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TR2/3/3A Rough running / a lot of carbon on the plugs

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GTP1960

GTP1960

Jedi Knight
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I recently swapped out my mechanical fuel pump for a facet electric.
But I haven't adjusted the carbs. & I am starting to think that might be my problem.

previously she was running great, until I decided to "upgrade" several disciplines. (Note to self: don't make multiple changes, with out a test after each one)

So my question is : how do I lean out these. SU hs6 carbs? I think I might have more fuel flowing when I accelerate, than the current carb setting likes.

at idle she hums along fine, and I don't think I have a vac. Leak, as I tested with starter fluid & had no rpm effect.

also I disassembled & cleaned the carbs & refilled the dash pots, and switched back to champion y87
(I think) plugs


i will say the Macy's worm & peg steering rebuild & my rear suspension rebuild made a world of difference in handling and feel.

thanks for reading.
 
To let the mixture go leaner when you first open the throttle, use lighter oil in the dashpots. Also make sure they aren't overfilled, they aren't supposed to be "full".

But changing the fuel pump should have no effect at all on mixture, unless the pump is overwhelming the float valves. In that case, you would have to fix the problem, rather than trying to adjust the mixture.
 
Thanks Randall.

Must be something else then, I don't think the float valves are overwhelmed as no fuel is leaking out or pooling in the carbs. I used 5/30 in dash pots right after I cleaned up the carbs.
Could fuel starvation cause a rough run on acceleration?
( what would you make of the carbon deposit on the plugs? )

thx again
 
The fuel pressure for a stock tr3 is like 2 to4 psi. I do not like the newer electric fuel pumps because they are set higher than that and often require a fuel pump regulator to reduce the pressure. Moss sells and old type fuel pump that runs low, so if you have that the carbon might be coming from somewhere else. If the distributor does not return after advancement or just lets the timing float around, that can cause carbon deposits also. The old saying “ what is wrong will your SU carbs is your Lucas ignition” is often true, but it sounds like you have done modifications, so I would not know. Sometimes what looks like carbon is actually oil deposits and some carbon mixed in. If that is the case, your oil rings are bad and you will get a lot of dieseling from the oil glowing red and running the engine with the key off.

I do not know much about the H6S so I am not sure how to lean them down, but from what you have said my guess would be high fuel pressure push fuel into the carbs and running way to rich
 
sp53 said:
The fuel pressure for a stock tr3 is like 2 to4 psi. I do not like the newer electric fuel pumps because they are set higher than that and often require a fuel pump regulator to reduce the pressure.
Click to expand...

The Facet pump for the TR3 application shows 1.5 to 3 psi. I assume that's what Guy used. It should be fine but it would be good to put a gauge on it because a higher pressure would certainly cause the symptoms.

Tom
 
Disassembled and cleaned carbs? Is enriching cable returning completely? Use the shop manual or internet resource (e.g. https://britishclassicmotors.com/3301.html ) to tune and set them up.
Tom
Click to expand...

Tom, thanks for forwarding that link.
i have disassembled & cleaned the carbs.( but not the float bowels) They had a lot of carbon build up, but the jet needles looked fine.
though I can't claim success, with a smooth running 3A, I have learned a lot about the SU tuning process.

i did notice that the piston in the forward carb. had more resistance than the piston in the rear carb. ( when raising with your finger to check movement.). The rear piston slides up with no resistance, the first 1/2" or so. Not so with the forward piston, that has steady resistance from almost the start of its track.

You are correct, the facet fuel pump is suppose to be low output. I have it mounted parallel to the frame( because I mounted it inside the frame "I" beam, under the driver side rear shock housing for more protection) however facet recommends mounting it in a upward tilt angle. So I do need to ck my fuel line pressure, for that reason, also.

i'm going to take a step back and follow the "DIY engine check up" list you sent me.


thanks again
 
Thx SP53,
If the distributor does not return after advancement or just lets the timing float around, that can cause carbon deposits also. The old saying “ what is wrong will your SU carbs is your Lucas ignition” is often true, but it sounds like you have done modifications, so I would not know. Sometimes what looks like carbon is actually oil deposits and some carbon mixed in. If that is the case, your oil rings are bad and you will get a lot of dieseling from the oil glowing red and running the engine with the key off.
Click to expand...

my issues may very well be ignition timing (new flamethrower distributor & coil), But on the good side, I have no dieseling problems & she starts better than ever , hums along at idle with hardly a hiccup. ( though she's always had a bit of a throaty galloping idle @ 900rpm, I assume, is common for these TR3 engines.)

my next step is to start over & go by the #'s:
a compression test.
valve clearance check
fuel pressure & flow ck.
ignition timing
vac leaks
then back to the carbs.


