Very rough running

[nick]

I got the engine running with the SU carbs and manifold installed but it will only run at idle as long as the dynamic timing is set at 24 degrees BTDC. And it runs very rough. If I go to 2000 RPM it smooths out but the timing remains at 24 BTDC. It does not retard as it should. I rechecked the firing order at 1-3-4-2, verified that at TDC the rotor is pointing to the rear intake bolt and that the cam mark is at the index. I checked with my timing light that all plug wires are hot. The plugs and wires are new. I checked the static timing and it is at 8 degrees BTDC. I need some ideas on where to go with this problem.


[img][IMG]http://i615.photobucket.com/albums/tt234/nickmi/TR7%201975/Yellow.jpg[/img]
nick
'79 TR7 DHC
'76 TR7 FHC

[dursleyman]

Have you checked for air leaks?
That will mess up your idle every time.

Russ

1980 TR7 Sprint DHC
Dursley
UK

[Workshop Help]

Fee! Fi! Fo! Fum! I smell the blood of a Lucas distributor with frozen together bob weights! This is the subject of a topic from about a year ago(?) wherein I explained the technique for freeing up the distributor innards.

Have you checked the advance motion with your timing light yet? As the engine speed increases, the timing mark shown with the timing light should move forward on the scale.

As for the static timing, the factory setting for the U.S. models was 2 degrees AFTER TDC. This is because our engines do not have a vacuum advance unit, we have a vacuum retard unit that pulls the timing back. The timing is advanced by the bob weights swinging outward from centrifugal force.

The good news is, if the weights are frozen, the distributor does not need to be removed. The entire servicing is done with it in situ. Please use the RESEARCH button at the top right of the screen to view the article.

Mildred Hargis

[nick]

<blockquote id="quote"><font size="1" face="Century Gothic, Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Mildred</i>

Fee! Fi! Fo! Fum! I smell the blood of a Lucas distributor with frozen together bob weights! This is the subject of a topic from about a year ago(?) wherein I explained the technique for freeing up the distributor innards.

Have you checked the advance motion with your timing light yet? As the engine speed increases, the timing mark shown with the timing light should move forward on the scale.

As for the static timing, the factory setting for the U.S. models was 2 degrees AFTER TDC. This is because our engines do not have a vacuum advance unit, we have a vacuum retard unit that pulls the timing back. The timing is advanced by the bob weights swinging outward from centrifugal force.

The good news is, if the weights are frozen, the distributor does not need to be removed. The entire servicing is done with it in situ. Please use the RESEARCH button at the top right of the screen to view the article.

Mildred Hargis
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

Well, that is good to know because I thought the vacuum device on the distributor was an advance. And the static setting in the Leyland manual calls for 10 BTDC. Now, is that different from the UK cars because of the smog equipment or is it the higher compression pistons? In any case isn't static timing just a starting point? Isn't the dynamic timing the critical one?

I did check the advance motion with a timing light and it wasn't happening. Sounds like a distributor cleaning is in my future.


[img][IMG]http://i615.photobucket.com/albums/tt234/nickmi/TR7%201975/Yellow.jpg[/img]
nick
'79 TR7 DHC
'76 TR7 FHC

[FI Spyder]

<blockquote id="quote"><font size="1" face="Century Gothic, Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by nick</i>


Well, that is good to know because I thought the vacuum device on the distributor was an advance. And the static setting in the Leyland manual calls for 10 BTDC. Now, is that different from the UK cars because of the smog equipment or is it the higher compression pistons? In any case isn't static timing just a starting point? Isn't the dynamic timing the critical one?
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

Cars used vacuum advance in pre-emissions era and changed to vacuum retard after. By the time our cars went into production I think they all used vacuum retard (without checking the book). Old habits die hard (as well as terminology) and vacuum retard was called vacuum advance for a long time after (by the less than pedantic).

- - -TR7 Spider - - - 1978 Spitfire- - - - 1976 Spitfire - - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra - Yellow TCT

[Workshop Help]

Nick, my friend, what you're reading is a bit confusing, I'll grant you that. If the vacuum line from the manifold is disconnected and the vacuum blocked off, a U.S. model TR7 will show the ignition timing at an idle speed of about 800 RPM to be 10 degrees BTDC. With the vacuum line hooked up and there being no other major vacuum leaks to divert the suction pressure, the reading will be pulled back to the 2 degrees AFTER TDC mark on the ignition timing plate.

Other countries may have a different distributor that uses the traditional vacuum advance rather than than our vacuum retard units. In that case the reading IS the 10 degrees BTDC with the vacuum lines all connected.

Mildred Hargis

[nick]

<blockquote id="quote"><font size="1" face="Century Gothic, Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Mildred</i>

Nick, my friend, what you're reading is a bit confusing, I'll grant you that. If the vacuum line from the manifold is disconnected and the vacuum blocked off, a U.S. model TR7 will show the ignition timing at an idle speed of about 800 RPM to be 10 degrees BTDC. With the vacuum line hooked up and there being no other major vacuum leaks to divert the suction pressure, the reading will be pulled back to the 2 degrees AFTER TDC mark on the ignition timing plate.

Other countries may have a different distributor that uses the traditional vacuum advance rather than than our vacuum retard units. In that case the reading IS the 10 degrees BTDC with the vacuum lines all connected.

Mildred Hargis


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I agree Mildred. Very confusing. Both my cars have the Lucas Opus electronic distributors. One is a California car the other I'm not sure about. However, both have been converted to the Allison ignition. Interestingly the newer car does not have a vacuum retard attached to the back of the distributor.

I removed the distributor and cleaned the retard weights. They were moving but after the clean and lube they became much looser. I also tested the vacuum advance unit and it works. But not when hooked up to the carb. When I put my finger over the carb vacuum port I don't feel any vacuum pulling. However now the engine retards smoothly when accelerated. I set the timing to 8-10 BTDC at 900rpm as a gross starting point. Now I have to go through the SU tuning guide since this is my first shot at those carb.

The start problem turned out to be a pushed back spade connector inside the start relay connector. It would make intermittent contact. I also cleaned the contacts in the start relay and now it works fine.
I also found the Autozone test rig to be less than reliable since they stated that my started was bad. Even though I watched the guy test it he rushed through it and was glad to be rid of me.

[img][IMG]http://i615.photobucket.com/albums/tt234/nickmi/TR7%201975/Yellow.jpg[/img]
nick
'79 TR7 DHC
'76 TR7 FHC