TR6 Crankcase venting and general tuning advice?

Hello all,

I've been using this forum's archived posts to assist me in getting and keeping my car on the road. I bought the car after I left high school and drove it for two years relatively unrestored. Since then, the interior's been done, the suspension, the brakes, motor rebuilt, the works. The last part has had me pulling my hair out; getting it dialed in to make it run when I want it and like it should.

The issue I am specifically fighting is the apparent lean condition as manifested in light colored plugs (particularly on the front three) and pinging under acceleration in 3rd and 4th gear. I rebuilt the carbs myself, everything new. The temp compensators and bypass valves are eliminated. The mixture is set on each carb almost 2 turns out from full rich. The carbs are balanced and the idle hovers around 900-950RPM. Any lower than that and its not as smooth, probably due to the cam?

The distributor and vacuum advance module were purchased from British Vacuum Unit. The motor is rebuilt and has a mildly upgraded cam installed. This does result in lower vacuum readings at idle, around 11"HG. I have the timing set to 8* BTDC and the maximum advance as seen while revving the motor is somewhere around 28*(?)

I installed an electric fuel pump and in the place of the mechanical one, installed a plate with a port to help vent the crankcase. The hose runs from this to tee into the line coming from the valve cover, and this then tees to connect to each carb, on the port above the idle mixture screws.

Just yesterday, I changed the configuration from how I had it previously; each vent location (bloc and valve cover) going to a separate carb, in the hopes that maybe one was putting out more air under pressure than the other, and leaning out the mixture of the front carbs. This seemed to help reduce the pinging under acceleration at higher speeds and shorten the time it wants to run-on, as well as stop a funny problem I had that had the idle drop when the lights were on and want to stall the motor when the fan came on. I took these changes as improvements and proof that the motor is now close generating the HP it should, particularly at idle.

If I remove the tee to open the carb ports to the atmosphere, the motor will die almost immediately. If I shut the ignition off under normal circumstances, the car wants to run-on...

Are there any ideas out there as to what could be the lynchpin in my setup? My guess is that it's something with the crankcase vapor affecting the mixture. What do the experts say?

Regards,

Erich

If those are current pictures, you do not have the BVU module connected to the proper vacuum source.
You should use the nipple on the top of the rear carb and if there is a nipple on the bottom of the front carb, it should be tightly capped and sealed off.
I would also enrichen the mixture...only 1 and 1/4 counterclockwise turns from fully clockwise.
Hopefully the threads of the needle adjustment screw are still engaged with the threads of the needle carrier.
I would also eliminate the opening to the crankcase. Seal the fuel pump blanking plate hole.
You should have the valve cover "T"d to each carbs evacuation port...similar to your pictures, but without that "T" to the crankcase

Also...it looks like you have too much tension (not enough slack) in the RATCO cable.

Poolboy, I have seen your posts on many other topics, and am honored you've weighed in.

Silly me, I disconnected the line going to the dizzy right before I took the picture. The port seen on the top of the carb is where it connects to. Actually, Rob of BVU drilled it for me. Vacuum retard port is plugged off. Tomorrow, I'll reset the mixtures and plug off the crankcase vent at the fuel pump location. I'm familiar with the needles and their carriers (yuck) and know how to deal with that if they're acting up. I'll post a reply after this has been done.

Thank you!

-Erich

Hi Erich,

Also, you may want to play with the timing a little bit. I know you said you had a mild cam, but 11 HG seems pretty low....stock is somewhere around 17...maybe you might want to bump yours to 14 or so and see how it runs. You can always move it back if you need to.

Cheers
Tush

I was curious...what restricts the flow of gas from the crankcase into the carbs? Most cars I have dealt with use a PCV valve in the hose that limits the flow...then an overflow hose to the air cleaners for heavy acceleration when the gasses overwhelm the PCV valve. Is there a restriction on the carb connections on the TR6 to limit the gases to the carbs?

There is a plastic adapter that allows the hose from the valve cover to fit tightly on the carbs "evacuation port" nipples.
The early carbs 70 & 71 called the adapter a "restrictor". 72 thru 76 simply called "adapter" The size of the central holes are different.
'Restrictor' or 'adapter' the "evacuation ports" on the carbs open in the throat about 1 1/2" from the throttle disc.
The resulting vacuum that sucks on the valve cover (and Carbon Canister) varies with the throttle disc position.
Because of that, similar to a PCV, there is little getting sucked in when idling and more getting sucked in during high speed cruising...You can connect a vacuum gauge to the nipple and have a look at the variation.
I've fiddle around with the plumbing and found that the valve cover vapors taken in thru the evacuation ports are pretty much 'inert' as far as their ability to affect the fuel/oxygen mixture...although if the nipple is left open to atmosphere, the mixture is affected to the point that a needle adjustment is necessary to rebalance the mixture.

