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Rebuilt carbs / Idle racing to 3000

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M

MyDogJustice

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Well, I'm a little new to all of this so any insight would be greatly appreciated. I just got my carbs back from Chester at SUCarbs. Got everything mounted up and I'm having a hard time getting the idle down. Car fires up and races to 3K RPM. I've putzed with every thing I can think of and I'm at a bit of a loss. Help?

Josh
 
Welcome, Josh!

Ummm... what engine/car?

Are the return springs all on the right pieces of the linkage?

SU's aren't too hard to deal with once you grasp the concept.

Some photos could help us out, too.
 
Sorry! I'm sure that would be useful info! Its a 67 TR4A. Before the rebuild, it ran fairly well and idle was around 800 RPM so I dont think its related to anything other than the carbs at this point. (Which is not to say that it doesnt have its share of other problems) Idle adjustment screws are all the way out. I've toyed with the mixture, but dont get any significant change in RPM (although some obviously) The butterflies are shut the whole way at the resting position of the linkage. I've got 20W oil (motorcycle fork oil) in the dashpots. The gas tank was drained and refilled with 93 octane and some ethanol stabilizer additive. New inline fuel filter right before the first carb. Return springs are in place.

I'm just trying to walk through all of the details in case something is significantly relevant.
 

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so if you have unhooked all the linkage, butterflys are closed, are the piston all the way down? the butterflys do have an angle on them since they are not straight up and down when closed, how about the chokes, As I remember when you choke the SU carb the jet drops down to richen the mixture, are the chokes hanging up?

Hondo
 
Butterflys have a slight tilt to them. I think the plan for tomorrow is completely disconnect the linkage from the short throw bar. That will remove the long and short bars from the equation. I should have measured them before I shipped them out, but they don't look drastically different. I'm also gonna disconnect the choke cable and take that out of the equation. The jets do drop when the choke is on to slightly richen up the mix. I would believe that the pistons are fully down. I've raised and let them drop a few times on their own and they clunk down.

Anyone have insight as to the effect of having an oil thats too heavy in the dashpot? Its 20W oil, but its fork oil. I'd heard of other using it, but I must say that it feels awful stiff. I over filled initially (that thing takes almost no oil!) and managed to suck a bit of it back out. But putting the little piston back in took a bit of a shove to get down through the oil. The air piston takes quite a bit of a poke to move up now as well. I dont know what kind of oil was in it before as I havent had the car very long, but it seemed a lot lighter and things seemed to move a bit easier. IS there an easier way to get the oil back out or do I need to take the carb off and dump it upside down?

I really appreciate all the input so far! This is such a great community!!

Josh
 
Is that heat shield on correctly ? looks like there might not be a good seal between the carbs and the manifold the way it's installed..sucking air ?
 
Do you have 6 gaskets installed?

If you remove the dampeners and lift the air valves. Do they drop freely and click when they hit the bridge?
 
I'd put 20~50W motor oil in the dampers. Wick the fork oil out with paper towels and Q-Tips.

The choke linkage also tweaks the butterfly setting a bit but it appears the screws for the choke cams are well away from the cams in the second pic.

About all that's left are either a leak at the mating surfaces of the carbs-to-manifold or misaligned throttle blades.

Spray some WD-40 around the manifold seals/joints and see if it changes the running. That'd indicate a leak. You could use water in a spray bottle too.
 
FWIW, Chester at SU Carbs did my TR3 Carbs last summer, and I recall my carbs initially ran at 3K rpm, as well. Perhaps this is to ensure the car will actually run, instead of barely running at low RPM settings.

Anyway, I let it warm up, then disconnected the choke and accelerator pedal linkage, then synced them separately, and they're still idling nicely at 800 RPM... HTH
 
Weird. Are we the same person? I just got my carbs from him and the same thing is happening.

It's not reflective of his workmanship, though. His workmanship is excellent. One of the throttle discs needed adjusting, which is no big deal at all.
 
rlich8 said:
His workmanship is excellent. One of the throttle discs needed adjusting, which is no big deal at all.
Click to expand...
I guess we have different standards, then. The throttle discs are supposed to be installed the right way around and centered as part of the rebuild process, then the screws are tightened fully and staked in place. If they are disturbed/loosened, the screws should be replaced.

20W fork oil should work fine. There is a surprising amount of resistance involved, but it should have no effect whatsoever on idle (except when you are fiddling with the dampers). The dampers essentially act like the accelerator pump on conventional carbs, to give you a slightly richer mixture during acceleration for better power and to overcome the "lean bog" that would happen otherwise because air accelerates more easily than fuel. I actually prefer straight 20 weight to 20W50.
 
The new standsrd for excellent workmanship is the bling factor.
And chester isn't the only carb specialist being judged that way.
 
Its amazing how just a little progress on a car can reignite that fire inside of you and make you remember just why it is that we spend so many countless hours in the garage!

Disconnected the choke cable and the small rod engaging the gas pedal. Took a bit of work to get it started (reaching the key and the the choke assembly at the same time lol) Got a little heat in the motor and it came on around 2100 RPM. fiddled with the idle screws and it'll sit pretty at 900-1000. Its all been on sound today so far. Havent even gotten the sync tool or fiddled with the mixture yet! Soo thrilled! I know I've got a bit to go, but its so much more promising.

I think the throw bars must be a bit out of adjustment and I didnt quite realize just how sensitive they are and the smallest, most imperceptible changes are actually enough to hold the butterfly open just enough.

Its hard not to judge things on the bling alone. You send out these dirty old carbs and they come back so shiney and new! Kinda wish this had been the last "ugly" part of the car, but its far from it. As long as it runs like a boss, I guess I really dont care either! I ended up going working with Chester based on a lot of the feedback on this forum. We had a few small problems and after yesterday's issues, I was afraid I had [censored] away $300. In the end, Chester was great to work with and I'll probably send my next pair his direction too! Moral of the story? Dont be too quick to blame another person's workmanship for your own incompetence!

I'll certainly be checking back for help and giving updates. I've got a basic understanding of the next part of the process but does anyone have any pro tips for me? I read all that I can and watch all the YouTube I can find, but in the end, I've found the guys in these forums are the best resources possible!

I'm off to retrieve my sync tool and jet wrench. (Remind me again why I loan tools to friends that will "have them back next weekend"?)

Josh
 
TR3driver said:
I guess we have different standards, then. The throttle discs are supposed to be installed the right way around and centered as part of the rebuild process, then the screws are tightened fully and staked in place. If they are disturbed/loosened, the screws should be replaced.
Click to expand...

Well, I guess you're right - I used Jimmy Hilton for a previous rebuild and everything bolted right on.

I guess this is unacceptable after all. I won't get too upset about it but yeah, it should have come done right. He said that it shifted in the shipping process. I don't know whether to buy that or not.

Either way, I've got them fixed now.
 
you have a uni sinc tool, the ball and tube is junk with a capital J, when I tride to use one on my webers it would stall the car before the ball would move, I got the german made unisink and its great, I can even test how my lungs work.

Hondo
 
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