Thx again.
 
GTP1960 said:
i did notice that the piston in the forward carb. had more resistance than the piston in the rear carb. ( when raising with your finger to check movement.). The rear piston slides up with no resistance, the first 1/2" or so.
Click to expand...
Usually, that would indicate not enough oil in the damper. But it's also worth checking the plunger for obvious damage, misassembly, etc. Although the pistons are matched to the domes, the plungers are not matched, so it's OK to swap plungers (to see if the problem follows it).

If memory serves, some of the original HS6 floats were not ethanol-resistant and would sometimes sink when used with E10.
https://sucarb.co.uk/hs-stayup-float-kit-hs6-hs8-large-bore-needle-valve.html

Just as a side note, the little rectangular Facet pumps come in a wide range of pressure ratings; but look identical. You pretty much have to either check the stamped part number (and assume Facet didn't make a mistake), or check the pressure yourself.

With a stock cam, it should idle evenly (not necessarily smoothly but without the rpm varying) all the way down to 500 rpm or so. A "gallop" says to me that something is wrong. Of course, I've usually had something wrong, so my idle is currently set to about 800 rpm indicated. (Another common problem is that the old mechanical tachs read high at the bottom end.)
 
(Quote) "Sometimes what looks like carbon is actually oil deposits and some carbon mixed in. If that is the case, your oil rings are bad and you will get a lot of dieseling from the oil glowing red and running the engine with the key off."


Until the underlying cause is found I have used this trick successfully. As you're turning off the key, give the throttle a quick burst and hold the pedal down until the engine stops turning, this will draw in large amounts of cool air, preventing the run on. Hope this helps.
 
DougME said:

Until the underlying cause is found I have used this trick successfully. As you're turning off the key, give the throttle a quick burst and hold the pedal down until the engine stops turning, this will draw in large amounts of cool air, preventing the run on.
Click to expand...
Oddly enough, I used to do just that on an old tractor, because of the impressive backfire that would usually follow. Holding the throttle open with no ignition and the engine spinning ensures that the exhaust manifold gets filled with combustible fuel/air mixture. If the engine was good and hot, sometimes it would light off after a few seconds. (Obviously not my tractor :smile: ) Better yet was the rare occasion when a cylinder would fire before TDC and start it spinning backwards. Then it would suck in the fuel/air from the exhaust and actually run backwards for a second or two, blowing big clouds of blue exhaust out the intake.

Easier and more certain IMO to leave it in gear and let the clutch out, with your foot firmly on the brake, just after turning off the key.

Having the idle set too high seems to increase the tendency to run-on, and I used to run a "3/4 race" cam in a TR3A that didn't like to idle below about 1500 rpm, so I just got in the habit of killing it with the clutch every time.
 
Follow up:
Just as a side note, the little rectangular Facet pumps come in a wide range of pressure ratings; but look identical. You pretty much have to either check the stamped part number (and assume Facet didn't make a mistake), or check the pressure yourself.
Click to expand...

the facet fuel pump failed after only a couple months. Just stopped working, no obvious reason why.(could be because I had it mounted parallel rather than angled up).
i replaced it with an airtex low output (2.5-4psi) that actually fits the same location, works well & is quieter.

I did a compression test and found all cylinders held 160-165psi, dry.
wet they ran 175-180psi.
however I must have used to much oil, & have fouled my plugs.
i sprayed sea foam in the plug holes to breakdown the oil, cleaned & left the plugs out for a couple days. And will try to restart it tomorrow.

took the engine down opportunity to reset the valves to .010 ( For me, that dance took a little practice).

Randall, also thanks for pointing out about the mech. Tach not running true.
i found a inexpensive digital tester on Amazon.

Best regards

guy
 
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