79 70hp runs with carbs covered by hand

[Quintin66]

Howdy Gents...
1979 70hp... All new fuel lines in and out, new fuel pump. Freshly meticulously rebuilt carbs, 140# compression on all cylinders. Spark on all cylinders.
To get it to start I have to push the throttle full, then, after cranking for a second hit the choke,...as she catches on and begins to rev up I dethrottle to about 1200 RPM...any lower and she dies. I can cover the lower carb and she will stumble to a lower RPM, but still run. I can cover the middle carb and there's no effect at all. If I get my palm anywhere near the top carb it dies instantly.
.... I can see the reeds... Got the carbs off right now, they all APPEAR to be sealing.
Any thoughts???

 

[jbuote]

Still pretty new, and others will be of more detailed help I'm sure, but...

How did you test your spark?

​Maybe try a cylinder drop test to confirm all cylinders are firing.

​Your test of hand over carb says you can choke out the top carb and it dies, but the other 2 have less or no effect..
​Wrong mixture maybe on the lower carb, and I have to wonder if the middle is firing at all...

My newbie 2 cents... LOL

 

[Quintin66]

I didn't check spark strength, just watched spark on all the plugs when I had them grounded for the compression test. They seemed nice and bright.
I did do a search for Reed problems on j&e engines, seems that a gasket getting sucked out can cause what looks like reeds being bent, not saying that this is it, but I may pull the intake and see. I will get a spark tester also asap. I have never ran into this matter and I am willing to concede, but it seems as though if the cylinder is not firing, wouldn't it still draw the same air as the firing one?

 

[jbuote]

You definitely want to test your spark with an open air gap tester..
​Set it to 7/16" (I believe is correct).
​This gap simulates the compression in the cylinder. If it can jump the gap, then it will spark the .030 (or whatever the proper gap is) on your plug.
​If all cylinders can jump the gap, then ignition system is good. If one cylinder doesn't jump that gap, then ignition system troubleshooting is in order..

​Grounding the plug and watching the spark on the plug effectively tells you nothing about the strength and health of your ignition system.

​AS for drawing the same air...
​Yes it would draw the same air. But covering that carb if the cylinder is not firing will not affect how the engine runs. You're not affecting the air/fuel mix on a running cylinder.. I
​The engine at that point is running on the other 2 carbs..
​In theory, you could even remove that carb, leave the other 2 and it would still run.. LOL
​(Ok, exaggeration but I think you get what I mean right?)

Again, I'm still new, but I'll do my best and will defer to others as and when necessary..

 

[Quintin66]

Bein' a newby is sometimes a very good thing. It gives fresh eyes to some, like me, who've been wrenchin' on stuff more than 40 years. One of the main reasons I was critical of the airflow was because on the top cylinder I could feel the air moving when my hand was still 2" from the carb, the others ya can't even feel anything when 1/4" away. Almost like the air is going in AND out so fast there's no discernable vacuum effect.

 

[jbuote]

Ahh...
​I thought you were asking about why it had no effect, but now I get it.. LOL

​With 140 compression across the board, it isn't lack of compression causing lower airflow, so yeah.. I guess Reed Valves are a possibility..

​You said the reeds "APPEARED" closed, so my "Newbie" eyes would wonder if the carb is tight against the intake and the intake is tight..
​Gaskets for both (if and as required) are in place and intact so as not to cause an air leak pre-carb. That might lessen what you feel at the throat.
​I guess I'd be looking for any possible reason for air to make it's way into the crankcase OTHER than through the carb on that cylinder. ​Not sure what that might be, but a thought.. haha..

​I'll concede that I'm not so clear on reeds, other than the basics of what they are for, and how they work, so maybe pulling the intake to further inspect isn't a bad idea.. :noidea:

To get it to start I have to push the throttle full, then, after cranking for a second hit the choke,...as she catches on and begins to rev up I dethrottle to about 1200 RPM...

​Seems a bit backwards to me....
​I was taught that you pump primer in fuel line, put remote in fast idle (or whatever start position) then hold choke while cranking. When it catches, release choke and bump it as necessary to keep running.
​Not that it has anything to do with the rough running, but the throttle full to start then drop it back is concerning..

Hope it helps somewhat.. LOL

 

[Quintin66]

Yeah, on the throttle position... If ya go by the book, she'll just crank forever. Gotta throw it all the way forward,...then when it starts pull back fast or she'll push 10,000rpm before you blink an eye.

 

[flyingscott]

Is this motor new to you? Has it ever run right for you? Have you done a link and sync? Are all the carb butterflies in the same position?

 

[racerone]

Has this motor sat for any length of time ??-----Did you remove the high speed jets that are screwed into the carburetor bowl to clean them ?