I’m chasing a rough idle. Carbs rebuilt by Joe C. EDIS by Ray L (who has been very helpful in checking out that ignition system, which appears to be ok). Engine starts easily using choke, after warm-up engine responds well when throttle is snapped open, returns to idle without stumble or misfire. Car is not road ready so all this is car running in garage.
I received the carbs back from Joe C with the jets set 0.125 down from the bridge (Joe C adjustable jets) and Joe has been very helpful also with things to check. No problems found so far with the carbs…HOWEVER…the rear carb requires the jet adjusted way further down than the front carb to get it to idle at its best! Haven’t measured how far down it is but it’s quite obvious just looking at it. Some plugs look generally rich/sooty.
The car has it’s secondary throttles and plates removed and all holes plugged.
Question:
Does anyone have an idea where their jets are set relative to the bridge?
Any ideas on why the rough idle and why the rear carb appears to require setting on the very rich side (I haven’t taken the float bowls off to check float levels yet.
When mine has had rough idle it has been because of vacuum leaks, sticking float bowl valve or sinking float. I also had one float pontoon not secured very well to the metal on one of those solid foam type floats and it was dragging on the side of the brass plug some times. Since yours are just back from Joe Curto I would first suspect vacuum leak. My car has the cross-over pipe at the rear of the engine. A few years ago I found the gasket deteriorated where the cross-over mounts to the top of the rear exhaust manifold. The vacuum leak there stumped me for awhile.
Les
I have the same set-up on my 70. Follow up on checking for vacuum leaks as already stated. I keep fuel level on the low side with the new style floats. I have found that when tuned correctly jets are not at the same height for the two carbs. Mine are set using Innovate onboard air/fuel ratio meter.
Glenn
Swap the plugs/wires and see if the symptoms move with the parts. Then swap carbs and assuming that alters the rich cylinders try float bowls swap with their float and needle valve, plugs, wires etc. Have you got a fuel pressure meter and decent tee piece?
A common source of a vacuum leak on Strombergs is the bypass valve. If the diaphragm in it is torn, which is very common, it is easy to replace. See Burlin or SNG for a kit.
OK I took the bait. Just went and took the tops of the stroms off to do some measurements.
Mine have been set perfectly using O2 sensors to set A/F ratios under load. Joe Curto said to start @ .125, richer than originally for unleaded/ethanol gas. I know from past experience if set too rich I kill the O2 sensors, current ones have been in there a couple of years plus.
Using needle B1E as per Joe. Front carb set @.1385 Back Carb set @.1720. I also keep float level lower than spec with new style floats .
Glenn
Forgot to add.
Brass collar of needle should be flush with piston, use straight edge to check.
Also piston must drop quickly with a thunk. Can be adjusted with even torque of top bell screws.
Glenn
Thanks to all for the replies and info. Apologies for not getting back earlier, been out of town.
I’m surprised to learn that it’s not unusual to have the rear carb apparently richer, and quite a bit richer, than the other. This on apparently identical carbs!?
Looks like I need to remove the carbs and check float levels, just to be sure, something I’ve been reluctant to do with brand new rebuilds.
Vacuum leaks… seems a logical path to follow but as yet I’ve found nothing on that score, but will check again.
Pete,
I don’t have a fuel pressure meter and the car is running with the same pump as was used with the Weber carbs. I’ve just received a new SU pump from SNG because I thought perhaps there is too much fuel delivery. Will see how that works out. However, I would have thought that if this was the case then it would require the carbs to be set on the lean side. Easy to 2nd guess oneself on these issues!
