Custom engine

[Abe]

I have a little 6HP I picked up it didn’t have any compression but it was just rhe valves were to tight I fixed that by eye it ran then sat and only runs if I hold me thumb over the carb where the air intake is. Which means there is to much air? So does that mean it’s an air leak?

 

[Denny]

Or more likely a plugged up carb.

 

[Rat]

I have a little 6HP I picked up it didn’t have any compression but it was just rhe valves were to tight I fixed that by eye it ran then sat and only runs if I hold me thumb over the carb where the air intake is. Which means there is to much air? So does that mean it’s an air leak?

Dirty carb, bad gasket at the insulator, bad oring on the back of the insulator, or even slightly loose nuts holding the carb on.

Some of them seem to be a bit finicky about filter density as well, and don't run worth a damn without one there to add the right amount of resistance which boosts the negative intake pressure available to draw fuel from the pilot circuit.

 

[Abe]

Had old card that was clean didn’t work ordered a new one still didn’t work all the bolts are tight and I’m not sure about the gaskets but I have to like put my whole thumb over the intake covering basically completely

 

[Rat]

Had old card that was clean didn’t work ordered a new one still didn’t work all the bolts are tight and I’m not sure about the gaskets but I have to like put my whole thumb over the intake covering basically completely

Ah the equivalent of full choke... that's a really dirty plugged up carb for sure. Most likely all fuel varnish and ethanol mud (white chalky substance that resembles cheap white stick deodorant) probably some jet corrosion to go with it.

Only way to save a carb that gooped up is to tear it completely down and drop it in an ultrasonic, but even doing that can't save them sometimes

 

[Abe]

It’s a brand new carb

 

[Abe]

someone said on a past post that putting my finger on the carb cause it to pull in less air and more fuel

 

[Rat]

someone said on a past post that putting my finger on the carb cause it to pull in less air and more fuel

It's not wrong as much as it is inaccurate to what is going on.

The piston drops, the intake valve opens, the negative pressure created by this causes the atmospheric pressure to fill the void picking up gas on the way through.

Since any form of pressure be it fluid, or gaseous, negative or positive ALEAYS seeks the point of least resistance to equalize with the ambient atmosphere... by blocking the flow of air through the carb with your thumb you are forcing the negative pressure to draw harder from the bowl.

It would not be unheard of for a new carb to have a debris blockage, or even sticky float.

If it's a brand new carb I'd break it down and blow it out as well as check the float level.
If the carb has an A/F screw it could be the culprit as well (right in the side of the intake flange)
Turn it in till it stops (DO NOT CRANK IT) then back it out 2 full rotations to default it. Once the engine is running you'll set yourself a high idle and turn it in ¼ turn until the idle stops climbing.

 

[bob58o]

Check fuel filter and line for clogging.
Are you running an air box?

You are correct, covering the air inlet of the carb richens the mixture. It’s like choke. Choking the air.

If you haven’t used new gaskets, I’d check for leaks by getting it running (with your thumb) then spraying something (WD40, starting fluid, carb cleaner,…) in the spots where it might be leaking. The RPMs should change if the fluid finds its way into a leak. Might raise rpm, might lower, but it’s the change in rpm you are listening for.

An engine will run lean if there is too much air or not enough fuel. An engine will run rich if there is too much fuel or not enough air.

Running with no air box, more air, leaner
Covering carb with thumb, less air, richer
Air leak, more air, leaner.

clogged carb, fuel line, filter, less fuel, leaner

Oh ya, lastly…
Did you put gas in the tank?

 

[Abe]

There is gas in the tank and I’m just running a gas tank with a hose on it no filter I can go through the carb but I doubt that the issue and it doesn’t have a A/F screw but I do have another carb with one for the same model and I don’t have any air filter on there but I’ve tried it with it and still nothing could it be a valve issue because I adjusted them by eye

 

[bob58o]

If you are experienced enough to adjust valves by feel, then it’s probably ok. Do it enough times and you can wiggle the rocker and feel if it’s close. But it won’t hurt to check them.

I would check carb gaskets. Do the fluid spray test I mentioned. The gx200 style engines have carb gaskets that are a bit tricky. There’s a few gaskets and spacers that need to be on correctly.

 

[bob58o]

If you want to try to get it running without your thumb, you can use a sock, or tape, or a combo of random items to partially block some air.

Does the carb have a choke?
Have you tried to open the throttle a bit when starting? Maybe an issue with the pilot circuit can by bypassed by a bit of throttle?

 

[Abe]

Doesn’t not have a choke and I checked the gaskets and it looked all good when I gave it throttle when I had my thumb on it kinda died then gave it some more air and that worked and this engine is a 6HP techusmesah power sports motor but if I have to cover up the carb that much shouldn’t that mean something wrong with it

 

[bob58o]

Oh, it’s a a Tecumseh?
Does your carb look like the one in the photo?

I had a tecumseh, it had a primer button. Does yours have a working primer? I think those fail often. If not try the old gas down the throat to get it nice and rich for the cold start.

Is it a stock carb? With that long curved intake manifold thing? I think pz19 carbs fit, but not 100% sure.

 

[bob58o]

PZ19 style carbs are cheap and have a choke.

 

[Abe]

Yes exactly the old one the primer didn’t work but the new it works

 

[Abe]

So I should get one of those and just run it on choke?

 

[Rat]

So I should get one of those and just run it on choke?

No you need to figure out why it only runs choked to hell

What's the exhaust on it? Swapping to something far less restricted than a factory unit can make a lot of trouble.

Checking the valves isn't a bad idea especially since most engines have a compression release on the cam. I personally prefer to set the valve lash with the opposite valve at maximum lift instead of fishing for the TDC center line like some insist on doing. When one valve is wide open the other is sealed, and therefore lash can be set more accurately either by eye or gauge

 

[bob58o]

The only other things I can think of would be playing around with idle rpm and throttle position. Many industrial engines have throttle linkages that will hold the throttle open a bit when starting. With some aftermarket carbs, I’ve needed to open the throttle a bit when starting.

If you can turn idle rpm speed high, see if it works better then try to get the idle speed back down to 1200 rpm or what ever.

I’m not sure what this engine is powering.
If a kart or bike or something that moves, disconnect the chain/belt before turning up the rpm’s or cracking the throttle wide open.

 

[Abe]

I did swap the exhaust on it should I go back to stock? I’m going to play around with it and find out and it’s powering a mini four wheeler