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Spitfire Spitfire 1500, SU HS4 major issue

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mikecyc72usa

mikecyc72usa

Jedi Trainee
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Ok, I've scoured the archives, and tried everything mentioned. The whole story:
A few days ago I took off my carbs (SU HS4) to clean them. I disassembled them, cleaned everything with carb cleaner, and reassembled them. Before the cleaning there was an intermittent miss above 4k rpm.

I put the carbs back on, and the car can barely hit 60mph on a level road. Before it had no problem cruising at 85mph. Took carbs apart, front carb throttle plate was a little off. Fixed that, which fixed idle problem. Yet still no power. Hit the gas and it just bogs down. Mixture makes no difference. Timing is spot on. Fuel going to both carbs. Pump and filter are good. Plugs are perfect color. Float levels are spot on. If I had another set of carbs I'd throw them on to see what would happen.

I've checked for vac leaks. There is a slight leak on each throttle shaft. Surpise there, I know. I have one more thing to check. I wonder if a jet tube somehow got kinked and the fuel flow isn't quite right. Thoughts?
 
Have you checked that the throttle plates open all the way when you mash the loud pedal?

Tried doing a plug cut?

What about a fuel volume test, or actual pressure at WOT?
 
Plates work perfect. Plugs perfect. Not sure about the fuel volume. Just so weid that all I did was diasassemble and clean and this happened. I must have changed something that I'm missing without realizing it. Wait. I just realized that the spring loaded "valves" on the outside of each carb were stuck shut. These are the ones that if you push up on them the slide rises slightly. When cleaning they became unstcuk. I wonder if that could be causing a vac leak when I hit the accelerator.
 
You say you have disassembled both HS4s to clean them. Were you careful not to mix components when you put the carbs back together. Each piston and vacuum chamber are matched to each other and during tuning the needle is centered in the jet. If you mix components between the carbs you can expect issues.

The "valve" you mention sounds like you are describing the lifting pin used during tuning. No appreciable amount of air leak will occur around them. However, if they stick, they may be holding a piston up... or indicate that the piston is sticking.

Were these my carbs I would go through them again from scratch. Center the jets, start with the basic "first start" settings. Once the engine is warmed up, balance the air flow and set the mixture.

If you think you have mixed the pistons and vacuum chambers between the carbs, go to YouTube and look up John Twist's videos on how to check the "drop rate" of the carb components so you arrive at the best mix of parts when you put the carbs back together.
 
Sorry for asking, but we're sure it is not ignition?

It seems odd to me that the plugs would be showing good mixture with the behavior you are describing. (I mean this cooperatively of course).
 
No, I agree. I even reset the timing with the timing light, checked the advance, and used a colortune. At idle it's perfect. Could it be a needle isn't quite right after disassembly? I left the needles in the slide/piston to avoid that, but you never know. I'm really vexed. 30th Triumph of my life and I've never fought carbs this long.
 
Here would be really one of those "opps" questions, but you said you removed the carbs, did you remove the entire assembly, and disconnect the throttle cable, if so are you sure it is opening to full open, stranger things have happen, you can easily test this by having someone push the gas pedal to WOT position with the car not running and see if you can move the throttle linkage further by hand, if you can, then cable needs to be adjusted.

The other thing is to get all the air filter out of the way so you can actually see the piston motion in the carbs as the engine runs and make sure they are moving freely and not sticking.

As for your leaks at the sahft, HS4s are notorious for shaft leaks as the shaft wears and this can be redone duing a rebuild process with special machining tools.
 
I have the air filters off, and only took the carbs off the manifold, leaving all that in place. Even when I hand operate the throttle with the linkage between the carbs same thing. Instant response then tapers off almost immediately and almost total loss of power.
 
mikecyc72usa said:
It was very simple. Gasket from jet to float bowl on front carb was mangled and blocking fuel. Now time to reset all the other things I've done to make sure it's running properly. Thanks everyone!
Click to expand...

Well goodfor you, if you're talking about the rubber gland that goes on the end of the jet fuel tube, make sure you get a new proper part, Joe Curto has them, www.joecurto.com, a regular o-ring if used will fail in short order.
 
Hap, I did have a proper spare. I am going to still get another set of carbs, put them on the car, then decide if I want to rebuild or just sell these. I may fully rebuild them just to have an extra set since I also have a 1971 MGB nearing completion. Talk about a maddening experience.
 
If you have a PCV valve on your intake manifold, and it has become dislodged, this can cause the symtoms you are having.
 
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