I am working on tuning my carbs. Everything seems to be within 1/2 a unit on the intake meter. Here's the wonky bit Sometimes it idles at 2000 (after I rev it a bit). I use clutch resistance to drop it and then it idles at 900 for a time (few minutes usually) then slows down and dies. Throttle linkages are all good. No binding. Other times it idles fine. Any thoughts? Thanks Sent from my iPhone using Tapatalk
Distributors/ignition advance would be my guess. Had something similar on an engine years ago, sticky advance mechanism in the distributor & the ignition stays advanced after you rev it & the revs stayed high.
Much too high (should be more like 3~4 Kg/hr/barrel depending on the idle ignition timing setting). When you are at 900 RPM idle and 6 Kg/hr/barrel = some of the cylinders aren't actually running. When you rev the engine, these cylinders can start working, as at higher airflow, a mis-adjusted idle mixture is less of a problem.
6 too high Make sure the little ball joints in the linkage have some slop in them, dont screw the end cap all the way so its touching the ball.
That's confusing. How do you lower the number? Is this a timing issue? Seems like 900rpm and the corresponding air flow is a mechanical thing. (That engine at x rpm is simply going to draw x amount of air. ) Sent from my iPhone using Tapatalk
If all the cylinders are working at idle, then, yes, this is true, but the airflow in each barrel will be 3~4 Kg/hr. If a cylinder, or some cylinders, are not actually contributing at idle, then the airflow has to be increased to keep the the RPM the same. One way to determine if a cylinder is working or not at idle is to just be at idle and then close the mixture screw -- if the cylinder was working at idle, the RPM should drop when you close the mixture screw. Alternatively, you can unplug each spark plug at idle and see if the RPM drops (and the sound should change), but you'd want to be careful and not shock yourself.
Hmmm... deja vu. I wrestled with similar types of issues... tried everything with the carbs. Turned out to be an ignition problem.
Not to put too fine a point on it but you really don't want slop in the linkage at all otherwise the front and rear banks will not be synched and the engine will not make the power it could. You want to adjust the screw fittings on the end of the short linkage strut so that they just barely touch the balls but not so tight as they bind. Then insert the cotter pin through the holes that actually line up- don't adjust the screw so the holes line up as it will either be too tight or too loose. Make sure they are lubricated but not so much that they will attract and retain dirt................
I sold my 308 a while ago but those rods are in compression, and you can run it just fine without the screws even in the ball ends....
Usually is. Carb tuning is the last step in tuning yet when there is a running problem it is almost invariably the first addressed. If I tune a car completely and properly, start to finish and drive it until running and performance degrades the problem will not be the carburetors. They stay in tune far beyond any other aspect.
I had a Daytona come in a while back to fix the carbs. It had just had a major carb overhaul and ran like crap. I pointed out the distributor caps and valve covers had not been off since Christ was a Corporal and the dwell meter told us the motor was barely capable of running but the owner insisted it was a carb problem. I just sent it away. Time is something I cant afford to waste.
Okay I stopped messing with the carbs and looked to the distributors. Pulled the rear one and did a little r&r on it. Rinsed out the old hard grease and replaced it with shiny new grease. As I was looking over the unit (it only has r1) the advance mechanism seems to have just one way to adjust it. If I am reading this right you add or remove springs from one or more of the 4 little tensioners (for lack of a better term). Only one of the four has a spring in this unit. Is that right? On reassembly the car seems to be wanting to run better. So I am going to do the forward disty in a day or so. The carbs are pulling 3.5-4-5. So that is far closer to what it should be. After the next one I will return to the carbs to balance them and whatnot. Thanks for the input. It has been a lot of help and I am looking forward to actually having a car that starts cold and idles nicely when warm. Image Unavailable, Please Login Image Unavailable, Please Login
The sleeves in all four advance weight bores should have springs, and also usually have shim spring preload washers. The springs will be different lengths depending on which location they are in. You have to run both distributors on a distributor machine in order to get the advance curves, dwell, and rotor to cap phasing correct. They have to match each other and the factory specified advance curve. You can spend the better part of a day rebuilding two distributors and setting them up correctly. and that is if you have all of the correct tools and multiple springs and shims. Not to mention that the distributors can have significant wear in the advance mechanism that will need repair. They are like swiss watches and need proper attention if they are going to function as designed. Are you sure that your valve clearances, and cam timing are good? As Rifledriver said, carburation is the last thing that you do during a service. Well, distributors are the second to last thing that you do during an engine service. It seems like you are doing things backwards.
Yeah that doesn't sound like good news. If it advances and retards correctly is that okay to leave as is? The one with the spring has the paint marks... as if someone on a bench machine tuned it. This could explain why it gets stuck at 2000 rpm when warm at times. One spring couldn't contend with the old grease. I did the valve clearances two years ago when I replaced my cam pulleys. Cam timing is beyond me at the moment but I did set it to where is was when I started. I didn't look at the distributors because the PO said they had been tuned on a bench.
The yellow paint marks indicate that someone tried to keep the orientation of upper/lower and weight of the distributor in the a same place as before it was disassembled. The distributors must still be run on a machine to make sure that they are synchronized and the advance curves are correct.
