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Holley 1904 Carb Question

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  #31  
Old 04-30-2016, 07:46 PM
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I just tried starting my truck again. It's not hot, but not real cold either. The choke was still set to maintain idle from the last time it was running. With the accelerator partially depressed, it wouldn't start. It needed a couple of little pumps to get going. It's like it needed the little squirt of fuel from the carburetor accelerator pump to catch. Once started, I could take my foot off the accelerator. The little bit of choke was still needed, however.
 
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  #32  
Old 05-01-2016, 12:41 PM
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Something else is wrong. I agree with Ross. You should not have to pump the gas when hot. Pumping the gas may flood a hot engine causing it not to start.

I would suggest that you also need to get the phenolic spacer installed. Then I would suggest that you go back to old school testing with a vacuum gauge (they are not expensive if you don't have one) and use this chart to diagnose any problems.



Coils are also known to have problems when hot.

Let us know how you do.
 
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  #33  
Old 05-01-2016, 02:03 PM
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Originally Posted by 52 USCG Panel View Post
There is only one mixture adjustment screw on my carb. I turned it all the way in and then backed it out a complete turn. My engine acts like there is no stop on the throttle. If the throttle is not at least partially depressed, it's like the engine can't get any fuel.
Idle mixture adjustment of 1 to 1.5 turns say, is just a ballpark setting so it will run, each engine is going to be a little different. Maybe you know this, but some folks are sometimes under the impression that's all there is to it.

It needs to be leaned about as far as possible, while still maintaining a smooth idle. And the float level prior to that - the fuel level itself really - is going to play into the best setting as well, it's not SUPER critical but it is definitely important, and there's a safety angle too.

The mixture is best set with the engine fully warmed up, and while the air cleaner (Oil bath?) installed. One of the reasons for that is because all of that vaporised or boiling fuel fumes are now part of the idle circuit and this needs to be compensated for.

Good point about failure mode of ignition coil. Ignition condensers can do that too.
 
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  #34  
Old 05-01-2016, 07:47 PM
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Thanks for your continued patience and good advice. After spending a little more time with my truck today, I think I have the symptoms a little more refined.

With about 25% choke, the engine starts and runs great. Hot starts are not a problem and no pumping or throttle are required. A cold start this morning (39F) at this choke setting was not a problem either, but I did need some throttle and a couple of small pumps.

With no choke, some throttle and pumping are always required for hot or cold starts.

The engine will run with the choke all the way open as long as it has some throttle. If the throttle is backed off slowly, remarkably slow idle speeds can be achieved--almost like old time "hit and miss" farm engines.

Tomorrow I hope to have a knowledgeable friend check the timing, dwell, carb adjustment and linkage. I will also look into what happened to my phenolic spacer order and pick up a vacuum gage. Can vacuum be measured from the intake manifold? I have a port there for my wipers that is temporarily capped off.
 
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  #35  
Old 05-01-2016, 08:07 PM
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For the holey 847 on the 226, I started I think one turn out, then started it and got it warm. Then ran the mix screw in until it sagged then backed it out to level off. Then I backed it out until it sagged then back in until it leveled off. I kept track of the screw turns each way and set it dead middle of those two points. Runs perfect.....hits on the first touch of the starter either cold or hot. When you adjust the idle speed, you have to go back and do it again, to have just the right hum and carb performance. I would assume the 1904 would be similar.

JB
 
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  #36  
Old 05-01-2016, 08:31 PM
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Originally Posted by 52 USCG Panel View Post
...
The engine will run with the choke all the way open as long as it has some throttle. If the throttle is backed off slowly, remarkably slow idle speeds can be achieved--almost like old time "hit and miss" farm engines.

Tomorrow I hope to have a knowledgeable friend check the timing, dwell, carb adjustment and linkage. I will also look into what happened to my phenolic spacer order and pick up a vacuum gage. Can vacuum be measured from the intake manifold? I have a port there for my wipers that is temporarily capped off.
It sounds like you simply have the idle speed screw set for too low an idle. Having a faster idle won't hurt a thing while you dial in the mixture screw setting. You can lower it after that.
 
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  #37  
Old 05-01-2016, 08:48 PM
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It sounds like your idle mixture is set too lean. I typically set the idle adjustment by ear, but the best results are by using a vacuum gauge. Yes, the vacuum wiper port is where you want to connect your gauge. You set the idle speed down as low as the engine will run, then adjust the idle mixture to attain the highest vacuum reading. Then you speed the idle back up to a reasonable speed, around 500 to 600 r.p.m.
 
