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TR2/3/3A Running rich SUs.

sp53

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Running rich SUs. I have rebuilt these carbs twice and still have trouble with running rich. The sad part is--- I think I am so smart when it comes to these cars. I am looking for a second opinion on what I could be missing. I got the kits from Joe. The engine in new with probably 3 hrs on it, and I believe everything is correct, timing, points ect…What I have not done is take the car out and drive it, so that it gets plenty of air. Most of what I have done is in garage. I have driven around the block a few times, but not on the open road, and when I get back from going around the block the plugs are carboned up.

I had my nephew who is a modern mechanic help me. We got it idling nice with clean plugs after a couple of attempts and when we lifted the piston pins the car would shut off like it was lean, so carefully moved the jets one flat at a time until it would idle ok (when lifting pins no raise up in idle trying to keep it on the lean side), but when I pulled the plugs it is back to rich carbon. He felt I needed to get it out of the garage and drive it and open it up to get air going through it.

Anyways my experience is these cars seem to run rich; I figured it is the quality of fuel today. Do others have this rich running problem especially on new motors?

The running rich is usually the choke with these cars and maybe I am over choking with this new tight motor on startup to keep it running and the carbon comes from that, and maybe if I got it out on the road with air moving through at like 3 or 4K the carbon would fall off. Any ideas? Does my theory sound right, maybe kinda sorta. I might just have to go for it, and if I break down--- deal with it. Can anyone help me push……

Steve
 

Mickey Richaud

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Hey, Steve -

Your nephew may be on to something. Couple of questions, though: Are the jets located properly in the carb body with regard to height at the "bridge"? Needles centered properly? New needles of proper size?

Mickey
 

karls59tr

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Along the lines of what you and your nephew have already concluded.Take the car for a good run on the highway. When you are in an area of no traffic shift into neutral,shut the motor off and coast to the side of the road. Pull a spark plug or two and check them. You may be surprised to find that the plugs are a light tan color instead of being carbon fouled. Most of the carbon fouling may be just from too much idling and not from a rich mixture at all.
 

CJD

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Always better rich than lean. If it is running strong I would tend to give it a few hundred good driving miles to break in before getting too detailed about the carbs. It's often hard to differentiate a bit of oil burn from rich mixture too. A new engine may be using a bit more oil than it will once it's broken in. Glad to hear you've got it out on the road!
 
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sp53

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Yes Micky the pistons drop freely, so everything seems correct. Karl I have tried that with a different tr3, but found out later that in that car the oil rings were defective, so no luck. When I get it out again and moving I will try that. At first I had it rich, and then reset the jets to how Steve G suggested in one of his post by looking down from the top to I think it is about a 1/16 below barrel on the jet (mine was about 3/16) and got it to run lean by spraying started fluid in but then needed to back the jet out because it would not idle. I am frustrated with the car now plus I have some back problems, but when I start problems sometimes I get possessed by the problem. I try do something different each time so I am doing the same thing over and over, the Einstein thing. Perhaps this time as soon as I get it running, I will drive it cold go around the block and keep the RPMs up in first and second then look at the plugs. Like Karl stated I need to get on the highway maybe in 3rd at 3K.

Does anyone know if copper washers 90 and 96 can let extra fuel in?

steve
 

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sp53

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Thanks John that makes sense. Our city has grown so much here that it is a nightmare to break down on the roads. There really is not a lot of friendly places to pull over if the car breaks down, and friends are not around like the old days. I guess I could get towed to one of the mountains around here and roll down. Maybe pull a wire and call Hagarty and tell them I am broke down, and I move to Eatonville; it is in the mountains, but bad Karma. Looks like I will tool up and go for it with a cell phone, my gal hates my hair brain car problems.

steve
 

DavidApp

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Hello Steve

I have been going down a similar path. Runs good and will idle at 800 rpm no issues but my plugs are black. The carbs were rebuilt by Joe C.

I checked the chokes are fully off. Did the bit lifting the pistons and decided I was running rich. Wound the jets in about 3 to 4 flats. It then indicated it was lean so I went back down 2 flats. So far the plugs are looking better but on cold mornings I have to keep the choke pulled for several miles or it stumbles as I pull away from a stop. After it warms up it does not stumble any more.

