Rebuilt 40hp not staying running (during break in)

[KingAir42]

I think I may have already damaged my rebuilt 40 horse. They say during the break in to not shut off the engine for anything, other than a potential fire hazard or something. My engine had started and died about 5 times already.

The engine started (it was slow to start, but it started). It revved fine, but really would not idle. It took forever to restart it, and once it did it would run for near 10 seconds with my foot holding revs, then it cut out and died.

I only had the engine apart for one month to rebuild it. Before that everything ran perfectly well. I have a restored 4r5 fat cap distributor. My fuel pump is from sparkworks and works flawlessly.

I have a spare restored 28 pict carb which did the same thing. That carb does not have the fuel shut off solenoid, instead it has some sort of delete screw. The other 28 pict (my current driver) has the solenoid, but I think it went bad because it does not make a clicking sound. It worked perfectly well a month ago before I “rebuilt” my engine.

This is my first time rebuilding and I am sorta nervous that I fucked up something major, somehow.
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A stitch in time saves nine

[supercub]

I wouldn't worry too much about damaging the new engine running it for 10 seconds a few times. That said I'd definitely double check everything fuel/ignition-wise before starting it anymore. You said it ran fine before you rebuilt it. Was the distributor restored before or during the rebuild? Did you rebuild the carb or just take it off and store it? Is it the same fuel pump from before?

Did it backfire or pop or make any other "bad" sounding noises or did it just sputter out? Black smoke out the exhaust?

I'd start with the basics. Point gap, timing, firing order, everything else connected right. Check the valve lash adjustment.

Take off the air cleaner and pull the throttle a couple times to see if gas come out the discharge nozzle to ensure there is fuel getting to the carb.

It may sound rudimentary but is there gas in the tank and nothing left crimping off the fuel line or some other silly "gotcha" like that. I've definitely been guilty of missing some seemingly obvious little things like that when doing a big job.

All that said, I would be very surprised if that little bit of run time actually damaged anything internally.

[KingAir42]

[rcooled]

[KingAir42]

That was it. Left side intake was not fully tight. I was concerned about stripping it, so I kept it mild on the tightness. Guess that didn’t work out very well. I also changed the fuel solenoid shut off valve too. Just finished the 20 minute break in and drained the oil. Tomorrow I’ll adjust the valves and take it for a ride!
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A stitch in time saves nine

[rcooled]

[KingAir42]

Yes, Thankyou
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A stitch in time saves nine

[zerotofifty]

I dont think any harm was done to your motor by the stalling and restart. Dont worry about it. Recheck the valve lash just to be sure and fire her up again.
Special break-in oil is an added insurance for good life. Use break in oil

Check the oil level frequently at first, as an new engine can burn a lot of oil if rings take a while to seal. A friend of mine had an engine that ran out of oil even though it was brand new rebuild, It burnt oil the first 100 miles or so, and he didnt check the oil level. Make sure to monitor the oil level frequent like at first

I like to do an early oil change on a rebuild and always run magnets on the oil sump late to collect ferrous wear particles. This is most important on an oil filterless engine such as on our Bugs. Also recheck valve lash soon for the first time after a rebuild.

But that start stop you have, no worries, Get break-in oil if you aint got it already and place some magnets ion the sump plate under the screen

Brad Penn makes some good high zinc oil for our classic Bugs,and offers a special Break-in oil too.


Have fun with your new motor. By the way, what motor you have now? Tell us about it!!! Photios please!!!
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Sorry About That Chief.

Give Peace a Chance.

Words to live by.

[KingAir42]

I will post some pics soon. It’s a 40 hp, actually it’s the original engine to the car. I got the bug on the road in 2023, after I put it back to basically stock form.
I had the engine rebuilt by local builder.

He used the slip in 83mm’s and made it a 1385cc. I ran that engine daily and racked up about 13k miles before I pulled it out for this current rebuild. It was developing too much end play. I am pretty confident that was my fault. I had the clutch not properly adjusted for way too many miles. Also the throw out bearing was falling off, so that wore away at the thrust bearing since it was making contact all the time.

This time I decided to go back with the 77’s bringing it back to a 1200. It’s a stale air engine but I am running a later style thermostat/flap setup, opposed to the throttle ring type. I have the throttle ring setup I recently purchased but that will go on my other spare standby 40hp. I just picked up this other engine a few days ago as a backup. It’s a really beautiful engine. It also has the stock air cleaner, just like my main engine does. The builder chose to use an aftermarket cheap fresh air 36hp style shroud, so I located an original stale air shroud. The aftermarket shroud will go into the trash. I will need to put those rings over the cylinders though, before I use that spare Engines heat as a stale air.
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A stitch in time saves nine

[KingAir42]

I am curious as to why the engine would start (slowly) and run for about 10 seconds at a steady rev, then just fall flat and die. Once I tightened the intake manifold on the 3/4 side, it started up instantly, like it always did before the rebuild.

