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Howdy from Katy, Texas.  I just purchased a new Speedster from Vintage Motorcars and am struggling with a lean spot that occurs just off idle at about 2,000 rpm when accelerating moderately.  The accelerator pumps seem to be properly adjusted because when I accelerate quickly it bypasses the lean spot.  The motor is equipped with twin Solex H40 carburetors and has 2,332 ccs .

Any ideas on how I should go about correcting this problem?'



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Two choices.

1. Call Vintage and find out if there is a smaller air jet available(which will richen the transition). A bigger air jet will lean the transition even more. If not available, you can solder the hole and re-drill it smaller.

2. Replace dual Solex 1 barrels with Weber IDF 44 or 48 or Dellorto DRLA 45. If you get Webers, I recommend Italian or Spanish, not the Chinese copies which still say Weber on them.

Last edited by DannyP

Respectfully, and in deference to the man from NY whose advice you should always listen to: 95% of all carburation problems are ignition. What are you running for an ignition system? How are you setting timing? If you are setting it properly (at 28*- 32* at full advance), where does the initial timing fall?

If the initial timing is at TDC and your advance doesn't come in quickly enough, it'll have a flat spot just off idle. I'd like to see at least 20*+ at 2000 RPM.

Generally speaking, you're on your idle jets a lot longer than most people think. You may not even be in transition at 2000 RPM.

Do you have access to an A:F meter?

Thank you for the replies Danny and Stan.  No, I don't have an A/F meter.

Notably soon after I received the car I had idle problems.  After pulling and reading the spark plugs I concluded that the passenger carburetor was too lean and could not be cured by adjusting the idle jet screw.  I pulled the idle jet and discovered it was plugged with some sort of hard debris.  I dislodged the debris with a small gauge wire, reinstalled the jet and the motor now idles perfectly. I'm now beginning to wonder if something has clogged the low speed port in the body of that same carburetor.


Quick update: I removed the passenger side carburetor and worked a small gauge wire through all the transition ports.  I then blew high-pressure air through each port and it appears that a result of this work my lean spot is mostly gone. The carburetors are new so I suspect some metal flashing from the castings or possibly machining swarf became lodged at the transition ports, similar to what happened with my idle port on this particular carburetor.


Might I add that it might not be something to do with bits in the new carbs, but more likely due to bits in the fuel supply system.  and clogged idle jets are a topic probably discussed more here than any other single thing.  It's good you have gotten your OJT on how to do a quick R&R and blow out.  My lengthy battle with such troubles on my 44 IDF webers did finally resolve favorably, and I could go in to all that entailed, but not now, not here, only to say one component to the fix very well could have been using the right spec fuel line hose (good for FI and ethanol laced gas)  PLUS, and this is a biggie I believe, a proper fuel filter.  Do your research and you will discover that fuel filters come in an array of particle sizes that they filter down to.  I got one that catches very small stuff.  As I said, many things were done to get things right with my Webers, so its hard to tell which may have been the basic problem.  I believe very fine fuel line filtering played a part.  Those plastic and paper filters you see all over might work OK for your lawn mower, but not so good for finicky idle jets.

As Jason found out, new carbs are dirty. I have always advocated disassembly and cleaning and adjustment before installation. The manufacturers don't care if you have problems. They just want to sell more carbs. They DO NOT clean them enough, maybe at all.

Float heights MUST be set, they are not done with any accuracy at all in the factory. I set Bob's carbs but then shipped them to Florida. I would not be surprised if they were out of adjustment when they got there. Nor would I be insulted if they were opened up to check.

A friend of mine bought PMO carbs recently for his 911. I asked if he had cleaned them as I suggested, and he did not. I'm quite sure they are dirty and also 100% positive the float heights don't match. The triple throat carbs have a sight glass for float height, so that was easy to see.

@Robert M posted:

Just say something like, "I drank way too much last night and I swarfed myself.".

When they ask what it means just say you simultaneously barfed and $hit yourself at the same time. I'm making up a new definition so the word is easier to use.

And you think at your age everyone will still treat you with the same respect and enjoy your charm after that little tell-all?  I don't think so, Robert!

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