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Some major bogging/see-saw action.

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L

lesingepsycho

Jedi Warrior
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I swapped back to my SUs and now I'm getting a serious bogging/see-saw on take-off or on high load/low RPM acceleration. It occurs mostly from 1000 to 2000 RPM at part throttle. If I go full throttle off the line, there is no bogging. But even if I'm rolling and give it part throttle, say less than half, I can hear the carbs sucking like crazy but the engine bogs down and and the car see-saws. If I'm sitting in neutral and rev the engine, it is plenty responsive however with no sign of bogging.

They are complete matched rebuilds including shafts, jets and needles. I've balanced air flow many times using a uni-sync, and matched the jets for turns. I can't find any vacuum leaks but if I give it choke, i.e. more jet, then it takes away some or all of the bogging/see-sawing. The problem there is that I'm already running at 14 flats out and it seems to be running rich even with the choke off so I'm not sure more jet is the answer.

Anybody? Any advice will be appreciated. I don't want to give up on the SUs as they are great when they're functioning properly, but right now.... :cryin:

JACK
 
Check your float height?

i had trouble getting mine to richen up..and i screwed my jet nuts all the way to the bottom, turned out i had my floats set a bit too low.

just a thought

m
 
I was getting ready to start looking for another carb when I remembered to check my plugs - they were sooty - too rich. Turned the carb up one flat and already it's better. Point of this is, check you plugs before you do anything with the carb and see what they tell you. BTW I've not heard of anyone running jet nuts all the way out - that seems way to rich
 
Take your dash-pots off and turn on your fuel pump. You should be able to see that your fuel level is approximately 1/8" below the saddle, if the level is significantly different than this then adjust your floats so that it is.
BillM
 
I guess I'll start by double checking the float heights.

Dashpot oil was one of my first thoughts and so i cleaned it out and filled it back with the actual "SU Dashpot Oil". I also cleaned and checked the movement of the pistons at that time and they seemed fine. They react in sync WHEN I'm sitting in the driveway looking down the barrels of the chambers.

I tried a few new things but I haven't driven it yet. I'll drive again today and see if any of my adjustments have made a difference.

JACK
 
My guess is it'll turn out to be something simple, and you'll kick yourself when you find it. Something like a spring that's come loose from a centrifugal advance weight, vacuum line with a hole in it, dead squirrel caught in the intake...

(OK, forever the optimist...!)
 
OK, well the only thing I could figure after working the dizzy over real well and eliminating that as a possibility is that it was indeed not seeing the fuel it needs. I guess I forgot to mention that I'm running velocity stacks on the carbs :whistle: :whistle: :whistle: (doh-dee-doh, did I forget to mention that?) :whistle: :whistle: :whistle: and my only guess is that it increased the airflow SO MUCH that 12-14 flats wasn't cutting the mustard. :square: I kept cranking the jets until it seems to be running pretty well now. The see-sawing and bogging are pretty well gone although it still smells rich at the tail pipe. I lost count but I must be at something like 18-20 flats out total. I'm most likely going this saturday to get an O2 sensor installed and then I'll have an altogether better idea of exactly what is going on after I hook it up to my Autometer Sport Comp Ultra-Lite Air/Fuel gauge. Plus then I'll have the O2 already in place when my EFI system is ready.

JACK
 
That 12-flats number is really approximate. If the mixture seems right, don't worry much about the position of the adjustment. It depends a lot on the needle, on needle and jet wear, and a couple other things. I've seen these tune up with the adjustment far from that position.

An air-fuel gauge would be neat to have, but remember, you have two carbs and one sensor. So, it seems to me, it would be easy to get one too rich and the other too lean, but the sensor would indicate that the mixture is just right. I'm not sure how to get around that problem, but I suppose someone else might have a suggestion.
 
I love SU's I've a single HIF44 on my 1275 frogeye & a BDL needle. It's a big improvement over the twin 1 1/4" carbs that I took off.

What's wrong with warm beer anyway? :cheers:
Propper Ale that is, not your mamby pamby Bud-wise-errrrrr. chuck :pukeface:
 
You know, I've always been intrigued by the Colortune. Such an interesting and cool idea; seeing in the spark plug. I would love to try one just to see what the heck it looks like! :confuse:

Also, I have a single HIF44 with 1275 manifold sitting on my bench. It is from the Metro Turbo kit and it's going to be used eventually on my car. I'll need to modify the hood/bonnet first however. But still, it's like a personal mission now to have the SUs running good. The set I built for my Mom's car are like brand new. I want these to be at least that good before I take them off.

And finally, I actually don't mind warm beer. I primarily drink Guinness Draught anyways. :thirsty: I am totally offended by Lucas Electronics however. :nonod:

JACK
 
See my post re. Bog, Sputter, Backfire, etc. Did you check to see if Intake Manifold wasn't leaking. I did it all and found a problem with a bad manifold gasket. WD-40 or BrakeCleaner will quickly pinpoint the source of a leak.
 
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