Good advice; I'll try and advance the timing a little with the goal of finding maximum vacuum and then backing it down an in/Hg or so. I know this will mean I need to disconnect the linkage and bring the idle down to a reasonable level, but will I need to change the mixtures, perhaps? I replumbed the vent lines and set each carb 1-1/8th ccw from full clockwise last night and took the car for a spin. Seems like most of the predetination went away except under load and at partial throttle but the motor still wants to run on. I figure advancing the timing at idle will aggravate this condition?

I *almost wish that I slid a new stock cam in the motor when it was rebuilt. Seems like a lot of my issues stem from the valve overlap and subsequent inability on my part to smell, hear, and otherwise sense when things are 'right' inside there. My other ride is a '69 Alfa Berlina, and that motor has a nice smooth idle and pulls a rock solid 20"Hg.

I do not have the restrictors/adapters on the evac ports of the carbs. I just pinched the tubing on there with hose clamps.

When my TR6 had a S-2 cam and 20 over pistons, I had to use 93 octane to prevent run-on.
I'm using the same head, but a stock cam and standard pistons in this engine and 87 octane is OK, but the compression (CR) is calculated to be about 9.4 because of head shaves so I been burning 89.
If you haven't already, see what high octane does to your run-on situation.
BTW, with that S-2 cam, 13 in-Hg at about 1100 rpms was where I was at....the overlap even at that idle speed did make the gauge needle fluctuate or quiver noticeably more than the stock cam (19 in-Hg) at 900 rpm.

I've got close to what your setup was, sounds like. My pistons are also 20 over. I have only ever put premium in The Beast as it's only around 2.50 a gallon here in TX, so why not? I suspect it can't make the run on worse to get everything else as dialed in as possible. I will endeavor to get the idle as low as possible, too; which will probably be somewhere around 950-1000rpm.

Please keep us posted, Erich...good luck.

Regarding the mixture--you might want to check the float height.

I have set the float heights to 16mm, and through this process of tweaking and testing, checked them more times than i'd like to remember. What a pain!

I settled on setting the mixtures in each carb right at one turn out from full rich, and took some time to fiddle with timing settings, taking the car round the block after each adjustment, a circuit which includes ashort but very steep incline, to test it under load.

First, I advanced the timing from 8btdc to 14btdc, as per bvu's advice. Vacuum reading at this setting, with idle somewhere around 1100rpm, was centered at almost 14"Hg, with the needle fluttering above and below 1". However, this produced some wild pinging throughout the rpm range, even in first gear. Backing it down to 12* was better, and around 11/10* even more so. This produces 12"Hg give or take an inch. There is still a barely detectable crackle if I get on the gas while cruising, say around 1/4 throttle and punching it to 1/2, but it goes away once you get past halfway.

The acceleration doesn't feel as 'snappy' as it did at more retarded settings; in fact, the loss of power at higher advance was plainly felt. I assume that the same would be true with a more retarded spark.

A 40 mile trip last night resulted in what seemed to have been pretty good mileage; something like 1/8th of a tank.

Just to fill in a few more 'blanks'....What spark plugs do you have in there, Erich ?
And I'm not sure you told us what cam you have and how you have the lash set

I am using NGK BP6ES (?) plugs.

Concerning the cam and valve clearances; that answer lies at the end of a long, painful story....

3 years ago, I discovered my original motor was tired and needed an overhaul. Bad results of a compression test, low oil pressure, excessive end float. I ran across a man at a car meet, who apparently made his living restoring British cars and developing aftermarket parts. Chris Cancelli of none other than prirace.com. Unfortunately, his reputation hasn't preceded him and I had no reason not to trust him. We agreed that he'd rebuild my motor to his 'stage 1+' specifications. A few months after dropping my car off at his shop, the motor was still in it, so I pulled it myself for him so it could get to the machine shop. He was working alone, and very busy, you see. He then promptly moved his outfit from Austin to Houston and it was almost TWO years before I finally went down and picked up the car. The machine shop apparently took a long time getting to the bloc. I drove it away and it threw #3 cylinder out the side of the motor at 70mph on the highway less than 30 miles out from his shop.

After very measured but harsh words, he agreed that he would have a new motor done up in six months. At 8 months later I went to pick up the car. The motor was rebuilt, but the rest of the car was in a state of disassembly. I spent months putting the car back together. He has subsequently fallen off the map, after his 'business' collapsed and he suffered a massive heart attack. I'm glad I didn't visit him at night with a bat as I'd fantasized knowing that he had a bad ticker.

I'd never pursued litigation, even though i'd paid most of the cost up front, because I knew he didn't have any money. He was robbing Peter to pay Paul and couldn't get the work done because machine shops wouldn't do business with him.

All that's to say that I don't know what cam is in the car and I can't contact him now to find out. On the advice of a local mechanic with some history of working on Triunphs, I set the valves at 10 intake and 11 exhaust (thou.)

