]

This is very well trodden ground. 36's, even with small valves, can make a big difference BUT without porting and new manifolds you will end up with an underperforming pig that gives you lousy fuel economy and all sorts of odd problems caused by reversion issues caused by the huge step in the inlet tract.

A slightly less dreadful cam will pay further dividends.

If your machine still has chrome bores it's all pissing in the wind.

Pete

[Furbo]

Well,

36's in good shape are hard to come by. I hear the round slide 30's give better gas mileage. You'd at least have to open the intake and exhaust to get anything. And.....the eldo cam is actually hotter than the T/Cal II ones.

Now - if you can find a B10 or such cam, yeah, but you're starting down a dark road as every thing done requires two others to get the most bennies.

If you just gotta do something, find some 30' rounds, they're easily available and rebuildable, jet them well and get/make teflin loned throttle cables. It'll 'feel' faster.

[Turin]

I got my 36s from Dellorto direct. They come prejetted and are pretty close out of the box.

My engine recipe consists of a Norris s (x9) cam, fully ported heads, thinner head and base gaskets, and bub mufflers. It's a nice mildly sporty set up.

[Tony F]

This is very well trodden ground. 36's, even with small valves, can make a big difference BUT without porting and new manifolds you will end up with an underperforming pig that gives you lousy fuel economy and all sorts of odd problems caused by reversion issues caused by the huge step in the inlet tract.

A slightly less dreadful cam will pay further dividends.

If your machine still has chrome bores it's all pissing in the wind.

Pete

+1 absolutely!

I put 36mm Dellortos and Le Mans manifolds on my SP1000 with the ports cleaned up and inlets matched to the manifolds and a cam grind somewhere between stock and a B10. A huge difference, the best way to describe it is that  it moved the lower end torque curve 1000rpm lower. Serious punch available from 3000rpm.  Just for fun I then went to 38mm flat slide Mikunis.

Given the passage of time the T3 engine may well be a bit tired. You are sure to need to reline the valve guides and new exhaust valves might also be in order. And rings?

[Simon_London]

The T3 is massively detuned, I believe a marketing decision at the time to clearly differentiate it from the sporty Le Mans.
In stock form they feel like 400cc went missing.
This is in fact an 850 motocycle!

Do put on 36mm carbs. Do change the flywheel to the lighter but still pretty heavy Le Mans one.
You will need Le Mans inlet manifolds. These take 6mm bolts. Simply wind in some helicoils to the 8mm holes and the holes become 6mm.
On one bike I stuffed a rag down the intake ports and took a dremel to them to enlarge the opening to 36mm without even removing the heads. I'm not proud of this or recommending it but it worked. They do need to be enlarged but a rough finish actually helps the mixture.

You will also need to trim the edge of the side panels to fit the 36mm carbs.

[JukeboxGothic]

HMB in Germany have tapered manifolds for converting to 36mm carbs. They also have adapters for the screw holes. Their stuff is beautifully made.
https://hmb-guzzi.de/Inlet-manifold-set-CNC-for-PHF-36-carbs-tapered

[Turin]

On one bike I stuffed a rag down the intake ports and took a dremel to them to enlarge the opening to 36mm without even removing the heads. I'm not proud of this or recommending it but it worked. They do need to be enlarged but a rough finish actually helps the mixture.

If you go this route, I recommend making sure the valves are closed, and ball up a piece of making tape and stuff it in there before the rag. When done, remove the rag and tape and blast anything left behind out the exhaust pipe with carb cleaner.

[guzzista]

Quote from Simon London :You will also need to trim the edge of the side panels to fit the 36mm carbs. if you are using Guzzi, Malossii or HMB manifolds you do not need do trim the side panels.  You can bend in the front part of the side panels , use angled air filters ( K& N, copies  of or Unifilter). I have the slightly larger PHM's on my  SP and have not trimmed anything. Using the Delrin manifold may still require trimming as I have not installed those on any of my Guzzis

[pete roper]

Look, with the very greatest of respect getting the heads off a T3 is an hour's job if you aren't trying hard.

The idea you are saving something, (Time, money, whatever.) by going at them in situ with a die grinder is so far beyond mad it makes my brain hurt.....

Pete

[Rough Edge racing]

If you go this route, I recommend making sure the valves are closed, and ball up a piece of making tape and stuff it in there before the rag. When done, remove the rag and tape and blast anything left behind out the exhaust pipe with carb cleaner.

 Better yet is a helper holding the nozzle of a vaccum cleaner close to the work...

   An interesting bit, car engine guys sometimes use mismatches in the intake system, like what's being discussed here, for tuning purposes..maybe for increased intake port turbulence..There's also theories on the how the air flows in a port and doesn not flow around tapers like you think it might...
  But if experience says it must be done on a Guzzi, then you do it....but a before and after report would be interesting

[Simon_London]

HMB in Germany have tapered manifolds for converting to 36mm carbs. They also have adapters for the screw holes. Their stuff is beautifully made.
https://hmb-guzzi.de/Inlet-manifold-set-CNC-for-PHF-36-carbs-tapered

Thanks for the tip JukeboxGothic . I didn't know about these. HMB are great!

