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Triumph TR6 - Vacuum down, poor hot idle
|I've just done Pertronix, cap, rotor, plugs, and set the valves on my desmogged '75. Dwell is 35 degrees, timing is +8 ATDC running, plugs gapped at .035. All the smog connections on the manifold are plugged, all vacuum lines on carbs and retard on distributor plugged. No leaks show up around the carbs doing the propane test, and spraying B12 all around. However, I'm only making 14 vacuum, and although the car runs well, and idles well while driving around for the first 20 minutes, after awhile it begins to drop off from its 850 or 900 down to 400 and croaks. I understand I should be doing more vacuum, but can't find any leaks. My brakes are fine, servo seems fine, all plugged stuff seems fine, cannister seems fine. |
"and set the valves on my desmogged '75" I presume you set valve gap at 10 with engine cold. Proper oil in the dampers and not loosing any. Also at correct level. Maybe the 2 carbs are out of sync. Remember the canister should also have a reducer in it.
|I noticed my vacuum retard line had fallen off over the weekend but noticed no difference in operation. After reconnecting, still: car runs fine. Is vacuum retard not working? Need I bother repairing it?|
BTW: aren't dwell settings used with points rather than the petronix?
I noticed the same thing with my vacuum retard line when I got my '71. On the advice of several sources (this BBS, too!) I plugged the end but plugged it into the carb for looks.
It may be my imagination but my 6 seems to run better with the line plugged.
|Charlie: I was afraid of that. Good in theory but poor in design. Plug it up but leave it in place sounds like the way to go.|
|Sorry about the dwell, that was before I decided to ditch the points. Pertronics in there now. Valve gap was set at 010 with engine cold and double checked. All holding nicely with a good fit on the feeler. The vacuum was down before the tune up, and came up from 13 to 14 after setting the valve gap. The carb near the firewall was pulling 1 bar on the unisyn at idle while the far carb pulled two, so I upped the idle screw on the rear but haven't checked the pull at 2 to 3000 rpm to check the linkage. I also backed off the mixture a half turn on the rear carb because I was rich on plugs 5 and 6. But none of that affected the vacuum. It was down at idle and remains down...Intake manifold bolts are snug, carb bolts to the manifold are snug, and no leaks around the carb. I'll check the reducer (?) in the cannister.... what should it look like?|
Make sure that there are no holes in the carb diaphragms. adjust carb needles so that they are even (flush with face of air valve). Synch carbs. Disconnect the vacuum retard line and block the inlet on the underside of the rear carb. Set dynamic timing at 1000 rpm to 10 degrees BTDC. Take it out for a road test. If it pinks under load back it off in 2 degree increments until it no longer pinks. Fine tune the carb richness. Other areas to check for vacuum leaks are the temp compensators and by-pass valves. Leave the vacuum retard disconnected. If you do reconnect the retard you will find that you are running at around 4 degrees ATDC. If all is in harmony you should be running at 15 to 17 hg at idle. Good luck
Mike '71 TR6 (with triple Z-S)
|Based on your time and hours and effort spent on trying to solve a problem on your TR6 you are automatically granted a pass into the "TR6 Hobby Elite" group of owners who refuse to be downtroden by simple physics and other automotive wear and tear impacts....and spend hundereds of countless hours improving apon the drunken agry british assembly line workers!!! Hahahahah|
Now having said all that, how could you post all this stuff and not talk about what the hell kind of carburetors you are running on your motor. And of cours the emphasis is on the part about YOUR MOTOR cause you are now on your own there dude.
Better bone up on the TR6 Tune-up theory and call back.
|Hmmmm,....I just read the thread in here from Kent and I noticed he said the plug gap was .035, Is that the right gap? I've been told for my 72 its .025 How much of a difference will this make?|
|Mike- Will you be at Bellevue W/ your triple Z's|
|Never mind Mike, I saw your post on the Bellevue Thread|
|Marcello- The archives indicated that a lot of guys running Pertronix and a stronger coil have upped their plug gap from .025 to .040 to have a 'stronger spark and better burn'. I went with .035.|
John- factory Strombergs. Thanks for your feedback, we're all here to help each other.
Others may differ but I am using NGK BP6ES plugs gapped at .030. I am too using a Pertronix with a Lucas Sports coil. Also running a 150PI cam and 1.65to 1 roller rockers, 9.5to1 comp ratio. Triple Z-S with B1AF needles. Had dizzy recurved to advance no more than 24 degrees but have pinking at anything more than 4 degrees BTDC. I really think that if I wax the TR one more time it will run perfectly. Added an octane booster last night and eliminated the pinking but still have a low speed stutter. Must find a better wax.
Mike Crane '71 money pit
|Kent, have you tried putting in a set of plugs gapped at .025 just to see... if you run an increased gap I think it critical to make sure you are getting the charge all the way to the plug. You haven't mentioned but I guess you're running some good plug cables...just some ideas.|
|Kent--Is your cam stock? If not, that could explain the low vacuum.|
One of the great mysteries of our carbs is the by-pass valve. You should have a closer look at this critter and see if it is working properly.
The top hose out of the canister that goes to the valve cover. If you remove the hose at the canister, you wiil notice that there is a small plastic piece inserted into the canister that effectively reduces the size of the hole into the canister. This is the same plastic piece (reducer) you see at each carb connection.
Kent, as a side note here, good idea on the Pertronix. Did you also change the coil to a High Output coil to take advantage of the EI? Do I dare mention ballast vs non ballast ignition system:)??
Your note to Kent.."Is your cam stock? If not, that could explain the low vacuum"
I'm not sure I understand..my cam is stock along with the rest of the engine and my vac sits @ 20
|Charlie--My point to Kent was that he may have a performance cam installed and not know it. Such cams typically reduce intake vacuum due to a combination of higher valve lifts, longer durations, and wider overlaps. Your 20" WG vac is perfect for a stocker; no need to worry.|
|Apologies for not responding on this thread sooner. Rick C, Rick O, and Charlie-- you guys were right on. I bought this car with a fast street cam in it. I didn't realize it would impact the vacuum. I found the paper work on the cam and emailed Piper, the manufacturer. They confirmed that it will definitely reduce vacuum. Its an HR270/2 and my intake valves are now set at .012, and the exhaust values at .014, per their instructions. They said 14 vacuum was right on for the cam. |
By the way, I did upgrade the coil when I put in Pertronix, and went with the magnecor 8.5 wires.
The car is running strong right now, but what was a low idle, has now become a fast idle when the car gets hot. see my latest post...
Can someone point me toward the Fuel injection guy who has the ZS carb tops mounted on the top? I'm curious how much that setup costs...
I believe Rick Patton did Aaron Cropley's TBI (throttle body injecion). Company is Topsham Motor Sports or something. Below is an address where Aaron has a few pictures of the installation of the TBI.
Aaron can get you in touch with Rick Patton or do a search on the web.
1971 TR6 CC61212L
|Thanks, I'll really be interested if it doesn't just break me financially.|
|Good one Rick O|
Now there is an engine guy for 'ya.
|Danke Rick C. For those of us who have secretly spent $$$ on engine restoration, you learn these sorts of things. The knowledge makes the expense a bit more tolerable.|
This thread was discussed between 19/07/2005 and 13/09/2005
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