In lieu of taking the cam out and inspecting it, how do I find out what the clearances should be?

That was pretty rough times you were put thru, Erich....I'd probably end up in jail if it were done to me.
NGK "6's" are the colder of the 2 NGK's; 5's are a bit hotter and may burn cleaner especially in town driving.
0.10" is the cold lash for the intake and exhaust for the US stock cams... Performance cams seem to have a bit wider lash.
One common cam which is a fairly mild upgrade is the GP2.
The designer recommends 0.015 Intake/0.017Exhaust.
Based on that you might want to play around with a bit wider lash than your current 10 and 11.
I guess you could measure the "lobe lift" to get a ball park idea of your cam.
Here's a list you might use for comparison if you get that measurement.
https://www.hottr6.com/triumph/tr6cams.html

Measuring lobe lift procedure extract
"Measuring lobe lift is extremely simple. All you need is a valid indicator with an extension so you can reach the cam lobe through the lifter bore. The indicator should be in the same line that the lifter would follow in order for the readings to be accurate.
Spin the crankshaft until the dial indicator is on the cam lobe’s base circle. That is the area on the back side of the lobe that provides zero lift. When you know the dial indicator is on the base circle, zero out your gauge. Now, spin the crank and keep an eye on the indicator. As the lobe moves underneath the end of the dial indicator, the needle will start moving. Watch until the needle stops and begins to move in the opposite direction. This is maximum lobe lift"

I have an S-2 cam, 30 over pistons, shaved head, and SU HS6's. I am very pleased with the way my engine pulls, strong from 2,500 to 5,000. I also had a bit lower vacuum, @12-14. I set up the timing to get max vacuum, @18 I think. I also have the mixture screws down @ 1 1/2 turns so not too rich, but with Champion N12Y's it works well. Have you considered the SU's and removing the emissions stuff?

Perry

Yes, it was a period of great stress, for sure.

I understand that without proper valve clearance I won't be able to get everything else in line and have the fuel economy or performance I should with my setup. I don't have a dial gauge, but can find someone who does. Meanwhile, I don't suppose it would hurt to open up the clearances a little? I didn't write it down, but the guy who put it all together, I think, had them set @ 14 for the intake and 16 for the exhaust, and that is very close to the GP2 specs.

At this time, I have all the ancillary components of the ZS carbs eliminated; bypass valves are capped off with a plain piece of gasket material and the temp compensators have a little plug of the same held down by the plug on the end of the bi metal Spring. I considered for a time changing them out to SU's, but I more or less know these carbs inside and out and want to start spending money on gas and weekend getaways with my wife rather than buying more parts!

I wouldn't worry too much about fuel economy, Erich...it's a sports car, an old sports car with 50+ year old technology, but somewhere between 20 and 28 mpg should be reasonable.
Of course that depends on how and where you drive. You really should check it correctly though...miles driven/gallons between 2 consecutive fillups.
On the Interstate on about an uninterrupted 200 mile leg, I can get 28-30 if I don't do too much passing, I can pretty much count on 25 otherwise...that's using OverDrive in 4th gear.
Around here in the country, I don't even bother checking...it's a sports car ...not that I drive crazy, but there's a lot of 3rd gear and there's hills and curves that suck a little more gas and that's to be expected.
I think, I would try those valve lash settings...14 and 16

Erich72TR6 said:

I do not have the restrictors/adapters on the evac ports of the carbs. I just pinched the tubing on there with hose clamps.

Click to expand...

I don't know is this is all the issue, but having unrestricted blowby feeding back into the carbs is going to throw off the mixture. Also, how does the crankcase vent at full throttle? If you are building back pressure in the crankcase it will significantly reduce performance.

That hasn't been a problem, John, if plumbed correctly. I think those guys in the lab coats had figured it out..When missing, a inch and a quarter long section of 5/16 fuel line can be substituted for the adaptor....but because of the oxygen depleted vapors...mixture isn't affected beyond the ability of the needle's adjustment.

poolboy said:

There is a plastic adapter that allows the hose from the valve cover to fit tightly on the carbs "evacuation port" nipples.
The early carbs 70 & 71 called the adapter a "restrictor". 72 thru 76 simply called "adapter" The size of the central holes are different.
'Restrictor' or 'adapter' the "evacuation ports" on the carbs open in the throat about 1 1/2" from the throttle disc.
The resulting vacuum that sucks on the valve cover (and Carbon Canister) varies with the throttle disc position.
Because of that, similar to a PCV, there is little getting sucked in when idling and more getting sucked in during high speed cruising...You can connect a vacuum gauge to the nipple and have a look at the variation.
I've fiddle around with the plumbing and found that the valve cover vapors taken in thru the evacuation ports are pretty much 'inert' as far as their ability to affect the fuel/oxygen mixture...although if the nipple is left open to atmosphere, the mixture is affected to the point that a needle adjustment is necessary to rebalance the mixture.

Click to expand...