David
 

pdplot

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Like the man said, take the car out and thrash it good, then come home, shut it off and check the plugs. Don't worry if its a bit rich. As long as the plugs aren't gas fouled, you're ok. Too lean, you may burn valves. SU's - set 'em and forget 'em.
 

titanic

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If your jet is 3/16" below the bridge , I think it could be the cause of your rich running problem. Normally, I think the jet height should be about .050" below the bridge. Sometimes the old washer (#90) isn't removed when removed when the carbs are overhauled and a new one added, which makes it impossible to get the mixture lean enough. I fought the problem on my TR3 many years ago and solved by machining about .020" from the upper jet bearing. A dial caliper is helpful in measuring the jet height.
Berry
 

Mickey Richaud

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sp53

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Thanks David glad to see I am not alone. I have fought this rich problem for ever. Getting a tr3 to idle at 800 takes skill and precision, I am happy when I get a car there. Getting the engine warm is another very important thought I need to look out for also David. I live a cool wet climate and I have a tropical fan and an original radiator and i might have been to cool. I know from driving in summer around here, the engine temperature changes everything and that last little bit say from 165 to 180 + or- matters a lot for precision of a tune. 800 RPM very nice!

Berry I believe I have got the carbs back together correct and I see what you mean about the washer. My thoughts were those thin copper washers are there to help with the sealing and yes the lower is more of shim and I have seen different thickness. The brass washers are probably there to help the matting surface and not so much sealing the fuel out. But I do remember the assembles looked a fuse different and I have a few of those bearings so I will not forget that adjust you mentioned. I did move them in from the 3/16 but have not looked at where I am at know.

The more I think about it seems these carbs are very simple and if put together by the book with 7/16 float and the piston dropping it should work. My thoughts on the brass washers being a sealer is probably wrong; it looks like the fuel is held in the pocket between the glad washers and if a small amount goes around the assembly it could be made up for in the adjustment or it would just leak a little.

Yeh pdplot I think I am there and fear itself and over thinking is holding me back. Thanks all of you for your help!

Steve
 

CJD

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If everything is in order, but you are still running rich, Joe has different jets and needles to lean the mixture. The jet will change the entire throttle range, while the needle can fine tune one area of the curve. It's always possible your needles are worn from being installed off-center at some point in their lives.
 

steveg

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Like to put in a plug for Tom Bryant here.

He re-bushes SU carbs with Delrin bushings which he line-bores for better-than-new sealing around the butterfly shafts. He's a Volvo guy, so most of his experience is on HS-series carbs.

Never could get my HD8s to idle and had them bushed - now I can get them to idle at any speed I want. Price very reasonable.

Lots of SU information on his site - including many picture articles on rebuilding several different SU series:

https://thosbryant.wordpress.com/category/su-carburetors/
 

karls59tr

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If everything is in order, but you are still running rich, Joe has different jets and needles to lean the mixture. The jet will change the entire throttle range, while the needle can fine tune one area of the curve. It's always possible your needles are worn from being installed off-center at some point in their lives.

In terms of getting the idle down to 800 rpm what affect would having a mild street cam have on needing a higher idle? Also I wonder how accurate a 62 year old tachometer is? My TR3 runs alright but will stall out if it's not idling around 1300 rpm. What's the first thing to adjust if I need to bring the idle down?:indecisiveness:
 

steveg

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If everything is in order, but you are still running rich, Joe has different jets and needles to lean the mixture. The jet will change the entire throttle range, while the needle can fine tune one area of the curve. It's always possible your needles are worn from being installed off-center at some point in their lives.

Anyone contemplating different needles should check out one of the online needle comparators. This is a real rabbit hole. Check this out or search for "su needle comparison":

http://www.mintylamb.co.uk/suneedle/
 

mctriumph

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The dirty little secrete on SU carbs is that different cams ,pistons and valves WILL require
a trip to a professional tuner. He will select from the dozens and dozens of available needles
a profile that gets you into the ballpark where you can THEN fine tune it to your driving needs.
All else is guess work and will NEVER get you where you need to be. This should be done on a chassis
dyno for optimum results......
 

