Triumph Runs Rich

[TR3Barney]

Overhauled a TR3 engine with 83mm pistons & new rings. The carburators were sent to Apple Hydraulics in New York for rebuild. They were rebushed and sm needle and 100 jet. The plugs are black and I used a colortune. It was running rich so I sent them back to Apple and they were returned to me saying that there was nothing wrong with them. It is still running rich. I checked for air leaks. Any suggestions?

 

[Moseso]

Two things occur to me.
1) Are your jets adjusted up as far as they will go? If not, they may need to be raised.

2) The needle <span style="font-style: italic">can</span> be inserted too deeply into the piston, causing richer mixture. The needle has a square shoulder which should be flush with the bottom of the piston, when it is inserted to the correct depth.

Use of colortune... I know nothing of this device. All I know is that I set the mixture the way they lay it out in the shop manual (lift the piston slightly, listen for engine speed changes) and my car runs right. Maybe try that?

 

[TR3driver]

I'll ditto the jet adjustment. Also make sure the jets are returning against the mixture nut after the choke is released.

Have you checked the fuel pressure? Improper assembly can cause the pump to put out too much, or I've heard reports of replacement pumps having the wrong spring installed.

Assuming Apple has done their job, next thing I would check on a freshly built engine is cam timing. Having the cam timing off by a tooth can cause the mixture to go way rich, due to reversion.

 

[TR3Barney]

The needles are at the right depth with groove and the pistons. The jets according to the book to start with are 6 or 7 flights down and you can move the jets clear up without any difference. In reference to the cam tooth, it was timed off of the #4 cylinder and rocked both ways of dead center to obtain equal distance on timing pulley left and right using a ten thousandth feeler gauge. If you say it could be off a tooth, which way would you turn the cam? Would I loose the equal spacing left and right?

 

[prb51]

Barney,
So you can lean the mixture adjusting nut all the way up and it is still running rich?

 

[TR3Barney]

that is correct

 

[poolboy]

The fuel level in the SU's float chambers (bowls) are an important factor for getting the right mixture.
https://www.zparts.com/zptech/articles/mal_land/ml_sucarb2/images4/SUcarb_111601d.htm
https://sw-em.com/su_carbs.htm

 

[prb51]

Are these DM2's 40480's?
Barney, I'd start at square one and check every adjustment as per the manual...measuring the jet distance from the bridge etc....and especially the set up of the choke/return springs and full on off of that system.
If the fuel pump/float bowls are working/adjusted properly and the choke is operating as it should be then I'd check to make certain you have the correct needles/jet and that they are properly matched.
I'd also check the airflow with an appropriate meter to check the carb balance/amount and observe the action of the throttle discs.
Finally, if all else is correct, I'd lower the needles beyond the shoulder (slightly and measured) to see if leaning were possible.
Has anyone else here had carbs rebuild by this vendor?

 

[TR3driver]

The equal spacing should indicate the cam is timed right, assuming your crank mark is good.

Wish I could remember ... it <span style="font-weight: bold">might </span>have been Apple that did the carbs for a local club member and sent them back with the jets off-center (and loose). Have you checked the pistons for free movement, and landing with a distinct click ?

 

[prb51]

Randall has a good point, if the jets are off center the needles will bind in an up (won't seat) position creating a rich run. Your idle and all would be off too I suspect.

 

[TFR]

What's your ignition timing? Too far retarded will cause a rich condition.

 

[newmexTR3]

Stupid question, but I need a sanity check. The degrees of ignition timing on when setting it on the timing cover run counter clockwise, right?

...so 4 degrees would be to the left of the marker if looking at it straight on, correct (if using a timing light)?

 

[martx-5]

Stupid question, but I need a sanity check. The degrees of ignition timing on when setting it on the timing cover run counter clockwise, right?

...so 4 degrees would be to the left of the marker if looking at it straight on, correct (if using a timing light)?

That doesn't sound right. The engine runs CW when looking from the front, so advance would fall on the right side of the mark. If you have the original distributor with points, just set the timing statically as it was originally designed.


The procedure as I do it...Make sure your points are set to spec first.

