Lazy U20

[Daniel]

Hello All,
I'm working out the bugs on the roadster before Shasta. It seems like the engine runs out of breath around 5,500 RPM. What I mean is, it revs pretty evenly up to that, then slowly gains up to 6,500 or 7,000. It just doesn't seem "snappy". My previous stock 68 2LTR would rip your head back when you cracked it and would rev from 4K to 7.5K almost instantly. I don't know anything about this engine as I bought the car in running (poorly) condition and have coaxed it back to life. It does leave a carbon trail on the garage floor on start up, but I don't notice any smoking or rich smell while driving. Any advise, wisdom, comments or questions would be greatly appreciated.
Thanks,
Dan
Particulars:
69 U20
Smog removed
EI distributor set 15 degrees advance at 700 (pinged at 20)
SU carbs (new needle and seat sets, floats, 10W fork oil)
Electric fuel pump

[fj20spl311]

It could be cam timing, a coil problem or Mixture (lean or rich)
Start with a "plug check"
Check you max advance.

[nismou20]

I've always felt the stock SU needles were lazy as well. With smooth idle they seemed too lean on top and when adjusting for better top end performance they idled too rich. RA Brit needles work very well even with stock U20. I used to hit that flat spot right around 5500K rpm. Oem N17 and N25 needles are just too lean.

[Gregs672000]

As noted, you're gonna have to work through each system, starting with the basics. Unless you have a wide band air/fuel meter installed, your spark plugs are your best indicator about how the engine is running and where. So, start with a clean new set of NGK BPR6ES plugs, properly gapped for the EI. Go for a drive, noting exactly what it does and where (like you have). Pull each plug and see what they look like... black, tan or white (rich, right, lean). There is a little different feel to an engine running lean vs rich... lean sounds different, higher pitch, like you're saying "yaaaaaa", the engine sounds hesitant and starving; rich is more flat and throaty, kinda "Oooooooo", like it's drowning. Go for a drive where you can HOLD the engine at the rpm where it runs poorly for a length of time, then take it out of gear without letting the engine rpms drop, turn off the key/ignition (don't lock your ignition if yours has that feature!), shut the throttles, coast to the side of the road to a pre-planned, safe place and pull the plugs (bring cloth gloves, they are hot!) and see what they say.. rich or lean or right. That will tell you some of what is going on at that rpm range.

We're going to assume that the EI is working right, but let's confirm total advance with a timing light, best done with a dial back timing light, but it's more important that you just confirm it's advancing about as expected.

After that, we can make some crude evaluation about cam timing and can probably identify a cam that is way off. Understand that using the factory marks on the crank to determine true top dead center is a best guess, but carefully turn the engine to TDC on cylinder #1 (aline your crank timing mark with the pointer as absolutely as close as you can, easiest with the spark plugs out), pull the valve cover off and confirm the lobes on #1 are pointing upward, then look at the position of the locating dowel or pin on the cam gear and note how it lines up with the little arrow on the #1 cam tower. It should line up. If it is clearly way off one side or the other, your cam may be way out of time due to a very stretched chain, incorrect assembly initially, changes to cylinder head height without shimming the towers, or other changes. Again, understand that the marks are crude, and as JT and others have noted, a few degrees of cam timing can change how an engine runs. However, if it's way off you should be able to tell. You can take pics and post them if you like.
Hope that helps.

[DivinDave]

Mine did that and drove me crazy chasing all sorts of possible issues. After going thru carbs, fuel pump, cam and ignition settings put a new coil on it and problem fixed. Moral, start simple work towards complex.

[Gregs672000]

+1, sage advice...

[Daniel]

thanks to you all!
The EI I got came with all related parts and pieces, coil / cap / wires. I ordered the complete kit and installed it with Tom on the phone with me. I'm leaning toward the needles as the problem. I'll attend the carb tuning seminar at Shasta and let you guys drive it (if you want) to see what you think, real world. Thanks again!
See you there!

[AC77]

thanks to you all!
The EI I got came with all related parts and pieces, coil / cap / wires. I ordered the complete kit and installed it with Tom on the phone with me. I'm leaning toward the needles as the problem. I'll attend the carb tuning seminar at Shasta and let you guys drive it (if you want) to see what you think, real world. Thanks again!
See you there!

I know this is way old, but I'm curious what the problem was and how you fixed it.

[Daniel]

So... it turns out that I had overlooked the adjustment of the throttle cable! I took it to Dave's place, a local roadster guru, and the first thing he asked me to do was push the pedal to the metal while he observed under the hood. He determined that it was only getting about 80% full throttle, Oops. He then adjusted the carb mixtures and idle. It now runs great and I'm very happy with the results. I will need rebuilds at some time in the future, as the shafts are worn and allowing air to bleed in at times. Maybe this winter

[AC77]

Ah, glad it turned out to be a quick and inexpensive fix. Those are the nice ones.

[Gregs672000]

Yep, start with the basics! Well done Dave.