Strombergs Run Rich

[Bruce100]

HI all, It seems no matter what I do my TR6 runs rich throughout all rpm ranges as verified by colortune and by the color of the spark plugs. I have them set 3 turns counterclockwise now. I have set valves, a newly rebuilt dizzy, proper dwell/timing, new proper plugs, distributor cap, wires, coil, etc. through the ignition. For the carbs, I have verified the float level, diaphrams have no holes I can detect, and have replaced both air bypass valve diaphrams and set them per Joe Curto to keep the diaphragm "piston" shut. Te only thing odd is I have noticed that if I pull the hose on the top of the carbon canister, the RPMs jump up, which has been cited as a cause to always run rich https://www.bmcno.org/tech tips/zenith stromberg tech tips.htm Before I buy a new carbon canister, is there a way to test it? Any other thoughts? I have a manual choke and no anti run on valve.

 

[poolboy]

I think what John Twist is saying that by pulling that hose off and the rpms rise, the diagnosis is a rich mixture... which you already knew.
I don't think he meant that the CC was causing the engine to run rich. I don't see how it could, actually. Aside from a thin layer of activated charcoal, the CC is just an empty storage container with no moving parts.
Did you say what spark plugs you're using ?
and you're not using Grose jets instead of the original plunger type needle valve ?

 

[Bruce100]

He actually says blocked; 2.The ELC system is pressurized. This is very uncommon, but easily checked. Remove the vapour line, the vent line, the overflow line from the carburetor. This line travels across the valve cover on the MGB to the charcoal adsorption canister, or directly to the canister on the Midget. There should be NO CHANGE in the idling or operation of the engine. If there is any change, then the ELC system needs to be cleaned, and checked for blockages. It is far more common for this system to develop a vacuum which creates a lean running condition, in fact the primary reason for lean operation!

 

[poolboy]

What's he say about a TRiumph ?

 

[70herald]

Pulling the CC is just allowing a new source of air into the Fuel/Air mixture "correcting" the over rich mixture.

You might want to check if they floats are in good condition, if they become soaked with gas, they will not float and the carbs will run rich no mater what you do.

Also verify that the choke fully closes when you push the handle in. (I had a bad cable which wasn't returning the choke all the way ..... the outer housing separated from the base under the dash and moved in and out a bit when the handle was pushed in)

 

[TR3driver]

I disagree. Although most other cars are different, the carbon canister on a TR6 should act like an open passage to free air (unless the anti-runon solenoid is stuck or activated). If the mixture changes when you pull off a line, that is proof enough that the canister is clogged (or fuel logged) and needs to be serviced or replaced. They definitely do not last forever, ISTR the factory recommendation was to replace every 48,000 miles (even the early canisters that could be disassembled for cleaning).

When I pulled the canister for my 71 Stag apart, I found that the cotton filter was caked with mud; and the screen under the charcoal was almost totally clogged with rust.

 

[Bruce100]

Randall, I don't have an antirunon valve. My filter was dirty, I cleaned it. How do you service the carbon? I am hesitating to buy a canister as a tshooting step. Joe Curto recommended for now that I just plug the vacuum ports on the carbs where the ECL connects, which I have done. That did not help, so the canister is out of the equation for now. So here is where I am at with this. I decided to try a whole other approach and use a vacuum gauge to troubleshoot - and started the process by advancing timing to determine my max vacuum, which is 21 rock steady. Set to max vacuum I am WAY advanced. And set this way FINALLY I can lean it out with the adjusters so colortune shows blue. So timing may be the problem. Since I have had this problem both before and after having Jeff at advanced distributors rebuild the dizzy, I am thinking the dizzy is not at fault, but something else. I aggravated my chronic back problems in the process and took it easy last week, so I haven't yet taken the next step, which is to set timing by backing off 1.5 to 2.0 on the vacuum to see what the actual setting is. I've never done this particular way of determining timing before, and am having fun with it. Looking forward to seeing what the final results are, and if this solves it.

 

[70herald]

Why do you think the advance is so far off?
If you have the original vibration damper the pulley may well have moved over time. the only way to determine where TDC is now is to figure out when the front piston is and verify if the mark on the damper is in the correct location.

 

[Bruce100]

I just checked the marks on the pulley with my advanced toolset - a piece of dowel. The marks appear to be correct. I also took a quick shot at setting the timing, and it is advanced enough that it is in a part of the scale that I haven't cleaned off yet, so can't quite tell how far advanced. Over 20 degrees it looks like. About all my back can take today, so i'll clean it tomorrow and see where it is at.

 

[thechileman]

70 herald has a good point about the floats.. I had a similar problem when I bought my tr4... The carbs had been "professionally rebuilt" by the previous owner. I took them apart, the floats were WAY off. Adjusted the floats, my rich condition went away...

 

[Bruce100]

already checked the floats, one was off and I adjusted that prior to posting this. Advancing the timing has leaned it out as verified with colortune, and the timing I range I have it set at is verified by the vacuum gauge check. So I think I am closing in on it as a timing problem.

 

[Bruce100]

deleted this post, was a duplicate

 

[poolboy]

While the marks on the damper may still approximate the true position of the piston in the combustion chamber, because of the stretch of the timing chain and worn sprockets, the valves may not be doing their thing at the same time in relation to the height of the piston in the bore as when all was fresh and new.
And that's where the Vacuum Gauge comes in handy. It will indicate the new sweet spot for your engine.
In other words the manifold vacuum takes into consideration and reflects the position of the valves rather than just the position of the piston and the damper marks become pretty much irrevalent when setting the ignition timing.