7 replies to this topic

[miniGTS]

Is there a way to test or to know if timing is out of fueling is incorrect at certain revs?

Idle seems fine at just under 1000 rpm but when I take the revs up to around 2000 rpm it sounds like it's running on 3 cylinders but higher revs seems fine.

It's electronic ignition at 12 degrees on idle. Carb is twin hs2 with GY needles and red spring.

Any thoughts on what I should check or do to get it running smoother at around 2000 rpm?

At that rpm I'd be doing around 60km/h and it drives OK just sounds a bit off.

[timmy850]

The best way is:
Check the timing at the problem rpm using a timing light
Check the air fuel ratio using a sensor

From there once you know what the problem is (or rule out what it isn’t) you’ll be able to adjust it back to the right spec for your engine

You can mess around by adding or subtracting timing, but it changes the timing everywhere and may cause other issues.
You can also mess around by pulling out the choke to see if it needs to be richer or leaner at that point, but proper measurement and adjustment will be needed to make it run properly across the rpm and load range

[68+86auto]

If you can find someone with one, an automotive oscilloscope can easily identify the cause.

 

 

There are some cheap Chinese USB ones (Hantek 1008C) but the software isn't great which is typical of Chinese software. Proper ones are in the $1000s of dollars.

[Steam]

There are a number of things to consider here, Twin carbs need to be balanced extremely accurately. They can mask other faults aswell. Given the rether specific rpm fault I would heck the vac advance and also bear in mind that faulty electronic modules can give all sorts of wierd faults.
If it were mine I would start by switching out the module for points and lock the vac advance to eliminate them. Then with the timing set to the correct figure for your engine, if the fault persists it will either be a problem with the mech advance / weights or it is fuelling.
A dyno session with an experienced operator will save heaps of time and effort.

[miniGTS]

Thanks for the feedback. Though the carbs are not perfectly synced, I noticed that the throttle linkage wasn't synced so at the rev range that was a problem, on side opened a bit before the other side. I adjusted it and seems better, though finer tuning will no doubt get it running better.

While busy in the engine bay, I noticed that when the temp gauge reached Normal, just about everything is almost too hot to touch. So carb linkages, dashpots, rocker cover are all really hot. Is that kinda normal?

[miniGTS]

I think the hotness was just because of the long idling in the garage. Took it for a 15min drive and was much cooler in the engine bay when I got back

[Lplus]

Thanks for the feedback. Though the carbs are not perfectly synced, I noticed that the throttle linkage wasn't synced so at the rev range that was a problem, on side opened a bit before the other side. I adjusted it and seems better, though finer tuning will no doubt get it running better.

While busy in the engine bay, I noticed that when the temp gauge reached Normal, just about everything is almost too hot to touch. So carb linkages, dashpots, rocker cover are all really hot. Is that kinda normal?

Yes, there's a lot of heat coming off the exhaust manifold.  Once you start to move the increased air flow will reduce the temp.  The carbs will get quite cold once the car is driving, since the pressure drop across the carb bridge involves a drop in air temperature.

[miniGTS]

Yes, the dashpots felt cold after the drive.