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  #38  
Old 05-01-2016, 10:20 PM
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Ross, the spring loaded screw (Pictured) that I assume controls idle speed seems rather to influence the angle of the choke plate then to independently control the throttle. As the screw is tightened, the idle speeds up but the choke also closes. Tightening the screw also takes away my ability to open the choke fully with the hand control. As the screw is loosened, the choke opens, the idle slows down, and the ability to control the choke is restored to the hand control.

I'm thinking that something may be wrong with the way the linkage is set up. The carb is a junk yard find, and I'm not even sure what it came off of. Someone else "harvested" it for me. I seem to have trouble with the simplest things. Sorry.





 
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  #39  
Old 05-01-2016, 10:54 PM
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Make sure the butterfly is completely closed, no light hardly let through even, at idle. The idea is only the idle circuit itself is in play at idle RPM. Only a tiny stream of fuel is necessary, that's what the idle mixture screw is all about. A little back and forth between mixture screw and RPM screw and it will be purring.
 
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  #40  
Old 05-01-2016, 11:43 PM
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I disagree, Ted. The throttle plate needs to be open slightly at idle. The idle fuel system provides fuel, no air to speak of.

USCG, if adjusting the idle speed moves the choke, then the choke cable isn't holding the choke linkage fully open. There must be some slack in it. On the V8 carbs there is a spring-loaded detent to hold the choke in the open position, I don't see one in the diagrams for your carb.
 
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  #41  
Old 05-02-2016, 01:43 AM
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"Slightly", yes. What I meant by that, it's possible to mis-adjust the throttle plates partially open, and have the transition circuit dumping fuel, while the idle circuit is leaned out.
 
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  #42  
Old 05-02-2016, 05:23 PM
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My appointment with my mechanic friend was postponed. The people at Classic In-lines (my carb spacer order) were not answering their phone and I had to settle for another e-mail message. The auto parts store where I do business did not have a vacuum gauge but ended up giving me an old used one they had laying around. It ended up not working, however--the dial wouldn't move off of zero. So that's how my truck to do list for today turned out.

On a more positive note, I ended up fooling around some more with the idle speed adjustment screw and the choke wire and cable attachment. After re-positioning the cable in its holder and the wire's attachment to the choke plate, the throttle now--miraculously--moves independently of the choke plate. I can now speed up the idle without opening the choke. In short, everything seems to be working now like it's supposed to. Imagine that!

I still want to finish up the tune-up and test the vacuum. I will also track down a phenolic carb spacer. Thanks everyone for seeing me through yet another little crisis on my journey to getting my Dad's old truck back on the road and looking presentable.
 
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  #43  
Old 05-06-2016, 07:39 PM
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My truck is running and starting, and I feel ready now to turn the page on the carb issues I was experiencing. My friend the mechanic, as it turned out, didn't have a timing light for a 6 volt system. I was, however, able to get a working vacuum gauge and used it and some trial and error to dial in the timing a little.

The vacuum at a moderately fast idle is about 17 inches--at a slow idle it is more like 14 or 15 inches. I tried advancing the timing a little to boost the vacuum. I was able to get higher readings, but the engine did not run or start properly with the timing advanced far enough to achieve these higher (normal) readings.

The vacuum gauge needle is steady at idle with just a very slight tremor. When the throttle is opened and closed, the needle rapidly swings up and down going well beyond 20 and down probably to 0. Thanks Pete for the very helpful little vacuum diagnosis chart. My truck uses about a quart of oil every 100 miles, and with the vacuum going to zero upon acceleration, I guess it would be fair to conclude that my engine is pretty much worn out. Hopefully though it will keep running for awhile.

I determined that my old vacuum advance was working, and I'm still trying to track down the carb spacer that was recommended. Next up is to finish the rear wheel tub project started this winter (compatibility thread).
 
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  #44  
Old 05-06-2016, 08:09 PM
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First thing, unless the vacuum gauge has been calibrated recently, I'd look at its readings as "relative". I wouldn't feel bad about 17 at idle, nor would the drop to zero on blipping the throttle (see the second gauge on Pete's chart).

Unless your truck looks like a mosquito fogger going down the road, 100 miles per quart is more likely from a leak than a worn engine. A really worn out engine with no leaks will get 500 miles/qt and will have a very blue exhaust, the kind people pull alongside and shake their fists at you...
 
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Old 05-06-2016, 08:50 PM
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So far no fists or negative comments. I've tried on occasion to make it smoke by tromping on the gas--coasting for awhile--and then tromping on it again. I've had cars leave a very visible cloud in the rear view mirror given this treatment. My truck may be smoking, but not so much that I can see it from the drivers seat. On thing that it does do, however, is leave a pretty substantial black patch of soot spreading back and out from the tail pipe when the engine is raced in the driveway. The breather pipe and oil filler cap also smoke pretty good.

The vacuum gauge was new. Would it still need to be calabrated?
 
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