Robin engine popping and not winding up.

Heliarc

I have my own theories on why this might be but I don't want to muddy the waters.I'll just give you guys the symptoms.

I start up and it starts ok, but I hit the gas and it doesn't want to wind up hardly.If I pull the choke for a second or two and push it back with the throttle open it sometimes decides to take off.Once the engine is at speed it runs great.But if you let it slow down it's back to playing with the choke until you can get it to wind up again.

I've had the carb apart twice, all the jets and everything that would come off, hit it with carb cleaner and the air compressor.I've also done the body of the carb this way.The fuel pump seems to be delivering nicely as well.I took the line off and cranked it and it shoots a foot and a half in the air.I've changed plugs, new crank bearings and seals, and it still runs pretty much the same as when I first got it going.Not sure where to look next.

BGW

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Heliarc

To add to it, I was sure to get a nice thin film of red sealant on both mating surfaces of the case halves before I put it back together.I have not run a compression test yet.

I was thinking the reed valves might be faulty.Can I take the block out and just turn the valves over?

Heliarc

Just got done checking the reeds out.They let air in and they hold a vacuum the other way.Guess it's time for a compression test.

racin161

Are you still using the original ign system ? I think at this point I would consider the HEI upgrade I guess you could look at the reeds but I really don't think your going to find the problem there. Just a thought. Keep us posted.

LOU

kgsc

Sounds like it may be getting too much fuel at lower RPM. Float may be bad or needle sticking. Will flood at lower RPM but once spun up will burn it. Try running it for a few seconds then disconnect the fuel hose from the tank. Then try it again. The bowl should be full enough to run for maybe 30-45 seconds or so. If it runs ok this way I would suspect flooding.

Heliarc

@Lou The HEI conversion was the first thing I did to this cart.When I got it everything was dead except of course the reverse warning banshee.Now I get a nice fat blue spark so I'm sure the ignition isn't at fault here.I had the reeds out but they look fine and even hold a vacuum.As far as I can tell they're perfect.

@kgsc Float and needle are working fine as far as I can tell.When I had the carb off I turned it upside down and blew in the fuel inlet.There was no leak.Turning it right side up allowed me to blow into the carb.That's my static test for the needle anyhow.And if the float were shot I'd expect fuel to be pumping out the vent.

Also if it were getting too much fuel at low RPM wouldn't you think the choke would make it worse?

I remember an old car I had with a burnt valve.It would be a dead miss on one cylinder at an idle, but increasing RPM gave the compressed air/fuel less time to escape and it would fire reliably once you got to speed.With this, sometimes the choke gets it to wind up, but if you go down hill it winds up every time and will keep running great even uphill if you keep the RPM up.The p/o says he put a new piston and jug on, but I wonder.I mean should there be any slop at all in the piston to cylinder wall, or is it pretty much a slip fit.When I had it apart I noticed some movement that I didn't think anything of, but on a smaller engine I would imagine tolerances are smaller as well.A V8 won't mind a few thousandths here and there, but a single cylinder bugger like this, it might really matter.

Regardless, I'll be doing a compression test tomorrow and I'll know more.I swear by all that is holy, this cart will run!

junior1954

Respectfully, if the float were sticking and creating a rich mixture, the cart wouldn't start and idle well. Pulling the choke out makes the mixture richer (more gas, less air). A lean condition will cause backfiring/hesitation. The fact that the cart runs well at idle and full speed indicates a lean condition as the cart is transitioning from the idle circuit to the high speed circuit (runs fine at full throttle, when you get it there with the choke and at idle=proper mixture at those speeds, lean in between). Once you get it up to speed, if it pulls strong up hills, it isn't the ignition as poor spark shows up under load.

racin161

Another thought have you disconnected the exh pipe and tried it.

Heliarc

The exhaust is sort of iffy as it is.It leaks from the downpipe and also a bit at the muffler.I do know the sound of a blocked muffler and also the symptoms.A few months ago my neighbors quad would not run for a ****.It smelled literally like roasting hot dogs.Turns out the chipmunks had filled it full of dog food.I would like to put it on the grill though as I've heard about to burn crap out.

kgsc

I sit corrected, carry on...