Tri-carb questions.

Hi everyone,
I'm hoping someone will share their knowledge with answers to a couple questions:

Can anyone provide details on overflow pipes? I see they were a transparent plastic tube with a spring-like coil of wire inside to prevent collapse attached to 1/4" tubing for the vertical section. Any specifics regarding lengths and dimensions of the individual components very appreciated.
My second question pertains to air/fuel ratio sensors and gauges. I've synchronized and adjusted them and they run acceptably well but I would like to know they're optimal.
Should permanently mounted sensors and gauges be installed?
Or heated sensors, temporarily mounted on the end of exhaust pipes?

Three carbs, two sensors; am I going to get information I can use? Is there a sequence that the jets could be adjusted to allow adjusting three carbs with two sensors?
How would one best go about adjusting the mixture with sensors?
Any help, advice, suggestions greatly View attachment 55831appreciated.

Hi Thealey. Welcome.

Is pnw Pacific North West?

Three colortunes might work out. Two o2 sensors in the exhausts are never going to match up to 3 carbs as the center carb is going to feed both exhausts.

If your carbs are recently rebuilt & have no shaft air leaks, recommend checking the main jet depression on all 3 with a dial caliper to make sure they're the same. Ditto same float level all 3. Make sure all 3 carbs have identical volume in float chambers.

I've installed ports on the vacuum side of both carbs so they can be synchronized with a manometer - no air cleaner removal needed. Otherwise, you may want to build an easy way to remove your air cleaners for synchronizing. There are threads here on that.

Dave (Red57) from Washington state has interesting posts about using exhaust gas temp sensors for tuning. Tube headers would be required with a sensor for each cylinder or at least each carb.

steveg said:

Hi Thealey. Welcome.

Is pnw Pacific North West?

Three colortunes might work out. Two o2 sensors in the exhausts are never going to match up to 3 carbs as the center carb is going to feed both exhausts.

If your carbs are recently rebuilt & have no shaft air leaks, recommend checking the main jet depression on all 3 with a dial caliper to make sure they're the same. Same float level all 3.

I've installed ports on the vacuum side of both carbs so they can be synchronized with a manometer.

You may need to build an easy way to remove your air cleaners for synchronizing. There are threads here on that.

Dave (Red57) from Washington state has interesting posts about using exhaust gas temp sensors for tuning. Tube headers would be required with a sensor for each cylinder or at least each carb.

Click to expand...

Can you post photos of your carb ports and Manometer hookup? I’ve been considering that setup.

Does anyone know if the Gunson AF instrument works? I’ve been looking for one to check my AF by hooking it up to my exhaust pipes on my BJ8.

Patrick67BJ8 said:

Can you post photos of your carb ports and Manometer hookup? I’ve been considering that setup.

Does anyone know if the Gunson AF instrument works? I’ve been looking for one to check my AF by hooking it up to my exhaust pipes on my BJ8.

Click to expand...

Patrick - see this previous thread:
https://www.britishcarforum.com/bcf/showthread.php?111391-Mickey-Mouse-Manometer&highlight=manometer

There are lots of YouTube videos of homemade manometers for syncing snow machines, motorcycles, etc.

Also multi-cylinder mercury manometers are not that expensive on Amazon.

Steve,
Thank you for sharing your knowledge and helping me avoid any exercises in futility. And yes, I'm in the sunny Pacific north-west in Washington.
A friend told me positive things about the a/f ratio sensors but his experiences were with a Weber two barrel and a four cylinder.

I set the floats at 1/8 inch. The levels seem quite uniform although I have considered removing one more time for a final volume check. I installed new shafts and bushings sealed with loctite. Polished the throats at the point they intersect with the vacuum piston, set the jets at .060 and used a synchronometer to check the air flow for uniformity. Idles nice at about 800 RPM with BJ8 mild race cam from Delta in Tacoma. Originally I had floats at 3/16"; changed to 1/8" and idle improved. Starts good, runs good. Idles a little more evenly when warm. 10-15 pounds difference in compression from highest to lowest. Engine not broken in yet only a couple hours on it, hoping compression evens out as it breaks in.
The car is still not completely assembled so test driving has been limited.
My color perception is terrible so I'm a bit hesitant to try the color tune but I might. It sounds like your experience with it has been positive.
Car seems to run great but I would like to know for sure it's optimal. At the very least I'll be checking the spark plugs.
Thanks for steering me away from the oxygen sensors and any other words of wisdom and if any can help with my upside down pics, I'd appreciate that too

These books (Amazon) will be right up your alley - lots of great pnw-liquid-sunshine-day reading:


See these threads for more tuning discussion:
https://www.britishcarforum.com/bcf/showthread.php?110197-Colortune-for-HD8-Carbs&highlight=hammill
[url]https://www.britishcarforum.com/bcf/showthread.php?111137-HD8s-easily-rebuilt-at-home&p=1064900&highlight=hammill#post1064900
[/URL]

Thanks, Steve, I've got 'em.
They're what allowed me to achieve the degree of success I was able to achieve and also guided me through rebuilding my fuel pump.
I thought about re-profiling the throttle shafts as described in the performance tuning book and kind of regret not doing it.
I wish I would have at least filed off the throttle shaft screws. As many times as I've had them off and on I could go back and redo them.
(A little project for the liquid sunshine season)
From your experience is it worthwhile? I read somewhere it could increase flow by 10% or more.
What is the consensus on the piper/cross air filters? Beneficial or no?

I haven't done the super-duper stuff like shaving the throttle shafts. Dave (Red57) is the guy who turned me on to the books. Perhaps he'll respond.

I'm happy to have books that tell how the carbs function and stress how important equal float levels are, etc. The dark blue SU book also has illustrated step-by-step rebuilding for all the carb models - a big benefit.

Hi Threaley,
You sound to be on the right track. As Steve said, I have gone overboard with a/f meters & egt gages because I was racing and having trouble with lean conditions at high revs. I melted a couple of pistons and warped or distorted valve seats several times over several years and the frustration/cost drove me to try an find solutions. I am not pro, just a guy that wants it right and can't afford to pay someone else to do it for me. Unfortunately there are no rolling roads near me, so made my car into a data collection device and utilize local back roads instead.

The books Steve mentioned are very useful - I particularly like "how to power tune SUs" buy Des Hammil. One of the key take-aways for me from that book is, (and Steve said in his first post in this thread) the need to have all carbs set the same - all jets need to be the same depth. The piston springs need to ne the same length and spring rate. The float needles need to be set the same. And the air flow needs to be the same...… on air flow, do not rest when you have the idle flow the same - IMO far more important is that the off-idle flow is the same (I usually take it up to about 2500-3000rpm) because the vacuum applied to the top of the piston controls the piston rise which needs to be the same so the air flow is the same and that air is picking up the same amount of fuel.

One thing I nave learned is the all carbs affect all cylinders because of the balance tube in the tri-carb set-up and the balance hole in the twin carb log manifold. In the past I had a tendency to adjust jets for the 'best running' I could achieve and then found I had one jet at .040 down and another at .060 down (twin carb set-up). If, in that situation, you adjust them to a uniform .050, it will actually run better and be more balanced. YMMV

Anyway, as I said I went overboard and bought an aircraft egt that has 6 probes so I could monitor all cylinders. I also have 2 UEGO 5-wire A/F gages in the collectors of the headers so they show the front 1/2 and rear 1/2 of the motor.

I don't know what revs you will be revving to but consider this. The factory set a 'red-line' for max revs - for the 100-6 at 4800 and early 3000 at 5200 - that is roughly the point the pistons reach full rise. If you are modifying the motor and plan to run higher revs (I always used 6k as my 'red-line), then you need to use piston springs that don't allow the pistons to reach top until full revs - if the pistons reach top at, say 5200, and you rev to 6k then the increase in 800 rpm does not have any corresponding fuel increase and just like that you go lean and hurt things..... I know because I have, several times.

So, once you get the basics working well, the A/F gages can tell you where you are lean and then you can progress into needle polishing to achieve optimum AF ratios. They say 14.something is Stoichiometric and will produce the most power from the btu's of the fuel. Can't find anything in researching online but after talking to numerous old time wrenches around various race tracks, I was told the max safe EGT is under 1300 deg. F. I then found that, if I ran at stoichiometric the EGT shot up - 1700, 1800, 1900 and heading higher. I finally determined I had to have the A/F around 10 to 10.5:1 in order to keep the temps below 1300F.

The above is just my opinion and my experiences and you may have different experiences.

Lastly Threaley, I am not far away in Sedro Woolley so pm me if you want any additional info/help.
Dave

Dave
Thank you!
Right now I'm in information overload. I'm going to have to do some reading to absorb and understand everything you have said. You have brought things to my attention I was previously unaware of. I am not going to be at the level that you are but like you I want it right for my purposes which won't be as demanding as yours. Like you I'm doing this myself so have to learn as I go.
Also need to shift some attention to the other details needed to get the car on the road. I still have paint and finish work to go.
When I did the carbs I did understand the necessity of uniformity. I've been lurking here for a while so I've had the benefit of advice you've given others.
Again, thank you!