1. On the side of the distributor is a knurled nut that is used to advance and retard the timeing. You will see an A and an R with an arrow. There are also graduations there. One of the graduations is longer then the rest. That's the midpoint...set the timing adjuster there.
2. Bring the engine up to the timing mark on the pulley by turning the engine clockwise as looking from the front. If you go by it, don't back off. Go around again, as you don't want to introduce timing chain slop into this. Now the engine is at TDC.
3.Loosen the clamp on the dizzy.
4. Hook up a test light or voltmeter to the point side of the coil, and turn on the ignition.
5. If the test light is on, turn the dizzy CCW until the light goes out, and then turn it back (CW) until it just goes on.
If the test light is out, turn the dizzy CW until it just goes on.
6.Tighten the dizzy clamp.
7.Turn the knurled nut in the advance direction 2 graduations. Each gaduation is two degrees.

Timing is now set for 4 deg BTDC. You can use the knurled nut to make any running adjustments now, and always know where your timing is set.

 

[newmexTR3]

Thanks Art.

I have the pertronix, so I've been using a timing light. I have a non-standard cam that I don't know the specs for, so I've been tuning it to "feel." So far that seems to be about -4 degrees retarded.

I was just wondering if my timing could be causing it to run too rich, but obviously given the timing I'm using, it probably isn't since I'm not running very advanced.

 

[TR3driver]

The engine runs CW when looking from the front, so advance would fall on the right side of the mark.

Hmm, I guess it depends on which is the "mark". On a TRactor motor, there is a pointer attached to the timing cover, and a hole in the front pulley. Before TDC, the hole is on the manifold side of the pointer(which is the left if you are standing in front looking back towards the engine).

Your "non-standard" cam could be the problem with the mixture. A camshaft optimized for high rpm operation will have more overlap (both valves open at the same time), which at lower rpm will cause reversion. Reversion is when some amount of fuel/air mixture flows backwards through the carbs, and then gets sucked in again. In the process, it picks up a triple load of fuel, which of course makes the mixture very rich.

You might try doing a "plug cut" with the engine running in the power band and see what the result is. Basically drive the car under the condition of interest, then kill the ignition and shift to neutral; coast to a stop and pull the plugs.

Performance cams also usually require much more valve lash than the stock cam. Running with the lash too tight can also cause the mixture to go rich.

If the cam is the problem, the only solution may be to choose different needles to match your modified engine. Or switch to a less radical camshaft. Or just live with the mixture being fat at idle. But what you emphatically do NOT want to do is let it go too lean in the power band, which might happen if you lean it out at idle with the stock needles and other changes to the engine.

 

[martx-5]

The engine runs CW when looking from the front, so advance would fall on the right side of the mark.

Hmm, I guess it depends on which is the "mark". On a TRactor motor, there is a pointer attached to the timing cover, and a hole in the front pulley. Before TDC, the hole is on the manifold side of the pointer(which is the left if you are standing in front looking back towards the engine).

Yes Randall, I see what you're saying, and maybe I misinterpreted the post by Gavin. The TDC hole would be to the left of the pointer at advance, but what I was saying is that advance would be to the right of the TDC hole...I should have been more specific.

Edit: When I installed the damper on the engine (I eliminated the engine driven fan), besides making a mark at TDC and another at 180 deg for valve adjustments, I made a mark at 4 deg BTDC as I have a Mallory distributor. That mark is to the right of the TDC mark.

 

[sp53]

Barney I would check and make sure the needle seat does not have a small piece of something like a rubber thread that can cause gas to just run through. The obvious stuff like the choke not returning is a common problem and if the vacuum advance is floating around the gas will not burn right either. Like mentioned the fuel pump pressure should be at about 2lbs. In addition, really bad ignition leads anywhere can create a weak spark that will also cause the fuel to not burn. I once witnessed spark plug bodies that were not grounding to the head that created a weak spark also. When you find it, please speak up.

 

[TR3driver]

Well, that was why I tried to be as specific as possible. It seemed to me that you were both right

 

[newmexTR3]

The engine runs CW when looking from the front, so advance would fall on the right side of the mark.

Hmm, I guess it depends on which is the "mark". On a TRactor motor, there is a pointer attached to the timing cover, and a hole in the front pulley. Before TDC, the hole is on the manifold side of the pointer(which is the left if you are standing in front looking back towards the engine).

The TDC hole would be to the left of the pointer at advance

I should have been more clear- this is what I was talking about. with the timing light on, the hole is at about 4 degrees to the left side of the pointer. So I am running advanced. That will help suss out some of the issues I'm having.

Randall & Art, maybe you should consider doing a TR tuneup tour of the North East. :wink:

Thanks for the help... again!

 

[TR3Barney]

we are now checking the cam timing to the crank to double check if it is right As you now the cam gear can be install 4 different positions A "0" B 1/4 tooth C 1/2 tooth D 3/4 tooth why you have that opption I have no clue