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TR5 & TR250 Forum

tr250 cam

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oregon250 Chris P
Salem, Oregon, USA   USA
does anyone have a link to the specs for the stock tr250 camshaft? I took a rock in the radiator on the way back from idaho and running down the road at 80 the temp snuck up on me....and only 40k since the last tear down. bummer. so i got the engine torn down and while i'm at it am having thoughts of upgrading the cam a notch. I usually run between 2-4.5k... all recreational driving. is there an upgrade anybody has done to the cam while leaving everything else stock without loosing anything on the lower rpm's?
the engine is all stock, but hoping one day to add a third stromberg if i can sneak it by my wife and my buddy in wyoming....(they both like the "original" aspect)

thanks chris

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TR3driver Randall Y
Confusion, Los Angeles, USA   USA
My SPC lists the same 307621 cam for TR250 as used on early (69-72?) TR6. So it should match the early TR6 info at http://www.hottr6.com/triumph/tr6cams.html



Randall
56 TR3 TS13571L daily driver
71 Stag LE1473L awaiting engine rebuild
7? Stag awaiting gearbox rebuild

YankeeTR5 Dan M
Seattle, washington, USA   USA
Hi Chris,
The easiest bump in performance is to shave the head to a deck height (measured from the top of the head where the valve cover gasket goes to the bottom of the head where it sits on the block) of 3.4 inches. This will give you a compression of 9.5 to 1, a factory compression ratio for the rest of world TR5's & 6's. This will also set you up down the road for a better performing cam (I'd recommend using the TR5/early TR6 PI cam profile from the factory but there are lots of choices out there).

With these two additions, you really don't need any addt'l carburation. The dual ZS's are good up to about 145 bhp, although you may have to swap out needles to a profile that provides a bit more fuel flow depending on the cam choice you go with.

As an fyi - while I'm not against the whole triple carb setup just beware that there's a lot of mixed reviews out there. The problem is that not all three carbs are paired to cylinders 180 degrees apart in their firing order(so, it'd be great if each intake runner was paired with another cylinder that was 180 degrees out of phase so each cylinder is gulping fuel exactly opposite of the other). The middle two cylinders are not 180 degree apart so one cylinder is not filling up the same as the other. Makes idling a bit rough. I'm pretty sure this is why both Austin Healey and Jag dropped their triple setup as they were hard to "keep in tune". In any case, the addition of the third carb is more bling than performance anyway, especially without the bump in compression and a longer duration cam that can suck in more fuel

One other tip for you if your still running stock 250 carbs. The pistons can be directly swapped out with one from a later TR6 and you'll then have adjustability of the needles, allowing for easier tuneups. This used to be fairly straight forward when there were lots of these cars in junkyards....maybe not so much nowadays, but maybe you can find some beat up carbs cheap on craigslist or at a swap meet. As bad as the bodies may look, the pistons and needles receive little wear.

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titanic Berry P
Albany, Oregon, USA   USA
Chris-The stock 250/early TR6 cam gives the smoothest idle, but slightly less performance. The later 18/58 cam might be a better choice. Especially if the CR is raised and the later dual pipe exhaust manifold is fitted.
Shameless self promotion-I have an extra set of carbs with the adjustable needles and am about 25 miles from Salem.
Berry

oregon250 Chris P
Salem, Oregon, USA   USA
thanks for the replies guys.
I ended up getting the 270 cam from BPNW. block and head are in the machine shop now. my carbs are early and i have got a small adjustment in the past with them, but am going to get with Joe Curto and get the adjustable ones that he has. I probably will stick with just the 2 carbs. When I bring the brass plugs and valve guides down to the machine shop I'll measure the head Yankee and see about taking it down a bit. again, thanks for all the input. The old girl turns 50 next month. (built in Nov '67)

Stampy Avatar
Stampy Silver Member Scott Stamp
Victoria, BC, Canada   CAN
Thought i'd ask a carb question here as i am about to do the exact same thing to my 250. (cam and shaved head).

Are all the 175's on the 250 lacking the mixture needle adjustment?

I was thinking of doing the throttle body up grade.

Cheers from soggy Victoria
Scott



Edited 2 time(s). Last edit at 2017-10-19 09:09 AM by Stampy.

Brian Oklahoma Brian Plotkin
Edmond, 73012, USA   USA
1968 Triumph TR250 "Kevin"
Yes Scott. Originally, they didn't have mixing needles. I believe it was due to EPA concerns that you could adjust your carbs to run better and worsen your emissions.

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oregon250 Chris P
Salem, Oregon, USA   USA
Scott, Did you run up to Campbell River last year for the ATDI? It was my first time to the Island. We explored all over. You live in one beautiful place.....and that Longboat chocolate porter of Philips was tough to beat. smileys with beer

Stampy Avatar
Stampy Silver Member Scott Stamp
Victoria, BC, Canada   CAN
No I didn't make it there. I only got my TR in late June and since then have been staying local as i work out the bugs. I'm pulling the engine next weekend (hopefully) and doing the cam head shave such as you are doing.

Van Isle is indeed a wonderfull place. I first came here for work in 2000 and never left. My employer at the time managed to get me to Vancouver for a year but i kicked up enough of a fuss they sent me back. Lol.

And as for Phillips Brewery .... well. I live close enough to justify walking there. But i take the TR instead.

Keep me posted on your progress.

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Stampy Avatar
Stampy Silver Member Scott Stamp
Victoria, BC, Canada   CAN
So back to the carbs.

Is there no other mixture control on those 1968 Stromberg's then?

I've got one that is running really rich after a rebuild. Fouls the plugs really fast.

oregon250 Chris P
Salem, Oregon, USA   USA
Scott.....does your jet and plug assembly look like this? If so, when you pull out the bottom plug, the jet screws into it. The threads are 1/4 inch by 32 tpi. (extra fine). There is a small o-ring, brass washer and a spring that go on the shaft first as you screw it in. Also when you pull out the bottom plug, the jet doesn't always follow. I ususally screw a 1/4 x 32 die on it and give it a small pry. ( the o-ring makes it stick). Sometimes when you screw the plug back in the carb body, the inner jet doesn't stay in the same place and will screw in further as you screw the bottom plug in, thus remaining low in the carb body and giving you a rich mixture. either lift up the air piston and peek through to see the height of the jet or to get a better look pop off the carb top, diaphram, and piston and make sure the jet isn't low in the carb body. I've had the best luck putting the jet just a hair (1/32nd) or so below the bridge in the carb body for a decent mixture. Did you replace the metering needles when you rebuilt them? The jets are pretty elusive to find. Hope this might help.

Chris

oregon250 Chris P
Salem, Oregon, USA   USA
Whoops, here's a picture of the jet.


Attachments:
carb jet.jpg    3.2 KB
carb jet.jpg

Stampy Avatar
Stampy Silver Member Scott Stamp
Victoria, BC, Canada   CAN
Mine looks like this.


Attachments:
366-075_1.jpg    7.4 KB
366-075_1.jpg

oregon250 Chris P
Salem, Oregon, USA   USA
so your jets must be pressed in the carb body? is the jet just below the bridge?

titanic Berry P
Albany, Oregon, USA   USA
Chris-That jet assembly looks like the same one that was used in TR4s' with ZS carbs. If so, the jets are available from Moss (probably other suppliers, too) for about $11 each.

The mixture on the fixed needle carbs is adjusted by raising or lowering the jet. However, the rich mixture on one carb could be caused by the choke mechanism not being fully closed or by needle/jet wear from the biased needle rubbing against the jet.
Berry

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