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Fuel and vacuum pressure gauge


Iain T

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28 minutes ago, Pete Lewis said:

22hg is a bit too high  i would drop it nearer 18

I thought so and currently have it at 17-18.

I need to get some petrol so I'll take it for a spin and see if it pinks. According to the timing marks it's about 20 degrees.....?!

Iain 

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1 hour ago, Pete Lewis said:

with the dizzy  vac unit disconnected  or left connected ???

I left the dizzy vac hose connected. I could try clamping the hose (it's rubber not the hard plastic pipe)?

Driving to the petrol station the engine pinked when at low revs in high gear and then WOT. Put it back to just over 13 degrees and 14hg vacuum but the needle does shake a small amount. Check the compression or disconnect a plug lead? 

I can't hear any air going into the manifold and the gaskets are all new. 

Iain 

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you need to just disconnect it when using a strobe /engine idling  as there will be some advance which you need to add to the static figure 

without digging through the manual i would not expect 6 deg from the vac unit but its certainly possible 

just pull the pipe off the dizzy  and a soft rubber pipe will collapse under the max vacuum it supposed to carry a hard tube is far better

dont take the HG readings as gospel  its an indication , needle vibration as i said fit a short bit of bundy and squeeze it to make a restrictor

just keep squeezing till the needle goes steady 

and its my guess with twin carbs you get a lower manifold vacuum as you have two throttles all sucking air so manifold depression at idle could be less

sorry forgot about all this stuff from  my emission testing  days 

take it for a drive whats the vac to cruise with a light foot  ( to get the highest reading without loosing speed )

stick in 3rd and decel  whats that giving ??? 

Pete

 

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Iain,

I have a vacuum gauge on the dashboard and set the timing by it. The most you'll get out a 6 cylinder is 21 and then back 1 bar to 20. (22 and 21 for a 4 cylinder) I suspect if your getting 22 on a 6 cylinder your gauge is reading high. You can check it by ear, turn the dizzy for maximum revs and back a gnats. On mine the "ear" and "eye" methods line up exactly. Most satisfying. I have no idea what the BTDC is, gave up checking that for the reasons Pete's detailed.

Doug

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1 hour ago, dougbgt6 said:

The most you'll get out a 6 cylinder is 21 and then back 1 bar to 20.

Doug,

To satisfy my paranoia I've ordered a piston stop plug to check if the tdc pointer and pulley marks line up. The vacuum did just go up to 22 if I set it at 20 the timing, according to the pulley, would be over 20degrees btdc! When I set at 17-18 on the vacuum gauge it definitely pinked under load. I want to check the pulley calibration before I proceed. If the pulley marks are out I'm wondering if the cam is set correctly? 

I'll do another check tomorrow with the dizzy vac hose (it's thick wall vac hose) blocked as I had it connected when I took the readings. 

I'm going one step at a time! 

Please look out for updates! 

Apologies the max reading was 21!

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On 08/03/2022 at 16:22, dougbgt6 said:

The most you'll get out a 6 cylinder is 21 and then back 1 bar to 20

Been tweaking today. I pulled the vac hose off the dizzy and it made no difference to the timing left to atmosphere or with my finger over the end. I advanced the timing until the vac gauge read 18-19 then backed it of to a reasonably steady 17. I checked the afr gauge and tickover and all seemed fine at about 13.5 and 750rpm. When I checked the timing its about 25btdc. The piston stop should arrive on Saturday and all will be revealed as to if the pulley timing marks are correct! The only other thing I'll do is the valve clearances which according to Newman Cams has to be done cold. 

I would put the post in say the Engine section but not sure how to do it! 

 

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Iain, of course the definitive timing set up test is the WSM recommended 'pinking should just end as you get to 2000rpm under full acceleration in top gear on the flat'. Obviously the engine should be as hot as it gets and the fuel octane what you normally use...

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13 minutes ago, johny said:

Iain, of course the definitive timing set up test is the WSM recommended

I'll try that tomorrow, it was nearly 4pm after I'd tinkered and the traffic around here is not conducive to calm test driving! 

Iain 

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if you read the wsm you can check std cam timing all you need is feeler gauges and some simple rocker settings 

from memory  set 11 and 12 on the rock/balance  adjust 1 and 2 to 0,040"   turn to align TDC  the gap under 1 and 2 should be the same  doesnt matter what size but the same 

Pete

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Checked the timing marks on the pulley and tdc is where it should be. Bisecting the two piston stop points on the pulley corresponds to the tdc line. 

Top tip. Loosen nuts on rocker assy or as your valves open they can hit the piston stop! I have a small nick in the side of the stop.....then the penny dropped why! Hope the valve is ok🤞

It seems so far all is where it should be but I haven't checked the cam timing. The engine was put together by a guy who has assembled hundreds of engines so I'm hoping that will also be fine. 

I'm going to put everything back and run it up to 2000rpm and see if the vac gauge is stable (I think that's another test for manifold leaks). Then take it for a spin and see if 20 degrees btdc pinks!? 

Iain 

 

 

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pleased  the damper ring is in the right place 

dont get paranoid about the readings   youre ears will give the same results as the gauge

ie as you increase the dizzy advance it makes the idle increase   the gauge shows the same climb in vacuum.most carbs  use 18 to 21"hg 

but this can be too much for some carbed engines

on a light economy cruise you should get around 10 to 15"hg  with just enough throttle to maintain speed

drop a gear and thrttle back expect 28 to 30 "hg 

puling hard at a full throttle expect near to 0 "hg 

if the needle vibrates or waggs around damp it by making a supply pipe restriction 

if you go to the net there are some realy wild ideas of what the readings are, you dont need a gauge to tell you a valve is burnt out or a S plug is failed 

constant depression carbs often do give lower vac readings than a fixed jet downdraft carb 

keep playing and to drive with a 10 to 15 is no fun at all 

dont forget a poor air filter will affect some of the readings 

Pete

 

 

 

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On 12/03/2022 at 14:58, Pete Lewis said:

dont get paranoid about the readings   youre ears will give the same results as the gauge

I'm learning readings are for a perfect world, Triumphs aren't perfect!

As suspected it pinked at 20 degrees, knocked it back to about 15 and it seems OK. Vac is 16. Adjusted the mixture and tickover. 

Time to stop fiddlin and drive the thing..... 

Iain 

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I have to get out of lockdownitis, too much time and nuffin' to do but twiddle and buy must haves on tinternet. 

Oh well this little episode added to my box of toys...... 

Ta for everyone's help, I'm virtually back to my original settings!

Iain 

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