Coolerman
SILVER Star
So what were the other cylinder compression numbers for comparision?
Valves out of wack?
- Thread starter CruisinMT
- Start date
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So what were the other cylinder compression numbers for comparision?
THAT sucks for a recently rebuilt engine. A burned or stuck valve could give you that and your vacuum findings.
- Thread starter
- #25
I've got it running pretty good now. I'll put new plugs in it. Does anyone else have to run with the choke pulled about 1/8 of the way out? I've adjusted everything on my carb and have done a rebuild. I believe its an aisin sd-40 single barrel. I've been running it like that for about a year. just kinda sucks i have to choke it to get it started then fiddle until i find the sweet spot again. I don't have the coin or time for a jim C rebuild nor a weber with adapter plate. It's the little things that bug the hell outta me.
If you have to close the choke in order to get an engine to run properly you are compensating for too little fuel, based on too small of a primary fuel jet, or a vacuum leak someplace on the engine.
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- #27
I dont think i have a vacuum leak nothing shows up on my vacuum gauge wihich is set at about 22 inches and is quite steady now. I bought the carb from Mark at Marks Offroad about a year and a couple months ago. Hwere do I find a larger primary jet? Is this caused by the difference in elevation from sea level where it came from to 3000 ft above SL?
Well, since you mention it, it's interesting that I have to do exactly that (pull the choke 1/8 to get it to run it's best) on my F135 with SD50 carb. I've searched hard and unsuccessfully for a vacuum leak, too, but I guess I could be missing something. I've been contemplating rejetting, but it seems very odd that at elevation (I'm at 5000 feet) the standard jet would be too small.
BTW, my vacuum gauge is nice and steady. It's only at 17 inches at idle, but I live higher than you do....
BTW, my vacuum gauge is nice and steady. It's only at 17 inches at idle, but I live higher than you do....
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- #29
Well, since you mention it, it's interesting that I have to do exactly that (pull the choke 1/8 to get it to run it's best) on my F135 with SD50 carb.
BTW, my vacuum gauge is nice and steady. It's only at 17 inches at idle, but I live higher than you do....
My gauge actually reads 19 inches but I compensated for elevation in my post. Yeah I don't get it, I'm not muc for Carb knowledge maybe someone else with more knowledge will chime in.
Well, since you mention it, it's interesting that I have to do exactly that (pull the choke 1/8 to get it to run it's best) on my F135 with SD50 carb. I've searched hard and unsuccessfully for a vacuum leak, too, but I guess I could be missing something. I've been contemplating rejetting, but it seems very odd that at elevation (I'm at 5000 feet) the standard jet would be too small.
BTW, my vacuum gauge is nice and steady. It's only at 17 inches at idle, but I live higher than you do....
You either have too small of a fuel metering orifice, creating a lean condition or are allowing un-metered air into the engine, again, creating a lean condition.
If you have to provide and enriched fuel mixture to make your engine run better by restricting the air flow via actuation of the choke mechanism, then you have a lean running situation when the engine is at proper operating temperature.
The carburetor cannot be tuned correctly if actuation of the choke is required to make the engine operate "better".
I would start with the next larger primary jet.
This is precisely the conclusion I've come to in my case (there are no other reasons). I just have been compensating until the weather warmed up, the snow melted, and I have had time to fiddle with it.
But it still strikes me as strange.
I would talk with one of the carburetor guys out here and see if they have or will sell you one. You will likely have to remove your jet to get the number off of it so that they could look in their inventory and see if they have one larger.
I dont know about your carb, but on my fathers 2f carb. when you pull the bowl plugs the extra set of jets were in the plugs. Diffrent sizes for elevation tuning.
The SD50s have a very different system from the 2F, 1979fj40.
There are 3 jets from what I can tell. Low speed jet, metering rod jet, and the accelerator pump jet.
The metering rod jet is the high speed system.
The SD50s came with 2 metering rods: the standard and the "O/S", which is kept in a spare compartment within the body of the carb. The O/S rod, being oversized, reduces fuel flow for when lean conditions are desirable, such as at altitude, and I think that's really the only adjustment.
(actually, Mark Algazy I think posted up a picture of 5 or so different metering rods he's come across)
The thing is, the O/S rod is often gone from these carbs (not that I would want that). The rod that I have appears to be the skinnier standard rod. Maybe there's a bigger metering rod jet available, too, but I haven't read mention of it in my manuals.
There are 3 jets from what I can tell. Low speed jet, metering rod jet, and the accelerator pump jet.
The metering rod jet is the high speed system.
The SD50s came with 2 metering rods: the standard and the "O/S", which is kept in a spare compartment within the body of the carb. The O/S rod, being oversized, reduces fuel flow for when lean conditions are desirable, such as at altitude, and I think that's really the only adjustment.
(actually, Mark Algazy I think posted up a picture of 5 or so different metering rods he's come across)
The thing is, the O/S rod is often gone from these carbs (not that I would want that). The rod that I have appears to be the skinnier standard rod. Maybe there's a bigger metering rod jet available, too, but I haven't read mention of it in my manuals.
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