13B with weber carb not reving under load
 

I have a 13B with a weber 45DCOE carb with a racing beat intake manifold installed in a Triumph Spitfire. The car sat for several years, but went through a complete suspension and electrical system rebuild and is now operations again. The car used to pull strong all through the rev range, but now starts to hesitate around 5500 rpm with a noticeable drop in power, and won't pull beyond around 6,500 rpm. It also is running rich at idle (fumes!) around 1,000 to 1,200 rpm depending on where I set the timing. Outside of the fumes, the exhaust is clear, no smoking. Needless to say, performance is very poor compared to where it was before. Any ideas on where I should start on debugging this?

Mike Melnyk

thoroughly clean the fuel system yet?..tank,filter.lines,etc??

Yes, replaced the fuel filter, and checked the fuel pressure, which was running around 3.5 psi. During the carb rebuild, everything was disassembled, soaked in carb cleaner, and all holes were blown out with air to make sure they were open. I didn't flush the gas tank, but I hope the filter would prevent anything from getting through to the carb. The float chamber was checked and OK. The idle jet is a 60F9 (although the number is hard to read due to wear, it might be a 65F9), the emulsion tube is F11. The vacuum advance diaphrams on the distributor are not connected and open to the air (they were this way as modified, no recent change). I haven't pulled the plugs yet to look at their condition. They were new and the car has 250 miles on it since the rebuild. Would a photo of the installation be helpful?

You would be surprised at what you will find in the tank.
I'd check it.
Even if you don't find anything,it does rule out that aspect.Better safe than sorry.

45 dcoe is way to small for a 13b to breath well....

yes. the 45 is less than ideal on that engine. you should really have a 48 or 50. however if you dedicate some time and money :) (jets, venturis, tubes, etc.) to it, you should be able to get SOME street service out of it.

If it ran well before, it should still. Yes, the fuel pickup in the tank could well be the culprit. Ask me how I know.

Appreciate the advice. Pulled the mesh filter in the carb and found bits of corrosion caught in it. I went back and replaced the fuel filter and found some in there too. I then leaned the idle mixture screws slightly and it now revs up fine under no load with no issues at all. Under acceleration it still gets rough a little above 5,500 rpm, and would now rev north of 6,000. Pulled like it used to through 5,500 rpm though. The car is very light, and it now has that good old push in the seat up through 5,500 now, then stumbles. I pulled out my old timing light to see about that, but the light failed after just a couple of minutes of use. Will pick up a replacement tomorrow and check it out. The idle jets and the emulsion tube were all clear. I'll take a look at the fuel pick up next, and take the top of the carb off to check the accelerator pump.

Just how did you discover the fuel pick up was a problem? Also, I'm guessing my 45DCOE intake won't work on a 48 or 50 DCOE, so I'd need to replace that as well? If I do switch, I have to have the side draft to fit under the hood, and would the 48 or 50 be best? What would be the best jetting, choke and emulsion tubes for those set ups?

- Mike M

I went through a half dozen filters in 1500 miles on a car that sat 5 years. Thinking I could clean the tank a filter at a time. Finally on a new filter shed barely run. Dropped the tank and the mesh pickup filter was fully disintegrated, and the tube so clogged I was surprised it ran at all.
Clean tank, new pickup sock, no troubles.

I'm not a weber guy, but I think your manifold will be sufficient for the bigger carb. I'd make what ya got work as well as possible before replacing it, though. For ultimate driveability smaller is better, though top end suffers.