[Simon_London]

Look, with the very greatest of respect getting the heads off a T3 is an hour's job if you aren't trying hard.

The idea you are saving something, (Time, money, whatever.) by going at them in situ with a die grinder is so far beyond mad it makes my brain hurt.....

Pete

That was just for you Pete. In my young and foolish days.

[Simon_London]

Better yet is a helper holding the nozzle of a vaccum cleaner close to the work...

   An interesting bit, car engine guys sometimes use mismatches in the intake system, like what's being discussed here, for tuning purposes..maybe for increased intake port turbulence..There's also theories on the how the air flows in a port and doesn not flow around tapers like you think it might...
  But if experience says it must be done on a Guzzi, then you do it....but a before and after report would be interesting

A friend of mine uses 36mm manifolds on 30mm heads without opening them for this reason. It works for him but it didn't work for me

[Simon_London]

In terms of the jetting for 36mm carbs on small valves heads, I experimented around standard Le mans jetting but in the end found the best set up to be the one recommended by HMB.

K19 3rd notch from top (=2nd from bottom)
AR-266
154 Main (with bellmouths)
65 Idle (HMB recommend 56 but I needed 65)
60/3 slide

The huge main jet may surprise you but it works well in conjunction with the leaner atomiser / needle combination

[Rick4003]

I run 36mm PHFs also on my small valve T5, using the HMB tapered intake manifolds. Runs quite well, but still needs some fiddling with the jetting. I might have to try out the jetting proposed above.

I haven't tried the bike with 30mm carbs so can't really say how much different it is with the 36mm PHFs but it is pulling very well.

-Ulrik

[earemike]

Thanks all, very comprehensive.

Brilliant!

[Roy gardner]

 Simply wind in some helicoils to the 8mm holes and the holes become 6mm.
[/quote]

Ah, no, actually they wont, sorry, where did that fairy tale spring from?

M8 has 1.25mm pitch & M6 is only 1mm pitch so there is a fundamental mismatch straight away. I wont bore you with the diameter issues because I cant be bothered looking up the detail.

[Tusayan]

I installed Le Mans manifolds and 36-mm PHF carbs on small valve 949 cc heads in roughly 1988 and have since ridden the bike about 80,000 miles.  As I remember I tapered the thick gaskets between heads and manifolds and nothing more - it was a long time ago. It runs very well regardless.

Installing 36-mm carbs is the first thing I have done on several small valve bikes owned over the last few decades, for example I also installed 36-mm carbs on late 1000 SP rubber manifolds on a bike I had sometime in the 90s and it ran similarly well with whatever step that creates, no modification to the ports or manifolds.  The stock 30-mm carbs require a lot of twist grip motion to make power and the bigger carbs don't, the effect of the change is essentially like a quick turn throttle regardless of whatever peak power change also results.

The other thing to do with 36-mm PHFs is to install one of the lighter variety of Dellorto return springs.  I've done that on three bikes with 36-mm carbs, two 949 cc small valve engines and a LM III, in each case making the throttle feel about as light/heavy as a modern injected bike.  The heavy springs used by Guzzi on 36-mm carbs are not necessary, notwithstanding issues with bigger 40-mm carbs.

My overall fuel mileage on small valve bikes with 36-mm PHFs has varied between roughly 41 and 48 US mpg depending on jetting.

[Simon_London]

Simply wind in some helicoils to the 8mm holes and the holes become 6mm.


Ah, no, actually they wont, sorry, where did that fairy tale spring from?

M8 has 1.25mm pitch & M6 is only 1mm pitch so there is a fundamental mismatch straight away. I wont bore you with the diameter issues because I cant be bothered looking up the detail.

M6 Helicoil M6 1.0 bolt M8 1.25 nut. Don't ask me but it seems to work. Maybe someone else would like to check?

[wirespokes]

Some labels would be helpful. Give us the details.

I'm assuming you've taken an M8x1 nut, M6x1 helicoil and threaded it all together with an M6x1?

[Turin]

I used step studs. got em from ACE hardware. Easy peasy.

[Simon_London]

Some labels would be helpful. Give us the details.

I'm assuming you've taken an M8x1 nut, M6x1 helicoil and threaded it all together with an M6x1?

M6 Helicoil M6 1.0 bolt M8 1.25 nut. Don't ask me but it seems to work. Maybe someone else would like to check?

[Simon_London]

I used step studs. got em from ACE hardware. Easy peasy.

Nice !

[s1120]

I used step studs. got em from ACE hardware. Easy peasy.

I used to sell those all the time when I worked at VW. The techs used to use them when the studs got stripped..  Going back a lot... but I believe air cooled stuff..