I did do one more thing too, I removed the fuel shut off solenoid and replaced it with some fixed screw port that the other carb had in it. I determined the shut off solenoid went bad somehow during the one month rebuild because I did not hear any sort of a clicking sound when applying power to the terminal.

Just trying to learn more
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A stitch in time saves nine

[KingAir42]

Well got it running good, but I fear I did something wrong. I know a 40 horsepower is not a speed demon but this is ridiculous. 0 to 60 mph in like damn near a minute. I was reading it should be more like 25 seconds or so from 0 to 60 miles per hour. It's got to be something with the compression ratio. My first time rebuilding it and I just took off the 83 mm pistons and slapt in 77s and called it a day. Well I realize now that that was a very stupid thing to do. Live and learn the hard way I guess.
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A stitch in time saves nine

[mukluk]

Let me guess, the 77mm piston and cylinder set you used was by AA?

For some unexplained reason, when AA decided to make a P&C set for the early 40 horse they used the same pin height on the pistons as for the 36 horse, which of course is wrong for a 40 horse. The effect this has is when you assemble the engine you end up with a rather cavernous 0.090" or more deck height, netting at best a 6.5:1 compression ratio and a very lazy burn. Low compression plus a large deck equals a gutless turd of an engine.

Your choices going forward are to either embrace the suck that you currently have, tear the engine back down to a short block to get the barrels machined so as to correct the excessive deck height, tear the engine back down and swap the AA pistons out with some good OEM pistons with the correct pin height, or tear the engine back down and install a big bore 83mm P&C set (which they did make correctly).
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1960 Ragtop w/Semaphores "Inga"

[my3bugs]

sounds like a hard lesson to learn

[KingAir42]

Okay well I will tear it down. Before I do, just another stupid question but if I had low fuel pressure which I will test later would it do something similar like rob my power although the engine runs very smoothly?
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A stitch in time saves nine

[zerotofifty]

[KingAir42]

Ok, I will test it tomorrow. What happened was my carb was drowning itself with fuel. It was pouring out of the thicker vent tube from the float bowl. Out of desperation, I added two shims, and that resolved the problem.

It's hard to imagine that I could have lowered the pressure (or volume) enough to cause this problem, but maybe that's it. I will hook it up to my pressure gauge tomorrow. Worst case, I'll pull the engine and use my other standby 40 hp while I figure something out.

Mukluk, yes they are AA. I tried locating an OEM set, but no luck. I searched eBay, vwnos, etc. I tend to lean towards just throwing some 83mm back in since I can't seem to find OEM 77's.
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A stitch in time saves nine

[supercub]

That's a bummer about the poor performance on the rebuild. I have the AA piston/cylinder set in my 40hp too. I never really thought much about the performance but after you posted your dismal 0-60 time, I had to check mine out. I very unscientifically did three 0-60 pulls at different locations and got 33 sec, 36 sec, and 30 sec. This 40hp has over 110k miles on it, so I'm not surprised it's a bit slower than advertised but nowhere near as bad as what you're experiencing. I never did any machining on the barrels or case and honestly had never heard about the AA 40hp piston issues until this thread.

Have you done some hard uphill pulls and downhill coasting to help seat the rings? If the rings aren't seated yet, the compression will definitely be low leading to less power. I doubt it would be that much less though.

After hearing about the carb flooding issue with 2 different carbs I would definitely check your fuel pressure. Should be 2.5-3 psi. When you said you added 2 shims, I am assuming you meant under the needle valve in the carburetor for a total of 3? I had one carburetor that needed 2 or it would drip from the throttle shaft after shutdown. Needing three shims to stop it from flooding while running seems excessive like there's something else going on. Too high of fuel pressure could push fuel past the needle valve and flood the carb. You can add gaskets under the fuel pump to lower the pressure. I've got 3 or 4 gaskets stacked under my fuel pump because the pressure was too high.

Aside from the fuel issue, how's the ignition timing? Even a couple degrees retarded can impact performance noticeably. I guess the piston/cylinder set could be causing the low performance issue, but I'd drive it hard a bit to be sure the rings are seated decent and check the ignition timing, fuel pressure and anything else easy like that before pulling the engine apart again.

[mukluk]

[supercub]

[KingAir42]