Tom Bryant

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<snip>
My thoughts were those thin copper washers are there to help with the sealing and yes the lower is more of shim and I have seen different thickness. The brass washers are probably there to help the matting surface and not so much sealing the fuel out.
<snip>
My thoughts on the brass washers being a sealer is probably wrong; it looks like the fuel is held in the pocket between the glad washers and if a small amount goes around the assembly it could be made up for in the adjustment or it would just leak a little.
<snip>
Steve

You were correct the first time: That thin copper washer between the upper jet bearing and the carburetor body is very much intended to work as a seal and to keep fuel from bypassing the jet by flowing around the jet bearing. I also have seen different thicknesses for this seal. Unfortunately. They're supposed to be 1/32" (0.031") thick. I frequently encounter ones that are considerably thinner, usually 1/64" (0.016") thick. Such thin washers are frequently supplied with rebuild kits. They will not work, but the unknowing buyer installs them anyway, and he instantly has a problem that he never had before. Two things go wrong:
1. Fuel bypasses the jet, causing an overly-rich mixture, no matter how much the jet is adjusted.
2. The jet bearing (usually) cannot be tightened sufficiently to hold it in place while turning the adjustment nut, so the mixture can't be properly adjusted, whether or not the fuel is bypassing the top jet bearing.

To check for this problem, you need to turn the adjustment nut all the way up, and then keep on turning it... if you can... If you can continue to turn the nut after it's all the way to the top, then you probably have one of those too-thin copper washers. If you can't turn it, then you're probably okay.

Someone on this thread mentioned machining 0.020" of material off the upper jet bearing. That would be a mistake, leading to the exact same sort of problem as installing a too-thin copper washer.

Of course, if the top gland seal is leaking, that too would allow fuel to bypass the jet orifice and could result in an overly-rich mixture. Cork gland seals can leak. Teflon o-rings (-010 size) are far superior and are readily available. See:
https://www.theoringstore.com/store...product_info&cPath=367_93_96&products_id=4168
You need two o-rings in place of each cork seal, four o-rings per jet, 8 per pair of SUs.

Someone also alluded to picking the proper needle as being somewhat of a fine art, requiring expert judgment. Not so. Just about any needle profile will get you in the ballpark and make the car run reasonably well. With rare (or possibly no) exceptions (assuming the jet itself is properly sized and unworn) the jet can be adjusted to accommodate any needle profile at the adjustment point, where the car will run "perfectly" (or as well as it can run, given whatever else might be wrong with the engine) and the car will run reasonably well on both sides of that adjustment point. And most drivers will be perfectly happy with the way that car runs; any differences are unlikely to be noticed except at the racetrack or on the dyno.

As for the piston lift pin: Forget it; the thing is pretty much useless and far too subjective to be of significant value in adjusting. Here's an alternative procedure that should work for just about any SU owner, of any experience level:

https://thosbryant.wordpress.com/2015/10/04/su-carburetor-tuning/

Tom Bryant
 
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sp53

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The carbs are rebuild with new sm needles and .1 jet, the standard stuff. Many years ago I bought some of the needles that Moss sells for rich or leaning the mixture with no joy. At the time it seemed- IIRC- the needles did not seem to work in .1 jet. I will ask Joe and see if he suggests replacing both jet and needle and with what?

The last time I talked to him he seemed busy and frustrate with our conversation. I was asking the same questions I asked here about the thin brass washers and sealing and he wanted none of that. One thing is clear, he is a New Yorker; he was gruff. I am old school Seattle area, like loggers and Carpenters, not this new world. I keep my mouth shut, but it was not easy. He has the knowledge and parts and this question should be easier to answer.
steve
 
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sp53

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Karl I know nothing about unstock cams, but I would say if your idle is high, you are probably pulling air in from a second source. Like throttle shafts or manifold leak. Spray some carb cleaner on the shafts and or manifold; if the idles goes up faster, the shafts are letting in too much air. Advanced timing will raise idle also and incorrect dwell compensated by advanced timing will also. Probably throttle shafts--- they are the moving part that wears out. A distributor with incorrect weights or sloppy something will advance the timing and raise the idle also because it pulls forward to easy.

steve
 
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