As you know, I have discovered the problem...pre-ignition. What was troubling is why everything got so far off from my initial efforts. Maybe I didn't bolt it all down.
I do have the light putt...putt...type backfire at idle. My other one does the same thing. For me, no valve adjustment has solved this putt...putt. I've tried setting the valves at .014, .015, and .016. So, at this point, this type of backfire doesn't really bother me. The engine runs fine otherwise.
This other backfire on Whitey that I am dealing with is the type that happens after you let off the accelerator. Not super loud, but still a "Pop!" Which tells me I still have some work to do. I may have eliminated it with my last static adjustment, but I'm not sure. I plan to hook up the vacuum gauge and dwell this weekend.
I've been following you on this Hawk. I need a better understanding of how the vac and dwell do their stuff. Vids just don't stick with me-gotta be there when it's happening. How bout I show up at your place tomorrow, say noonish??
OD MULE MC51986 DOD 01-52 RED MULE '50 CJ-3A "coming soon to a trail near you"!! We have Miles to Jeep before we Sleep!
Been following Hawky also. Timing can do just what he is describing. The bang in exhaust is caused by two things, a cylinder firing with a open exhaust valve ( or burned valve with a v in it), or too rich a mixture that is building up excess fuel in the muffler. A carb that is worn and leaking fuel past the butterfly when closed will cause this. Like when going down hill with your foot off the gas. I know about this stuff. . A good one: I had a '76 Ford F 600 shear it's distributor gear drive rollpin going down a hill on the highway. It ran on propane. Ka-Boom. Blew open my brand new 80.00 muffler from fuel build up and detonation due to firing at the wrong time. Engine died, rolled to a stop on the bridge in the bottom of the valley going into Deadwood. When I got there to try and fix it, it started raining cats and dogs. I figured the points had worn and closed. I removed the cap and looked. Nope, points were fine, but I could turn the rotor anywhere I wanted to point it!!!!!!!!! New roll pin and she started right up. You did have to find TDC on one and install it so the rotor pointed to # 1. It was then that I noticed the loud exhaust------------ Oilly
Summary: How can these carbs get away with being so small?
So I'm blastin' up the hill the other day. Say 4 miles WOT 1000' climb going 30-50 mph. (winging along pretty good.) I scan the instrumentation panel and I notice I'm pullin' 2" of vacuum with the throttle wide open while at high RPM. My first thought is that, "well I need a bigger carb on this bucket!"
So I start thinking. (Yeah I know, bad idea.)
My 170 cubic inch engine turns about the same RPM as a lawn mower and has about a 1.25" venturi. A 13 cubic inch lawn mower might have a .58" venturi. That's close to 1/2 the size of my carb for an engine that is 10x smaller?!
A low/no performance stock 1960s VW beetle with a 1.3 liter engine (close to half of my studebaker 2.8) ran a 30mm (1.18") carburetor! I don't think a VW ran really high RPM either. What? 4k RPM at 80 mph if you could get a long enough downhill?
OK, what about modern throttle body stuff? A BMW 2.8 liter has a stock 2.5" or so throttle body. Sure it'll run a lot more RPM, but still, that's 2x the intake diameter. A bigger, 242 cubic inch jeep TJ has a 60mm (also about 2.5") throttle body. It won't pull much more RPM than the studebaker. but still has 100% more intake diameter for 40% more displacement.
So why are these carbs so small? Is it a sacrifice in top end performance for great low RPM drivability because of high air velocity in the carb? Maybe I should get the dual carb manifold for my studebaker, eh?
1947 CJ2a with a studebaker Champion 6, PTO winch, Rear locker front LSD.
Post by Scoutpilot on Aug 15, 2018 11:11:47 GMT -5
When the L134 was designed in the mid-thirties, paved roads weren't as common as they are today. Speed limits were more like "At your own risk". Most vehicles could only travel at 45-55 without throwing their riders out. The weather made many roads impassable. Who needed a bigger carb?
I'm no mechanical engineer or anything close, but Sir Rudy raised an interesting point 👆, Why do older engines have smaller carbs., and got me to thinking 🤔 I believe it's in the fact the old long stroke flatheads are an "Under Squair" engine, or the "Stroke" is "Longer" than the "Diamiter" of the bore. A modern engine is "Over Squiar" or the "Bore" is bigger in "Diamiter" than the "Stroke" is long. Different air velocities I guess. Here is a link on topic!...
After reading the article, it seems to my thinking that the over-square came about in response to a growing need for more powerful engines. Increasing the bore answers the call for that. Increasing cylinder volume calls for more fuel in the mix, faster.
Post by Scoutpilot on Sept 9, 2018 14:05:40 GMT -5
When you get your kit, there will be a sheet on the YS637. I have not been able to acquire yet, the full spec sheet for the YS950. I'll be happy to assist you in the rebuild. It is fairly straightforward if you pay attention to the correct metering rod and the correct diaphragm spring arrangement. Call me if you need me.