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Help with carbs

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livinginthepast

livinginthepast

Jedi Trainee
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Wow, what a day.

First, let me say that when you buy a car, always check the obvious things for faults. Today I discovered that a PO jammed the wrong bolt into the upper hood support rod attach point when it suddenly gave way and came down with a thud as I was closing the bugeye's hood - this after a particularly frustrating and prolonged effort at setting up the carbs. But that's just a minor pain. I'll order the correct bolt and hopefully be done with that! My plea for help is with my carbs.

I need some feedback/advice on my attempt to balance and tune the carbs. Something just isn't quite right.

Here's the run down: I rebuilt the H1s on bugeye w/948. Rear carb 'seems' to run lean at 12 flats out), front carb seems to run really rich (again at 12 flats out). I think that I'm getting a correct mixture at three complete turns down on the rear carb, but I can't seem to lean out the front carb adequately.

Further, I can't seem to get the idle down to an acceptable level. While I try to balance the carbs (with the throttle linkage disconnected, etc.), it runs at about 800 rpm at the minimum. However, when I fasten down the throttle linkage, the idle speed always jumps up to about a thousand rpms (yes, I've checked the throttle cable) and then ,when I drive the car, the idle jumps to about 1200.

It ran better yesterday after just throwing the whole assembly together with very little adjusting! Now it idles higher and runs on after shutting off the key.

There are no obvious leaks, at least there was no indication when I sprayed starter fluid on the intake while running the car, but maybe I'm missing something.

Is this just my being stupid noob or is something else going on? Or both?
Thanks in advance!
 
Ok, lemme see if I can sort through this.

First, the 12 flats number is really approximate. Some carbs tune up pretty far from this point. One thing that affects it, for example, is how far the needle is inserted into the piston--a few thousandths more or less is easily a flat or two.

By the way, did you replace the jets and needles? It's a good idea to do this. That can also affect the adjustment. Also, you might not have the right needles; my spare set of H1s arrived with needles that were way wrong.

Second, when you tighten the linkage after syncing the carbs, it's really easy for it to move a smidgeon, and the idle speed changes. That part isn't unusual, and it just requires some care and creeping up on it.

However, not being able to get the idle speed down, and then having it change when you tighten the linkage AND a very lean carb, starts to sound like an air leak. This often comes from air around the throttle shafts where they go through the body. These should have only a few mils of clearance, just enough so they move smoothly. If the shafts rattle around in the hole noticeably, it's probably too loose and you might have an air leak. The standard test is to spray something like carb cleaner or even WD-40 on the shaft, right where it emerges from the carb, and if the speed changes, there's a leak. The intake isn't where you want to spray it; I don't think that will tell you anything.

By the way, feeling the shafts for looseness is probably more reliable than the spraying test. My carbs were leaking like sin and passed this test the first couple times I did it.
 
Hi Steve,

Well, you nailed it. I sprayed wd40 into the rear throttle shaft and the idle speed changed significantly. Less so, but but still perceptable on the front throttle shaft.

So, the next question is repair. Is this just a matter of replacing the throttle shafts? Will the carbs typically need any machine work (bushing maybe)?

Thanks for your help!
 
You'll probably need both bushings and a shaft. When you take it apart, take a look at the shaft and you'll probably see a fair amount of wear. The shaft is easy to replace; bushings are harder since you have to get them precisely in line or else the shaft will bind. It's possible that just the shaft will be enough, but if the shaft has worn, it seems pretty likely that the bushings have, too.

I think these are available from the Usual Suspects (Moss & VB). When I did it, I made my own, so I can't be much more help with that.

Glad you found the problem, though!
 
Yeah, I'm just going to take the carbs off the car and bring them down to my guys at Brooklands (my local British car repair shop) - let them do the bushings. :smile:

Thanks again for your help!
 
Hi Bill,

H1's eh?
Please let me know what happens when you take them in.
As I'm sure you are aware, I have a set of H1's too.
:wink:
 
Hey there Rick,

I sure will. As I recall, your carbs were leaking from the bottom, like mine. I discovered the larger of the cork seals in my carbs were almost completely disintegrated - there was hardly a washer left! Now the carbs don't leak at all.

After removing the carbs (again), I inspected that rear throttle shaft and it has massive amounts of free play. The front one isn't so bad, but it's definately worn. I wasn't aware that they could cause such problems -- until today, after sitting in front of an idling engine for an hour in 90 degree weather adjusting, adjusting some more, starting over, adjusting some more --- and finally getting frustrated and coming to the forum for help!

I am so thankful for this Web site.
 
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I am so thankful for this Web site.[/QUOTE]

Amen, over and over.

I remember decades ago trying to fix problems on my MG's and only being able to go to the parts places for help. That seems like such a "pioneer" situation compared to the way things are now.

There are many times that I have the laptop in the car I'm working on so I can post the things that I don't know the answers to here and while I'm working I get the answers.

I like it, I like it a lot. :laugh:
 
Well, picked up the carbs from the shop today - equipped with shiny, new, oversized throttle shafts. No bushings required. They look great!

The old shafts showed significant wear and were deeply grooved. Looks like I have something to do this weekend. (after I re-attach the hood strut that fell apart last weekend.)
 
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